Helpful tip on retapping a threaded hole after drilling out old bolt.

[cathead]

The other day I was making some repairs to my old C-60 dump truck. One of the 1/4 x 20 bolts was broken off
on the front wheel hub cover. I started with a tiny pilot bit in the center of the broken bolt and then drilled out most of
the bolt with a larger bit. The final step is to run in a tap and clean out what is left of the old bolt. The truck is a few
miles from home so took along several taps for the job. As it turns out, neither tap would clean up the threads but
I could make a little progress with one tap, then the other, a little more progress and after about 10 or so interchanges,
the threads were nice and clean. As you can see, the chosen taps were vastly different which turned out to be a big
help. Another thing to know when tapping holes is to know your own strength so as not to break off the tap. This is a
learned thing mostly after breaking off a few taps. That's why I alternated the taps rather than risk a broken tap.

I hope this is handy to you HM folks out there that took the time to read this.

 

[Cadillac STS]

One tap designed to drive cuttings down through the hole and the other designed to pull them out the top. Nice discovery..

 

[brino]

That's a great idea.
Thanks for sharing the tip!

Another thing to know when tapping holes is to know your own strength so as not to break off the tap. This is a
learned thing mostly after breaking off a few taps.

I know what you mean and I've been there.
It can be expensive to "calibrate" yourself.

-brino

 

[WV_almostHeaven]

Another great tip thanks.

Sent from my LGUS992 using Tapatalk

 

[RJSakowski]

For difficult tapping jobs, I will sometimes alternate between plug and taper taps. The plug tap will finish the last few partially cut threadsleft by the taper tap which eases the cut for the taper tap on the next pass.. I leapfrog one or two threads at a time until the fiull thread is cut.