Tc 9-524 fundamentals of machine tools

TAPPING AND HAND DIE THREADING
The lathe can be used as a device to hold and align a tap or
hand die to cut internal or external threads quickly for threads
that do not require a high degree of accuracy or a fine finish.
More information on taps and dies can be found in TM 9-243.
Hand Tapping on the Lathe
Tapping can be done on the lathe by power or by hand.
Regardless of the method, the hole must be drilled with the
proper sized tap drill and chamfered at the end. The shank end
of the tap is supported by the tailstock center. A slight
pressure is maintained against the tap to keep its center hole
on the center and to help the cutting teeth of the tap engage
the work (Figure 7-99).

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TC 9-524
The work will rotate when tapping using lathe power. Use a
very slow spindle speed (10 to 30 RPM) and plenty of cutting
fluid or coolant. Install a tap and reamer wrench on the end of
the tap to keep it from turning. Support the wrench on the
compound rest. Power is not recommended for taps under 1/2
inch in diameter or when tapping steel. Ensure that the tap
wrench handle contacts the compound rest before engaging
power or the end of the handle will whip around and could
crush a finger or cause other injury or damage. Do not attempt
to start the tap into the hole with the work revolving. Always
keep the tap snug in the center hole to prevent the tap from
coming out of alignment and ruining the threads.
The setup for hand tapping in a lathe is similar to that used
in power tapping. The headstock chuck is held steady and not
rotated. The tap is turned by using an adjustable wrench. Lock
the lathe gears so that the headstock will not move when using
a large tap. Back off the tap frequently when tapping to break
the chips and allow for a clean thread.