broken tap!!!!!!!!!

I just broke a tap in an aluminium casting, LM25[T6].
it's a 3/8 unc roll tap in a blind hole, it's in the length of the
thread[~21mm].
the hole was a few thou undersize, i have done almost 250 holes
with it, all drilled the same size..
the casting is to valuble to waste so it has to come out.
I was going to heat teh broken bit with the tig to soften it, so
I can bore it.
I remeber someone saying about a home made discharge thing to remove
taps, how did it work?
any other suggestions?
--
thanks richard
Reply to
richard
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Don't try heating the tap. You can't get it hot enough, long enough to do you any good. The aluminum will melt long before you'd reach the annealing temperature of the tap, which I assume is HSS.
Your only real option is an EDM. Check with a local machine shop to see if they have one. There used to be an Elox that was made expressly for tap removal, a small machine, sort of resembles a drill press. One of them would be adequate in the hands of someone that is skilled. Beyond that, a typical sinker type EDM would work, but may cost a bit more to hire. Dunnno.
Harold
Reply to
Harold & Susan Vordos
It can be eaten out with acid. I forget which acids go into the mix but a google search will surely bring up the formula. Another way, if you have a good rigid setup, like a bridgeport, is to use a carbide drill or end mill. If using an endmill then a ball nose is best. If a heli-coil or other thread insert is OK to use then you can make a hollow cutter and cut around the tap. Finally, when drilling more holes the proper drill for a 10-32 form tap is a # 16 drill. ERS
Reply to
Eric R Snow
Walton tap extractor!
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Reply to
RellikJM
Isn't there a chemical solution for AL - something that will attack the steel but leave the AL alone? I'm sure I've read about it here. Google might turn up something.
Reply to
John Hofstad-Parkhill
Richard,
If you can get to the upper end of the tap, TIG weld a small(1/4") nut onto the end of the tap on the INSIDE of the nut. This will leave you the shoulders to put a crescent wrench or socket onto to back the tap out. I've had to do this many times, it is not uncommon to have to re-tack the nut a couple of times to get the tap to back out. Welding it on the inside keeps most of the heat away from the Al too.
Best of luck, Jim C Roberts
Reply to
Jim C Roberts
IIRC, it is nitric acid. To be sure Google RCM for "broken tap" + nitric.
Bob
Reply to
Bob Engelhardt
IIRC, nitric acid will dissolv e the tap and not hurt the Al.
Reply to
Nick Hull
Nitric Acid will disolve the steel, but not touch the aluminum. IIRC...
Reply to
Kevin Archibald
Nitric acid will work if you have the time. A carbide drill may well work, I keep some broken or chipped ones around just for things like this. EDM is the best method. Price may be reasonable if your casting is worth some bucks, or euros.
BTW, the best threads when form tapping 10-32 in aluminum result from a 4.45 mm drill. If you have one.
michael
Reply to
michael
Nitric acid will eat away at the tap and leave the aluminum unharmed.
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Reply to
Roy
Depending on the aluminum alloy, nitric can have a minor effect. For example, aluminum with copper or zinc in its content. I've used nitric to clean the buffing wax from 6061-T6 and discovered that it has a slight etching effect, although the aluminum itself is unaffected, as you state. There was a minor dimensional change in the parts, which were close tolerance items.
Harold
Reply to
Harold & Susan Vordos
I jus gotta, "it's a 3/8 unc roll tap in a blind hole, it's in the length of the
Where is the acid going to go? This is like a solid piece of metal, part aluminum and part steel.
wws
Reply to
bzzzt
Richard;
I had a similar thing happen and could not use a tap extractor. I machined a simple hollow mill and cored out the tap, broke off the cored section, and then tapped the hole over size and screwed in an aluminum plug, drilled and tapped it to the correct size. Problem solved and part saved.
JRW
Reply to
J.R. Williams
It will eat it from the top going down. You may have to renew the acid periodically. Keeping it warm (100 deg) or so will speed the process.
Lane
Reply to
Lane
And you build a dam around it with modeling clay or something similar, to keep it confined to the area where the tap is. Otherwise, it will go where gravity tells it to go. :-)
Then be prepared to wash it down thoroughly, once the acid has done its job.
Good Luck, DoN.
Reply to
DoN. Nichols
Hmm ... probably not. You may have missed where he said "roll tap" above. Note from the page you pointed out:
====================================================================== The hardened steel fingers of Walton Tap Extractors fit in the flutes of a broken tap to back it out simply and safely. ======================================================================
The only problem is that a roll tap (or form tap) has no flutes, thus no place for the fingers to go.
A roll tap works by pushing the metal aside from the roots of the threads to form threads at the crests.
Otherwise, the extractor you indicated is a useful product -- and probably as good a *mechanical* removal system as you will find.
Enjoy, DoN.
Reply to
DoN. Nichols
Agree with using tap extractor. Other brands available. Maybe borrow one. Brent Wegher
Reply to
bw
Yes I missed that on the first reading. I went back and read it again after I posted and realized that. Sorry!
Reply to
RellikJM
Exactly why I suggested it's an EDM job in my first post.. I've worked with nitric acid for years and understand all too well how poorly it would perform in this instance. If aluminum could resist HCL, it would be the acid of choice in this case, but it can't.
Harold
Reply to
Harold & Susan Vordos

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