Grinding a Bottoming Tap

Fri Jun 04, 2010 6:19 pm

One of the tools needed in Helicoiling Ellie's Real Final was a bottoming tap. I have both a high end STI tap and an economical NAPA Balkamp BK 7703071 STI Tap Kit. I chose to utilize the Balkamp kit throughout this first Helicoiling exercise which would necessitate grinding the Balkamp into a bottoming tap after I got the first stage of the helicoil process done. The Balkamp was chosen as I got it on :eBay: for $19.95US and my good STI tap cost me over $50.00Cdn. What follows is my first attempt at actually creating this tool.

Prior to attempting this, I talked to Cecil and a few others a lot trying to pick up some tips on how to helicoil. I got some good first hand visual experience during CubFest Northeast 2009 - but it still is not the same as doing it yourself. When it came to making a bottoming tap Cecil gave me some good advice -- take your time and keep the tool cool. I also got some great advice from Earl Fauble - one of the master machinists here on the forum. This is Earl's advice on grinding taps:

Earl wrote:

  • Grind on the edge of the grinding wheel till about finished, then dress up on the side. A belt or disk sander might do well for finishing.

  • Dip in water often to COOL.

  • It would be good to leave one or two of the starting threads on. I am calling the threads on the end which are flattened starting threads.

  • It would be good to put some duct tape on the grinder tool rest.

I followed the advice given to me by Cecil and by Earl :!: :D

This is the kit that I started with:



The key to a good start is to ensure that you start off square/perpendicular to the stone.


Dip the tap in cold water often ... after a couple seconds or so.


Check the end of the tap often as well. Rotate 90 degrees each time to ensure an even grind across the face.


Check for low spots or angled edges



Grind down to the first starting thread.


Check the an even square bottom. This is pretty good for the first time.


I cleaned the threads and then employed the bottoming tap to finish Helicoiling Ellie's Rear Final.

Re: Grinding a Bottoming Tap

Sat Jun 05, 2010 4:28 pm

Once again, Rudi, your post is wonderfully enlightening. Thanks, Jeff