Tc 9-524 fundamentals of machine tools

Supporting Drills in the Headstock
The drill can also be held and rotated in the headstock with
the work held stationary against the tailstock. Straight shank
twist drills are supported in the headstock by a drill chuck or
collet which is mounted in the headstock spindle. A universal
or independent jaw chuck can also be used to hold and turn
twist drills if a headstock drill chuck is not available. Tapered
shank twist drills can be mounted in the headstock by using a
special adapter, such as a sleeve with an internal taper to hold
the tapered drill, while the outside of the sleeve is made to fit
into the headstock spindle.
Mounting Work for Drilling
If the work is to be rotated and the twist drill will be fed into
the end of the work, the work should be mounted in a chuck,
on a faceplate, or in a collet. The center of the hole to be
drilled should be accurately marked and punched as described
for drilling setups.
Always start holes by using a center drill, since this method
will be the most accurate and the most efficient. Center-drill
by rotating the spindle at computed drill speed and gently
bringing the point of the center drill into the end of the work
until the proper depth is reached.
If the twist drill is to be rotated by the headstock spindle and
the workpiece is to be supported by a V-center mounted in the
tailstock, the work should be carefully positioned by hand and

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TC 9-524
the drill moved lightly into contact with the workpiece before
starting the lathe. The workpiece must be well supported
during drilling operations to prevent the work from being
thrown from the lathe or rotating with the drill.
Drilling Operations
To start the drilling operation, compute the correct RPM for
the drill and set the spindle speed accordingly. Ensure the
tailstock is clamped down on the lathe ways. The feed is
controlled by turning the tailstock handwheel. The graduations
on the tailstock spindle are used to determine the depth of cut.
If a large twist drill is used, it should be proceeded by a pilot
drill, the diameter of which should be wider than the larger
drills web.
Use a suitable cutting fluid while drilling (Table 4-3 in
Appendix A). Always withdraw the drill and brush out the
chips before attempting to check the depth of the hole. If the
drill is wobbling and wiggling in the hole, use a tool holder
turned backwards (Figure 7-96) to steady the drill. Always
use a drill that is properly ground for the material to be drilled.
Use care when feeding the drill into the work to avoid
breaking the drill off in the work. The drill should never be
removed from the work while the spindle is turning because
the drill could be pulled off the tailstock spindle and cause
injury or damage.