The guide screw and die are both movable, and are substituted when a screw of different pitch requires to be chased; thus the different screw threads are cut without the aid of change wheels. The changes of cutting, turning, and boring are in this arrangement effected with ease. and facility. The turret can carry a full complement of tools for any specific work, and thereby effects a considerable saving of time after once fixing. Internal and external screws, with right or left hand threads of 8, 11, 14, 19 and 28 per inch (which are the standard pitches) can readily be cut by simply changing the guide screw and die. The concentric chuck is not always used, but chucks having three or four jaws; universal, or independent, or "bell" chuck may be fixed on the spindle as required. Capstan Lathes.-The lathe illustrated in Fig. 102 is also fitted with a special saddle for chasing square or vee threads by means of a "leader" (screw). Four different pitches, either right or left hand, can be cut by each leader, the change being made by levers. By means of a frictional arrangement on the headstock, the back gearing may be removed and single speed introduced without having to stop the spindle. The capstan slide has an automatic feed, and is fitted with a dead stop for each tool. The spindle is hollow, and will take bars up to 2 in. diameter; when, however, required, this lathe is equally adapted for chuck work in cast iron, steel, or brass. Revolving Valve Chuck.-The valve chuck shown in Fig. 103 is fitted with ball bearings to the revolving jaws, whereby the friction is so much reduced that the jaws can be rotated by using the spanner on the square shaft B without slackening the chuck, and consequently without shifting the work. The dividing mechanism is provided with a screw for holding the FIG. 103.-Herbert's valve chuck. catch firmly in position when dealing with heavy work. The dividing plate is in one piece with the jaw spindle, by which means back-lash is obviated. Small Capstan Lathe.-Fig. 104 represents a capstan lathe made for high-speed brass and steel work from the bar. It will admit in. through the automatic chuck. This chuck is operated by a hand lever, which also moves the bar forward in the chuck. The chuck is adjusted for varying diameters by two knurled nuts at the rear end. The capstan slide revolves automatically upon the backward. stroke; this slide has two independent adjustable stops, thus providing greater ease in setting than when only one stop is provided. The cutoff rest carries two tools, one at the front and one at the back, and has adjustable stops in both directions. The operating lever passes through a split bearing, and can be clamped upon the shaft in any position found most suitable. A special feature of this machine is that it is made dust-proof. On these high-speed machines dust is the great enemy of accuracy and durability. It is therefore imperative to protect the vital parts from the action of dust. In order to withstand the shocks inherent to highspeed work, the locking mechanism is made of tempered tool steel. Another feature, to obtain a uniformity in running, is that the speed cones are carefully turned inside and fitted to their spindles by a cone bearing, no keys being used. On these light spindles keys have been found in many cases to spring the work out of truth. : The following are some of the leading dimensions :- Working stroke of capstan, 4 in. Automatic Screw Machine.-The machine shown in Fig. 105 is suitable for producing bolts, screws, pins, collars, bushes, etc., direct from the bar, up to about 8 in. long x 2 in. diameter. The machine is equipped with a set of standard cams and tools; that is to say, such cams and tools as will produce any of the above kinds of work without requiring any alteration to suit the different pieces. When the machines are employed upon one kind of work all the time, special cams and tools are used, but in general practice the standard arrangement is preferred, on account of its more useful application to a wider range of work, or in cases where on simple work having few operations it is advisable to produce two pieces at each cycle of the machine. The spindle of the machine is fitted with an automatic chuck for gripping and releasing the bar, and automatic arrangements for feeding |