Tc 9-524 fundamentals of machine tools

DRILLING WITH THE LATHE
Frequently, holes will need to be drilled using the lathe
before other internal operations can be completed, such as
boring, reaming, and tapping. Although the lathe is not a
drilling machine, time and effort are saved by using the lathe
for drilling operations instead of changing the work to another
machine. Before drilling the end of a workpiece on the lathe,
the end to be drilled must be spotted (center- punched) and
then center- drilled so that the drill will start properly and be
correctly aligned. The headstock and tailstock spindles should
be aligned for all drilling, reaming, and spindles should be
aligned for drilling, reaming, and tapping operations in order
to produce a true hole and avoid damage to the work and the
lathe. The purpose for which the hole is to be drilled will
determine the proper size drill to use. That is, the drill size
must allow sufficient material for tapping, reaming, and
boring if such operations are to follow.
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TC 9-524
The correct drilling speed usually seems too fast due to the
fact that the chuck, being so much larger than the drill,
influences the operator’s judgment. It is therefore advisable to
refer to a suitable table to obtain the recommended drilling
speeds for various materials, such as Table 4-2 in Appendix
A.
Supporting drills in the tailstock
Methods of supporting the twist drill in the tailstock can
vary (Figure 7-95). Straight shank drills are usually held in a
drill chuck, which is placed in the taper socket of the tailstock
spindle. Combination drill and countersinks (center drills),
counterbores, reamers, taps, and other small shank cutters can
also be supported in this way.
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Tapered-shank twist drills may be held directly in the
tailstock tapered spindle as long as a good fit exists. If the drill
shank is not the correct size, then a drill socket or sleeve may
be used in the tailstock spindle.
A twist drill holder is used to support large twist drills with
the tailstock center. The drill is inserted into the holder and the
tailstock center is placed in the center hole which is located at
the rear of the drill holder. The holder will rest on the cross
slide or compound rest and must be supported by hand until it
is held secure by pressure between the tailstock and
headstock. When using this method, never withdraw or loosen
the tailstock spindle while the lathe is rotating or the
workpiece can be thrown out at the operator. Always stop the
machine before attempting to withdraw the twist drill.
Another method of supporting a large twist drill in the
tailstock is to fasten a lathe dog to the drill shank and support
the rear of the drill with the tailstock center in the center hole
in the tang of the drill.