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Broken Tap Removal
by John
This isn't so much a project as it is a useful trick. I was working on a large steel plate today and I had several hours machine work invested into it. I was in the final stages of my work, with the tapping of a large handful of 1/4-20 holes being saved for last. Of course, the tap snapped on me on the second to last hole.
If you've ever had this happen to you, you know how frustrating it can be to remove the broken part of the tap from the hole. Since the tap doesn't break off flat, a drill bit will never drill through the tap with out wandering off center and potentially damaging the work piece even more. Not to mention that a HSS drill bit on a HSS tap is bound to do nothing but destroy the drill bit that is trying to cut through the same material that it's made of. My bad luck today resulted in me learning a completely new method to remove the tap.
Previously, I've tried two different methods to remove a broken tap. One method is to try and unscrew it, the other one is to try and destroy it. The first method can be done using vice grips or by sticking a small punch in the flutes of the tap and hitting it with a hammer to unscrew it. The vice grip method is great when it works, but when it doesn't, you run the risk of damaging the work piece with your punch and hammer. The other method is to take the punch and hammer and try to break the tap apart by repeatedly hammering the punch into the top/bottom of the tap. There are also some caustic mixtures out there that are designed to dissolve the steel tap. Once again, the punch and hammer can damage whatever your machining. The dissolving method, while handy, wasn't very useful to me. First of all, since the solution disolves steel, it would damage my steel plate also. Secondly, I would have had to have the solution on hand, and I would have had to wait a day (or more) until the tap was fully disolved.
Of course, the way the tap broke on me today, only a very small section of the tap was left sticking up above the hole and the vice grip method did nothing but break the tap further since it didn't have enough to grab on to. Of course by this time I was really frustrated and saw myself damaging a very lage piece of steel plate that would cost quite a bit to replace (time and money). So while I'm sitting there with curse words floating around in my head, I had a stroke of brilliance, a great idea! What if I take a nut and weld it to what's left sticking out of the hole? Then I could use a wrench to unscrew the broken tap without fear of damaging the work piece.
No one who I work around has ever done this before, so I figured it probably won't work or else they'd have done it by now. I decided to give it a try anyway. I fired up the TIG, set a 1/4" nut on top of the 1/4" tap, and welded the nut to the tap, adding a lot of filler rod (to the point I filled the nut), being careful at first not to weld the tap to the steel plate it was stuck in. When I got finished it was time for the moment of truth. I grabbed a wrench and the tap came right out without a fuss..
It wound up being a quick 2 minute job compared to the half an hour I would have spent otherwise trying to remove it. I couldn't believe it was that easy and no one had taught me that trick before. If you ever find yourself in a jam, don't be afraid to try it.