Center both ends in the centering machine. The size of the center in
this shaft should be from ³⁄₁₆ to ¼ of an inch in diameter. Larger work
should have deeper centers.
[Illustration: Fig. 1]
[Illustration: Fig. 2]
[Illustration: Fig. 3]
[Illustration: Fig. 4]
If a centering machine is not available, the work may be centered by
first locating the center with a pair of dividers and center punch and
then using a combination drill and countersink in the lathe as shown
in Fig. 1. In this case the work is held by hand to prevent it from
turning. As this work is to be turned, it is necessary to center it
only approximately true.
=Accurate Centering.=—When the work is to be centered accurately, it
may be done by putting one end in the lathe chuck and the other in a
steady rest. A pointed tool is then used in the tool post as shown in
Fig. 2. The point of this tool has an angle of 60 degrees, the same as
the lathe centers, and is ground like a flat drill so that it cuts on
both sides.
After the shaft is centered with this tool, a center hole about ⅛ of an
inch in diameter should be drilled. This is done by holding the drill
in the tail-stock of the lathe with a drill-chuck, as shown in Fig. 3.
The object of this center hole is to give the center of the shaft a
bearing on the lathe center a short distance back from the point, as at
A in Fig. 4.