Fig. 23. First Operation on Shell Illustrated in [Fig. 22]—Rough-turning and Boring
In finishing this shell, five different operations are required. During the first operation the shell is rough-bored and turned by one passage of a box-tool, [Fig. 23], and the recess A, [Fig. 22], at the outer end, is finished to size by a second cutter located in the boring-bar close to the turret. The turret is then indexed to the second station which brings the threading attachment G into position, as shown in [Fig. 24]. After the thread is finished, the recess B, [Fig. 22], is turned by a flat cutter K, [Fig. 25]. The inner and outer surfaces are then finished to size by a box-tool mounted on the fourth station of the turret and shown in position in [Fig. 26]. The final operation, [Fig. 27], is performed by three tools held on an auxiliary turret cross-slide, and consists in rounding the corners at b and c, [Fig. 22], and severing the finished shell.
One of the interesting features connected with the machining of this shell is the finishing of the inner and outer tapering surfaces. The taper on the outside is 3/32 inch per foot, while the bore has a taper of only 1/64 inch per foot, and these surfaces are finished simultaneously. The box-tool employed is of a standard type, with the exception of an inserted boring-bar, and the taper on the outside is obtained by the regular attachment which consists of a templet D ([Fig. 23]) of the required taper, that causes the turning tool to recede at a uniform rate as it feeds along. To secure the internal taper, the headstock of the machine is swiveled slightly on its transverse ways by the use of tapering gibs. By this simple method, the double taper is finished to the required accuracy without special tools or equipment.
Fig. 24. Second Operation—Cutting Internal Thread
Fig. 25. Third Operation—Turning Recess at Rear End; Tool is shown withdrawn