Bottoming Tapped Holes – An Overview
Bottoming tapped holes are nothing but holes which has tread (tap) to the very bottom of the hole. This bottoming will ensure maximum usage of holes space for threads.
Production of bottoming tapped holes can be done with a bottoming tap tool. These taps have only 1 to 1 ½ chamfered threads. But bottoming taps never used to cut thread in an unthreaded hole as its got only few chamfered cutting edges at the tip. So need use taper tap (8 to 10 tapered threads) and intermediate tap (3 to 4 tapered threads) before final bottoming tap.
So, to make a bottoming tapped hole,
- Drill a plain hole just a little longer than the intended thread length
- Run down the taper tap
- Run down the intermediate tap, bringing the fully tapped region deeper
- Run down the bottoming tap, bringing the fully tapped region very close to the bottom of the hole.