MACHINE TOOLS The machine tools employed in modern engineering factories number many hundreds of well-defined and separate types. Besides these, there are hundreds more designed for special functions, and adapted only to the work of firms who handle specialities. Most of the first named and many of the latter admit of grouping in classes. The following is a natural classification:
I. Turning Lathes. These, by common consent, stand as a class alone. The cardinal feature by which they are distinguished is that the work being operated on rotates against a tool which is held in a rigid fixture the rest. The axis of rotation may be horizontal or vertical.
II. Reciprocating Machines. The feature by which these are characterized is that the relative movements of tool and work take place in straight lines, to and fro. The reciprocations may occur in horizontal or vertical planes.
III. Machines which Drill and Bore Holes. These have some features in common with the lathes, inasmuch as drilling and boring are often done in the lathes, and some facing and turning in the drilling and boring machines, but they have become highly differentiated. In the foregoing groups tools having either single or double cutting edges are used.
IV. Milling Machines. This group uses cutters having teeth arranged equidistantly round a cylindrical body, and may therefore be likened to saws of considerable thickness. The cutters rotate over or against work, between which and the cutters a relative movement of travel takes place, and they may therefore be likened to reciprocating machines, in which a revolving cutter takes the place of a single-edged one.
V. Machines for Cutting the Teeth of Gear-wheels. These comprise two sub-groups, the older type in which rotary milling cutters are used, and the later type in which reciprocating single-edged tools are employed. Sub-classes are designed for one kind of gear only, as spur-wheels, bevels, worms, racks, etc.
VI. Grinding Machinery. This is a large and constantly extending group, largely the development of recent years. Though emery grinding has been practised in crude fashion for a century, the difference in the old and the new methods lies in the embodiment of the grinding wheel in machines of high precision, and in the rivalry of the wheels of corundum, carborundum and alundum, prepared in the electric furnace with those of emery.
VII. Sawing Machines. In modern practice these take an important part in cutting iron, steel and brass. Few shops are without them, and they are numbered by dozens in some establishments. They include circular saws for hot and cold metal, band saws and hack saws.
VIII. Shearing and Punching Machines. These occupy a border line between the cutting and non-cutting tools. Some must be classed with the first, others with the second. The detrusive action also is an important element, more especially in the punches.
IX. Hammers and Presses. Here there is a percussive action in the hammers, and a purely squeezing one in the presses. Both are made capable of exerting immense pressures, but the latter are far more powerful than the former.
X. Portable Tools. This large group can best be classified by the common feature of being readily removable for operation on large pieces of erection that cannot be taken to the regular machines. Hence they are all comparatively small and light. Broadly they include diverse tools, capable of performing nearly the whole of the operations summarized in the preceding paragraphs.
XI. Appliances. There is a very large number of articles which are neither tools nor machine tools, but which are indispensable to the work of these; that is, they do not cut, or shape, or mould, but they hold, or grip, or control, or aid in some way or other the carrying through of the work. Thus a screw wrench, an angle plate, a wedge, a piece of packing, a bolt, are appliances. In modern practice the appliance in the form of a templet or jig is one of the principal elements in the interchangeable system.
XII. Wood-working Machines. This group does for the conversion of timber what the foregoing accomplish for metal. There is therefore much underlying similarity in many machines for wood and metal, but still greater differences, due to the conditions imposed on the one hand by the very soft, and on the other by the intensely hard, materials operated on in the two great groups.
XIII. Measurement. To the scientific engineer, equally with the astronomer, the need for accurate measurement is of paramount importance. Neither good fitting nor interchangeability of parts is possible without a system of measurement, at once accurate and of ready and rapid application. Great advances have been made in this direction lately.
I. LATHES, 1 The popular conception of a lathe, derived from the familiar machine of the wood turner, would not give a correct idea of the lathe which has been developed as the engineer's machine tool. This has become differentiated into nearly fifty well-marked.types, until in some cases even the term lathe has been dropped for more precise definitions, as vertical boring machine, automatic machine, while in others prefixes are necessary, as axle lathe, chucking lathe, cutting-off lathe, wheel lathe, and so on. With regard to size and mass the height of centres may range from 3 in. in the bench lathes to 9 or 10 ft. in gun lathes, and weights will range from say 50 Ib to 200 tons, or more in exceptional cases. While in some the mechanism is the simplest possible, in others it is so complicated that only the specialist is able to grasp its details.
Early Lathes. Space will not permit us to trace the evolution of the lathe from the ancient bow and card lathe and the pole lathe, in each of which the rotary movement was alternately forward, for cutting, and backward. The curious thing is that the wheel-driven lathe was a novelty so late as the lAth and isth centuries, and had not wholly displaced the ancient forms even in the West in the 19th century, and the cord lathe still survives in the East. Another thing is that all the old lathes were of dead centre, instead of running mandrel type; and not until 1794 did the use of metal begin to take the place of wood in lathe construction. Henry Maudslay (1771-1831) did more than any other man to develop the engineer's self-acting lathe in regard to its essential mechanism, but it was, like its immediate successors for fifty years after, a skeleton-like, inefficient weakling by comparison with the lathes of the present time.
Broad Types. A ready appreciation of the broad differences in lathe types may be obtained by considering the differences in the great groups of work on which lathes are designed to operate. Castings and forgings that are turned in lathes vary not only in size, but also in relative dimensions. Thus a long piece of driving shafting, or a railway axle, is very differently proportioned in length and diameter from a railway wheel or a wheel tire. Further, while the shaft has to be turned only, the wheel or the tire has to be turned and bored. Here then we have the first cardinal distinction between lathes, viz. those admitting work between centres (fig. 29) and face and boring lathes. In the first the piece of work is pivoted and driven between the centres of head-stock and tail-stock or loose poppet; in the second, it is held and gripped only by the dogs or jaws of a face-plate, on the head-stock spindle, the loose poppet being omitted.
These, however, are broad types only, since proportions of length to diameter differ, and with them lathe designs are modified whenever there is a sufficient amount of work of one class to justify the laying down of a special machine or machines to deal with it. Then further, we have duplicate designs, in which, for example, provision is made in one lathe for turning two or three long shafts simultaneously, or for turning and boring two wheels or tires at once. Further, the position of the axis of a face lathe need not be horizontal, as is necessary when the turning of long pieces has to be done between centres. There are obvious advantages in arranging it vertically, the principal being that castings and forgings can be more easily set and secured to a horizontal chuck than to one the face of which lies vertically. The chuck is also better supported, and higher rates of turning are practicable. In recent years these vertical lathes or vertical turning and boring mills (fig. 30) have been greatly increasing in numbers; they also occur in several designs to suit either general or special duties, some of them being used for boring only, as chucking lathes. Some are of immense size, capable of boring the field magnets of electric generators 40 ft. in diameter.
Standard Lathes. But for doing what is termed the general work of the engineer's turnery, the standard lathes (fig. 29) predominate, i.e. self-acting, sliding and surfacing lathes with headstock, loose poppet and slide-rest, centres, face plates and chucks, and an equipment by which long pieces are turned, either between centres or on the face chucks, and bored. One of the greatest objections to the employment of these standard types of lathes for indiscriminate duty is due to the limited height of the centres or axis of the headstock, above the face of the bed. This is met generally by providing a gap or deep recess in the bed next the fast headstock, deep enough to take face work of large diameter. The device is very old and very common, but when the volume of work warrants the employment of separate lathes for face-work and for that done between centres it is better to have them.
Screw-cutting.^ A most important section of the work of the engineer's turnery is that of cutting screws (see SCREW). This has resulted in differentiation fully as great as that existing between centres and face-work. The slide-rest was designed with this object, though it is also used for plain turning. The standard " selfacting sliding, surfacing and screw-cutting lathe " is essentially the standard turning lathe, with the addition of the screw-cutting mechanism. This includes a master screw the lead or guide screw, which is gripped with a clasp nut, fastened to the travelling carriage of the slide-rest. The lead-screw is connected to the headstock spindle by change wheels, which are the variables through which the relative rates of movement of the spindle and the lead-screw, and therefore of the screw-cutting tool, held and traversed in the slide-rest, are effected. By this beautiful piece of mechanism a guide screw, the pitch of which is permanent, is made to cut screw-threads of an almost infinite number of possible pitches, both in whole and fractional numbers, by virtue of rearrangements of the variables, the change wheels. The objection to this method is that the trains of change wheels have to be recalculated and rearranged as often as a screw of a different pitch has to be cut, an operation which takes some little time. To avoid this, the nest or cluster system of gears has been largely adopted, its most successful embodiment being in the HendeyNorton lathe. Here all the change wheels are arranged in a series permanently on one shaft underneath the headstock, and any one of them is put into engagement by a sliding pinion operated by the simple movement of a lever. Thus the lead-screw is driven at different rates without removing any wheel from its spindle. This has been extensively applied to both small and large lathes. But a moment's thought will show that even this device is too cumbrous when large numbers of small screws are required. There is, for example, little in common between the screw, say of 5 or 6 ft. in length, for a massive penstock or valve, and J-in. bolts, or the small screws required in thousands for electrical fittings. Clearly while the self-acting screw-cutting lathe is the best possible machine to use for the first it is unsuitable for the last. So here at once, from the point of view of screw cutting only, an important divergence takes place, and one which has ultimately led to very high specialization.
Small Screws. When small screws and bolts are cut in large quantities, the guide-screw and change wheels give place to other devices, one of which involves the use of a separate master-screw for every different pitch, the other that of encircling cutting instruments or dies. The first are represented by the chasing lathe, the second by the screwing lathes and automatics. Though the principles of operation are thus stated in brief, the details in design are most extensive and varied.
In a chasing lathe the master-screw or hob, which may be either at the rear of the headstock or in front of the slide-rest, receives a hollow clasp-nut or a half-nut, or a star-nut containing several pitches, which, partaking of the traverse movement of the screwthread, imparts the same horizontal movement to the cutting tool. The latter is sometimes carried in a hinged holder, sometimes in a common slide-rest. The attendant throws it into engagement at the beginning of a traverse, and out when completed, and also this is an economical system, but in others not. It cannot be considered so when bolts, screws and allied forms are of small dimensions.
Hollow Mandrel Lathes. It has been the growing practice since the last decade of the 19th century to produce short articles, required in large quantities, from a long bar. This involves making the lathe with a hollow mandrel; that is, the mandrel of the headstock has a hole drilled right through it, large enough to permit of the passage through it of the largest bar which the class of work requires. Thus, if the largest section of the finished pieces should require a bar of ij in. diameter, the hole in the mandrel would be made if in. Then the bar, inserted from the rear-end, is gripped by a chuck or collet at the front, the operations of turning, screwing and cutting off done, and the bar then thrust farther through to the exact length for the next set of identical operations to be FIG. 30. Boring and Turning Mill, vertical lathe. (Webster Bennett, Ltd., Coventry.)
A, Table, running with stem in vertical bearing.
B, Frame of machine.
C, Driving cones.
D, Handle giving the choice of two rates, through concealed sliding gears, shown dotted.
E, Bevel-gears driving up to pinion gearing with ring of teeth on the table.
F, Saddle moved on cross-rail G.
changes the hobs for threads of different sections. The screwed stays cf locomotive fire-boxes are almost invariably cut on chasing lathes of this class.
In the screwing machines the thread is cut with dies, which encircle the rotating bar; or alternatively the dies rotate round a fixed pipe, and generally the angular lead or advance of the thread draws the dies' along. These dies differ in no essentials from similar tools operated by a hand lever at the bench. There are many modifications of these lathes, because the work is so highly specialized that they are seldom used for anything except the work of cutting screws varying but little in dimensions. Such being the case they can hardly be classed as lathes, and are often termed screwing machines, because no provision exists for preliminary turning work, which is then done elsewhere, the task of turning and threading being divided between two lathes. In some cases H, Vertical slide, carrying turret J.
K, Screw feeding F across.
L, Splined shaft connecting to H for feeding the latter up or down.
M, M, Worm-gears throwing out clutches N, N at predetermined points.
O, Cone pulley belted up to P, for driving the feeds of saddle and down-slide.
performed, and so on. This mechanism is termed a wire feed, because the first lathes which were built of this type only operated on large wires; the heavy bar lathes have been subsequently developed from it. In the more advanced types of lathes this feeding through the hollow spindle does not require the intervention of the attendant, but is performed automatically.
The amount of preliminary work which has to be done upon a portion of a bar before it is ready for screwing varies. The simplest object is a stud, which is a parallel piece screwed up from each end. A bolt is a screw with a head of hexagonal, square or circular form, and the production of this involves turning the shank and shoulder and imparting convexity to the end, as well as screwing. But screw-threads have often to be cut on objects which are not primarily bolts, but which are spindles of various kinds used on mechanisms and machine tools, and in which reductions in the form of steps have to be made, and recesses, or flanges, or other features produced. Out of the demands for this more complicated work, as well as for plain bolts and studs, has arisen the great group of turret or capstan lathes (fig. 31) and the automatics or automatic screw machines which are a high development of the turret lathes.
Turret Lathes. The turret or capstan (fig. 32) is a device for gripping as many separate tools as there are distinct operations to be performed on a piece of work; the number ranges from four to as many as twenty in some highly elaborated machines, but five or six is the usual number of holes. These tools are brought round FIG. 31. Turret, Lathe. _ (Webster & Bennett, Ltd., Coventry.)
A, B, C, D, E, F, H, J, K, M, Bed.
Waste oil tray.
Cones keyed to D.
Split tapered close-in chuck, actuated by tube G.
Toggle dogs which push G.
Coned collar acting on H.
Handle to slide / through sleeve on bar L.
Rack slid on release of chuck, moving bearing /V lorward.
0, P, ft 5, T, V, Bearing to feed the work through mandrel (constituting the wire or bar feed). A collar is clamped on the work, and is pushed by the bearing N at each time of feeding.
Hand-wheel operating screw to travel 0.
Cross-handle moving Q to and fro.
Turret or capstan.
U, Sets of fast and loose pulleys, for open and crossed belts.
Cone belted down to E on lathe.
FIG. 32. Plan of Set of Turret Tools. (A. Herbert, Ltd.)
A, B, C, Turret.
Tool for first operation or chucking.
Cutting tools for second operation, starting or pointing.
D, Box tool carrying two cutters for third operation, rough turning.
E, Similar tool for fourth opera- tion, finish turning.
F, Screwing tools in head for final operation of screwing.
in due succession, each one doing its little share of work, until the cycle of operations required to produce the object is complete, the cycle including such operations as turning and screwing, roughing and finishing cuts, drilling and boring. Severance of the finished piece is generally done by a tool or tools held by a cross-slide between the headstpck and turret, so termed because its movements take place at right angles with the axis of the machine. This also often performs the duty of " forming," by which is meant the shaping of the exterior portion of an object of irregular outline, by a tool the edge of which is an exact counterpart of the profile required. The exterior of a cycle hub is shaped thus, as also are numerous handles and other objects involving various curves and shoulders, etc. The tool is fed perpendicularly to the axis of the rotating work and completes outlines at once: if this were done in ordinary lathes much tedious manipulation of separate tools would be involved.
Automatics. But the marvel of the modern automatics (fig. 33) lies in the mechanism by which the cycle of operations is rendered absolutely independent of attendance, beyond the first adjustments and the insertion of a fresh bar as often as the previous one becomes used up. The movements of the rotating turret and of the crossslide, and the feeding of the bar through the hollow spindle, take place within a second, at the conclusion of the operation preceding. These movements are effected by a set of mechanism independent of that by which the headstock spindle is rotated, viz. by cams or cam drums on a horizontal cam shaft, or other equivalent device, differing much in arrangement, but not principle. Movements are hastened or retarded, or pauses of some moments may ensue, according to the cam arrangements devised, which of course have to be varied for pieces of different proportions and dimensions. But when the machines with their tools are once set up, they will run for days or weeks, repeating precisely the same cycle of operations; they are self-lubricating, and only require to be fed with fresh lengths of bar and to have their tools resharpened occasionally. Of these automatics alone there are something like a dozen distinct types, some with their turrets vertical, others horizontal. Not only so but the use of a single spindle is not always deemed sufficiently economical, and some of these designs now have two, three and four separate work spindles grouped in one head.
Specialized Lathes. Outside of these main types of lathes there are a large number which do not admit of group classification. They are designed for special duties, and only a representative list can be given. Lathes for turning tapered work form a limited FIG. 33. Automatic Lathe or Screw Machine. (A. Herbert, Ltd.)
A, Main body.
B, Waste oil tray.
D, Wire-feed tube.
E, Slide for closing chuck.
F, Shaft for ditto.
H, Piece of work.
J, Turret wich box tools.
K, Turret slide.
L, Saddle for ditto, adjustable along bed. M, Screw Tor locating adjustable slide.
N, Cut-off and forming crossslide. O, 0, Back and front tool-holders on slide. P, Cam shaft. Q, Cam drum for operating chuck. R, Cam drum for operating turret. S, Cam disk for actuating cross-slide.
a, a, a, Cams for actuating chuck movements through pins b, b. The cam which returns D is adjustable but is not in view.
c, Feeding cam for turret.
d,<i,Return cams for turret.
e, e.Cams on cam disk for operating the lever /, which actuates the cut-off and forming slide.
T, Worm-wheel which drives cam shaft by a worm on the same shaft as the feed-pulley U.
V, Handwheel on worm shaft for making first adjustments.
W, Change feed disk.
g, g.Change feed dogs adjustable round disk.
X, Change feed lever.
Y, Oil tube and spreader for lubricating tools and work.
Z, Tray for tools, etc.
number, and they include the usual provisions for ordinary turning. In some designs change wheels are made use of for imparting a definite movement of cross traverse to the tool, which being compounded with the parallel sliding movements produces the taper. In others an upper bed carrying the heads and work swivels on a lower bed, which carries the slide rest. More often tapers are turned by a cross adjustment of the loose poppet, or by a taper attachment at the rear of the lathe, which coerces the movement of the top or tool-carrying slide of the rest. Or, as in short tapers, the slide-rest is set to the required angle on its carriage. Balls are sometimes turned by a spherical attachment to the slide-rest of an ordinary lathe. Copying lathes are those in which an object is reproduced from a pattern precisely like the objects required. The commonest example is that in which gun-stocks and the spokes of wheels are turned, but these are used for timber, and the engineer's copying lathe uses a form or cam and a milling cutter. The form milling machine is the copying machine for metal-work. The manufacture of boilers has given birth to two kinds of lathes, one for turning the boiler ends, the other the boiler flue flanges, the edges of which have to be caulked. Shaft pulleys have appropriated a special lathe containing provision for turning the convexity of the faces. Lathes are duplicated in two or three ways. Two, four, six or eight tools sometimes operate simultaneously on a piece of work. Two lathes are mounted on one bed. A tool will be boring a hole while another is turning the edges of the same wheel. One will be boring, another turning a wheel tire, and so on. The rolls for iron and steel mills have special lathes for trueing them up. The thin sheet metal-work produced by spinning has given rise to a special kind of spinning lathe where pressure, and not cutting, is the method adopted.
Methods of Holding and Rotating Work. Chucks. The term chuck signifies an appliance used in the lathe to hold and rotate work. As the dimensions and shapes of the latter vary extensively, so also do those of the chucks. Broadly, however, the latter correspond with the two principal classes of work done in the lathe, that between centres, and that held at one end only or face work.
This of course is an extremely comprehensive classification, because chucks of the same name differ vastly when used in small and large lathes. The chucks, again, used in turret work, though they grip the work by one end only, differ entirely in design from the face chucks proper.
Chucking between Centres. The simplest and by far the commonest method adopted is to drill countersunk centres at the ends of the work to be turned, in the centre or longitudinal axis (fig. 34, A), and support these on the point centres of headstock and poppet. The angle included by the centres is usually 60, and the points may enter the work to depths ranging from as little as A in- in very light pieces to J in., f in. or i in. in the heaviest. Obviously a piece centred thus cannot be rotated by the mere revolution of the lathe, but it has to be driven by some other agent making con- FIG. 34.
A, Centring and driying; a, point B, Face-plate driver or _ catchcentre; 6, carrier; c, driver fixed in slot in body of point centre; d, back centre; e, work.
plate; a, centre; b, driver.
C, Common heart-shaped carrier.
D, Clement double driver; a, face- plate; 6, 6, drivers; c, loose plate carrying drivers.
nexion between it and the mandrel. The wood turner uses a forked or prong centre to obtain the necessary leverage at the headstock end, but that would be useless in metal. A driver is therefore used, of which there are several forms (fig. 34), the essential element being a short stiff prong of metal set away from the centre, and rotating the work directly, or against a carrier which encircles and pinches the work. As this method of driving sets up an unbalanced force, the " Clement " or double driver (fig. 34, D), was invented, and is frequently made use of, though not nearly so much as the common single driver. In large and heavy work it is frequently the practice to drive in another way, by the dogs of the face-plate. Steadies. Pieces of work which are rigid enough to withstand the stress of cutting do not require any support except the centres.
FIG. 35- A, Travelling steady with adjust- slotted bolt holes a, a; 6, b, able studs a, a; b, work; brass or steel facings.
c, tool ; d, slide-rest. C, Fixed steady with hinged top B, Steady with horizontal and and three setting pieces.
vertical adjustment through But long and comparatively slender pieces have to be steadied at intermediate points (fig. 35). Of devices for this purpose there are many designs; some are fixed or bolted to the bed and are shifted when necessary to new positions, and others are bolted to the carriage of the slide-rest and move along with it travelling steadies. In some the work is steadied in a vee, or a right angle, in others adjustable pins or arms are brought into contact with it. As the pressure of the cut would cause an upward as well as backward yielding of the work, these two movements are invariably provided against, no matter in what ways the details of the steadies are worked out. Before a steady can be used, a light cut has to be taken in the locality where the steady has to take its bearing, to render the work true in that place. The travelling steady follows immediately behind the tool, coming in contact therefore with finished work continually.
Mandrels. Some kinds of work are earned between centres indirectly, upon mandrels or arbors (fig. 36). This is the method FIG. 36. Mandrels.
A, Plain mandrel. B, Stepped mandrel. C, Expanding mandrel, adopted when wheels, pulleys, bushes and similar articles are bored first and turned afterwards, being chucked by the bore hole, which fits on a mandrel. The latter is then driven between point centres and the bore fits the mandrel sufficiently tightly to resist the stress of turning. The large number of bores possible involves stocking a considerable number of mandrels of different diameters. As it is not usual to turn a mandrel as often as a piece of work requires chucking, economy is studied by the use of stepped mandrels, which comprise several diameters, say from three to a dozen. A better device is the expanding mandrel, of which there are several forms. The essential principle in all is the capacity for slight adjustments in diameter, amounting to from j in. to | in., by the utilization of a long taper. A split, springy cylinder may be moved endwise over a tapered body, or separate single keys or blades may be similarly moved.
Face-Work. That kind of work in which support is given at the headstock end only, the centre of the movable poppet not being required, is known as face-work. It includes pieces the length of which ranges from something less than the diameter to about three or four times the diameter, the essential condition being that the unsupported end shall be sufficiently steady to resist the stress of cutting. Work which has to be bored, even though long, cannot be steadied on the back centre, and if long is often supported on a cone plate. The typical appliance used for face-work is the common face-plate (fig. 37). It is a plain disk, screwed on the mandrel FIG. 37. Face-plate. A, Screwed hole to fit mandrel nose. B, Slots for common bolts.
C, Tee-slots for tee-head bolts, nose, and having slot holes in which bolts are inserted for the purpose of cramping pieces of work to its face. There are numerous forms of these clamps, and common bolts also are used. The faceplate may also serve to receive an intermediary, the angle-plate, against which work may be bolted when its shape is such as to render bolting directly to the plate inconvenient.
Jaw Chucks. When a face-plate has fitted to it permanent dogs or jaws it is termed a dog or jaw chuck (fig. 38). In the commonest form the jaws are moved radially and independently, each by its own screw, to grip work either externally or internally. In some cases the dogs are loosely fitted to the holes in a plain faceplate. In all these types the radial setting is tentative, that is the jaws being independent, there is no self-centring capacity, and thus much time is lost. A large group, therefore, are rendered self-centring by the turning of a ring which actuates a face scroll FIG. 38. Independent Jaw Chuck.
A, Body. b. Square heads of screws for a,' Recess to receive face-plate. key.
B, Jaws or dogs. c, Tee-grooves for bolts.
C, Screws for operating jaws.
FIG. 39. Scroll Chuck, ungeared.
A, Face-plate screwed to man- E, Jaws in chuck face, having drel nose.
B, Back of chuck screwed to A.
C, Knurled chuck body with scroll a on face. D, Chuck face.
sectional scroll teeth engaging with scroll a, and moved inwards or outwards by the scroll when C is turned.
b, Tommy or lever hole in C.
F, Piece of work outlined.
B, C, FIG. 40. Combination Geared Scroll Chuck.
A , Back plate ; o, recess for faceplate. Pinions.
Circular rack with scroll b on face.
D, Chuck body.
E, Jaws fitting on intermediate pieces c that engage with the scroll b.
d, Screws for operating jaws independently.
FIG. 41. Spiral Geared Chuck, concentric movement. (C.Taylor, Birmingham.)
C, Spiral plate with teeth engag- ing in jaws D.
E, Bevel pinions gearing with teeth on back of C.
(fig. 39) or a circular rack with pinions (fig. 40), turned with a key which operates all the jaws simultaneously inwards or outwards. But as some classes of jobs have to be adjusted eccentrically, many chucks are of the combination type (fig. 40), capable of being used independently or concentrically, hence termed universal chucks. The change from one to the other simply means throwing the ring of teeth out of or into engagement with the pinions t>y means of cams or equivalent devices. Each type of chuck occurs in a large range of dimensions to suit lathes of all centres, besides which every lathe includes several chucks, large and small, in its equipment. The range of diameters which can be taken by any one chuck is limited, though the jaws are made with steps, in addition to the range afforded by the operating screws. The " Taylor " spiral chucks (fig. 41) differ essentially from the scroll types in having the actuating threads set spirally on the sloping interior of a cone. The result is that the outward pressure of each jaw is received behind the body, because the spiral rises up at the back. In the ordinary scroll chucks the pressure is taken only at the bottom of each jaw, and the tendency to tilt and pull the teeth out of shape is very noticeable. The spiral, moreover, enables a stronger form of tooth to be used, together with a finer pitch of threads, so that the wearing area can be increased.
The foregoing may be termed the standard chucks. But in addition there are large numbers for dealing with special classes of work. Brass finishers have several. Most of the hollow spindle lathes and automatics have draw-in or push-out chucks, in which the jaws are operated simultaneously by the conical bore of the encircling nose, so that their action is instantaneous and self-centring. They are either operated by hand, as in fig. 31, or automatically, as in fig. 33. There is also a large group used for drills and reamers the drill chucks employed in lathes as well as in drilling machines.
II. RECIPROCATING MACHINE TOOLS This is the only convenient head under which to group three great classes of machine tools which possess the feature of reciprocation in common. It includes the planing, shaping and slotting machines. The feature of reciprocation is that the cutting tool is operative only in one direction; that is, it cuts during one stroke or movement and is idle during the return stroke. It is, therefore, in precisely the same condition as a hand tool such as a chisel, a carpenter's plane or a hand saw. We shall return again to this feature of an idle stroke and discuss the devices that exist to avoid it.
Planing Machines. In the standard planer for general shop purposes (fig. 42) the piece of work to be operated on is attached to a horizontal o table moving to and fro on a rigid bed, and passing underneath the fixed cutting tool.
The tool is gripped in a box having certain neccssary'ad- justments and movements, so that the tool can be carried or fed transversely across the work, or at right angles with the direction of its travel, to take successive cuts, and also downwards or in a vertical direction. The tool-box is carried on a cross-slide which has capacity for several feet of vertical adjustment on upright members to suit work of varying depths. These up-(j , rights or housings are bolted to the sides of the bed, and the whole framing is so rigidly designed that no perceptible tremor or yielding takes place under the heaviest duty imposed by the stress of cutting.
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.,. !fJJt.& Moreover, after the required adjustments have been made and the machine started, the travel and the return of the work- table and the feeding of the tool across the surface are performed by self-acting mechanism actuated by the reciprocations of the table itself, the table being driven from the belt pulleys.
To such a design there are objections, which, though their importance has often been exaggerated, are yet real. First, the crossrail and housings make a rigid enclosure over the table, which sometimes prevents the admission of a piece that is too large to pass under the cross-rail or between the housings. Out of this FIG. 43. 2O-in. Side Planing Machine.
B, B, Feet.
C, C, Work tables adjustable vertically on the faces D, D, by means of screws E, E, from handles F, F, through bevel gears.
(G. Richards & Co., Ltd., Manchester.)
G, Tool-box on travelling arm H, travelled by fast and loose pulleys J for cutting, and by pulleys K for quick return. L, Feed-rod with adj ustable dogs a, a, for effecting reversals through the belt forks b, b. M, Brickwork pit to receive deep objects.
FIG. 44. 8-in. Shaping Machine.
B, Work-table, having vertical movement on carriage C, which has horizontal movement along the face of A, D, Screw for effecting vertical movement, by handle E and bevel gears.
F, Screw for operating longitudinal movement with feed by hand or power.
G, Tool ram. H, Tool-box.
a, Worm-gear for setting tool-holder at an angle.
b, Crank handle spindle for operating ditto.
c, Handle for actuating down feed of tool.
(Cunliffe & Croom, Ltd., Manchester.)
J, Driving cone pulley actuating pinion d, disk wheel e, with slotted disk, and adjustable nut moving in the slot of the crank /, which actuates the lever g, connected to the tool ram G, the motion constituting the Whitworth quick return; g is pivoted to a block which is adjustable along a slot in G, and the clamping of this block in the slot regulates the position of the ram G, to suit the position of the work on the table.
k, Feed disk driven by small gears from cone pulley.
j, Pawl driven from disk through levers at various rates, and controlling the amount of rotation of the feed screw F.
K, Conical mandrel for circular shaping, driven by worm and wheel /.
objection has arisen a new design, the side planer (fig. 43), in which the tool-box is carried by an arm movable along a fixed bed or base, and overhanging the work, which is fastened to the side of the base, or on angle brackets, or in a deep pit alongside. Here the important difference is that the work is not traversed under the tool as in the ordinary planer, but the tool moves over the work. But an evil results, due to the overhang of the tool arm, which being a cantilever supported at one end only is not so rigid when cutting as the cross-rail of the ordinary machine, supported at both ends on housings. The same idea is embodied in machines built in other respects on the reciprocating table model. Sometimes one housing is omitted, and the tool arm is carried on the other, being therefore unsupported at one end. Sometimes a housing is made to be removable at pleasure, to be temporarily taken away only when a piece of work of unusual dimensions has to be fixed on the table. Another objection to the common planer is this. It seems unmechanical in this machine to reciprocate a heavy table and piece of work which often weighs several tons, and let the tool and its holder of a few hundredweights only remain stationary. The mere reversal of the table absorbs much greater horse-power there is no limitation whatever to the length of the work, since it may extend to any distance beyond the base-plate.
Shaping Machines. The shaping machine (fig. 44) does for comparatively small pieces that which the planer does for long ones. It came later in time than the planer, being one of James Nasmyth's inventions, and beyond the fact that it has a reciprocating noncutting return stroke it bears no resemblance to the older machine. Its design is briefly as follows: The piece of work to be shaped is attached to the top, or one of the vertical side faces, of a rightangled bracket or brackets. These are carried upon the face of a main standard and are adjustable thereon in horizontal and vertical directions. In small machines the ram or reciprocating arm (see fig. 44, G) slides in fixed guides on the top of the pillar, and the necessary side traverse is imparted to the work table B. To the top of the main standard, in one design, a carriage is fitted with horizontal traverse to cover the whole breadth, within the capacity of the machine, of any work to be operated on. In the largest machines two standards support a long bed, on which the carriage, with its ram, traverses past the work. These machines are frequently made double-headed, that is carriages, rams and work tables are dupli- FIG. 45. 12-in. Stroke Slotting Machine A, Main framing.
B, Driving cone.
C, D, Gears driven by cones.
E, Shaft of L.
F, Tool ram driven from shaft E through disk G and rod H , with quick return mechanism D. J, Counter-balance lever to ram.
than the actual work of cutting. Hence a strong case is often stated for the abandonment of the common practice. But, on the other hand, the centre of gravity of the moving table and work lies low down, while when the cross-rail and housings with the cutting tool are travelled and reversed, their centre of gravity is high, and great precautions have to be taken to ensure steadiness of movement. Several planers are made thus, but they are nearly all of extremely massive type the pit planers. The device is seldom applied to those of small and medium dimensions.
But there is a great group of planers in which the work is always fixed, the tools travelling. These are the wall planers, vertical planers or wall creepers, used chiefly by marine engine builders. They are necessary, because many of the castings and forgings are too massive to be put on the tables of the largest standard machines. They are therefore laid on the base-plate of the wall planer, and the tool-box travels up and down a tall pillar bolted to the wall or standing independently, and so makes vertical cutting strokes. In some designs horizontal strokes are provided for, or either vertical or horizontal as required. Here, as in the side planer, (Greenwood & Batley, Ltd., Leeds.) K, Flywheel. L, Driving-disk.
M, N, Feed levers and shaft operated from disk, actuating linear movements of slides 0, P, and circular movement of table E, through gears R. ed motions to table. T, Countershaft.
cated, and the operator can set one piece of work while the other is being shaped. In all cases the movement of the reciprocating arm, to the outer end of which the tool is attached, takes place in a direction transversely to the direction of movement of the carriage, and the tool receives no support beyond that which it receives from the arm which overhangs the work. Hence the shaper labours under the same disadvantages as the side planer it cannot operate over a great breadth. A shaper with a 24-in. stroke is one of large capacity, 16 in. being an average limit. Although the non-cutting stroke exists, as in the planer, the objection due to the mass of a reciprocating table does not exist, so that the problem does not assume the same magnitude as in the planer. The weak point in the shaper is the overhang of the arm, which renders it liable to spring, and renders heavy cutting difficult. Recently a novel design has been introduced to avoid this, the draw-cut shaper, in which the cutting is done on the inward or return stroke, instead of on the outward one.
Slotting Machines. In the slotting machine (fig. 45) the cutting takes place vertically and there is a lost return stroke. All the necessary movements save the simple reciprocating stroke are imparted to the compound table on which the work is carried. These include two linear movements at right angles with each other and a circular motion capable of making a complete circle. Frequently a tilting adjustment is included to permit of slotting at an angle. The slotting machine has the disadvantage of an arm unsupported beyond the guides in which it moves. But the compound movements of the table permit of the production of shapes which cannot be done on planers and shapers, as circular parts and circular arcs, in combination with straight portions. Narrow key grooves in the bores of wheels are also readily cut, the wheels lying on the horizontal table, which would only be possible on planer and shaper by the use of awkward angle brackets, and of specially projecting tools.
Quick return in planers is accomplished by having two distinct sets of gearing a slow set for cutting and a quick train for return, each operated from the same group of driving pulleys. The return travel is thus accomplished usually three, often four, times more quickly than the forward rate; sometimes even higher rates are arranged for. In the shaper and slotter such acceleration is not practicable, a rate of two to one being about the limit, and this is obtained not by gears, but by the slotted crank, the Whitworth return, on shapers and slotters, or by elliptical toothed wheels on slotters. The small machines are generally unprovided with this acceleration.
The double-cutting device seems at first sight the best solution, and it is adopted on a number of machines, though still in a great minority. The pioneer device of this kind, the rotating tool-box of Whitworth, simply turns the tool round through an angle of 180 at the termination of each stroke, the movement being self-acting. In some later designs, instead of the box being rotated to reverse the tool, two tools are used set back to back, and the one that is not cutting is relieved for the time being, that is tilted to clear the work. Neither of these tools will plane up to a shoulder as will the ordinary ones.
Allied Machines. The reciprocation of the tool or the work, generally the former, is adopted in several machines besides the standard types named. The plate-edge planer is used by platers and boiler makers. It is a side planer, the plates being bolted to a bed, and the tool traversing and cutting on one or both strokes. Provision is often included for planing edges at right angles. The key-seaters are a special type, designed the speed of the tools, and this controls the design of the driving and feeding mechanism. Another important difference is that between drilling or boring one or more holes simultaneously. With few exceptions the tool rotates and the work is stationary. The notable exceptions are the vertical boring lathes already mentioned. Obviously the demands made upon drilling machines are nearly as varied as those on lathes. There is little in common between the machines which are serviceable for the odd jobs done in the general shop and those which are required for the repetitive work of the shops which handle specialities. Provision often has to be made for drilling simultaneously several holes at certain centres or holes at various angles or to definite depths, while the mass of the spindles of the heavier machines renders counter-balancing essential.
Bench Machines are the simplest and smallest of the group. They are operated either by hand or by power. In the power machines generally, except in the smallest, the drill is also fed downwards by power, by means of toothed gears. The upper part of the drilling A, Base-plate.
C, Radial arm.
D, Spindle carriage.
E, Drill spindle.
F, Main driving cones driving vertical shaft G through mitre-gears H.
J, Spur-wheels, driving from C to vertical shaft K.
L, Mitre-wheels, driving from K to horizontal shaft M, having its bearings in the radial arm.
N, Nest of mitre-wheels driving the wheel spindle E from M.
O, Feed-gears to drill spindle, actuated by handwheel P or worm-gears Q.
FIG. 46. Pillar Radial Drilling Machine, 5 ft. radius.
R, R, Feed cones driving from shaft M to wormshaft S, for self-acting feed of drill.
T, Change-speed gears.
U, Hand-wheel for racking carriage D along radial arm C.
V, Clutch and lever for reversing direction of rotation of spindle.
W, Worm-gear for turning pillar B.
d, Handle for turning worm.
X, Screw for adjusting the height of the radial arm.
Y, Gears for actuating ditto from shaft C.
i, Rod with handle for operating elevating gear.
mainly to remove the work of cutting key grooves in the bores of wheels and pulleys from the slotting machine. The work is fixed on a table and the keyway cutting tool is drawn downwards through the bore, with several resulting practical advantages. Many planing machines are portable so that they may be fixed upon very massive work. Several gear-wheel cutting machines embody the reciprocating tool.
III. DRILLING AND BORING MACHINES The strict distinction between the operations of drilling and boring is that the first initiates a hole, while the second enlarges one already existing. But the terms are used with some latitude. A combined drilling and boring machine is one which has provision for both functions. But when holes are of large dimensions the drilling machine is useless because the proportions and gears are unsuitable. A 6-in. drill is unusually large, but holes are bored up to 30 ft. or more in diameter.
Types of Machines. The distinction between machines with vertical and horizontal spindles is not vital, but of convenience only. 1 he principal controlling element in design is the mass of the work, which often determines whether it or the machine shall be adjusted relatively to each other. Also the dimensions of a hole determine spindle being threaded is turned by an encircling spur-wheel, operated very slowly by a pinion and hand-wheel by the right hand of the attendant, the movement being made independent of the rotation of the spindle. A rack sleeve encircling the spindle is also common. In the power machines gears are also used, but a belt on small cone pulleys drives from the main cone shaft at variable speeds. From three to four drilling and feeding speeds are provided for by the respective cone pulleys. Work is held on or bolted to a circular table, which may have provision for vertical adjustment to suit pieces of work of different depths, and which can usually be swung aside out of the way to permit of deep pieces of work being introduced, resting on the floor or on blocking.
Watt Machines. One group of these machines resembles the bench machines in general design, but they are made to bolt to a wall instead of on a bench. Their value lies in the facilities which they afford for drilling large pieces of work lying on the floor a on blocking, which could not go on the tables of the bench machines. Sometimes a compound work-table is fastened to the floor beneath; and several machines also are ranged in line, by means of which long plates, angles, boilers or castings may be brought under the simultaneous action of the group of machines. Another type is the radial arm machine, with or without a table beneath. In each case an advantage gained is that a supporting pillar or standard is not required, its place being taken by the wall.
Self-contained Pillar Machines include a large number having the above-named feature in common. In the older and less valuable types the framework is rigid, and the driving and feeding are by belt cones. But the machines being mostly of larger capacities than those just noted, back-gears similar to those of lathes are generally introduced. The spindles also are usually counterbalanced. The machine framing is bolted to a bed-plate. A circular work-table may or may not be included. When it is, provision is made for elevating the table by gears, and also for swinging it aside when deep work has to be put on the base-plate.
Radial Arm Machines, In these (fig. 46) the drilling mechanism is carried on a radial arm which is pivoted to the pillar with the object of moving the drill over the work, when the latter is too massive to permit of convenient adjustment under the drill. The driving takes place through shafts at right angles, from a horizontal shaft carrying the cones and back-geared to a vertical one, thence to a horizontal one along the radial arm, whence the vertical drilling makers and platers. In others the spindles are adjustable in circles of varying radii, as in those employed for drilling the bolt holes in pipe flanges. In many of these the spindles are horizontal. Some very special multiple-spindle machines have the spindles at different angles, horizontal and vertical, or at angles.
Universal Machines are a particular form of the pillar type in which the spindle is horizontal, moving with its carriage on a pillar capable of traversing horizontally along a bed; the carriage has vertical adjustment on its pillar and so commands the whole of the face of a large piece of work bolted to a low bed-plate adjacent to the machine. The term " universal " signifies that the machine combines provision for drilling, boring, tapping screws and inserting screw studs, facing and in some cases milling. The power required for boring is obtained by double and treble gears. These machines are used largely in marine engine works, where very massive castings and forgings must be operated on with their faces set vertically.
Boring Machines. Many machines are classified as suitable for drilling and boring. That simply means that provision is made on FIG. 47. Lincoln Milling Machine.
B, B, Legs.
D, Spindle or arbor.
E, Headstock, carrying bearings for spindle D.
F, Tailstock, carrying point centre for tail end of spindle.
G, Hand-wheel for effecting adjustment in height of headstock, through bevel-gears H and screw ./.
K, Cross-bar connecting head- and tail-stocks, and ensuring equal vertical adjustment of the spindle bearings from the screw /.
spindle is driven. The latter has its bearings in a carriage which can be traversed along the arm for adjustment of radius. The spindle is counterbalanced. Hand as well as power adjustments are included. In the work-tables of radial and rigid machines there is a great diversity, so that work can be set on top, or at the sides, or at an angle, or on compound tables, so covering all the requirements of practice.
Sensitive Machines have developed greatly and have superseded many of the older, slower designs. The occasion for their use lies in the drilling of small holes, ranging up to about an inch in diameter. They are belt-driven, without back-gears, and usually without bevel-gears to change the direction of motion. The feed is by lever moving a rack sleeve. A slender pillar with a foot supports the entire mechanism, and the work-table, with a range of vertical adjustment.
Multiple Spindle Machines. Many of the sensitive machines are fitted with two, three or more spindles operated in unison with a belt common to all. In other machines the multiple spindles are capable of adjustment for centres, as in the machines used by boiler (John Holroyd & Co., Ltd., Milnrow.) L, Speed cones for driving spindle, through pinion M and wheel N. 0, Frame, carrying the bearings for the cone pulley L, and pivoted to the bed at a, and to the headstock E. This device keeps the gears M and N in engagement in all variations in the height of the spindle D. P, Q, Cones for driving the table R through worm-gears S, T, and spurs U, V, to the table screw. W, Stop for automatic knock-off to feed. X, Hand-wheel for turning the same screw through worm-gears Y, Z.
a drilling machine for boring holes of moderate size, say up to 8 or 10 in., by double and treble back-gears. But the real boring machine is of a different type. In the horizontal machines a splined bar actuated by suitable gears carries a boring head which holds the cutters, which head is both rotated with, and traversed or fed along the bar. The work to be bored is fixed on a table which has provision for vertical adjustment to suit work of different dimensions. The boring-bar is supported at both ends. In the case of the largest work the boring-bar is preferably set with its axis vertically, and the framing of the machine is arch-like. The bar is carried in a bearing at the crown of the arch and driven and fed there by suitable gears, while the other end of the bar rotates in the table which forms the base of the machine. Some boring machines for small engine cylinders and pump barrels have no bar proper, but a long boring spindle carrying cutters at the further end is supported along its entire length in a long stiff boss projecting from the headstock of the machine the snout machine. The work is bolted on a carriage which slides along a bed similar to a lathe bed. Many of these machines have two bars for boring two cylinders simultaneously.
In milling machines rotary saw-like cutters are employed. To a certain extent these and some gear-cutting machines overlap because they have points in common. Many gear-wheel teeth are produced by rotary cutters on milling machines. In many machines designed for gear cutting only, rotary cutters alone are used. For this reason the two classes of machines are conveniently and naturally grouped together, notwithstanding that a large and increasing group of gearcutting machines operate with reciprocating tools.
The French engineer, Jacques de Vaucanson (1709-1782), is credited with having made the first milling cutter. The first very crude milling machine was made in 1818 at a gun factory in Connecticut. To-day the practice of milling ranks as of equal economic value with that of any other department of the machine shop, and the varieties of milling machines made are as highly differentiated as are those of any other group. An apparent incongruity which is rather striking is the relative disproportion between the mass of these machines and the small dimensions of the cutters. The failures of many of the early machines were largely due to a lack of appreciation of the intensity of the stresses involved in milling. A single-edged cutting tool has generally a very narrow edge in operation. Milling cutters are as a rule very wide by comparison, and several teeth in deep cuts are often in simultaneous operation. The result is that the machine spindle and the arbor or tool mandrel are subjected to severe stress, the cutter tends to spring away from the surface being cut, and if the framings are of light proportions they vibrate, and inaccuracy and chatter result. Even with the very stiff machines now made it is not possible to produce such accurate results on wide surfaces as with the planer using a narrow-edged tool. Because of this great resistance and stress, cutters of over about an inch in width are always made with the teeth arranged spirally, and wide cutters which are intended for roughing down to compete with the planer always have either inserted cutters or staggered teeth. Hence the rotary cutter type of machine has not been able to displace the planing machine in wide work when great accuracy is essential. Its place lies in other spheres, in some of which its position is unassailable. Nearly all pieces of small and medium dimensions are machined as well by milling as by single-edged tools. All pieces which have more than one face to be operated on are done better in the milling machine than elsewhere. All pieces which have profiled outlines involving combinations of curves and plane faces can generally only be produced economically by milling. Nearly all work that involves equal divisions, or pitchings, as in the manufacture of the cutters themselves, or spiral cutting, or the teeth of gear-wheels when produced by rotary cutters, must be done in milling machines. Beyond these a large quantity of work lies on the border-line, where the choice between milling and planing, shaping, slotting, etc., is a matter for individual judgment and experience. It is a matter for some surprise that round the little milling cutter so many designs of machines have been built, varying from each other in the position of the tool spindles, in their number, and in the means adopted for actuating them and the tables which carry the work.
A very early type of milling machine, which remains extremely popular, was the Lincoln. It was designed, as were all the early machines, for the small arms factories in the United States. The necessity for all the similar parts of pistols and rifles being interchangeable, has had the paramount influence in the development of the milling machine. In the Lincoln machine as now made (fig. 47) the work is attached to a table, or to a vice on the table, which has horizontal and cross traverse movements on a bed, but no capacity for vertical adjustment. The cutter is held and rotated on an arbor driven from a headstock pulley, and supported on a tailstock centre at the other end, with capacity for a good range of vertical adjustment. This is necessary both to admit pieces of work of different depths or thicknesses between the table and the cutter, and to regulate the depth of cutting (vertical feed). Around this general design numerous machines small and large, with many variations in detail, are built. But the essential feature is the vertical movement of the spindle and cutter, the support of the arbor (cutter spindle) at both ends, and the rigidity afforded by the bed which supports head- and tail-stock and table.
The pillar and knee machines form another group which divides favour about equally with the Lincoln, the design being nearly of an opposite character. The vertical movements for setting and feed are imparted to the work, which in this case is carried on a bracket or knee that slides on the face of the pillar which supports the headstock. Travelling and transverse movements are imparted to the table slides. The cutter arbor may or may not be supported away from the headstock by an arched overhanging arm. None of these machines is of large dimensions. They are made in two leading designs the plain and the universal. The first embodies rectangular relations only, the second is a marvellous instrument both in its range of movements and fine degree of precision. The first machine of this kind was exhibited at Paris in 1867. The design permits the cutting of spiral grooves, the angle of which is embodied in the adjustment of a swivelling table and of a headstock thereon (universal or spiral head). The latter embodies change-gears like a screw-cutting lathe and worm-gear for turning the head, in combination with an index or dividing plate having several circles of holes, which by the insertion of an index peg permit of the work spindle being locked during a cut. The combinations possible with the division plate and worm-gear number hundreds. The head also has angular adjustments in the vertical direction, so that tapered work can be done as well as parallel. The result is that there is nothing in the range of spiral or parallel milling, or tapered work or spur or bevel-gear cutting, or cutter making, that cannot be done on this type of machine, and the_ accuracy of the results of equal divisions of pitch and angle of spiral do not depend on the human element, but are embodied in the mechanism.
FIG. 48. Vertical Spindle Milling Machine. (James Archdale & Co., Ltd.)
A, Main framing.
C, Spindle, having its vertical position capable of adjustment by the sliding of D on A. E, Driving cone, belt driving over guide pulleys F to spindle pulley G.
H, Enclosed gears for driving spindle by back gear. J, Hand-wheel for adjusting spindle vertically. K, K, Pulleys over which spindle is counterbalanced. L, Feed pulley, driven from counter shaft. M, Vertical feed shaft, driven from L through mitre-gears. N, Change gear box. O, Horizontal feed shaft, operating longitudinal and transverse feed of table through spiral and spur-gears.
P, P, Handles for operating changes in feed speeds, nine in number. Q, Handle for reversing direction of motion of table R. S, Hand-wheel for longitudinal movement of table. T, Hand-wheel for effecting cross adjustments. V, Spiral gears indicated for effecting self-acting rotation of circular table W.
X, Hand-wheel for rotation of table. Y, Hand-wheel for vertical movements of knee B on screw Z.
Machines with vertical spindles (fig. 48) form another great group, the general construction of which resembles that either of the common drilling machine or of the slotting machine. In many cases the horizontal position is preferable for tooling, in others the vertical, but often the matter is indifferent. For general purposes, the heavier class of work excepted, the vertical is more convenient. But apart from the fitting of a special brace to the lower end of the spindle which carries the cutter, the spindle is unsupported there and is thus liable to spring. But a brace can only be used with a milling cutter that operates by its edges, while one advantage of the vertical spindle machine is that it permits of the use of end or face cutters. One of the greatest advantages incidental to the vertical position of the spindle is that it permits of profile milling being done. One of the most tedious operations in the machine shop is the production of outlines which are not those of the regular geometric figures, as rectangles and circles, or combinations of the same. There is only one way in which irregular forms can be produced cheaply and interchangeably, and that is by controlling the movements of the tool with an object of similar shape termed a "form" or " former," as in the well-known copying lathes, in the cam grinding machine, and in the forming adjuncts fitted to vertical spindle milling machines, so converting those into profiling machines. The principle and its application are alike simple. An object (the form) is made in hardened steel, having the same outlines as the object to be milled, and the slide which carries the cutter spindle has a hardened former pin or roller, which is pulled hard against the edges of the form by a suspended weight, so causing the tool to move and cut in the same path and in the same plane around the edges of the work. Here the milling machine holds a paramount place. No matter how many curves and straight portions may be combined in a piece, the machine reproduces them all faultlessly, and a hundred or a thousand others all precisely alike without any tentative corrections. Piano-millers, also termed slabbing machines, form a group that grows in value and in mass and capacity. They are a comparatively late development, becoming the chief rivals to the planing machines, for all the early milling was of a very light character. In general outlines the piano-millers closely resemble the planing machines, having bed, table, housings and cross-rail. The latter in the pianomiller carries the bearings for the cutter spindle or spindles under which the work travels and reciprocates. These spindles are vertical, but in some machines horizontal ones are fitted also, as in planers, so that three faces at right or other angles can be operated on simultaneously. The slabbing operations of the piano-millers do not indicate the full or even the principal utilities of these machines. To understand these it must be remembered that the cross-sections of very many parts which have to be tooled do not lie in single planes merely, but in combinations of plane surfaces, horizontal, vertical or angular. In working these on the planing machine separate settings of tools are required, and often successive settings. But milling cutters are built up in " gangs " to deal with such cases, and in this way the entire width of profile is milled at once. Horizontal faces, and vertical and angular edges and grooves, are tooled simultaneously, with much economy in time, and the cutter profile will be accurately reproduced on numbers of separate pieces. Allied to the piano-millers are the rotary planers. They derive their name from the design of the cutters. An iron disk is pierced with holes for the insertion of a large number of separate cutters, which by the rotation of the disk produce plane surfaces. These are milling cutters, though the tools are single-edged ones, hence termed " inserted tooth mills." These are used on other machines besides the rotary planers, but the latter are massive machines built on the planer model, with but one housing or upright to carry the carriage of the cutter spindle. These machines, varied considerably in design, do good service on a class of work in which a very high degree of accuracy is not essential, as column flanges, ends of girders, feet of castings, and such like.
V. GEAR-CUTTING MACHINES The practice of cutting the teeth of gear-wheels has grown but slowly. In the gears used by engineers, those of large dimensions are numerous, and the cost of cutting these is often prohibitive, though it is unnecessary in numbers of mechanisms for which cast wheels are as suitable as the more accurately cut ones. The smallest gears for machines of precision have long been produced by cutting, but of late years the practice has been extending to include those of medium and large dimensions, a movement which has been largely favoured by the growth of electric driving, the high speeds of which make great demands on reduction and transmission gears. Several new types of gear-cutting machines have been designed, and specialization is still growing, until the older machines, which would, after a fashion, cut all forms of gears, are being ousted from modern establishments.
The teeth of gear-wheels are produced either by rotary milling cutters or by single-edged tools (fig. 49). The advantage of the first is that the cutter used has the same sectional form as the intertooth space, so that the act of tooth cutting imparts the shapes without assistance from external mechanism. But this holds good only in regard to spur-wheel teeth, that is, those in which the teeth lie parallel with the axis of the wheel. The teeth of bevel-wheels, though often produced by rotary cutters, can never be formed absolutely correctly, simply because a cutter of unalterable section is employed to form the shapes which are constantly changing in dimensions along the length of the teeth (the bevel-wheel being a frustum of a cone). Hence, though fair working teeth are obtained in this way, they result from the practice of varying the relative angles of the cutters and wheel and removing the material in several successive operations or traverses, often followed by a little correction with the file. Although this practice is still commonly followed in bevel-wheels of small dimensions, and was at one time the only method available, the practice has been changing in favour of shaping the teeth by a process of planing with a single-edged reciprocating tool. As, however, such a tool embodies no formative section as do the milling cutters, either it or the wheel blank, or both, have to be coerced and controlled by mechanism outside the tool itself. Around this method a number of very ingenious xxvn. 2 machines have been designed, which may be broadly classed under two great groups the form and the generating types.
In the form machines a pattern tooth or form-tooth is prepared in hardened steel, usually three times as large as the actual teeth to be cut, and the movement of the mechanism which carries the wheel blank is coerced by this form, so that the tool, reciprocated by its bar, produces the same shape on the reduced dimensions of the wheel teeth. The generating machines use no pattern tooth, but the principles of the tooth formation are embodied in the mechanism itself. These are very interesting designs, because they not only shape the teeth without a pattern tooth, but their movements are automatically controlled. A large number of these have been brought out in recent years, their growth being due to the demand for accurate gears for motor cars, for electric driving, and for general high-class engineers' work. These are so specialized that they can only cut the one class of gear for which they are designed the bevel-wheels, and these in only a moderate range of dimensions on a single machine of a given size. The principal bevel-gear cutting machines using forms or formers, are the Greenwood & Batley, Le Progrfes Industriel, the Bouhey (cuts helical teeth), the Oerlikon, which includes two types, the single and double cutting tools, the Gleason and the Rice. Generating machines include the Bilgram (the oldest), the Robey-Smith, the Monneret, the Warren, the Beale and the Dubosc.
FIG. 49. Gear Cutting.
A, Rotary milling cutter pro- D, Action of " Fellows " cutter, ducing tooth space. planing teeth.
B, Planer tool operating on tooth E, Shape of " Fellows " cutter.
flank. F, Hobbing cutter.
C, Planer form-tool finishing G, Tapered hob beginning worm- tooth space. wheel.
H, Ditto finishing.
As the difficulties of cutting bevel-wheels with rotary cutters, consequent on change of section of the teeth, dp not occur in spurgears, there are no examples of form machines for spur-wheel cutting, and only one generating planing type of machine, the Fellows, which produces involute teeth by a hardened steel-cutting pinion, which shapes wheels having any number of teeth of the same pitch, the cutter and blank being partly rotated between each cut as they roll when in engagement.
The worm-gears appropriate a different group of machines, the demands on which have become more exacting since the growth of electric driving has brought these gears into a position of greater importance than they ever occupied before. With this growth the demand for nothing less than perfect gears has developed. A perfect gear is one in which the teeth of the worm-wheel are envelopes of the worm or screw, and this form can only be produced in practice in one way by using a cutter that is practically a serrated worm (a hob), which cuts its way into the wheel just as an actual worm might be supposed to mould the teeth of a wheel made of a plastic substance. To accomplish this the relative movements of the hob and the wheel blank are arranged to be precisely those of the working worm and wheel. Very few such machines are made. A practical compromise is effected by causing the hob both to drive and cut the blank in an ordinary machine. When worms are not produced by these methods the envelope cannot be obtained, but each tooth space is cut by an involute milling cutter set at the angle of thread in a universal machine, or else in one of the general gear-cutting machines used for spur, bevel and worm gears, and only capable of yielding really accurate results in the case of spur-wheels.
The previous remarks relate only to the sectional forms of the teeth. But their pitch or distance from centre to centre requires dividing mechanism. This includes a main dividing or wormwheel, a worm in conjunction with change gears, and a division plate for setting and locking the mechanism. The plate may have four divisions only to receive the locking lever or it may be drilled with a large number of holes in circles for an index peg. The first is adopted in the regular gear-cutters, the second on the universal milling machines which are used also for gear-cutting. In the largest number of machines this pitching has to be done by an attendant as often as one tooth is completed. But in a good number of recent machines the pitching is effected by the movements of the machine itself witnout human intervention. With spur-wheels the cutting proceeds until the wheel is complete, when the machine is often made to ring a bell to call attention to the fact. But in bevel-wheels only one side of the teeth all the way round can be done; the attendant must then effect the necessary settings for the other side, after which the pitchings are automatic.
As a general rule only one tooth is being operated on at one time. But economy is studied in spur-gears by setting several similar wheels in line on a mandrel and cutting through a single tooth of the series at one traverse of the tool. In toothed racks the same device is adopted. Again, there are cases in which cutters are made to operate simultaneously on two, three or more adjacent teeth.
Recently a generating machine of novel design has been manufactured, the spur-wheel hobbing machine. In appearance the hob resembles that employed for cutting worm-gears, but it also generates the teeth of spur and spiral gears. The hob is a worm cut to form teeth, backed off and hardened. The section of the worm thread is that of a rack. Though it will cut worm-wheels, spiral-wheels or spur-wheels equally correctly, the method of presentation varies. When cutting worm-wheels it is fed inwards perpendicularly to the blank; when cutting spirals it is set at a suitable angle and fed across the face of the blank. The angle of the worm thread in the hob being about 2j, it has to be set by that amount out of parallel with the plane of the gear to be cut. It is then fed down the face of the wheel blank, which is rotated so as to synchronize with the rotation of the worm. This is effected through change gears, which are altered for wheels having different numbers of teeth. The advantage is that of the hob over single cutters; one hob serves for all wheels of the same pitch, and each wheel is cut absolutely correct. While using a set of single cutters many wheels must have their teeth only approximately correct.
VI. GRINDING MACHINES The practice of finishing metallic surfaces by grinding, though very old, is nevertheless with regard to its rivalry with the work of the ordinary machine tools a development of the last part of the 19th century. From being a non-precision method, grinding has become the most perfect device for producing accurate results measured precisely within thousandths of an inch, ft would be rather difficult to mention any class of machine-shop work which is not now done by the grinding wheel. The most recent developments are grinding out engine cylinders and grinding the lips of twist drills by automatic movements, the drills rotating constantly.
There are five very broad divisions under which grinding machines may be classified, but the individual, well-defined groups or types might number a hundred. The main divisions are: (l) Machines for dealing with plane surfaces; (2) machines for plain cylindrical work, external and internal; (3) the universals, which embody movements rendering them capable of angular setting; (4) the tool grinders: and (5) the specialized machines. Most of these might be again classed under two heads, the non-precision and the precision types. The difference between these two classes is that the first does not embody provision for measuring the amount of material removed, while the second does. This distinction is a most important one.
The underlying resemblances and the differences in the main designs of the groups of machines just now noted will be better understood if the essential conditions of grinding as a corrective process are grasped. The cardinal point is that accurate results are produced by wheels that are themselves being abraded constantly. That is not the case in steel cutting tools, or at least in but an infinitesimal degree. A steel tool will retain its edge for several hours (often for days) without the need for regrinding, Dut the particles of abrasive in an emery or other grinding wheel are being incessantly torn out and removed. A wheel in traversing along a shaft say of 3 ft. in length is smaller in diameter at the terrrujnation than at the beginning of the traverse, and therefore the shaft must be theoretically larger at one end than the other. Shafts, nevertheless, are ground parallel. The explanation is, and it lies at the basis of emery grinding, that the feed or amount removed at a single traverse is extremely minute, say a thousandth or half a thousandth of an inch. The minuteness of the feed receives compensation in the repetition and rapidity of the traverse. The wear of the wheel is reduced to a minimum and true work is produced.
From this fact of the wear of grinding wheels two important results follow. One is that a traverse or lateral movement must always take place between the wheel and the piece of work being ground. This is necessary in order to prevent a mutual grooving action between the wheel and work. The other is that it is essential to provide a large range in quality of wheels, graded according to coarseness and fineness, of hardness and softness of emery to suit all the different metals and alloys. Actually about sixty grades are manufactured, but about a dozen will generally cover average shop practice. With such a choice of wheels the softest brass as well as the hardest tempered steel or case-hardened glass-like surfaces that could not possibly be cut in lathe or planer, can be ground with extreme accuracy.
FIG. 50. Universal Grinding Machine, 7 in. centres; 3 ft. 6 in. between centres. (H. W. Ward & Co., Ltd., Birmingham.)
Base or body, with waste water tray round top edge, and interior fitted as cupboards, with shelves and doors.
B, Sliding table.
C, Swivej table.
D, Grinding wheel.
E, Wheel guard.
F, Wheel headstock swivelling in a horizontal plane, and having the base graduated into degrees for angular setting.
G, Slide carrying headstock.
H, Hand-wheel for traversing table.
/, Headstock for carrying and driving work, used for chuck work or dead centre work ; the base is graduated into degrees.
a, Dogs, which regulate automatic reversals. An internal grinding fixture, not shown, is fitted to wheel head.
L, Countershaft pulley driving to wheel pulley.
M, Pulley driving to cones.
N, Pulley driving to work headstock pulley.
O, Belt from line shaft.
P, Water pipe from pump.
Q, Water guards above table.
Plane surfacing machines in many cases resemble in general outlines the well-known planing machine and the vertical boring mill. The wheels traverse across the work, and they are fed vertically to precise fractional dimensions. They fill a large place in finishing plane surfaces, broad and narrow alike, and have become rivals to the planing and milling machines doing a similar class of work. For hardened surfaces they have no rival.
Cylindrical grinders include many subdivisions to embrace external and internal surfaces, either parallel or tapered, small or large. In their highest development they fulfil what are termed " universal " functions (fig. 50), that is, they are capable of grinding both external and internal cylinders, plane faces, tapers, both of low and high angle, and the teeth of various kinds of tools and cutters. These machines occur in two broad types. In one the axis of the revolving wheel is traversed past- the work, which revolves but is not traversed. In the other the reverse occurs, the work traversing and the axis of the wheel with its bearings remaining stationary. Equally satisfactory results are obtained by each.
In all external cylindrical grinding, when the work can be rotated, the piece being ground rotates in an opposite direction to the rotation of the wheel (fig. 51, A). In all small pieces ground internally the same procedure is adopted (fig. 51, B). Incidentally, FIG. 51.
A, External cylindrical grinding. B, Internal ditto. C, External grinding when the work is fixed. D, Internal ditto.
mention should be made of the fineness of the fitting required and attained in the construction of the spindles which carry the wheels for internal grinding. The perfection of fitting and of the means of adjustment for eliminating the effects of wear in the ordinary spindles for external and internal grinding is remarkable. The spindles for internal work have to revolve at rates ranging from about 6000 to 30,000 times ,in a minute, yet run so truly that the holes ground do not depart from accuracy by more than say 5^3 to rsJnnr of an inch. Yet so long as the work can be revolved no special complication of mechanism is required to ensure good results. The revolution of the wheel and the work is mutually helpful. The real difficulties arise when the work, on account of its mass or awkwardness of shape, cannot be revolved. The principle embodied in machines designed to deal satisfactorily with such cases, though much diversified in detail, is the application of the planet device to the grinding wheels. That is, the wheel spindle rotating at a high speed, 6000 or 7000 revolutions per minute, is simultaneously carried round in a circular path, so that its axis makes about 25 or 30 revolutions per minute (fig. 51, C and D). The diameter of the path is capable of adjustment with minute precision within wide limits to suit bores of different diameters. The periphery of the grinding wheel which lies farthest from its axis of revolution sweeps round in a path -the diameter of which equals that of the bore to be ground. These machines are now used largely for grinding out the cylinders of gas and petrol engines, valve seatings, the bushed holes of coupling rods, and similar classes of work. Many of them have their spindles set horizontally, others vertically.
Allied to these are a relatively small but important group of machines used for grinding the slot links of the slide-valve gear of locomotive and other engines. The slot is mounted on a pivoted bar adjusted to the same radius as the slot to be ground, and the slot is moved relatively to the wheel, so producing the required curves.
In another direction much development has taken place jn the practice of grinding. The increasing use of the milling cutter has FIG. 52.
A, Grinding front edges of milling cutter. B, Grinding side edges of milling cutter; a, a, Tooth rests. C, Grinding face of formed mill.
been the occasion for the growth and high specialization of the cutter grinding machines. It is essential to the efficiency of such cutters that regrinding shall be done without drawing the temper, and this can only be effected by the use of an abrasive. In the early days of their use the temper had to be drawn to permit of filing and rehardening effected with its inevitable distortion.
Cutter grinding machines must possess universality of movements to deal with the numerous shapes in which milling cutters are made; hence they often resemble in general outlines the universal grinding machines. But as a rule they are built on lighter models, and with a smaller range of movements, because the dimensions of cutters are generally much smaller than those of the ordinary run of engineers' work which has to be ground. Frequently a single pillar or standard suffices to carry the mechanism. In an ordinary universal tool grinder all the teeth of any form of cutter can be ground pre^sely alike (fig. 52) excepting those having irregular profiled outlines, for which a special machine, or an extra attachment to an ordinary machine, is necessary. But little of this is done, because in such cases, and in many others, the faces of the teeth are ground instead of the edge. This idea, due to the firm of Brown & Sharpe, may seem a trifle, but nevertheless to it the credit is largely due for the economies of cutter grinding. The principle is that in the " formed cutter," as it is termed, the profiles of the teeth are not struck from the axis of revolution, but from another centre (fig. 20) ; grinding the tooth faces, therefore, has no effect on the shapes of the profiles, but only lessens the tooth thicknesses. Designed originally for the cutters for the teeth of gear-wheels, it has long been applied to profiles which involve combinations of curves. The pitching of the teeth is effected by a strip of metal, or tooth rest a (fig. 52), on which each successive tooth rests and is coerced during the grinding. If teeth are of special form the traverse movement of a spiral tooth along the rest ensures the required movement.
Besides the cutter grinders used for milling cutters, reamers and screwing taps, there are two other groups of tool grinders, one for twist drills o^Jry and the other for the single-edged tools used in lathe, planer, shaper and other machines. Both these in their best forms are of recent development. The machines used for grinding twist drills embody numerous designs. Hand grinding is practically abandoned, the reason being that a very minute departure from symmetry on the two cutting lips of the drill results inevitably in the production of inaccurate holes. It is essential that the two lips be alike in regard to length, angle and clearance, and these are embodied in the mechanism of the grinding machines. But formerly in all these the drill holder had to be moved by hand around its pivot, and one lip ground at a time There are now some very beautiful machines of German manufacture in which the necessary movements are all automatic, derived from the continuous rotation of a belt pulley. The drill rotates constantly, and small amounts are ground off each lip in turn until the grinding is finished. The other group for grinding single-edged tools is a very small one. The correct angles for grinding are embodied in the setting of the machine, with the great advantage that any number of similar tools can be ground all alike without skilled attendance.
Lying outside these broad types of machines there is a large and growing number designed for special service. The knife-grinding group for sharpening the planer knives used in wood-working machinery is a large one. Another is that for gulleting or deepening the teeth of circular saws as they wear. Another is designed for grinding the cups and cones for the ball races of cycle wheels, and another for grinding the hardened steel balls employed in ball bearings.
B C D FIG. 53. Typical Grinding Wheels.
A , Common disk held on spindle with washers and nuts.
B, Thin disk.
C, Flanged disk for grinding to shoulders.
D, Bevelled disk for cutter grinding.
E, F, Cupped and dished wheels for cutter grinding.
G, Cup wheel for grinding on face o; diameter remains constant.
Emery grinding is dependent for much of its success on a plentiful supply of water. Dry grinding, which was the original practice, is hardly employed now. The early difficulties of wet grinding were due to the want of a cementing material which would not soften under the action of water. Now wheels will run constantly without damage by water, and they are so porous that water will filter through them. Improvements in the manufacture of wheels, and the increased use of water, have concurred to render possible heavier and more rapid grinding without risk of distortion due to heating effects. In the best modern machines the provisions for water supply are a study in themselves, including a centrifugal pump, a tank, jointed piping, spraying tube, guards to protect the bearings and slides from damage, and trays to receive the waste water and conduct it back to the tank.
There are two points of view from which the modern practice of grinding is now regarded one as a corrective, the other as a formative process. The first is the older and is still by far the most important. The second is a later ideal towards which design and practice have been extending. As yet grinding cannot compete with the work of the single-edged tools and milling cutters when large quantities of material have to be removed. Just as some leading firms have been designing stiffer machines having fuller lubrication with a view to increase the duty of grinding wheels, the advent of the high-speed steels has given a new lease of life to the single-edged cutting tools. The rivalry now lies not with the tools of carbon temper steel, but with highspeed varieties. But as a corrective process grinding never occupied so important a position as it does to-day, and its utility continues to extend.
The commoner forms in which grinding wheels are made are shown in fig. 53. These are varied largely in dimensions, from tiny cylindrical rollers a fraction of an inch in diameter for hole grinding, to big wheels of 3 ft. or more in diameter. Safety mountings, two examples of which are shown in fig. 54, embody means of retaining the broken pieces of a wheel in case it bursts.
Sand-blast. The well-known erosive action of sand when driven against rocks and stones by the wind is utilized Fl G 54 Safety Devices industrially in the sand-blastapparatus, A, Grinding wheel, with the invention of B. C. Tilghman. The coned washer to retain sand . ls propelled by a current of steam broken pieces in case or *"' . an ,9 bem 8 delivered through a of fracture nozzle is directed against the surface of B, Cup wheel with encircling the ^ ork ' cutting it away by the action ring, moved backwards of ., t P e enormous number of grains as the wheel face wears. strlkln g th e face, each removing a very minute quantity of material. The action is very gentle, and may be modified by varying the class of sand and its velocity.
Other materials, such as emery, chilled iron globules, etc., are employed for certain classes of work. _In some instances the powder is used dry, in others it is mixed with water, being then in the condition of fluid mud. The plant includes an air-compressing engine, an air reservoir and the blast nozzle through which the air passes and propels the sand in the form of a jet. The pressures range from 8 Ib up to about 60 tb per sq. in., depending on the class of work which is done.
The peculiar advantage of the sandblast lies in its adaptability to the working of irregular surfaces, which could not be touched by any other class of grinding. The blast penetrates hollows and recesses, and acts over an entire surface. There are many classes of operation done with the sand-blast, including cleaning, frosting, ornamentation, engraving and sharpening. In engineers' works a large amount of cleaning is effected upon castings, forgings, sheets and other products, either preparatory to machining or to painting, enamelling, tinning, galvanizing or plating. Cycle frames are cleaned with the sand-blast after brazing. The teeth of files are sharpened by directing a stream of sand and water against their backs, with the result that the burr thrown up by the chisel when cutting is obliterated, and a strong form of tooth is produced. Worn files may also be sharpened up to equal new ones by sand-blasting them. Frosting glass is another useful application of the sand-blast, and by attaching suitable patterns or designs to the surface the sand may be caused to work ornamental figurings. It is a peculiar circumstance that the sand has little effect upon soft and yielding substances in comparison with the abrasion it produces on hard surfaces, so that the pattern will remain undamaged, while the glass or other object beneath is frosted where the sand reaches it, through the openings. Not only can designs be worked on glass, or cut in stone, but perforations may be made in glass, etc., by the continued action of the sand, without any risk of fracture occurring. Much sandblasting is performed inside closed chambers, having panes through which the workman watches the progress of the operation. But when the blast must be used in the open, protection is necessary and is afforded to the operator by a special helmet, which keeps out the flying dust and gives a supply of pure air through a tube in a similar fashion to the diver's helmet.
VII. SAWING MACHINES Metal-sawing machines are employed extensively in engineering works for cutting off bars, shafts, rails, girders and risers on steel castings, and for getting out curved pieces which would be difficult and expensive to slot. There are three classes of these saws, circular, band and reciprocating. The first named are used for straightforward work, operating at right or other angles, the second for straight cuts and also for curves which cannot be treated with circular saws, and the third for small pieces. The circular sawsembody a stiff spindle, carrying the saw disk and driven by gearing. This spindle may be mounted in a sliding bearing to carry it past the work held on a fixed table, or the spindle may be stationary and the work be moved along past the saw. The method of feeding should be sensitive, so that it will " give " and prevent damage A, Saw blade.
C, Sliding spindle carriage.
D, Driving pulleys.
, First pinion, connecting through train of gears to wheel F, driving splined shaft G.
H, Wheel driven from sliding pinion on G.
J, Bevel-gears, communicating the motion to spindle B.
K, Screw for feeding carriage C along.
FIG. 55. Cold-sawing Machine. (Isaac Hill & Son, Derby.)
L, Three-step cone on shaft G, belted to M , connected by bevel-gears N and worm-gear O, to the screw K. Clutch for throwing in O to drive K.
Gears connecting shaft of L direct to K, also through clutch P. R, Handle for operating clutch P, which thus gives slow feed when clutch is in mesh with O, and quick return when engaging with P. S, Tappet rod, having dogs struck by carriage to stop feeding. T , Work-table, with clamp to hold objects. U, H-Girder being sawn off.
to the teeth, should undue stress come upon the saw. This is usually effected by the use of weights or springs, which allow a certain freedom or latitude to the driving gears. The work is held by screw clamps, V-blocks being required in the case of circular objects. A number of pieces, such as shafts, rails or girders, can be fastened down close together in a pile and cut through in one operation.
There is a very useful class of circular saw, the flush-side (fig. 55), ti:at is valuable for cutting close up to a surface. The disk is bolted to a flange on the end of the spindle with countersunk bolts, so that the face is quite flat. Another class of saw used for dealing with girders and bars is carried in bearings upon a pivoted arm, which is pulled downwards by a weight to give the feed. The work is bolted to a table below the saw. Ample lubrication, by oil or soapy water, is essential in cutting wrought iron and steel; it is pumped on the blade, keeping it cool and washing away the cuttings.
Band-saw machines resemble in outline the familiar types employed for sawing wood, but they are necessarily stronger and stiffer, and the saws run at a much lower speed. The tables, moreover, differ in possessing compound slides for moving the work and in the provision of a series of slots on the top table, whereby the object to be sawn is secured with bolts and clamps. The tables are moved automatically or by hand. The rate of cutting must be varied according to the thickness of metal. Lubrication is effected by running the lower saw pulley in a bath of oil or soapy water, which is carried up, so keeping the blade cool and " easing " the cut.
The reciprocating class of saw has until recently been confined to small types for workshop use, termed hack saws, which have a small blade ranging from 12 to 18 in. long. This is strained between a couple of bearings in a frame which is reciprocated above the work clamped in a vice. An arrangement of weights feeds the saw downwards. The larger hack saws cut off bars and girders up to 12 in. across, and in some there is a provision introduced for giving intermittent rotation to the bar, thus presenting fresh faces to the saw. The hack saw is of great utility for comparatively light work, and, as the smallest blades are cheap enough to be thrown away when worn out, there is no trouble and expense connected with their sharpening, as in the circular and band saws. An adaptation of the reciprocating saw is that of the jig type, which has a small blade set vertically and passing up through a table on which the work is laid. It is handy for cutting out dies and various curved outlines, in the same manner that fret-sawing in wood is done.
VIII. SHEARING AND PUNCHING MACHINES These have much in common as regards their mode of operation. They are actuated either by belt and spur gearing, by steam-engine, by electric motor, or hydraulically. The first named is only suitable where arrangements can be made for driving from a line shaft. In view of the great convenience of the other methods of driving, they are coming into greater use, especially for ship-yards and other works where shafting is undesirable or inconvenient.
For boiler makers' and platers' use the function of punching, and shearing are usually combined in one machine, the rams being placed at opposite ends and actuated from the same source of power. The last shaft in the train of gearing is set to bring its ends within the boxes containing the rams, and eccentrics on the shaft are moved within die blocks fitted to the rams, so that as the shaft revolves it causes the rams to move up and down and operate the shear blade and FIG. 56. Hydraulic Punching and Shearing Machine. (Musgrave Brothers, Leeds.) A, Frame. E, Punch. /, K, Main and return rams for B Shear blades, set angularly. F & G, Main and return rams ditto.
C, Ram for operating blade. for punch. L, M, N, Attendant's control- D, Small ram for returning ditto. H, Angle shear. ling handles.
FIG. 57. Steam Hammer, small Overhanging Type. (B. & S. Massey, Manchester).
A, Standard. B, Base-plate.
C, Anvil block (independent of standards).
D, Tup or hammer head.
E, Pallets, or forging blocks, attached to anvil and tup.
Piston, solid with piston rod H.
Piston valve, regulating period of admission of steam, operated by hand by lever K or lever N. Stop or throttle valve for controlling admission of steam to valve chest, operated by hand lever M. Lever in contact with roller on tup D, which moves the valve J automatically as the tup rises and falls.
Lever for pre-ad justing the range of movement of N and J, according to its setting in the notches of the quadrant from a to b. Steam supply pipe from boiler. Q, Exhaust steam pipe.
the punch attached to the bottom end. Another class of machines is worked by means of massive levers, pivoted in the framing, and actuated by cams on the driving shaft which cause the levers to rock and move the punches or shears up and down by the opposite ends. The punch slides are constructed to " dwell " for a short period at the top of the stroke at each revolution, thus giving the attendant time to place and adjust the plate accurately beneath the punch. The same effect is obtained in the eccentric types of machines mentioned above, by a disengaging motion .which is thrown in by touching a lever, thus stopping the punch until the operator is ready for its descent. The more complete machines have an angle shear situated centrally, with V-blades for severing angle iron. The largest forms of shears, for massive plates, usually have the blade reciprocated by crank or eccentrics on the driving shaft, coupled by connectingrods to the slide.
Hydraulic punching and shearing machines are used largely on account of their convenience, since they dispense with all belts, engines or motors in the vicinity, and give a very powerful stroke. The hydraulic cylinder is generally direct-connected to the slides, and the operator turns on the pressure water by a lever.
work; they embody two circular blades placed with their axes parallel, and the sharp bevelled edges nearly in contact. The blades being rotated sever the plate as it is fed between them. Either straight or circular cuts may be made; true circles or disks are produced by mounting the plate on a fixed stud and rotating it through a complete revolution past the cutters.
IX. HAMMERS AND PRESSES The growth in the use of hammers actuated by steam and compressed air, and of presses worked by water power, has been remarkable. The precursors of the power hammers were the helve and the Oliver; the first named was operated by gravity, being lifted by a circle of cams, while the second was lifted by a spring pole overhead and pulled down by the foot of the workman, acting on a lever the hammer shaft. The first was used by the ironworkers and the second by the smiths, until displaced by the Nasmyth hammer and its extensive progeny. Even now the old helve and Oliver survive in some unprogressive shops.
Steam Hammers. The original hammer as invented by James Nasmyth was single acting, operating simply by gravity, the function of the steam being to lift the hammer for each succeeding fall. The first improvement was made by Rigby, who took the waste steam exhausted from the lower side of the piston to the upper side and so imparted some slight pressure in the descent. It was a stage between the early and the present hammers. In these, high-pressure steam is admitted above the piston to impart a more powerful blow, compounded of velocity X mass, than is obtainable by gravity; hence they are termed double-acting hammers (fig. 57). The principal difficulties which have to be surmounted in their construction are those due to the severe concussion of the blows, which very sensibly shake the ground over an area of many yards. Framings are made very rigid, and in the larger hammers double, enclosing the hammer head between them. The foundations are fay far the heaviest used in any machine tools. Deep piling is often resorted to, supporting crossing timber balks; or concrete is laid in mass on which the iron anvil block is bedded. This block weighs anywhere between 100 and 1000 tons. The piston and its rod and the hammer head are generally a solid steel forging, for the piston rod is a weak element and cottered or screwed fittings are not trustworthy. Piston valves are generally used in preference to ordinary D-valves, combining simplicity of fitting with good balance. The periods of steam admission are under the control of the attendant, so that the length of stroke and the force of the blow are instantly responsive to his manipulation of the operating lever. Many hammers can be set to run automatically for any given length of stroke.
Pneumatic Hammers. A successful type of hammer for the ordinary operations of the smithy is that which is actuated by compressed air. Though designs vary the principle is the same, namely, air compressed in a controlling cylinder (fig. 58), and brought into an operating or hammer cylinder above the piston. Cushioning,or releaseof the air below the piston, is under control, as is the pressure of the air above it. Drop Hammers. The requirements of forged work have, besides the power hammers opeFIG. 58 Pneumatic Forging rated by a po s i t i ve down stroke, Hammer.
(W. & J. Player, Birmingham.) A , Standards. Base-plate. Anvil block. Tup. Pallets.
C, D, E, E, C, been the cause of the development of an equally large group which are gravity hammers only the drop hammers. They are put into operation by a belt or belts, but the function of the belt is simply to lift the hammer Hammer cylinder, the piston to the height desired, at which rod of L which is attached point it is released and falls, to D. The place of the drop hammer Air compressing cylinder. is in the lighter class of smith's Belt pulleys which reciprocate work, as that of the steam by means of the crank O, hammer lies in the heavier, but the piston in H. there is much overlapping, since Handle controlling the valve small steam hammers are rivals between H and G. to the others in light forging.
But, speaking generally, the largest volume of repetitive die forging or stamping of light articles is done under drop hammers. The small arms factories and the regular stamping shops scarcely use any other type. They may be roughly divided into three great groups; the belt, the board and the latest form the Brett lifter. In each the hammer head or tup, is lifted to any height within the range of lift, the height being controlled by the attendant at each blow. In most machines setting can be done at any constant height and the blows delivered automatically. Control is effected by hand or foot or both. Drop hammers generally have the advantage of working with greater rapidity than steam hammers. The original drop hammers, which are believed to have originated with the locksmiths of Birmingham and district, consisted of a hammer head attached to a rope, one end of which ran up over a loose pulley suspended in the roof, and the other was pulled by a man or two men, so lifting the hammer, which was then allowed to drop. The principle is embodied in many belt hammers to-day, but the pulley is driven constantly by shafting, and when the attendant pulls at the free end of the belt the friction of the pulley draws the belt over and lifts the hammer until the attendant lets it go. The weight lifted is greater than in the old type, but the labour is nevertheless very severe, and the blows are not rapid enough for quick forging. A far better machine is the board hammer. In this (fig. 59) the place of the belt is taken by an ordinary strip of board which passes between two rollers at the top of the hammer, which rollers are belt driven. The rollers are fitted on eccentric pins, so that the movement of levers causes them to grip the board for the lift, or release it for the fall, these levers being under the control of the attendant. They can also be set to operate automically for any height of lift.
These types are all subject to much concussion and vibration, because the machines are self-contained ; anvil, standards and heads being rigidly bolted together, the concussion of every blow is transmitted through the entire mechanism. The Brett hammers (fig. 60) are designed to lessen this, in some cases by making the anvil distinct from the superstructure, and in all by connecting the lifting ropes to the ends of long levers which act something like elastic springs, absorbing vibration. The driving mechanism is also original, comprising a cylinder with a wing piston, which is rotated by steam pressure through an arc of a circle only, sufficiently to operate the lifting levers. Another advantage is that the lifter cylinder need not be immediately over the hammer, but may be situated elsewhere. The hammer can be operated by hand directly for each stroke, or be set to work automatically.
FIG. 60. 5 cwt. Belt Drop Hammer with Brett's Lifter. (Brett's Patent Lifter Co., Ltd., Coventry.)
arrest Buffer blocks which motion of lever c.
d, Lever for automatic regula- tion of valve. /, Lever for regulating amount of opening of valve by hand. K, Foot lever for holding tup in either of the stops L.
e, Spring for foot lever.
A, A, Uprights.
E, Lifter cylinder.
F, Valve casing.
G, Rod operating valve by lever H.
a, Rock shaft.
Spring Hammers are a rather smaller group than the others. In these a belt-driven pulley actuates the tup through the medium of elastic leaf springs. The length of stroke is adjustable across the face of a slotted disk on the driving shaft.
Forging Machines. The Ryder forging machine is fitted with four or five pairs of swage tools, the lower halves being fixed and the upper ones driven by a rotating eccentric shaft. The operations imitate those on the anvil by hand forging, but from 800 to 1200 blows are delivered in a minute. The swages are arranged in succession, so that an operation is begun at one end and finished at the other, the attendant moving the bar rapidly through the successive swages or dies.
Forging Presses. These are rivals to the hammers, especially for heavy forgings, from which hammers are being rapidly displaced (fig. 61). It is now well understood that a hammer will not effect the consolidation of a massive forging right to the centre as a press will. The force of the hammer blow is not transmitted to the centre as is that of a press, nor is the hammer so useful in work of large dimensions but of no great weight.
In railway and wagon shops the presses are used far more frequently than the hammers. A great advan- tage of the press is that two and three rams can be brought into operation so that a forging may be pressed from above, from below and to one side, which is of great value in complicated forms and in welding, but is not practicable in the hammers.
Hence the forging presses have be- come developed for work of average dimensions as well as for the most massive. Many are of horizontal type, termed bull-dozers.
Power presses for working sheetmetal articles include those for cutting out the blanks, termed cuttingout or blanking presses, and those for cupping or drawing the flat blank into shape if desired (fig. 62). The lower dies are held upon a bed, and the upper in a sliding ram, moved FIG. 61. Hydraulic Forgup and down by a cam or crank- ing Press. (Fielding & Platt, shaft. A clutch mechanism is fitted, Ltd., Gloucester.) by means of which this shaft is connected with or disconnected from ^4 fable ' , i j . . . . ...
the heavy driving-wheel at will to c Drawbac k ram for return- give a single stroke or a series of j ng g strokes to the ram. In the normal D Horizontal ram.
state the ram remains stationary at Controlling valves.
the top position. The lightest presses are driven direct by belt on the crank-shaft pulley, but in the heavier classes spur-gearing must be interposed between the pulley shaft and the final shaft. The operation of drawing requires an encircling die which presses on the blank as it lies on its die, the cupping of the blank being effected by the downward motion of the plunger.
Sectional Elevation. Front Elevation.
FIG. 62. Power Press.
A, Main frame.
B, Bed for attaching dies.
C, Central slide.
D, Outer slide.
E, Belt pulleys on shaft, geared to wheel F thrown in by clutch to drive its shaft, which has two crank pins to reciprocate D and a cam disk actuating C.
G Extractor rocked downwards as slide rises to raise lever H and work an ejector rod, forcing finished article out of die.
This is why the machine shown in fig. 62 has an outer slide D, which is made to " dwell " with an even pressure, while the middle ram is moving down and drawing out the article. Blanking and cupping may be done as one continuous operation if the work is shallow.
Inclinable presses are employed for certain classes of work, the object being to let the stamped articles slide down the slope of the bed as rapidly as they are produced, instead of having to be removed by the operator. Much work can be placed on the dies by hand, but for producing large quantities of small articles automatic feeds are employed whenever possible. A good deal of work is produced from flat sheet, supplied in the form of a roll and fed through rollers by intermittent movements to the dies. Circular turn-tables are also used, operated by ratchet devices, which turn the tables round to bring a ring of pockets, carrying the pieces, successively under the dies; the attendant keeps the pockets supplied, but his hands do not come near the dies.
X. PORTABLE TOOLS The growth of portable machine tools is one of the remarkable movements of the present day. To some extent they have always been used, notably in the drilling and tapping operations of locomotive fire-boxes, but 'not until recently to any important extent in the ordinary fitting and erecting shops. The main reason lay in the difficulties due to transmission of power by ropes or shafts. The employment of compressed air, water, electricity and flexible shafts, by which long distances can be covered, has given new life to the portable system, which is destined to occupy a place of even greater importance than it does at present. The reason for the growing desirability of these tools is to be seen in the massive character of much engine and machine construction of the present time. Although firms that undertake the largest work can generally arrange to tool the individual parts on machines of massive sizes, that only meets a part of the difficulty. Very big work cannot be treated like that of small or even medium dimensions, done repetitively; that is, it is not practicable to drill and bore and ream and provide for the fitting of every piece by the aid of templets and jigs, while the work lies on the machine, but a great deal of adjustment and mutual fitting has to be accomplished in the course of erection. Therein lies the opportunity for the portable machine. If this is not used the alternatives are partial dismantling of the work and the transference of certain portions to machines or hand work. Another cause has been the substitution of machining for much hand work formerly done on massive constructions.
The principal operations for which portable tools are designed are the following: Drilling, screwing, cutting the seatings for keys, planing short portions of work, facings for the attachment of other pieces, as brackets and bearings, hammering operations, as in making welded joints, caulking the edges of boiler plates, chipping with hammer and chisel, riveting, ramming sand in foundry moulds, planing ships' decks, and some operations of lesser magnitude.
Portable tools are used in various ways. The first and most obvious is to attach them directly to the casting, forging or machine which is being built up. Thus a drilling machine will be clamped just where it is required to operate. Or if it has to be used on a large plane surface as a ship's deck, an electrical machine is suitable, in which magnetic attraction is set up between the foot of the machine and the deck sufficient to hold it down. A key-seating machine will be clamped on the shaft in which a keygroove has to be cut. A drilling machine may be fastened to a pipe with a chain embracing the pipe. Very many of the drills, and all the caulking and chipping hammers, are grasped in the hands and so thrust to their work. The tapping of screw holes is mostly done in this way, a common example being the holes for the stay bolts in the fire-boxes of steam boilers.
Another later method which has been introduced and practised in a few shops consists in installing a cast-iron floor-plate of large area, planed truly and provided with bolt holes and slots. On this a massive casting, forging or piece of work undergoing erection will be bolted. Then the portable tools planers, drills, etc., as required will be bolted to the table and brought into operation on the various sections of the work, several sometimes operating simultaneously. This method is to a certain extent coming into rivalry with the abnormal growth of machine tools, the development of which has been greatly accelerated by the massive dimensions of productions which only became possible by the substitution of steel made by the Bessemer and Siemens processes for iron.
The reciprocating motion necessary to effect hammering, chipping or caulking operations is produced by the action of a solid piston, sliding in a cylinder (fig. 63) and driven sharply against the end of the tool by the inrush of compressed air, being then returned for another stroke. The strokes range in number up to as many as 2000 per minute in some cases. For heavy riveting a " longstroke " hammer is employed, having a longer barrel than the chipping hammer shown in fig. 63, in order to obtain a greater force of blow. The operator grasps the hammer by the handle, with his fingers or thumb on the controlling lever, and as long as this is held down the blows continue. The air-supply pipe is flexible, so that it does not impede the movements of the workman. The tools at the end of the cylinder are simply held in a socket, so that they can be changed rapidly.
Rotative motion can be produced either by electric or pneumatic motors, and both systems are in wide use. Pneumatic motors are very suitable when an air-compressing plant is already laid down for other tools, while if electricity is used in the works portable tools operated by this agent may be employed instead of the pneumatic ones. In the electric drills (fig. 64) a small motor is fitted within the body and_ connected by spur-gears to the spindle to effect suitable speed reduction. A switch provides for stopping and starting the motor; the current is brought through a flexible cable which, like pneumatic hose, is armoured with wire to protect it from damage. The smallest drills are simply gripped in the operator's hand and FIG. 63. Tierney Pneumatic Chipping Hammer. (The Globe Pneumatic Engineering Co., Ltd.)
B, Tool socket, carrying chisel C.
D, Piston, which strikes the back of C.
E, Handle, screwed and clamped to A.
F, Trigger or lever clasped by operator's hand and opening valve G, admitting compressed air through connexion H, up passage J, through valve-box K, past valve L, and so against end of D, moving it towards C. As soon as the groove in the piston D registers with the hole M, air is admitted from a small hole (not shown), passes round the groove through hole M and passage N to the rear of the valve. This acting on the back of the valve throws it forward, thus shutting off the supply to the rear of the piston and permitting a small quantity of air to flow to the forward end of the piston for driving it in a backward direction. As soon as the air pressure is relieved on the back of the valve by the uncovering of exhaust holes (not seen) by the piston D, the valve is returned to the original position, owing to the air constantly pressing on the small area of the valve.
pushed up to the work; larger ones are supported by a pillar and arm, against which the thrust is taken, and the feed given by turning a screw at intervals.
FIG. 64. Electrically-driven Hand Drill. (Kramos Ltd., Bath.)
A, Body, cast in aluminium, with handles a, a.
B, Motor, with revolving armature C, connected by spur-gears D, to the drill spindle E, fitted with ball thrust bearings. F, Switch, operated by attendant pushing in a plug; the current is brought by flexible wires through the right-hand handle a.
Pneumatic drills are usually worked by little motors having oscillating cylinders, by which the air and exhaust ports are covered and uncovered. They run at a high speed and are geared down to the spindle. In some cases two cylinders are used, but often four are fitted to give a powerful and equable turning moment. Grinding machines are also built with air motors directly coupled to the wheel spindle, the machines being moved about over the work by handles.
Another class of portable tools is driven, not by self-contained motors, but from an outside source of power, which is conveyed to the tools through flexible shafts built up of a series of spiral springs, or through flexible joints which form a connexion that permits the shaft to bend round corners and accommodate itself to any position in which the tool may be placed. The advantage of this is that the tool itself is much lightened, since there is no motor, and it can therefore be easily handled. Thus a drill simply contains the spindle, running in a frame which carries bevel-gears for transmitting the motion of the flexible shaft. Portable grinders also have nothing but the spindle, wheel and frame.
XI. APPLIANCES Appliances are vastly more numerous in a modern shop than in the older works, largely on account of the more repetitive character of the operations done and of the desire to eliminate human labour, with its greater cost and chances of inaccuracy in the finished product. On all machines there are numerous aids by which the fixing of the work is facilitated. Many of these consist of simple packing blocks, by which heights are adjusted. These reach their higher developments in wedge-shaped packings, some of which are operated by a screw, while others act directly by screws. In some cases the exact height can be ascertained by observing graduations on the packings. Circular work is held in V-blocks, which occur in numerous modified forms. Various kinds of straps, clamps and bolts are used for gripping work with sufficient security to enable it to withstand the stress of the heaviest cutting. The highest development of all is attained in the templets and jigs, which are now indispensable in all modern shops, and which increase in number and complexity as the product of the shop becomes more specialized. A templet is a piece of metal cut to a definite shape, which being laid upon the work becomes a guide for striking the same shape on the surface of the work with a pointed scriber, and by which the tooling of any number of similar pieces is done without the labour of lining out each separate piece. Obviously, in such a case the degree of accuracy of the tooling still depends on the machine hand, who may work exactly, or only approximately, to these lines. Hence a great advance is made in the jig, which may be defined generally as a templet that is clamped rigidly to the work, or a box in which the work to be tooled is held. No marking off is done, but the jig becomes the actual guide for the operation of the cutting tools. The operation most frequently performed in jigs is drilling. Then the holes in the jig receive and coerce the drills, so that the holes made cannot vary in the least degree from those already in the jig. As it will often happen that hundreds or thousands of similar pieces will have to be tooled in this manner, holes in jigs are generally bushed with hardened steel, which is capable of enduring very lengthy service, and which can be renewed when worn. This is a simple illustration, but many jigs are of an extremely elaborate character, for it is obvious that the cost of a jig, though it may run into many pounds, becomes a mere trifle when spread over some thousands of pieces of work.
XII. WOOD-WORKING MACHINERY There is a large range of various classes of tools for performing the operations on timber, from the rough log to the finished product. Division is effected by saws, planing and finishing to outlines by knives or cutters, boring by augers and smoothing by sandpaper.
The first operation is that of tree-felling, which is often effected by machine, consisting of a reciprocating blade, working horizontally in a frame and moved by a steam cylinder. The boiler is separate, so that the machine may be transported about and set to work over a considerable area, steam being conveyed to it by a flexible pipe. When the trees are brought into the saw-mills in the form of logs, i.e. with the branches lopped off, they are often cross-cut to reduce them to suitable lengths. This operation is effected either by a reciprocating saw, operated by a pulley and crank, or by an electric motor, or else with a circular saw, travelling on a carriage which moves the saw through the log laid in front of it. The next operation, that of division or breaking-down into smaller portions, is done by saws of various types, according to the class of work. The oldest form of machine is the frame-saw, which is still used very largely. It comprises a framing within which a saw-gate or sawframe is reciprocated up and down by a crank; the frame holds a number of saws or webs of flat form, strained up tightly with wedges or cotters between the top and bottom of the frame, the distance between the saws being capable of variation to, suit boards of all thicknesses. The log is fed longitudinally to the gang of saws upon carriages, which are of two types. In the roller-feed, which is suitable tor comparatively even and straight logs, ribbed rollers in front and behind the saws obtain a bite on the top and bottom of the timber and feed it forward by their rotation. In the rack-feed the log is mounted bodily upon a long carriage that runs by rollers upon a set of rails, and the carriage is travelled along by pinions and racks, which give a positive feed regardless of the shape of the log. The carriage in the roller-feed machines is only represented by a couple of plain trolleys supporting the timber at back and front. The feed is obtained through a friction wheel of V-shape, with a smooth pawl, called the silent feed; the wheel is given a partial rotation at each down stroke of the saw-gate to turn the rollers or the pinions for carrying forward the log. The division of the timber may be either into deals or flitches, or planks or boards. In the last-named case as many as fifty saw-blades are sometimes held in a frame.
For the more valuable hardwoods a single blade reciprocating saw, operated horizontally, is used very largely, the machine being termed a board-cutter. The log is clamped to a travelling table, passing underneath the saw, which is strained in a frame sliding on a cross-rail that can be adjusted up or down on a couple of uprights like a planing machine. The saw is worked from a crank and connecting-rod. As only one board is sawn at a time the attendant is able to see the figuring of the timber and to avoid waste when bad places are encountered.
A machine much more rapid in operation is the horizontal band- saw, modelled on the lines of the above machine, but with a bandsaw blade running over two pulleys, at a high speed, of about 7000 ft. per minute. The saws are very thin, so that a minimum of wood is wasted in the cut or " kerf,' a very important consideration in dealing with costly woods. Vertical band-saws, having one pulley above the other so that the blade runs vertically, are very popular in America; they occupy less floor space than the horizontal types. It is necessary to present the log from the side, and it is therefore clamped by dogs upon a carriage running on rails, with provision for feeding the log laterally to the saw by sliding ways on the carriage.
The use of circular saws for breaking-down is confined chiefly to squaring up heavy balks, which need only a cut on each side, or for cutting thick slabs. The thickness of the saw entails considerable waste of wood, and a large amount of power is required for driving. The machines are termed rack-benches, and comprise a long divided table built up of thin plates and travelling past the fixed saw upon rollers, the movement being effected by a rack and pinion.
Re-sawing machines are those designed for further cutting-up deals, flitches, planks, etc., already broken out from the log, into boards and other scantlings. The deal and flitch frames are built on the model of the frame-saws first described, but with the differences that roller feed is always used, because the stuff is smooth and easily fed, and that the back of the timber is run against fences to keep it moving in a straight line. In the double equilibrium frames, which are much favoured, there are two sets of saws in separate frames connected by rods to opposite crank-shafts, so that as one frame is rising the other is going down ; the forces are thus balanced and vibration is diminished, so that the machines can be speeded rather higher. Re-sawing is also done on circular and band saws of various types, fitted with fences for guiding the timber and controlling the thicknesses.
The cross-cut saws constitute another large group. They are employed for cutting-off various classes of stuff, after breaking-down or re-sawing, and are of circular saw type. The pendulum saw is a suspended form, comprising a circular saw at the bottom of a hanging arm, which can be pulled over by the attendant to draw the saw through a piece of wood laid on a bench beneath. Circular saws are also mounted in tables or benches and made to part off stuff moved laterally upon a sliding-table. When there is sufficient repetition work machines with two or more saws are used to cut one or more pieces to accurate length without the necessity for measurement.
The lighter classes of circular and band-saws, employed for sawing up comparatively small pieces of timber, embody numerous provisions for quickening output. The plain saw benches, with circular saws, are the simplest class, consisting merely of a framed table or bench carrying bearings for the saw spindle and a fence on the top to guide the wood. A mechanical feed is incorporated in the heavier machines to push the timber along. The rope-feed mechanism includes a drum driven at varying rates and giving motion to a rope, which is connected with a hook to the timber, to drag it along past the saw, roller supports on rails taking the weight at each end of the bench. Roller-feed saws propel the stuff by the contact of vertical fluted rollers placed opposite the fence. Other classes of saws for joinery work, etc., are constructed with rising and falling spindles, so that the saw may be made to project more or less from the table, this provision being necessary in grooving and tonguing with special types of saws. The same effect is obtained by making the table instead of the spindle rise and fall.
As it is necessary to use different saws for ripping (with the grain) and cross-cutting, some machines embody two saws so that work can be cut to shape on the same machine. These " dimension saws " have two spindles at the opposite ends of a pivoted arm that can be turned on a central pin to bring one or the other saw above as required. In cases where much angular and intricate sawing is done universal benches are employed, having in addition to the double saws a tilting motion to the table, which in conjunction with various special fittings enables the sawyer to produce a large range of pieces for any class of construction.
Band-saws, which have a thin narrow blade, are adapted especially for curved sawing and cutting-out work which the circular saw cannot manage. The usual design of machine (fig. 65) comprises a stiff standard supporting a lower pulley in fixed bearings, and an upper one in a sliding bearing, which by means of a weight or spring is caused to rise and maintain an even tension on the saw blade as it is driven by the lower pulley, and runs the upper one. India-rubber tires are placed around the pulley rims to prevent damage to the saw teeth. The table, placed between the pulleys, may be angled for cutting bevel work. It is necessary, in order to do true work, to guide the saw blade above and below the cut, and it is therefore run in guides consisting of flat strips, in combination with antifriction rollers which take the backward thrust of the saw. Fret or jig saws are a small class with a vertical reciprocating blade, employed chiefly for cutting out interior portions which necessitate threading the saw first through a hole.
Planing machines, used for truing up the surfaces of wood after sawing, depend for their action upon rapidly revolving knives fastened to flat-sided cutter blocks. The simplest machines, the hand-planers, have a cutter cylinder revolving between two flat -WORKING MACHINERY table slides adjustable for height to support the wood while it is pushed along over the knives by the hand. A fence guides it in a straight line. Exact thicknessing is done on another type of machine, the panel planer or thicknesser, in which the cutter cylinder revolves above -the table and the stuff is fed through by rollers above FIG. 65. Band-sawing Machine with 30 in. pulleys. (Thomas White & Sons, Paisley.)
A, Cast-iron cored frame.
B, Fast and loose pulleys driving pulley C. D, Belt shipper operated by handle E.
F, Upper saw pulley, with its shaft carried in swivel bearing.
G, Screw for raising or lowering F to suit saw.
H, Spring to maintain even tension on saw, by raising E.
J, Counterbalanced guide bar, having a Jackson guide K at bottom ; K has wooden strips embracing the saw and a ball-bearing roller against which the back runs, while / is adjusted up or down to bring K as near to the work as convenient.
L, Table, with slit for saw; it may be canted for bevel sawing, by means of hand worm-gear M.
N, Protective casing to saw.
0, Guard to prevent saw flying over in case of breakage.
and below. By altering the height of the table the thickness of wood can be varied. Double machines include a cutter cylinder above and below the timber, so that the upper and under sides are planed simultaneously. A combination of the hand-planer and the thicknesser is useful in cases where space or expenditure must be limited.
When large quantities of planed stuff are wanted, such as for flooring-boards, etc., other types of machines are employed. The four-cutter planers are the most rapid in output, and the timber is passed through them at a high rate, ranging up to 150 ft. per minute. There is first a revolving cutter cylinder, which roughs off the underside of the stuff, whence it passes (being propelled by rollers) to a fixed knife which imparts a very smooth face. A little farther on in the machine two vertical cutter blocks are encountered which carry cutters to plane or tongue or mould the edges, after which another cylinder above finishes the top face. Similar types of machines are made to produce mouldings, using four cutters shaped to suit the pattern required.
Moulding is also done on the vertical spindle shapers, which carry a cutter or cutters at the top of a spindle projecting through a flat table. The work is slid over the table and controlled by touching a collar below the cutter. Any form may be given to the cutters to produce different profiles. Some special moulding machines use a cutter at the end of a spindle projecting downwards from an arm overhanging a table, an arrangement which enables recessing and carving to be performed.
Boring machines comprise rotating spindles and feeding mechanism to actuate augers. The single spindle machines are satisfactory enough for ordinary work, but when a number of differently sized holes have to be bored in a single piece of work, or in rapid succession, it is the practice to employ a machine with a number of spindles, so that a succession of augers of graduated diameters may be ready to use at will.
Mortising or cutting slots is done in vertical machines with a reciprocating spindle, operated either by hand or by crank disk and pulleys. The tool that cuts the mortise resembles a woodworker's chisel, but is of stouter form and has a suitable shank to fit in the spindle. The latter can be reversed to turn round and let the chisel face in the opposite direction for cutting at each end of a Machine with graduated stroke. i Sons, Johnstone.)
FIG. 66. Mortising and Boring (John McDowall <5 A, Frame.
B, Auger head, driven by belt C.
D, Mortising chisel reciprocated up and down by crank-disk E.
F, G, Levers connecting crank-pin to spindle of D.
H, Treadle connected to F; a gradually increasing stroke is imparted to the chisel by depressing H, which brings F, G into play and continually lengthens the stroke of D, cutting the mortise without shock.
/, Fast and loose pulleys driving E.
K, Cord actuated from shaft of /, which reverses the chisel when the handle L is moved and makes it cut in the reverse position.
M, Knee raised or lowered by hand-wheel and screw.
N, Cross-slide, adjusted by hand-wheel and screw.
O, Longitudinal slide, moved by rack and pinion and handwheel.
P, Timber vice.
mortise. A boring spindle is often incorporated with the machine to make holes for the mortising chisel to start in (fig. 66). Another class of mortiser employs a square hollow chisel, inside of which an auger rotates and first bores a hole, leaving to the chisel the duty of finishing out the corners. The chain mortiser is another type; it has an endless chain of flat links, sharpened to make cutting teeth, and is run around a bar and a roller at a high speed, so that when fed into the wood a recess or mortise is cut out.
Tenoning machines, designed to cut the reduced ends or tenons to fit in mortises, perform their work by the aid of cutter blocks, revolved on horizontal sp : ndles above and below the timber, which is fed laterally upon a sliding carriage.
Dovetailing is effected by revolving cutters in machines having mechanism for pitching out the cuts, or if the work warrants it an entire row of dovetails is made at one traverse, by fitting a row of cutters and feeding simultaneously. Corner-locking, or cutting parallel tongues and grooves in the edges of boxes, etc., is a rather more rapid operation than dovetailing, and is done with suitable cutter blocks or disks of appropriate thickness and pitching apart.
The general joiner, as its name implies, will do a large variety of operations, and is used in shops and on estates where a complete plant of machines would be out of the question. It usually has a circular saw and sometimes a band-saw also, together with planing and moulding apparatus, a moulding spindle, boring spindle and tenoning apparatus.
The lathes used in woodworking comprise the plain hand types with a simple T-rest on which the turner rests the tools to deal with the work revolving between centres, and the copying or Blanchard lathes, in which a master form or copy is rotated and caused by the contact and coercion of a roller to move the cutter rest in a corresponding fashion, so that the work is cut away until it exactly matches the shape of the copy.
Sand-papering machines, which finish the surface of wood to a high degree, deal with both flat and curved faces. Flat boards, panels, etc., can be done by contact against revolving drums or disks covered with glass-paper, being fed along over them by hand or by rotating rollers. In one class of machine a revolving disk is placed at the end of a series of jointed arms, by which the disk can be moved about over the work resting on a table underneath.
XIII. MEASUREMENT An advance of the greatest importance made in mechanical engineering is that of measurement. Since the beginning of the 10th century steady movement has been going on in this direction until it seems impossible that much greater refinement can now be looked for. Probably the chief advances to be expected will lie in the general extension in workshop practice of the knowledge already acquired, rather than in the acquisition of higher degrees of refinement.
Methods of measurement adopted in woodworking have but little application in high-class engineers' work. They are adopted, however, to a considerable extent in the metal trades which are allied to engineering, as sheet metal working, girder work, etc. When a carpenter or joiner sets about constructing a door, window sash, roof or box he takes a two-foot rule, a flat lead pencil, and marks off the dimensions and lines by which he intends to work. If he has to work very carefully, then instead of using a pencil he cuts a line with the edge of a keen scriber or chisel-like tool, by which to saw, plane or chisel. If outlines are curved, the compasses are brought into requisition, and these cut a fine line or lines on the surface of the wood. But in any case the eye alone judges of the coincidence of the cutting with the lines marked. Whether the tool used be saw, chisel, gouge or plane, the woodworker estimates by sight alone whether or not the lines marked are worked by.
The broad difference between his method and that of the engineer's machinist lies in this, that while the first tests his work by the eye, the second judges of its accuracy or otherwise by the sense of touch. It may seem that there cannot be very much difference in these two methods, but there is. To the first, the sixty-fourth part of an inch is a fine dimension, to the second one-thousandth of an inch is rather coarse. Now the thickness of tissue paper is about one-thousandth of an inch, and no one could possibly work so closely as that by the eye alone. Engineers' steel rules usually have one inch which is divided into one hundred parts. Tolerably keen sight is required to distinguish those divisions, and few could work by them by ocular measurement alone, that is, by placing them in direct juxtaposition with the work. A thousandth part of an inch seems by comparison a fine dimension. But it is very coarse when considered in relation to modern methods of measurement. In what are called " limit gauges " the plugs and rings are made of slightly different dimensions. If a plug is made a thousandth of an inch less than its ring it will slip tnrough it easily with very perceptible slop. The common rule is therefore scarcely seen in modern machine shop, while the common calipers fill but a secondary place, their function having been invaded by the gauges. A minute dimension cannot be tested by lines of division on a rule, neither can a dimension which should be fixed be tested with high precision with a movable caliper of ordinary type. Yet it must not be supposed that the adoption of the system of gauging instead of the older methods of rule measurement relieves men of responsibility. The instruments of precision require delicate handling. Rough forcing of gauges will not yield correct results. A clumsy workman is as much out of place in a modern machine shop as he would be in a watch factory. Without correctness of measurement mechanical constructions would be impossible, and the older device of mutual fitting of parts is of lessening value in face of the growth of the interchangeable system, of international standards, and of automatic machine tools which are run with no intervention save that of feeding stock.
The two broad divisions of measurement by sight and by contact are represented in a vast number of instruments. To the firstnamed belong the numerous rules in wood and metal and with English and metric divisions, and the scales which are used for setting out dimensions on drawings smaller than those of the real objects, but strictly proportional thereto. The second include all the gauges. These are either fixed or movable, an important subdivision. The first embrace two groups one for daily workshop service, the other for testing and correcting the wear of these, hence termed " reference gauges." They are either made to exact standard sizes, or they embody " limits of tolerance," that is, allowances for certain classes of fits, and for the minute degrees of inaccuracy which are permissible in an interchangeable system of manufacture. The movable group includes a movable portion, either corresponding with one leg of a caliper or having an adjustable rod, with provision for precise measurement in the form of a vernier or of a screw thread divided micrometrically. These may be of general character for testing internal or external diameters, or for special functions as screw threads. Subtitles indicate some particular aspect or design of the gauges, as " plug and ring," " caliper," " horseshoe," " depth," " rod," " end measure," etc. So severe are the requirements demanded of instruments of measurement that the manufacture of the finer kinds remains a speciality in the hands of a very few firms. The cost and experience necessary are so great that prices rule high for the best instruments. As these, however, are not required for ordinary workshop use, two or three grades are manufactured, the limits of inaccuracy being usually stated and a guarantee given that these are not exceeded.
Measurement by Sight. Rules and Scales. The rules are used for marking off distances and dimensions in conjunction with other instruments, as scribers, compasses, dividers, squares; and for testing and checking dimensions when marked, and work in course of reduction or erection, directly or from calipers. They are made in boxwood and in steel, the latter being either rigid or flexible, as when required to go round curves. Rules are fitted in combination with other instruments, as sliding calipers, squares, depth gauges, etc. The scales are of boxwood, of ivory, the value of which is discounted by its shrinkage, and of paper. They are of flat section with bevelled edges, and of oval and of triangular sections, each giving a thin edge to facilitate readings. They are fully divided, or open divided; in the first case each division is alike subdivided, in the second only the end ones are thus treated.
The Gauges. Fixed Gauges. These now embrace several kinds, the typical forms being represented by the cylindrical or plug and ring gauges and by the caliper form or snap gauges. The principle in each is that a definite dimension being embodied in the gauge, the workman has not to refer to the rule, either directly or through the medium of a caliper. This distinction, though slight, is of immense importance in modern manufacturing. Broadly it corresponds with the difference between the older heterogeneous and the present interchangeable systems.
Plug and Ring Gauges. The principal ones and the originals of all the rest, termed Whitworth gauges after the inventor, are the plug and ring gauges (fig. 67, A and B). The principle on which they depend is that if the two gauges are made to fit with perfect accuracy, without tightness on the one hand or slop on the other, then any work which is measured or turned and bored or ground by them will also fit with equal accuracy. Bored holes are tested by the plug gauge, and spindles are tested by the ring gauge, and such spindles and holes make a close fit if the work is done carefully. Of course, in practice, there is very much variation in the character of the work done, and the finest gauges are too fine for a large proportion of engineers' work. It is possible to make these gauges within 5^ of an inch. AB p , nd But they are seldom required so c ' niffprem-p o-amrp fine as that for shop use; VA a is ' g D ed reference eau^e generally fine enough. For general " shop work the gauges are made to within about r^Va of an inch. Standard gauges in which the plug and ring are of the same diameter will only fit by the application of a thin film of oil and by keeping the plug in slight movement within the ring. Without these precautions the two would " seize " so hard that they could not be separated without force and injury.
Plug and Ring v. Horseshoe Gauges. The horseshoe, snap or caliper gauges (fig. 68) are often used in preference to the plug and ring types. They are preferred because the surfaces in contact are narrow. These occur in various designs, with and without handles, separately and in combination and in a much larger range of dimensions than the plug and ring. Ring gauges are not quite such delicate instruments as the fixed caliper gauges. But since they measure diameter only, and turned work is not always quite circular, the caliper gauges are not so convenient for measurement as the round gauges, which fit in the same manner as the parts have to fit to one another.
Fixed Gauges. Limit Gauges. Some fits have to be what is termed in the shops " driving fits," that is, so tight that they have to be effected by driving with a hammer or a press, while others have to be " working fits," suitable, say, for the revolution of a loose pulley on its shaft or of an axle in its bearings. The " limit " or " difference gauges " (figs. 67 and 68) are designed for producing these working fits ; that is, the plug and ring gauges differ in dimensions so that the work bored will drive tightly, or slide freely over FIG. 68.
A, Separate caliper or snap C, Difference gauge.
gauges. D, Newall adjustable limit B, Combined internal and ex- gauge.
ternal gauges. a, b, Plugs.
the work turned. These are variously sub-classified. The system which is generally accepted is embodied in the gauges by the Newall Engineering Co. These embrace force fits, which require the application of a screw or hydraulic press; driving fits, that require less power, as that of a hammer; push fits, in which a spindle can be thrust into its hole by hand; and running fits, such as that of shafts in bearings. Fixed gauges are made for each of these, but as this involves a heavy outlay the Newall firm have adjustable limit gauges (fig. 68, D) for external dimensions, the standard plug being used for holes. The setting is done by screwed plugs or anvils adjusted by reference bars. In all these gauges the " go on " and " not go on " ends respectively are stamped on the gauge, or the equivalents of -f- and .
Fixed Reference Gauges. Reference Disks and End Measuring Rods. Shop working gauges become in time so damaged by service that they fail to measure so accurately as when new. To correct these errors reference gauges are provided, by which the inaccuracy of the worn ones is brought to the test. These are never used in the shops for actual measurement of work, but are only kept for checking the truth of the working gauges. They include disk, stepped and end measurement gauges. The disk and the stepped are used for testing the ring gauges, the stepped kind comprising essentially a collection of disks in one piece (fig. 67, D). The end measure pieces test the external gauges. The end measure standard lengths made by the Pratt & Whitney Co. are so accurate that any sizes taken at random in any numbers from } in. to 4 in., varying by sixteenths of an inch, will, when placed end to end, make up an exact length ; this is a difficult test, since slight variations in the lengths of the components would add up materially when multiplied by the number of pieces. The ends are ground off with diamond dust or emery in a special machine under water, and are so true that one piece will support another by cohesive force, and this though the surfaces are less than } in. square.
Movable Gauges. This extensive group may be regarded as compounded of the common caliper and the Whitworth measuring machine. They are required when precise dimensions have to be ascertained in whole numbers and minute fractional parts. They combine the sense of touch by contact, as in the calipers, with the exact dimensions obtained by inspection of graduated scales, either the vernier or the micrometer screw. If gauges must not vary by more than nrfrinr of an inch, which is the limit imposed by modern shop ideals, then instruments must be capable of measuring to finer dimensions than this. Hence, while the coarser classes of micrometers read directly to tiftnv P art of an inch, the finest measure up to-iojftnnj of an inch, about 200 times as fine as the diameter of a human hair. They range in price correspondingly from about a sovereign to 100.
Ttif Calipers. Common calipers (fig. 69) are adjusted over or within work, and the dimensions are taken therefrom by a rule or a gauge. They usually have no provision for minute adjustment beyond the gentle tapping of one of the legs when setting. In some forms screw adjustment is provided, and in a few instances a vernier attachment on the side of the pivot opposite to the legs.
Vernier Calipers. The vernier fitting, so named after its inventor, Pierre Vernier, in 1631, is fitted to numerous calipers and caliper rules. It is applied to calipers for engineers' use to read toryinr of an inch without requiring a magnifier. The beam of the caliper is divided into inches and tenths of the inch, and each tenth into fourths and the vernier into twenty-five parts, or the beam is divided into fiftieths of an inch (fig. 70) and the vernier has 20 divisions to 19 on the rule. The caliperiaws are adapted to take both external and internal dimensions. These " beam calipers " are also made for metric divisions. Minor variations in design by different manufacturers are numerous.
FIG. 69. Calipers.
A, Ordinary external type, adjusted by tapping the legs.
B, Type adjusted by screw in auxiliary leg.
C, Screw calipers, opened by contraction of curved spring and closed by nut.
D, Self-registering caliper, with pointer moving over quadrant.
E, Common internal type.
F, Screw type with spring.
G, Combined internal and external for measuring chambered holes. H, Compass caliper for finding centres.
J, Keyhole caliper for measuring from hole to outside of boss.
FIG. 70. Vernier Caliper. A, Beam; B, vernier; C, fixed jaw; D, movable jaw; E, clamping head; F, abutment head, with adjusting screw a, for fine adjustment of D.
So oo FIG. 71. Measuring Machine. (The Newall Engineering Co.)
A, Hollow base or bed, mounted on three points.
B, Measuring or fast headstock.
C, Movable head, or tailstock.
D, Spirit-level to indicate alterations in length of piece being measured due to changes in temperature, termed the indicator or comparator.
E, Measuring screw.
F, Nut for rapid adjustment of ditto.
G, Knob of speed screw for slow movement of ditto. H, Dividing and measuring wheel.
J, Vernier or reading bar.
a, a, Points between which contact is made.
Micrometer Calipers are the direct offspring of the Whitworth measuring machine. In the original form of this machine a screw of 20 threads to the inch, turned by a worm-wheel of 200 teeth and single-threaded worm, had a wheel on the axis of the worm with 250 divisions on its circumference, so that an adjustment of IB oh) OB of an inch was possible. The costly measuring machines made to-day have a dividing wheel on the screw, but they combine modifications to ensure freedom from error, the fruits of prolonged experience. Good machines are made by the Whitworth, the Pratt & Whitney, the Newall (fig. 71), and the Brown & Sharpe firms. These are used for testing purposes. But there are immense numbers of small instruments, the micrometer calipers (fig. 72), made for general shop use, measuring directly to rjVj of an inch, and in the FIG. 72. Micrometer Calipers. (Brown & Sharpe Mfg. Co.)
A, Frames. a, Adjusting nuts for taking up B, Anvil or abutment.
C, Hub divided longitudinally. b, D, Spindle with micrometer 1 c, screw.
E, Thimble, divided circularly.
Ratchet stop, which slips under undue pressure to ensure uniform measurement.
hands of careful men easily to half and quarter thousandths ; these cost from i to i, IDS. only. In these the subdivision of the turns of the screw is effected by circular graduations. Usually the screw at a. a FIG. 73. Beam Micrometer Calipers.
C, Abutment block with screw c for fine adjustment.
d, Clamping screws.
B, Head, adjustable by equal inch divisions, by lines a, a, or holes b, b, and plug b' holes bushed.
pitch is 40 to the inch, and the circular divisions number 25, so that a movement of one division indicates that the screw has been advanced fa of 4 V r 10*00 f an . inch. Provision for correcting or taking up the effects of wear is included in these designs (e.g. at a in fig. 72), and varies with different manufacturers. A vernier is sometimes fitted in addition, in very high class instruments, to the circular divisions, so that readings of ten thousandths of an inch can be taken. Beam micrometer calipers (fig. 73) take several inches in length, the micrometer being reserved for fractional parts of the inch only.
Depth Gauges. It is often necessary to measure the depth of one portion of a piece of work below another part, or the height of one portion relatively to a lower one. To hold a rule perpendicularly and take a sight is not an accurate method, because the same objections apply to this as to rule measurement in general. There are many depth gauges made with rule divisions simply, and then these have the advantage of a shouldered face which rests upon the Upper portion of the work and from which the rule measurement is FIG. 74. Depth Gauges.
A, Plain round rod a, sliding in head b, and pinched with screw c.
B, Rule a, graduated into inches or metric divisions, sliding on head b, in grooved head of clamping screw c.
C, Slocomb depth gauge, fitted with micrometer, a, Rod marked in half inches, sliding in head b ; c, hub ; d, thimble corresponding with similar divided parts in the micrometer calipers; e, clamping screw.
taken (fig. 74). These generally have a clamping arrangement. But for very accurate work either the vernier or the micrometer fitting is applied, so that depths can be measured in thousandths of an inch, or sometimes in sixty-fourths, or in metric subdivisions.
FIG. 75. Rod Gauges.
A, Pratt & Whitney gauge, a, Tube split at ends; 6, 6, chucks clamping tube on plain rod c, and screwed end d. Rough adjustment is made on rod c, of which several are provided; fine adjustment is by screwed end d.
B, Sawyer gauge, a, Body; 6, extension rods for rough adjust- ment, several being supplied and pinched with screw c; d, screwed end with graduated head ; e, reading arm extending from body over graduations; /, clamping screw.
Rod Gauges. When internal diameters have to be taken, too large for plug gauges or calipers to span, the usual custom is to set a rod of iron or steel across, file it till it fits the bore, and then measure its length with a rule. More accurate as well as adjustable are the rod gauges (fig. 75) to which the vernier or the micrometer are fitted. These occur in a few varied designs.
Screw Thread Gauges. The taking of linear dimensions, though provided for so admirably by the systems of gauging just discussed, does not cover the important section of screw measurement. This is a department of the highest importance. In most English shops the only test to-day of the size of a screw or nut is the use of a standard screw or nut. That there is variation in these is evidenced by the necessity for fitting nuts to bolts when large numbers of these are being assembled, after they have been used in temporary erections or when nuts are brought from the stores to fit studs or bolts cut in the shop. This method may suffice in many classes of work, but it is utterly unsuited to an interchangeable system; and when there is a fair amount of the latter firms sometimes make thread gauges of their own, in general form like the plug and ring gauges, using a hard quality of steel for small sizes or a tough quality of cast iron for the larger. These, though not hardened, will endure for a long time if treated carefully. But FIG. 76. Screw Thread Gauges. (Pratt & Whitney Co.)
A, Plug gauge; a, size of tapping hole; b, thread.
B, Ring gauge; a, pins to prevent lateral movement; b, adjusting screw for opening gauge ; c, screw for closing ditto.
though very useful and far better than none at all they lack two essentials. They are simply accommodation gauges, made to an existing tap or die, and do not therefore embody any precise absolute measurement, nor do they include any means for measuring variations from standard, nor are they hardened. To produce gauges to fulfil these requirements demands an original standard to work by, micrometric measurements, and the means of grinding after the hardening process. These requirements are fulfilled in the screw thread gauges and calipers of the Pratt & Whitney and the Brown & Sharpe companies. The essential feature of a screw gauge is that it measures the sides of the threads without risk of a possible false reading due to contact on the bottom or top of the V. This is fulfilled by flatting the top and making the bottom of the gauge keen. The Pratt & Whitney gauges are made as a plug and ring (fig. 76), the plug being solid and the ring capable of precise adjustment round it. There is a plain round end, ground and lapped exactly to the standard size of the bottom of the thread, a dimension which is of an inch (fig. 77). They are used in some kinds of lathe chuck work, but their principal value is in fitting and erecting the finer mechanisms.
FIG. 77. Indicator.
A, Base; B, stem; C, arm; D, pointer or feeler, pivoted at a, and magnifying movement of the work E upon the scale b; F, spring to return D to zero.
Surface Plates and Cognate Forms. Allied to the gauges are the instruments for testing the truth of plane surfaces: the surface plates, straight-edges and winding strips. The origination of plane surfaces by scraping, until the mutual coincidence of three plates, is secured, was due to Whitworth. These surface plates (fig. 78, A) fill an important place in workshop practice, since in the best work plane surfaces are tested on them and corrected by scraping. To a large extent the precision grinding machines have lessened the value of scraping, put it is still retained for machine slides and other work of a similar class. In the shops there are two classes of surface plates: those employed daily about the shops, the accuracy of which becomes impaired in time, and the standard C, Common square.
D, Square with adjustable blade.
obliterated in the threaded end because of the bottoms of the angles being made keen for clearance. There are three kinds of this class of gauge made; the first and most expensive is hardened and ground in the angle, while the second is hardened but not ground. The first is intended for use when a very perfect gauge is required, the second for ordinary shop usage. The third is made unhardened for purposes of reference simply, and it is not brought into contact with the work to be tested at all, but measurements are taken by calipers; in every detail it represents the standard threads. The Brown & Sharpe appliance is of quite a different character. It is a micrometer caliper having a fixed V and a movable point between which the screw to be measured is embraced. By the reading of the micrometer and the use of a constant the diameter of any thread in the middle of the thread can be estimated.
Miscellaneous. The foregoing do not exhaust the gauges. There are gauges for the sectional shapes of screw threads of all pitches, gauges for drilled holes that have to be screwed, gauges for the depth and thickness of the teeth of gear-wheels, gauges for the tapers of machine spindles, gauges for key-grooves, etc. There are also the woodworker's gauges the marking and cutting, the panel, the mortise and the long-tooth.
Indicators are a small group of measuring instruments of a rather peculiar character. They magnify the most minute error by adaptations of long and short lever arms. The Bath, the Starrett and the Brown & Sharpe are familiar in high-class shops. Some simply magnify inaccuracy, but in one type an index reads to thousandths FIG. 78.
A, Surface plate ; a, protecting cover for ditto when not in use.
B, Large ribbed straight-edge.
plate or plates employed for test and correction. Straight-edges are derived from the surface plates, or may be originated like them. The largest are made of cast-iron, ribbed and curved on one edge, to prevent flexure, and provided with feet (fig. 78, B). But the smaller straight-edges are gener- ally parallel, and a similar pair constitutes " winding strips," by which any twist or departure from a plane surface is detected. Squares, of which there are numerous designs (fig. 78, C and D), are straight-edges set at right angles. Bevels or Devel-squares (fig. 79), are straight-edges comprising a stock and a blade, which are adjustable for angle in relation to each other. Shop protractors often p JG include a blade adjustable for ^ Common bevel angle, forming a bevel with gradua- B ' Universal bev l for test ; ng tions. Spirit-levels test the hon- , ana \K zontal truth of surfaces. Many levels have two bubble tubes at right angles with each other, one of which tests the truth of vertical faces. Generally levels have flat feet, but some are made of V-section to fit over shafting. The common plumb-bob is in frequent use for locating the vertical position of centres not in the same horizontal plane. When a plumb-bob is combined with a parallel straight-edge the term plumbrule is applied. It tests the truth of vertical surface more accurately than a spirit-level. (J. G. H.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)