Help with a tapping problem


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OAKVILLE SHOOTER
November 19, 2007, 04:12 PM
I am trying to drill and tap the barrel of my son's Henry Mini-bolt .22 so that I can install the cantilever scope mount that I purchased from Henry Arms. The holes were drilled with a #31 drill bit. I attempted to tap the holes with a 6-48 tap. This is where the fun began. As per the instuctions, I drilled the holes to .155" (.156" MAX tap drill depth, .120" MIN thread depth.) What I found was that a Taper tap bottomed out with out even touching the sides of the hole. The Plug tap touched the sides, but bottomed out before being able to cut any threads. I tried starting with the Bottom tap but had a tough time keeping it straight. I did not run it in far enough to cut any threads, just to see if it would work and decided against it. Next, I filed the end of the plug tap off a little, so that it at least be able to start threading the hole. Turned roughly 1/4 turn, backed it out, started again. Yes, this is the point where THE TAP BROKE!!!:cuss::fire::banghead: Yes, I was using thread cutting oil.

I realize that getting the tap out will be a major PITA, and that is if I can do it without ruining the barrel. So, now I have 2 questions:

1: What is the best way to remove the broken tap? Most of it is below the top of the hole, with a tiny piece sticking slightly above the top of the barrel.
2: If I am able to get the tap out, what is the best/proper way to tap a blind hole that is too shallow for a taper or plug tap to start?

Any help would be greatly appreciated and I thank you in advance

Oakville Shooter

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Jayb
November 19, 2007, 04:34 PM
Taps are hard enough to be brittle... I've taken a blunt punch and broken the tap apart and removed it. If the tap is bottomed out, you're gonna have to cut it into pieces with a carbide cutter in a dremel tool. If you have a dremel tool and need a cutter, PM me. If there's a machine shop close, they may have an EDM machine to burn it out (safely).

OAKVILLE SHOOTER
November 19, 2007, 05:56 PM
Thanks to Jayb, I was able to break the tap apart and get it out. Only a minor scratch or two on the top of the barrel, that will thankfully be covered by the mount base if I ever get it mounted.

Back to question 2. What should I use to start the threads with since the hole is too shallow for a taper tap or a plug tap (which is now broken)? I can try the bottom tap again. I think there may be enough thread started for it to work on the first hole. The second hole has not been touched yet, but I could shorten the taper tap so that it doesn't bottom out. Does this sound feasable?

Thanks again Jayb, and thanks for the offer of the carbide cutter.

Oakville Shooter

Jayb
November 19, 2007, 06:16 PM
I was only gonna assault you with one thing at a time. Glad you were able to get the tap out.

Now.. If you have access to a two-flute 6-48 tap, use it.... the flutes are stronger because there's only two of them. Either way...... insert the taper tap into the hole and take a look at the distance between the first thread on the tap, and the surface you're tapping into. That first thread will be a lead thread, not a full-depth thread. With a bench grinder, grind off the pointed end of the taper tap about .030" short of that amount.( try to match the profile of the drill you used to drill the hole, it will let you tap deeper ) At this point you should be able to start the tap.... g e n t l y....... using a lube designed for tapping. (it does make a difference) turn the tap in and out to keep the threads clear until you bottom out. Now go back and grind a bit more off the tap, and tap some more....... tap, grind, tap, grind...... until you get as deep as you can go. You can grind the tip off of the bottom tap as well, and it becomes a total depth tap. You won't have much success starting new threads with it, but it will allow you to tap all the way to the bottom of future holes.

Go get 'em......

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