removing a tap

[earlfor]

OK, I was working on the 750 engine and one of the exhaust header bolts was broken off flush in the head. (was when I got the engine) I centerpunched it and drilled it out. No problem. Then drilled it to rethread with an 8x1.25 mm tap. Got the hole threaded like new, everything going great! In turning the tap out for the last time, the tap turned out about 1/3 of the way and jammed. Jiggling, tapping, back and forth, oil, etc., to no avail.
Now I have a perfectly threaded hole and a 1/2 " of the tap broken off in the middle half of the threaded hole. I figure with patience, I can dremel grind the tap out and still leave the threads, but it will take some hours. Anyone know of a quicker way to remove the broken tap.

Earl

 

[SqDancerLynn1]

Tweesers or maybe small pair of needle nose pliers. Try turning it in an flood it with wd40 to wash it out then try turning it out. 8mm?? I'm guessing you threaded the existing stud to a smaller size the broken tap piece is threaded past the end of the stud If I am correct I would get a heli coil kit of the proper size and drill it out, this should alow you to get the broken piece out. and then insert a heli coil

 

[Anonymous]

I've heard that EDM (electric discharge machining) is used to remove broken bolts & such. It uses an electric arc to vaproize the metal, but it's not quick.

A short Google search came up with a link to a book that tells how to build an EDM device:

http://www.build-stuff.com/015book.htm

The electrics don't sound difficult; the tricky part (for me, because I'm not mechanically inclined) is building a device that gradually lowers the machining electrode as the offending material is removed. The parts should be readily available on the web or by mail order.

Or, maybe a machine shop in your area has an EDM setup already.

Dave

 

[mike J]

Earl, the best way I know of removing a tap is this. If you can reach the top of a tap get someone to tig weld a nut(down through the center of the nut) to the tap. They must use a stainless rod for this to work. Then after it cools put a wrench on the nut and spin it out. I have done this numerous times and it usually works like a champ. Mike

 

[Anonymous]

Now that's a first, a set of "build-your-own EDM" directions!!! Having bought several EDM's for my company, I would offer the opinion that building your own EDM is not a really fantastic idea... Wouldn't it just be cheaper to tote the engine over to a shop that already has a sinker EDM to do it? (Power supplies ain't cheap)

I have broken taps off myself and its a royal PITA. Larger taps can be (sometimes) gotten with a tap extractor, which basically has prongs to go down into the flutes of the tap. But I don't have one, so I have used my Dremel. I have also taken a punch and broken the tap into pieces, though that destroyed the new internal threads and I wound up Heli-Coiling it. I tried welding to the tap with my little wire feed welder but not only did I not have any success welding to the tap, I suspect the tap actually welded to the work instead.....

The Dremel, though slow, may be the most feasible option. Good luck!

 

[earlfor]

unfortunately, the broken off end of the tap is 5/16" below the surface.

Earl

Earl, the best way I know of removing a tap is this. If you can reach the top of a tap get someone to tig weld a nut(down through the center of the nut) to the tap. They must use a stainless rod for this to work. Then after it cools put a wrench on the nut and spin it out. I have done this numerous times and it usually works like a champ. Mike

 

[earlfor]

Nope, the stock exhaust bolts on an 81 TSCC 750 are 8mm x 1.25.
They are 10 mm on 77-79 750's. Just to see, I center ground the broken tap end with a dremel stone, then tried to drill it with a titanium bit. No go. The bit doesnt even begin to cut into the hardened tap. I'm not sure there is a drill bit that will drill a tempered tap.

Earl

I'm guessing you threaded the existing stud to a smaller size the broken tap piece is threaded past the end of the stud If I am correct I would get a heli coil kit of the proper size and drill it out, this should alow you to get the broken piece out. and then insert a heli coil

 

[mike J]

Earl, just have them build up the end of the tap with the stainless road till it's high enough to weld the nut to. You can't drill out a tap, it's as hard as the drill bit. The only other way is to put it in a milling machine and mill it out with carbide. I've have tried all the methods and the tig with the nut works the best by far. Mike

 

[Anonymous]

stud

stud

earl I used to just stick/weld the tig tip on the recessed stud, and grab it with some vise grips, always used a tip that was about gone, and did it while still hot, you must have still had a piece of old metal that jammed in the tap!!! I knew a german mechanic who could use and oxy/acely tourch and burn/blow the studs out of vw heads while still on the car the guy was incredable, never saw him damage a thread or head!!!

 

[earlfor]

Re: stud

Re: stud

Thats exactly what happened. As I was turning the tap out, I felt it grab a chip. At that point, I stopped turning it out and turned it back in to cut the chip. The tap went back in about 1/2 turn and jammed but could be turned out 1/2 turn before jamming again. I went back and forth for about 30 minutes, oiling and trying to cut the chip. Eventually, the constant jamming against the chip caused the tap to fracture.......at the chip, mid depth in the hole.

I tried working around aluminum with oxy/ace some years ago. I came to the conclusion, no matter long I try, its not a skill I am likely to develop.

I think I will take the easy way out and where the broken exhaust stud is, I will do as they do in racing. Drill a small hole to hook a spring into and install a small clamp on the header pipe.. Very simple and will cost about $2

Earl

you must have still had a piece of old metal that jammed in the tap!!!

I knew a german mechanic who could use and oxy/acely tourch and burn/blow the studs out of vw heads while still on the car the guy was incredable, never saw him damage a thread or head!!!

 

[Anonymous]

I have used a carbide drill bit, with a negative rake, to drill out a hardened dowel pin on the end of a Yamaha 750 (triple) crank. Regular drill bits wouldn't begin to put a dent in it.... But I don't know if a carbide bit would drill out a tap.

 

[Kaptain Ketchup]

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

 

[Anonymous]

tap

tap

thinking about it you may be able to buy some small needle nose pliers and grind them down to fit in the flutes and see if you can work it back an down and blow out the chip with air or flood it out while inverted and spraying wd 40 in the hole, you know that if you use the spring method that the darn thing will back its self out while riding, not only that on my BSA i have to change the springs every 6 months before they snap off,

 

[earlfor]

I guess the best news of the evening is I at least have a broken tap to practice drilling on. I dont know of any drill bit that is of harder temper than a tap. How do you cut a negative rake on a drill bit? I have frequently flat cut a bit for Mill like cutting into hardened stainless. but I never heard of negative raking a bit.

Earl

I have used a carbide drill bit, with a negative rake, to drill out a hardened dowel pin on the end of a Yamaha 750 (triple) crank. Regular drill bits wouldn't begin to put a dent in it.... But I don't know if a carbide bit would drill out a tap.

 

[Anonymous]

Is there any way you can get at the other side of the tap? If so you could could try to thread in a bolt from the back side. Taper and drill the end of the bolt so it mates and snags with the tap without binding on the bolt threads. You then have control over the tap again. Work it out.

But it has no viability if you can't get at the other side of the problem.

Michael

 

[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/sea...00F7-5BE8-42EB-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

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