Threads, Taps, and Tapping - 9: Hand Tapping Aids
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
Hand tapping aides will allow the tap to be manufactured properly and will avoid damaging the part. A broken tap is often difficult to remove and requires special tools like the tap extractor shown (figure 1).

The tap must be directly straight over the hole. This can be accomplished in a variety of ways. The simplest way is to use a square in (figure 2a and b) two positions 90 degrees apart. The difficulty here is maintaining this upright position while turning the tap.

There are other tools that will keep the tap square and steady, a solid or spring loaded tapping center used with a drill press (figure 3a and b), a tapping block (figure 4) or a tap and reamer aligner.

Taps are manufactured with a center hole or have a bevel ground at the square end of the tool. T-handles also come with center holes at the top of its body.
Figure 1
Figure 2a
Figure 3a
Figure 3b
Figure 2b
Be wary of the machinist who says he has never broken a 1/4-20 tap because he is either not a machinist, or he is a liar. R.S.
Figure 4
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