Threads, Taps, and Tapping - 11: Hand Tapping Procedure
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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.
Before tapping the following should be determined:

  1. The proper tap hole has been drilled.
  2. The tap has the correct specifications.
  3. The tap hole is clean and free of all chips (particularly for blind holes).
  4. A suitable cutting fluid has been selected for application during the tapping process.

Hand tapping should be performed by having both hands on the handle and equal pressure applied to rotate the handle. The tap will then tread itself into the hole. To break the chip and to avoid loading the tap with material, the tap should be backed off about a half a turn for each complete thread formed. On completion the tap is backed out of the hole, all chips are blown clear; and the threads are checked with a thread gage.

If the thread is too tight, "chase" the threads by running the tap through again until it meets specifications.