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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:

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

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

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

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Check for low spots or angled edges

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Grind down to the first starting thread.

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

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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
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