Fig. 14. Geometric Collapsing Tap
Collapsing Taps.—The collapsing tap shown in [Fig. 14] is one of many different designs that are manufactured. They are often used in turret lathe practice in place of solid taps. When using this particular style of collapsing tap, the adjustable gage A is set for the length of thread required. When the tap has been fed to this depth, the gage comes into contact with the end of the work, which causes the chasers to collapse automatically. The tool is then withdrawn, after which the chasers are again expanded and locked in position by the handle seen at the side of the holder. In all threading operations, whether using taps or dies, a suitable lubricant should be used, as a better thread is obtained and there is less wear on the tools. Lard oil is a good lubricant, although cheaper compounds give satisfactory results on many classes of work.
Fig. 15. Various Types of Tools for the Turret Lathe
Miscellaneous Turret Lathe Tools.—The chamfering tool shown at A, [Fig. 15], is used for pointing the end of a bar before running on a roughing box-tool. This not only finishes the end of the bar but provides an even surface for the box-tool to start on. The cutter is beveled on the end to form a cutting edge and it is held at an angle. The back-rest consists of a bell-mouthed, hardened tool-steel bushing which supports the bar while the cut is being taken.
The stop gages B and C are used in the turret to govern the length of stock that is fed through the spindle. When a finished piece has been cut off, the rough bar is fed through the spindle and up against the stop gage, thus locating it for another operation. This gage may be a plain cylindrical piece of hardened steel, as at B, or it may have an adjusting screw as at C; for special work, different forms or shapes are also required. The stop gages on some machines, instead of being held in the turret, are attached to a swinging arm or bracket that is fastened to the turret slide and is swung up in line with the spindle when the stock is fed forward.
The center drilling tool D is designed to hold a standard combination center drill and reamer. This type of tool is often used when turning parts that must be finished afterwards by grinding, to form a center for the grinding machine. The adjustable turning tool E is used for turning the outside of gear blanks, pulley hubs or the rims of small pulleys. The pilot a enters the finished bore to steady the tool, and cutter b is adjusted to turn to the required diameter.
The cutting-off tool-holder F (which is held on the cross-slide of the turret lathe) is usually more convenient than a regular toolpost, as the blade can be set closer to the chuck. The blade is held in an inclined position, as shown, to provide rake for the cutting edge; the inclined blade can also be adjusted vertically, a limited amount, by moving it in or out. The multiple cutting-off tool G holds two or more blades and is used for cutting off several washers, collars, etc., simultaneously. By changing the distance pieces between the cutters, the latter are spaced for work of different widths. The flat drill holder H is used for drilling short holes, and also to form a true “spot” or starting point for other drills.