Knurling tools are shown at I and J. The former is intended for knurling short lengths and is sometimes clamped on top of the cut-off tool on the cross-slide, the end being swung back after knurling (as shown by the dotted lines) to prevent interference with the work when the cutting-off tool is in operation. The knurling tool J has a shank and is held in the turret. The two knurls are on opposite sides of the work so that the pressure of knurling is equalized. By adjusting the arms which hold the knurls, the tool can be set for different diameters.
Three styles of drill holders are shown at K, L and M. Holder K is provided with a split collet (seen to the left) which is tightened on the drill shank by a set-screw in the holder. This holder requires a separate collet for each size drill. The taper shank drill holder L has a standard taper hole into which the shank of the drill is inserted. The adjustable type of holder M is extensively used, especially on small and medium sized machines when several sizes of drills are necessary. This holder is simply a drill chuck fitted with a special shank. For large drills the plain style of holder K is recommended, and if only a few sizes of drills are required, it is more satisfactory and economical than the adjustable type.
The various types of small turret lathe tools referred to in the foregoing for turning, threading, tapping, knurling, etc., are a few of the many different designs of tools used in turret lathe practice. Naturally, the tool equipment for each particular job must be changed somewhat to suit the conditions governing each case. The tools referred to, however, represent in a general way, the principal types used in ordinary practice. Some of the more special tools are shown in connection with examples of turret lathe work, which are referred to in the following.
Fig. 16. (A) Method of Boring and Turning Pistons in Gisholt Lathe.
(B) Special Chuck and Tools for Turning, Boring and Cutting Off Eccentric Piston Rings
Turning Gasoline Engine Pistons in Turret Lathe.—The making of pistons for gas engines, especially in automobile factories, is done on such a large scale that rapid methods of machining them are necessary. The plan view A, [Fig. 16], shows the turret lathe tools used in one shop for doing this work. As is often advisable with work done in large quantities, the rough castings are made with extra projections so arranged as to assist in holding them. These projections are, of course, removed when the piece is completed. In this case the piston casting a has a ring about 11/4 inch long and a little less in diameter than the piston, at the chucking end. The piston is held in suitable chuck jaws b which are tightened against the inside of this ring. The set-screws in these special jaws are then tightened, thus clamping the casting between the points of the screws and the jaws. This method of holding permits the whole exterior of the piston to be turned, since it projects beyond the chuck jaws. This is the object in providing the piston with the projecting ring by which it is held.
The first operation consists in rough-boring the front end of the piston. The double-ended cutter n is held in boring-bar m, which is, in turn, supported by a drill-holder, clamped to one of the faces of the turret. This bar is steadied by a bushing in the drill support c which is attached to the carriage, and may be swung into or out of the operating position, as required. After this cut is completed, the turret is revolved half way around and the casting is finish-bored in a similar manner, with double-ended cutter n1 held in bar m1, the drill support being used as in the previous case. The support is then turned back out of the way to allow the turning tools in the turret toolpost to be used.
The outside of the piston is next rough-turned with tool k in the turret toolpost, which is revolved to bring this cutter into action. The toolpost is then turned to the position shown, and the outside is finish-turned by tool j, which takes a broad shaving cut. The turret tool-holder is again revolved to bring form tool l into position. This tool cuts the grooves for the piston rings. Suitable positive stops are, of course, provided for both the longitudinal and cross movements of the turret toolpost.