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Broken tap... please help

 
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bcmchong
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PostPosted: Mon Jun 01, 2009 8:18 pm    Post subject: Broken tap... please help Reply with quote

I broke a tap in a bolt hole when trying to clean the threads. I can't get any extractors on it and was wondering if someone could suggest what type of drill bit to use that is harder than the metal that the tap is made of. Cobalt? Titanium? and what kind of taper is best to prevent "walking"?

Thanks much.
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Big Dave
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PostPosted: Mon Jun 01, 2009 8:52 pm    Post subject: Reply with quote

How far down in the hole is it? Could you weld something to theend of it? Does it have two flutes or four; with two you could use a needle nose plier to possibly back it out. Sounds like you were tapping by hand. If you do not have a drill press you stand a slim to no chance of cutting a straight hole in the tool steel tap no matter what bit you use (it would probably have to be a carbide tipped drill since the tool steel is as hard as the hinges of the gates to hell).

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clay
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PostPosted: Mon Jun 01, 2009 8:58 pm    Post subject: Reply with quote

There are a few ways we get out taps at work. I don't know what methods may be available to you, but I'll tell you what we have. We usually use machine taps that have helical flutes to pull the chips out so using extractors won't work on them. First method is the caveman method - hit it with a hammer and punch. Some of our taps are pretty hard and they break up pretty easy sometimes. If it is a cheap tap sometimes they are a little softer so this method won't work too good. Also not a really good option if it's broken off in aluminum as you will most likely tear up the threads - although now you can put in a helicoil. Next is the endmill method. Carbide is about all that will touch a tap. You can try a carbide drill, however they require a lot of pressure to actually cut hardened metal so doing this with a hand drill is all but impossible. Another problem with this method is chips, parts and pieces usually end up breaking the end mill edges and flutes so it is pretty much a one time use. If you try a drill, get one the same as the tap drill size so it is somewhat "guided" by the hole that is there otherwise it will try to walk off into a tap flute and snap off. We also have a tap disentegrator - basically a ram style EDM machine that will burn a tap out. We don't use this much at all anymore due to this next method. They make a specific style of stick electrode called a stud pull electrode. You position the part so the hole is vertical and put the stick straight down in the hole and weld. As long as you keep the stick pretty centered in the hole the flux actually protects the weld metal that is being deposited from flowing to the existing hole. It ends up building sort of a rod out of the hole and then you can weld a nut to it. This is a fantastic method for broken off rusty bolts which we have a lot of in the curing area - steam heated presses. The heat usually breaks the rust loose and it will screw out pretty easy. The heat will expand the tap slighty and as it cools it will sometimes contract and loosen up and come out pretty ease too. Like I said I don't know what you have available to work with, but this is what we do. If you have any specific questions, let me know. Clay
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bcmchong
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PostPosted: Mon Jun 01, 2009 9:43 pm    Post subject: Reply with quote

I'm a DIYer so all that nice welding/electrode equipment is not available to me... <sigh> I guess I'm down to a drill and drill bit. The surrounding material is aluminum so I don't really want to whack it with a hammer and punch. I guess a carbide bit it is then... thanks for the input.
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clay
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PostPosted: Mon Jun 01, 2009 10:01 pm    Post subject: Reply with quote

Unfortunately you have about the worst case senario - tap in aluminum. Don't expect much from the drill bit unless you can get it in a drill press. You may get it to cut with hand pressure, but it will be mostly dust coming out - not really chips. One thing you might can try that may help preserve the existing threads. Get a drill bit slightly bigger than the tap drill. Put it in a hand drill and run it backwards against a running grinding wheel. Do this until you have ground it down to where it just fits inside the existing threads. Most likely you don't have the "right" type of wheel for carbide, but it really doesn't matter in this case. This makes the o.d. of the drill round so it no longer has proper geometry to actually do any cutting anywhere but on the end. Otherwise as it gets pushed around it will cut on the sides too until the hole gets so chewed up that then out comes the hammer and punch followed closely by a helicoil. I really do wish you luck as that plays a big part in it too. Let us know what you finally wind up doing as I am always looking for a new solution to a problem. One thing I have thought of that maybe somebody here might have some input on is some sort of electrolyisis. There is a situation like yours sometimes where dissimialar metals exist and it may be possible to erode one or the other slightly to get the tap to loosen up so you can get it out with an extractor. I don't really know the chemistry that would be involved with this - all I really have is a thought. Clay
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10sec.et
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PostPosted: Mon Jun 01, 2009 10:49 pm    Post subject: Reply with quote

i just went through this on a 6.0L Chevy. instead of a tap, it had an E-Z Out broke off in the center of the bolt. from my past experiences, youre going to end up with a heli-coil one size larger no matter what you do. i ended up using my die grinder, a round ended carbide burr, and lots of WD-40 for cutting oil. i spent nearly three hours grinding that crap out smoking . once i had all the steel out, i cleaned the hole with brake cleaner, and filled it with JB Weld. after that, i drilled out the epoxy and tapped it for a 3/8 helicoil (the original size was 8mm).

i also just did a motorcycle head but was able to weld up the holes and re-drill/tap. what exactly are you working on ?

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clay
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PostPosted: Tue Jun 02, 2009 5:52 pm    Post subject: Reply with quote

Now a broken off easy out is as bad as it gets. The stud pull electrode might get it since it should release pretty easy if you can back it up (assuming it's the helical style). Pretty much on an easy out, I look at it like you do - there is going to be some sort of thread insert period. Clay
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Big Dave
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PostPosted: Tue Jun 02, 2009 9:26 pm    Post subject: Reply with quote

If you do not have access to a drill press it is time to take the head to a machine shop. If you attempt to drill with a hand drill you will be welding up the hole again and remachining the head.

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10sec.et
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PostPosted: Tue Jun 02, 2009 11:23 pm    Post subject: Reply with quote

clay wrote:
They make a specific style of stick electrode called a stud pull electrode. You position the part so the hole is vertical and put the stick straight down in the hole and weld. As long as you keep the stick pretty centered in the hole the flux actually protects the weld metal that is being deposited from flowing to the existing hole. It ends up building sort of a rod out of the hole and then you can weld a nut to it. This is a fantastic method for broken off rusty bolts which we have a lot of in the curing area - steam heated presses. The heat usually breaks the rust loose and it will screw out pretty easy. The heat will expand the tap slighty and as it cools it will sometimes contract and loosen up and come out pretty ease too. If you have any specific questions, let me know. Clay


how about some more info on that "specific style" stick electrode ? will it work with any machine ? if so, where can i buy them ?

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Knarley Darley
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PostPosted: Wed Jun 03, 2009 2:14 am    Post subject: Reply with quote

Dont ask me how he does it, but we have a guy who specializes in bolt extraction with a laser who can get them out 90 percent of the time without damaging the threads. Maybe you could check and see if you have a service that can do this. ?????
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MufflerBearings69
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PostPosted: Fri Jun 05, 2009 2:20 am    Post subject: Reply with quote

10sec.et wrote:
how about some more info on that "specific style" stick electrode ? will it work with any machine ? if so, where can i buy them ?


+1 these sound like fun, and i bet my bobcat 250 can light them off Very Happy
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clay
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PostPosted: Fri Jun 05, 2009 6:08 am    Post subject: Reply with quote

I'll get the information about the rods today if the guys are working in major press overhaul. Clay
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clay
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PostPosted: Fri Jun 05, 2009 8:38 pm    Post subject: Reply with quote

Here is the info. on the welding rods. One is the label off of the box and the other is the pamphlet that came with the rods. Also is a recent example a tap they got out using them. At one time they had a lot of really cool stuff, but it got tossed. One problem with them though - they're sort of pricey - they said $54.75 / lb. for the last one's they bought. Clay




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Knarley Darley
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PostPosted: Fri Jun 05, 2009 10:17 pm    Post subject: Reply with quote

Hey that tap looked reusable! LOL
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10sec.et
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PostPosted: Fri Jun 05, 2009 11:39 pm    Post subject: Reply with quote

thanks for the info Clay Cheers . $54.75 a lb is not that expensive when you consider how much i charge to spend 3 hours grinding out an EZ Out. it was still cheaper than pulling the heads though.
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