along the bed, the tool is gradually moved outward by the taper
attachment.

[Illustration: Fig. 12. Taper Attachment Set for Turning Taper End of
Piston-rod]

If the rod is being fitted directly to the crosshead (as is usually the
case), the approximate size of the small end of the taper could be
determined by calipering, the calipers being set to the size of the hole
at a distance from the shoulder or face side of the crosshead, equal to
the length of the taper fitting on the rod. If the crosshead were bored
originally to fit a standard plug gage, the taper on the rod could be
turned with reference to this gage, but, whatever the method, the taper
should be tested before turning too close to the finished size. The test
is made by removing the rod from the lathe and driving it tightly into
the crosshead. This shows how near the taper is to size, and when the
rod is driven out, the bearing marks show whether the taper is exactly
right or not. If the rod could be driven in until the shoulder is, say,
1/8 inch from the crosshead face, it would then be near enough to finish
to size by filing. When filing, the lathe is run much faster than for
turning, and most of the filing should be done where the bearing marks
are the heaviest, to distribute the bearing throughout the length of the
taper. Care should be taken when driving the rod in or out, to protect
the center-holes in the ends by using a "soft" hammer or holding a piece
of soft metal against the driving end.

[Illustration: Fig. 13. Tool Point should be in same Horizontal Plane as
Axis of Work for Taper Turning]

After the crosshead end is finished, the rod is reversed in the lathe
for turning the piston end. The dog is clamped to the finished end,
preferably over a piece of sheet copper to prevent the surface from
being marred. When turning this end, either the piston reamer or the
finished hole in the piston can be calipered. The size and angle of the
taper are tested by driving the rod into the piston, and the end should
be fitted so that by driving tightly, the shoulder will just come up
against the finished face of the piston. When the taper is finished, the
attachment is disengaged and a finishing cut is taken over the body of
the rod, unless it is to be finished by grinding, which is the modern
and most economical method.

=Height of Tool when Turning Tapers.=--The cutting edge of the tool,
when turning tapers, should be at the same height as the center o