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Broken Tap Extraction

Posted: Mon May 19, 2014 11:17 am
by Martin Pansch
Show me the person who has not broken a tap and I'll show you a person who has never tapped a hole (and probably doesn't know what a tap is). Breaking them off isn't tough but getting them out again is another story. Keeping in mind that I am not a subject matter expert he typical way I have dealt with this is:

- First have a good cry.

- Next if the tap is sticking up enough either try to back it out with a vise grips or MIG hex head bolt to it and try to back it out with than. If you do weld to the tap let the tap cool down before trying to back it out on the theory that the heat from welding expanded the tap faster than the hole and jammed it in tighter. Either a penetrating oil or heating the piece with the hole may help loosen the tap up. I wouldn't use both lube and heat though as it would be more nasty fumes for you to breathe in.

- When the previous method fails, or the tap is broken too close to the surface, I usually just grind it flush, drill another hole nearby and start thinking of ways to explain the misplaced hole as a "feature" instead of a "mistake."

Last year during the guillotine tool class I was introduced to a new method for dealing with taps broken close to the surface. I think Jim Moenck brought it up but it is tough to remember in workshops like this. You need a MIG or TIG, a couple washers, and a vise grips or similar. Having a Oxy/Acetylene torch or other localized heat source also helps.

First get a small washer with a hole close to the size of the tap in question. You are going to put this washer over the broken tap and MIG or TIG the washer to the tap so the closer the hole is to the size of the tap the less chance you are going to weld the whole thing to the piece you are trying to save making a bigger mess. Next we put a slightly larger washer over that weld you just made and welded it too. This second washer just gave a little more of something to grab onto. Hopefully the photo below of the extracted tap piece helps clarify.
Extracted tap.JPG
Extracted tap.JPG (88.04 KiB) Viewed 8857 times
In place of the larger washer you could us a scrap piece of bar stock with a hole drilled in the middle for a ready made handle verses using a vise grips. It might give you a little more even pressure on the tap.

Next you want to selectively heat the piece up to help loosen it. You want to try to heat it up fast and local to the hole so the hole expands more than the tap. For this reason a torch with a small tip it useful. I find having someone photobomb you during the heating helps.
Marty trying to extract tap photobomb.JPG
Marty trying to extract tap photobomb.JPG (114.6 KiB) Viewed 8857 times
If you have help you can heat it up at the same time you are trying to back the tap out.
Marty and Jim trying to extract tap.JPG
Marty and Jim trying to extract tap.JPG (127.74 KiB) Viewed 8857 times
If it works it is important to celebrate your victory.
Rick and the extracted tap.JPG
Rick and the extracted tap.JPG (75.64 KiB) Viewed 8857 times
During the class we still only had about a 50% success with this but it was still better that I did previously with taps broken that short. Short of getting an EDM machine it is the best method I have been shown so far. If other folks have another way of dealing with them I would like to hear about it.


Re: Broken Tap Extraction

Posted: Wed May 21, 2014 5:59 pm
by ardenhanson
Or you can buy or borrow a set of tap extractors. I have a set and they work really well.

Re: Broken Tap Extraction

Posted: Thu May 22, 2014 8:56 pm
by Martin Pansch
I guess I just never believed they would work. None of the screw extractors I ever tried worked worth a darn and I figured if the tap extractors were better I would have seen more folks using them. Since you recommend it Arden I'll pick one up for my next broken tap adventure.