removing a tap

[earlfor]

Yep, it was a four flute tap. Thanks for jogging my memory. I think I saw some of those on the specialty shelf at Sears a few months back. I'm going to check tomorrow. Be my luck they dont have one in the size I need. LOL With the wedged chip that caused the tap to break in the first place, it may be enough to also break the tap extractor, but what the H....,
not much difference between having one thing broken off and having two things broken off. LOL

Earl

I did the same thing on one of my turbo housing exhaust bolts. Had the whole thing tapped out and decided to tap it one last time just to clean and it broke as I was turning and shifted my balance to my other foot..... USE A TAP EXTRACTOR.

http://www.waltontools.com/products/extractr.htm (quick google search)

They work great. They come in sets and are different sizes for the specific tap that is broken in the work piece. The extractor has four fingers that slide into the 4 flutes of a tap (assuming it was a 4 fluted tap), a collar slides down to hold the fingers in and you turn the broken piece out. Very easy and any decent industrial tool shop will have them or will be able to get the size you need.

Mark

[Katamaniac]

Grizzly tools have some Cobalt drill bits that are pretty cheap. I saw a demo on one that cut through a flat file.

http://www.grizzly.com/products/searchresults.cfm?&gid=AB8900F7-5BE8-42EB-B9A1-FFFA43AD9EC3&site=grizzly

[mike J]

I've been machining for 20+ years and no cobalt drill in existance will drill through hardened steel period. If you saw a drill go through a file either it wasn't cobalt or the file was made out of butter. To drill hardened material your cutting tool has to be harder than the material your trying to cut through. Tool steel (taps, files, drills, etc) are all in the low 50 to low 60 Rockwell C range. Carbide I think is in the 80 range and ceramics are in the 90 range IIRC. When welding tool steel you have to preheat the material or it will just break off. That's why you can't stick or wire weld tool steel,have to use a tig unless you can preheat the whole part.

[earlfor]

Just my luck, the tap extractor broke off too. Damn!

Thanks for confirming my thoughts on drilling. :-) I find that I can grind the tap relatively easily. The problem exhaust bolt hole is the lower on the #3 cylinder. All the others are fine. My thought........... make a fixture that attaches to the cylinder head utilizing the 2 exhaust mount holes on the #4 cylinder and the upper mount hole on the #3 cylinder. Chuck a 5/16" diameter x 1 1/4" long grinding drum in my electric drill. Make a sliding fixture to hold the drill that will mount to the base plate that is bolted to the cylinder head via the exhaust mount holes. Put a light spring on the drill to hold pressure.
Align the drill to grind away the core of the tap, leaving the flutes intact, which will fall loose when the core is removed. I can put a depth stop on the drill easily enough and once set up, I can lock it on and leave it for how ever many days it takes.

Earl

[quote="mike J"]I've been machining for 20+ years and no cobalt drill in existance will drill through hardened steel period.

[Anonymous]

Is your drill rated for continuous duty? I'd be reluctant to ask a hand drill to run for hours or days at a time.

Dave

[Anonymous]

Correct, cobalt bits aren't hard enough, I tried one on the hardened dowel pin I needed to drill.

I bought the carbide bit from a tool supply company, it drilled through the hardened dowel just fine though.

[earlfor]

NO, theyre not rated for continuous use, but I have a half dozen old 3/8" vari speed drills. I'm willing to "sacrifice" a few. :-)

Earl

Is your drill rated for continuous duty? I'd be reluctant to ask a hand drill to run for hours or days at a time.

Dave

[Anonymous]

tap

Earl if you don't drink, now might be a good time to start!!!!! How much of the tap is broken off down in the hole??

[frosty5011]

hmmmm..........

Might be time to get a "broken tap extractor-extraction tool"

Sorry to hear that you're having so much trouble with that one threaded hole, Earl. Funny how a 5-minute job (tapping) can end up being a weekend long project. I've had a few of those myself, and know the "fun" you're going through .

[earlfor]

Re: tap

OH, not THAT much. About 3/4" of tap is sunk in the well, so to speak.
I went ahead with my drill and grinding cylinder sunk into the hole.
So far, I have used up 8 hours, 6 grinding stones at $3 each and have sucessfully gound away an awsome 1/4" of the tap. LOL D A M N !@@ !!!%#%!!!!

Earl

Earl if you don't drink, now might be a good time to start!!!!! How much of the tap is broken off down in the hole??

[Anonymous]

Re: tap

OH, not THAT much. About 3/4" of tap is sunk in the well, so to speak.
I went ahead with my drill and grinding cylinder sunk into the hole.
So far, I have used up 8 hours, 6 grinding stones at $3 each and have sucessfully gound away an awsome 1/4" of the tap. LOL D A M N !@@ !!!%#%!!!!

Earl
So I guess Its' 'Back to the grindstone' for you huh? Hey your One Third the way done...better than zero!
Rick...

Earl if you don't drink, now might be a good time to start!!!!! How much of the tap is broken off down in the hole??

[Footy.]

Earl.

In my experience of drilling out broken studs/bolts in 30 years in the engine business, i think you have to consider why the tap broke!

From your description, i would think a `sliver' of the original bolt was not removed by drilling. The tapping action then dislodged this, jamming the tap as you describe.

If this is the case, nothing is going to `turn' the broken piece of tap out, and i have yet to hear of any drill that would touch the carbon alloy steels taps are made of!!

The `electric arc' process refered too in this thread, is called `spark erosion' in the UK. We use a local shop who can perform this process, but it can be expensive and they usually require a `stripped' component (head off). You would have to make some enquires locally.

The alternative is to drill a series of small holes (2-3mm) around the 8 mm tap fragment to loosen it (not easy and risks a broken drill to add to the tap!). Then you would have to drill an oversize `clean hole' (if surrounding material allows), and make an oversize OD thread insert.

I would go for the spark erosion if you can, or persivere with the very slow and inefficient `spot' grinding!!

Just my thoughts.

Footy.

[earlfor]

Well Footy, you pretty accurately described the situation. I figure if I can "spot grind another 1/4" of depth, I'll have a hole a half inch deep (12mm) and that is enough to fit a thread insert into with a good chance of it holding. Fortunately, I dont need OMG tight on header bolts.

Earl

Earl.

In my experience of drilling out broken studs/bolts in 30 years in the engine business, i think you have to consider why the tap broke!

From your description, i would think a `sliver' of the original bolt was not removed by drilling. The tapping action then dislodged this, jamming the tap as you describe.

If this is the case, nothing is going to `turn' the broken piece of tap out, and i have yet to hear of any drill that would touch the carbon alloy steels taps are made of!!

The `electric arc' process refered too in this thread, is called `spark erosion' in the UK. We use a local shop who can perform this process, but it can be expensive and they usually require a `stripped' component (head off). You would have to make some enquires locally.

The alternative is to drill a series of small holes (2-3mm) around the 8 mm tap fragment to loosen it (not easy and risks a broken drill to add to the tap!). Then you would have to drill an oversize `clean hole' (if surrounding material allows), and make an oversize OD thread insert.

I would go for the spark erosion if you can, or persivere with the very slow and inefficient `spot' grinding!!

Just my thoughts.

Footy.

[argonsagas]

I have tried this before...it has worked for me, BUT, it is a questionable method and has a good chance of failure. On the plus side, if it fails, you are not likely to damage anything.

You need a reversible, variable speed drill, with a setting that allows for very slow RPMs, and you need to have some means of holding the drill firmly in place against the work.

You then need two drill bits the same diameter as the hole.

Your Dremel grinder will be of help for the next.

Flatten one bit, then counter-grind it so that the flutes are ground backwards, into the centre. This leaves you with extended flutes that can grab the end of the tap.

Do the same with the second one, but cut it to allow the flutes to grab in the normal direction.

The idea is to allow you to mimic the same action that you would do if you had a tap handle in place, and use the torque from the drill to do the work for you.

Before trying to use any of this, use a drift pin or long punch and hit the tap, gently, just hard enough to bend the threads a bit, so as to allow some chance of freedom for movement.

With the drill bit centred over the tap, and the drill firmly in place, turn it VERY slowly., and only a VERY little amount.

Once it moves a bit, switch bits, repeat the above, and continue doing so until it comes free.

[earlfor]

I'll give it a try Ron. I dont think I have ground enough out yet to have ground away the chip that caused the lodge. At the point I broke it off, the chip had it wedged pretty solid. As you say though, I dont really have anything to lose. :-) For the time being, I'm fabricating new engine mounts for the swap. An 81 TSCC 750 engine is a far cry from a bolt in into a 79
8 valve frame. None of the original eight mounts can be used.

Earl



[quote="argonsagas"]
I have tried this before...it has worked for me, BUT, it is a questionable method and has a good chance of failure. On the plus side, if it fails, you are not likely to damage anything.