Tc 9-524 fundamentals of machine tools

Tapping Large Holes
One method of hand tapping is to mount an adjustable tap
and reamer wrench on the square shank of the tap and install a
pointed tool with a center in the drilling machine spindle
(Figure 4-41). The tap is placed in the drilled hole and the
TC 9-524
tool’s center point is placed in the center hole. The tap is held
steady, without forcing, by keeping light pressure on it with
the hand feed lever of the drilling machine, while turning the
wrench and causing the tap to cut into the hole.
Tapping Small Holes
Another method of hand tapping, without power, is to
connect the tap directly into the geared drill chuck of the
drilling machine and then turn the drill chuck by hand, while
applying light pressure on the tap with the hand feed lever.
This method works well on small hand-feed drilling machines
when using taps smaller than 1/2-inch diameter.
REAMING
Reaming a drilled hole is another operation that can be
performed on a drilling machine. It is difficult, if not
impossible, to drill a hole to an exact standard diameter. When
great accuracy is required, the holes are first drilled slightly
undersized and then reamed to size (Figure 4-42). Reaming
can be done on a drilling machine by using a hand reamer or
using a machine reamer (Figure 4-43). When you must drill
and ream a hole, it is best if the setup is not changed. For
example, drill the hole (slightly undersized) and then ream the
hole before moving to another hole. This method will ensure
that the reamer is accurately aligned over the hole. If a
previously drilled hole must be reamed, it must be accurately
realigned under the machine spindle. Most hand and machine
reamers have a slight chamfer at the tip to aid in alignment
and starting (Figure 4-43).
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