Centring and driving; a, point B, Face-plate driver or catchby boy of verd 19b FIG. 34 8. g,Change feed dogs adjustable:fixed in slot in body of point C, Common heart-shaped carrier. centre; b, carrier; c, driver plate; a, centre; b, driver. Roisd centre; d, back centre; e, D, Clement doubledriver; a, facework bulbow plate; b, b, drivers; c, loose aomei ad and aidplate 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 rotat ing 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. 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 toa 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. slotted bolt holes a, a; b, b, brass or steel facings. Fixed steady with hinged top and three setting pieces. 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 carried between centres indirectly, upon mandrels or arbors (fig. 36). This is the method 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 B FIG. 36.-Mandrels. A, Body. FIG. 38.-Independent Jaw Chuck. a, Recess to receive face-plate. B, Jaws or dogs. C, Screws for operating jaws. 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 in. to in., by the utilization of a long taper. A split, springy cylinder may be moved endwise A, 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 B, C, D, b, Square heads of screws for key. c, Tee-grooves for bolts. 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. FIG. 40.-Combination Geared Scroll Chuck. A, Back plate; a, recess for faceplate. B, C, D, 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 E, 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 face-d, olate. In all these types the radial setting is tentative, that is, Pinions. FIG. 41-Spiral Geared Chuck, Circular rack with scroll b on concentric movement. (C.Taylor, face. Chuck body. Jaws fitting on intermediate pieces that engage with the scroll b. Screws for operating jaws independently. C, Spiral plate with teeth engag E, Bevel pinions gearing with teeth on back of C. 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 horizontalo 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 necessary adjustments and movements, so that the tool can be carried ar 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 upnights 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. G, G, Bevel-gears for elevating cross-slide by means of screws H. H. A, Base. 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 f 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 DI ni Dr 4. 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. Bat there is a great group of planers in which the work is always faxed, 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 rokes. In some designs horizontal strokes are provided for, or either vertical or horizontal as required. Here, as in the side planer, 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 All the takes place vertically and there is a lost return stroke. |