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 _n_{1}_ held in bar _m_{1}_, 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.

In the second operation, the piston _a_ is reversed and held in soft
jaws, which are used in place of the hardened jaws _b_ shown in the
illustration. These jaws are bored to the outside diameter of the
piston, so that when closed, they hold the work true or concentric with
the lathe spindle. In this operation the chucking ring by which the
piston was previously held is cut off, and the end of the piston is
faced true. If the crank-pin hole is to be finished, a third operation
is necessary, a self-centering chuck-plate and boring and reaming tools
being used. (These are not shown in the illustration.)

=Turning Piston Rings in Turret Lathe.=--One method of turning piston
rings is shown at _B_ in Fig. 16. The piston rings are cut from a
cast-iron cylindrical piece which has three lugs _b_ cast on one end and
so arranged that they may be held in a three-jawed chuck. This
cylindrical casting is about 10 inches long, and when the rings are to
have their inside and outside surfaces concentric, the casting is held
by the lugs in the regular jaws furnished with the chuck. (The
arrangement used for turning and boring eccentric rings, which is that
shown in the illustration, will be described later.)

The casting _a_, from which the rings are made, is first rough-bored
with double-ended cutter _n_ in boring-bar _m_, after which it is
finish-bored with cutter _n_{1}_ in