Thread: Broken Tap removal

I have a broken tap in a piece of aluminium and as luck would have it it was the last hole in a complex part. Rather than restart the piece again I believe that I can disolve the tap using nitric acid, I have never tried this before so I am not sure if it will work but does any one know where I can buy a small amount of nitric acid to do this?

thanks

Warren

I think the acid will dissolve the ally before the steel.

Nitric acid is extremely dangerous
I seem to recall it can go through the skin with little damage and dissolve bones
but its a long time since I read that so maybe I'm wrong

What size is the tap?
How much of the tap is in the aluminum?
Is any part of the tap proud of the surface of the aluminum?

Continuing on; how big is the tap, could you insert a pair of circlip pliers down into its gullets and wind out and if bigger a pair of rods or needle nose pliers again slipped into its gullets and wound out?

Hydrochloric dissolves Al, Nitric and Hydroflouric are in Stainless Steel pickling paste, yep this is nasty and will destroy calcium (bones), not exactly sure which one does the damage though.

Most aluminium alloys have a coefficient of thermal expansion about 1.5 times that of most iron alloys. If you heat the assemblage (favouring the aluminium for advantage), you may be able to grasp the tap with a needle-nose pliers in the flutes for removal. Depends on the size of the tap, of course.

Joe

Most aluminium alloys have a coefficient of thermal expansion about 1.5 times that of most iron alloys. If you heat the assemblage (favouring the aluminium for advantage), you may be able to grasp the tap with a needle-nose pliers in the flutes for removal. Depends on the size of the tap, of course.

Yep... That is very good advice.

How did you manage to break off a tap in aluminum?????

There are specialist companies that that use a spark eroder to get rid of broken taps.

http://www.rjmeng.com.au/disintegrators.htm

I'd try the heat and grab approach suggested by Joe first...you may be lucky, might come straight out.

And it's hydrofluric acid that dissolves bones as it really loves calcium ions (a burn covering around 2% of your body can kill you) - plus a hydrofluric acid burn is painless...for the first few hours, at least.

Hydrochloric acid is, on that scheme of things, pretty benign; for a starter, it's produced in your stomach so it's not a chemical that is foreign to your body, and when you splash some on you (of the typical strength found in hardware stores), you'll know about it as it itches like mad! (I know from the occasional personal experience)

Nitric acid will turn your skin yellow as it reacts with the keratin. It itches, too.

Sulphuric acid also itches like mad.

If you really want something nasty, try chlorine trifluride...it is hypergolic (causes ignition or explosive decomposition) with every known fuel, and will also ignite instantaneously on contact with everyday substances such as cloth, wood, sand, asbestos, water and people. One spill is known to have burned through 30cm of concrete and 90cm of gravel. Next to chlorine trifluride, the acid of the acid-for-blood Aliens in the eponymous movies is practically harmless!

http://www.airproducts.com/nr/rdonly...fetygram39.pdf

Thanks for all the interesting responses. The tap is or was 6mm. It is neatly broken off at the surface and the remainder, about 15mm of it is in the hole.

I have also reminded myself to no longer buy cheap Chinese taps.

I don't think heating is an option as the aluminium component is approx 60 x 100 x 80mm.

I think the only option is to use a small annular cutter and then plug the hole.

Warren

Originally Posted by warren

I don't think heating is an option as the aluminium component is approx 60 x 100 x 80mm.

Warren

I would still try the heating. A 6 mm tap should give plenty of meat to grip onto. Once you get a few threads out you can grab it with a pliers.

Disolve in acid , first time I have ever heard of that
Where did the tap break pictures help , if the tap snapped tapping while tapping Al then I would suggest it was because you had a swarf build up , this needs to be cleaned out first and if it snapped close to the surface snap a hacksaw blade in half grind a 45deg taper on one end of each piece and a flat end on the other, then putting the pointy end against one of the flutes of the broken tap and getting someone else to do the same on the opposite side gently tap the flat ends with a small hammer in unision anti clockwise once you get it to start to move use long nose plyers to grip the broken tap to unscrew and remove

Great idea Ashore, I've never heard of that technique before.

Fill the hole if blind with WD 40 and using a centre punch and hammer gently tap the inner flute area in an anti-clockwise - this of course will only work if the top of the flutes are exposed near the top of the hole. Once enough as exposed out of the hole you can use some pliers and gently remove the tap from the hole.