Figure 4-102. Correct Drill Sizes for Tapping
Turn the tap backwards about 1/3 turn for
every full revolution forward in order to break off the
chip and make cutting easier.
After the tap is started, the threads will
draw it into the work.
Clean threads with a rag and check
threads with a thread gauge before installing screw or
Removing broken tap. Even when used
with care, taps will sometimes break A broken tap may
be removed with a pipe wrench when enough of the tap
protrudes to allow a grip. When the broken tap does not
protrude, it should first be started with a center punch
and then completely removed with a tap extractor, as
discussed in paragraph 4-20b(2).
Tap wrenches. The two types of tap
wrenches commonly used are the straight-handled and
the T-handle tap wrench. These are shown in figure 4-
Figure 4-103. Tap Wrenches
Care. Observe the following practices for
the care and upkeep of taps:
Do not attempt to sharpen taps.
Keep cutting edges lightly oiled.