aft Turning]

=Special Crankshaft Lathe.=--A lathe having special equipment for
rough-turning gas engine crankshaft pins is shown in Fig. 26. This
lathe is a heavy-duty type built by the R. K. LeBlond Machine Tool Co.
It is equipped with special adjustable headstock and tailstock fixtures
designed to take crankshafts having strokes up to about 6 inches. The
tools are held in a three-tool turret type of toolpost and there are
individual cross-stops for each tool. This lathe also has a roller
steadyrest for supporting the crankshaft; automatic stops for the
longitudinal feed, and a pump for supplying cutting lubricant. The
headstock fixture is carried on a faceplate mounted on the spindle and
so arranged as to be adjustable for cranks of different throw. When the
proper adjustment for a given throw has been made, the slide is secured
by four T-bolts. A graduated scale and adjusting screw permit of
accurate adjustments.

The revolving fixture is accurately indexed for locating different
crank-pins in line with the lathe centers, by a hardened steel plunger
in the slide which engages with hardened bushings in the fixture. The
index is so divided that the fixture may be rotated 120 or 180 degrees,
making it adjustable for 2-, 4- and 6-throw cranks. After indexing, the
fixture is clamped by two T-bolts which engage a circular T-slot. The
revolving fixture is equipped with removable split bushings which can be
replaced to fit the line bearings of different sized crankshafts. The
work is driven by a V-shaped dovetail piece having a hand-nut
adjustment, which also centers the pin by the cheek or web. The crank is
held in position by a hinged clamp on the fixture. The tailstock fixture
is also adjustable and it is mounted on a spindle which revolves in a
bushing in the tailstock barrel. The adjustment is obtained in the same
manner as on the headstock fixture, and removable split bushings as well
as a hinged clamp are also employed.

The method of chucking a four-throw crank is as follows: The two
fixtures are brought into alignment by two locking pins. One of these is
located in the head and enters a bushing in the large faceplate and the
other is in the tailstock and engages the tailstock fixture. The
crankshaft is delivered to the machine with the line bearings
rough-turned and it is clamped by the hinged clamp previously referred
to and centered by the V-shaped driver. The locking pins for both
fixtures are then withdrawn