Broken Tap

[tcb1188]

I was trying to tap a hole in to a piece of aluminum and the tap broke off in the hole. It is probably a quarter inch down inside the hole. The hole is threaed between the top and where the piece of the tap now sits. Any help as to how to get this tap out would be greatly appreciated.

 

[Broncitis]

If it is a valuable piece (time invested, $, etc.), you can buy a tap extractor from places like MSC, McMaster Carr, etc. A good local hardware might even have them.

They have fingers that slip between the taps flutes, allowing you to remove it. Since it is aluminum, it may be fairly easy to break free, so you might even be able to make something similar and improvise (thin needle nose or round nose pliers?).

On very valuable pieces, you can try to find a machine shop that has a "tap buster" . This is basically what led to more sophisticated EDM (Electric Discharge Machining) machines that are now widely used in complex mold making and aerospace applications. This proces is not detered by a metals hardness or toughness as most traditional machining methods are. I used to use a few variatons of the EDM process in the manufacture of aircraft and land based turbine blade and vanes, i.e. Sinker EDM for creating a complex female shape into metal, wire EDM for cutting complex shapes similar to a scroll saw, and a specialized sinker/ multi wire comb method we used to create rows of cooling holes in blades.

Basically, the Tap Buster or EDM is a controlled spark erosion prosess where it "eats" the tap or other target base metal away. Much like when you strike an arc with a torch, you will notice pit in the base metal, same basic idea but highly controlled.

Anyway, mostly likely the top suggestion is the most appropriate, but I thought I'd share some other methods as well just in case or just for some general knowledge of avaialble processes if nothing else.


Drew

 

[Rustytruck]

How big is the tap. If its big enough you can blow it out with a carbon arc rod in an arc welder. Otherwise turn the part over get a punch and hammer it straight out drill with an oversize bit to make sure you remove all the pieces then weld it up and start over. Removing a broken tap with a tap extractor is an art and sucess is dependent on wether the guy tapping the hole knew what he was doing in the first place and just had bad luck. I have removed several in the 20 years as a machinist so good luck.
Edm removal is a viable option as long as your near a big city and have about a hundred bucks to blow. If the part was steel you could just blow it out with a cutting torch but in your case your stuck. You can make a tap extractor from your old broken tap if there are threads left on it. Grind the tap flat on the broken end. screw on a nut of the right thread take some pieces of spring stock and bend it into an L shape. put one L shaped piece in each flute of the tap and screw on anothe nut to hold the piece in the grouve and trap the short piece of the L between the nuts and the long piece of the L under the nut between the flutes. the the end of the L overhang the end of the tap about a quarter of an inch. Now lube up the aluminium piece and heat up the aluminium and slip these fingers between the broken tap end and the hole of the aluminium threads and start wiggiling back and forth. You have to have the patience of stone and dont force too much and what ever you do dont screw up the threads on top that you have to back up into. If your lucky you may just get it out if not you just wasted time and a few bad words. Next time use tapping fluid when you cut threads. In a pinch you can use STP oil treatment the thick honey like stuff. I use a spray called Microfinish invented for tapping and machining space age metals Like Titainium, Hastelloy and Inconel. If its good enough for that stuff its good enough for anything. Never tap dry or with just any kind of oil and never WD-40

 

[tcb1188]

Since the remaining paqrt of the tap backed out easily would one of those bolt extractors from sears possibly work. The part is the head to my four wheeler that I am trying to put together and sell so I can pay off the loan on my bronco and start redoing it. A new head costs $500 which is way more than I want to pay considering I could get a wiring harness for the bronco for that much.

 

[Blue71]

I have used the pointed attachement on an air chissel . The tap should be hard, which in turn will make it brittle. Pulled the trigger on the air chissel and hit mine up in the hole with the pointed end and it shattered into peices. I was working with steel, not sure about aluminum though.

Good Luck,

Blue71

 

[Broncitis]

Since the remaining paqrt of the tap backed out easily would one of those bolt extractors from sears possibly work. The part is the head to my four wheeler that I am trying to put together and sell so I can pay off the loan on my bronco and start redoing it. A new head costs $500 which is way more than I want to pay considering I could get a wiring harness for the bronco for that much.

Since we now know this part falls in the valuable catagory, you may be best off taking it to a local machine shop if you're not comfortable wiht the process.

I'm aware of a few styles of bolt extractors at Sears. One is your typical tapered, left hand threaded EZ-Out style. You will not easily be able to drill into the tap to use this type (not if it's a decent tap).

Another style is similar, but has a left hand drill point at the tip for a one step operation, same problem with this one.

The last is the newer bolt extractors for rounded bolt heads. These won't work for this application.

With that said, if you have a high quality carbide burr for a die grinder, you may be able to grind a hole in the tap to try an EZ-Out. (What size bolt are you dealing with and how deep down in is the broken surface?)


The tap extractor I originally mentioned and that Rustytruck described how to make works differently (these only work on straight flute taps, the relitively newer spiral flute taps won't work with these). Check out http://www.mcmaster.com/ on page 2229 to see that these look like and what one in your size range costs (you're in the $10 range from the part you decribed).

When I was an airframe mechaninc on F/A-18's, we often had to remove stripped or frozen panel screws. Occasionaly we'd break off an EZ-out in them which is very hard like a tap. Sometimes I could shatter the broken piece as has been mentioned (although I'm not sure I'd try this in your case ince the head is alumimum), and sometimes I'd use a carbide burr to grind them out and then remove the countersunk head so we could pull the pannel over the shank and grab the shank with vise grips or a stud remover.

Do a search the site I listed above for "Carbide Burr" (they have a page for Dremel compatible in cae you don't have a larger 1/4" shank die grinder) or "Carbide Drill" if you want to try to drill it out.

Good luck!