2I4 THE MACHINE-SHOP lathe group in some classes of work, owing to the simplicity of its functions, the ease of setting-up, and its substantial build. Illustrations of Turret Work.—Some examples of this kind, done on lathes by Messrs. Alfred Herbert, Ltd., are given in succeeding figures. Fig. 49 shows the distribution case of a rotary aero-engine being produced on a combination turret lathe. The tool seen in operation is a counterbore, the one swung round towards the front is a trepanning tool, which cuts a recess of lo-in. bore, irV in. wide by 4 in. deep. These two tools are used Fig. 49.—Distribution Case of a Rotary Aero-engine being turned on a Combination Turret Lathe with feeds as coarse as 8.8 cuts per inch, and between them they remove over 100 Ib. of metal. Fig. 50 illustrates the second operation on a propeller boss for an aero- engine. The work is held on a face plate form of fixture, and located from the tapered bore with a spring tapered peg. The boss is turned with an allowance for grinding, faced and counterbored, and the hole threaded with a collapsing tap, Fig. 51 shows the rough-turning of the fins of an air-cooled aero cylinder, one of which is seen on the turret. The work is being done with a gang of tools similar to parting-tools mounted in a special tool holder at the back of the cross slide, all operating simultaneously. The piece is chucked with an expanding arbor, and steadied with a revolving support carried in the turret.