Thread: Bugga. Broke a tap

Originally Posted by PDW

Might work but I wouldn't try it - might cut the CI. Oxy is known to work. The minute gap between the tap & hole is sufficient to not gouge. Needless to say you use a *welding* tip - small - NOT the big cutting torch.

There won't be any heat induced distortion - the heat needed to bring the end of a 3mm tap to bright red is minimal and the oxy converts the red hot steel to iron oxide. It won't burn into the CI.

Agree about trying freezing first.

PDW

I wonder if simply heating the tap to the annealing temperature with a torch would soften the it enough to allow it to be drilled out?

Apparently it can be done, see the first paragraph of the left column here: http://books.google.com/books?id=YeY...page&q&f=false

Originally Posted by Pete F

Without trying to drag this too far OT, it is however an interesting sideline, as we've all broken taps at one stage or another. In this particular case the hole is horizontal, which is going to make EDM very difficult.

Horizontal shouldn't make that much difference, you might need to glue a plastic container to the side to retain the dielectric... but my suggestion is to advance the electrode manually until it just touches and then back off and do it again repeatedly, essentially doing manually what that the solenoid does.

Thanks for those links, Ben Fleming wrote a book on how to do the RC type edm, but as you already know, it's slow and crude.. His latest book is about Pulsed EDM, which is quite different to the RC type.

The book I'm waiting on is this one.. http://www.amazon.com/Build-a-Pulse-.../dp/0976759624

Anyway, as you say we are drifting off-topic...

Originally Posted by rob streeper

I wonder if simply heating the tap to the annealing temperature with a torch would soften the it enough to allow it to be drilled out?

Nice idea, that would work nicely if it's a high carbon tap, not so much if it's HSS,

If it is a high carbon steel tap, then you wouldn't even need to get red hot, just heat enough to draw the temper to a point where it could be drilled.

( I know someone who has a spreadsheet for tempering high carbon steel )

Ray

Plan B.

1. Set up a TIG ( with power off ) arrange the hand torch with clamps or whatever to align the electrode with the tap, so that the tip is touching the tap... grind down the electrode if needed to fit in the hole without touching the sides.
2. Adjust the amps to minimum, and switch on for a few seconds.

The tap should get red hot and expand the hole, then cool and become loose..

Repeat at higher amps if needed, don't go too high there might be a danger that you end up welding the tap in place....

Ray

Originally Posted by RayG

Plan B.

1. Set up a TIG ( with power off ) arrange the hand torch with clamps or whatever to align the electrode with the tap, so that the tip is touching the tap... grind down the electrode if needed to fit in the hole without touching the sides.
2. Adjust the amps to minimum, and switch on for a few seconds.

The tap should get red hot and expand the hole, then cool and become loose..

Repeat at higher amps if needed, don't go too high there might be a danger that you end up welding the tap in place....

Ray

And the tap will anneal making it possible to drill.

Originally Posted by rob streeper

And the tap will anneal making it possible to drill.

It's not that simple with HSS Rob. (Assuming the tap is HSS)


Freeze Spray has been mentioned here but has anyone actually used it with success in this type of Situation?

From my basic calculation the 3mm tap will shrink between .002 and .003mm but the surrounding metal will also shrink with a net effect close to Zero.

Originally Posted by Techo1

It's not that simple with HSS Rob. (Assuming the tap is HSS)


Freeze Spray has been mentioned here but has anyone actually used it with success in this type of Situation?

From my basic calculation the 3mm tap will shrink between .002 and .003mm but the surrounding metal will also shrink with a net effect close to Zero.

I agree, HSS will take a much higher temperature for annealing. I've been reading around about this issue and apparently some have used friction generated by a steel rod in a drill or drill press to spot anneal various things such as case hardened rifle receivers for drilling scope mounting holes.
Another thought occurs. Freeze spray is generally some kind of fluorocarbon or compressed hydrocarbon that is relatively cold, maybe -50 to -80 ^oC You may check around for liquid nitrogen. It is the coldest cryogen commonly available (-196 ^oC) and if you manage to get the tap cold enough it should shatter like glass.
My local welding supply carries it at about $3.00/liter. Somewhat dangerous to handle if you're not familiar though. Safety mostly consists of keeping it off of your skin and avoiding using it in a confined space so you don't suffocate. You can carry it in a good plastic Thermos bottle. Rig up a funnel, piece of vinyl tubing and arrange the end of the tubing such that it is pointed at the hole containing the tap. Slowly pour the nitrogen into the funnel and flood the hole with the nitrogen. There will be lot's of white clouds and hissing but the heat of vaporization of LN₂ is relatively low so small splattering drops are of little consequence. Nonetheless wear an apron, face shield, insulated gloves and be careful. Of course you need to be careful with your CI that it doesn't shatter too...

Cheers,
Rob

Originally Posted by RayG

but my suggestion is to advance the electrode manually until it just touches and then back off and do it again repeatedly, essentially doing manually what that the solenoid does.

Ray

I think the sinkers typically oscillate at around 50 Hz, ie 50 times per second. Doing it manually, maybe 1 Hz, if you're lucky. Reports I've heard is that it takes a couple of hours to disintegrate a tap using the primitive solenoid setups, so yes I guess if you were prepared to sit there for around 2 weeks working 8 hours a day it may be possible. You certainly have more patience than me I'll say that Ray

Freeze Spray has been mentioned here but has anyone actually used it with success in this type of Situation?

Yes I've used that on carbon taps and it worked. I was talking with Michael off forum about some other things and said then that I meant the reference to carbon taps, and don't know how well it works on HSS as I've never tried it on HSS. It's the type of solution however that is no jeopardy, and if it doesn't work there's not much more lost than a bit of freeze spray. I'm not sure I agree with you regarding shrinking, as that's the basis of getting a lot of stuff on (and off). I did just that only yesterday except with heat. The surrounding metal is an excellent heatsink and the temperature hardly changes, the target however is small and has a poor thermal bond to the metal it's in. I know a lot of people suggest using freeze spray for larger components when shrink fitting and that definitely doesn't work past Google searches. Well, maybe if they were sponsored by a freeze spray manufacturer! It takes a LOT of freeze spray to cool down a big component!!! Anyway, that all by the by, as it's not the point in this case, just a nice byproduct. The idea of the freeze is not so much to shrink the tap, that's however nice, it's to make the carbon steel really cold so it becomes even more brittle. That's why you hit it hard and quickly (after freezing it) with a pointed object of choice, something that will help to smash the tap apart more. How well it works on HSS I couldn't say, possibly not well, but I haven't ever tried it. Speaking of which, I wish all those the very best of luck in trying to anneal a HSS tap

One of the alloys used commonly used for taps and band saw blades is M-2. It anneals at 1600 ^oF, well below OA flame temp. So believe it or not it is feasible, you need to cool it slowly though to avoid hardening. The other common HSS like M-36 and M-43 are similar.

Originally Posted by rob streeper

One of the alloys used commonly used for taps and band saw blades is M-2. It anneals at 1600 ^oF, well below OA flame temp. So believe it or not it is feasible, you need to cool it slowly though to avoid hardening.

..... and there lies the problem. A broken HSS tap in a solid mass of CI is *not* going to anneal worth a damn. The surrounding metal is going to suck the heat right out of it.

PDW

Originally Posted by PDW

..... and there lies the problem. A broken HSS tap in a solid mass of CI is *not* going to anneal worth a damn. The surrounding metal is going to suck the heat right out of it.

PDW

I agree, the surrounding iron must be heated to near the same temp and thus the cooling rate problem will likely be minimized. However the thermal mass of the CI is going to be a problem with the cooling methods too. Given that this is a milling machine part the thermal distortions from either method may be limiting. No good getting the tap out if the part is misshapen as a result. Of the heating methods I like the torch heating followed by oxygen jet and Ray's welder heating methods the best as they will put the least heat into the workpiece. If the answer was obvious there would be no need for the speculations but this problem is a tough one. Tiny tap stuck in a big precision machined piece of cast that costs big money. Maybe the best suggestion is to contact a machinist or machine repair specialist rather than us Internet loopers.

There is nothing postive to report.
The tap is a spiral flute HSS Sutton by the way.

• Tried the freeze spray but I think there is too much thermal mass in the CI and the other thing is that spraying into a small blind hole is tricky - I'm not sure how much really gets in there. Would not back out and would not shatter.
• Dremel works until the tool is blunted (around 10 seconds). For coolant I used CRC but the effect does not last long.
• I don't have an oxy, so can't comment on that one.
• Tried TIG but the arc tended to flip to the side of the hole as the tap is in deep. Like the freeze spray there is a lot of thermal mass so I don't think I'll be getting the tap up to red hot very easily.

Currently working on making up a hole saw as per Ian's suggestion. I'd love to get the tap out and retain the existing hole but I think it's going to be a patch job.

Michael

Sounds like I real problem that's a small tap. I did remove an m4 tap using a soild carbide slotdrill and a pick set. But I could put it on the mill which isn't really an option

I would maybe try a soild carbide drill but have no idea how such a small drill in a power drill would go, might work if you have a steady hand

Following this thread closely as I broke off a 6mm tap into a cylinder shaped piece with a 9mm hole offset from centre by 5mm, thru the end. I had counter bored half the depth. The hole was for a locking grub screw. It is not a huge issue as I can just remake the part. This will be the 4th attempt. I am getting great practice at off setting to an exact amount in the 4 jaw. It is not super critical, but I am treating it as tho it is. Wish I had thought about the welding a nut on thing earlier. I did not even think of it. This is my standard practice for broken bolts and studs.

Dean

Originally Posted by Michael G

There is nothing postive to report.
The tap is a spiral flute HSS Sutton by the way.

• Tried the freeze spray but I think there is too much thermal mass in the CI and the other thing is that spraying into a small blind hole is tricky - I'm not sure how much really gets in there. Would not back out and would not shatter.

Michael

Michael the freeze spray normally sells with a nozzle, you basically just poke it in the hole and let her rip. I'm personally doubtful a HSS tap will shatter like the carbon steel ones do, but always worth a go.

What I'd personally try if it were in my workshop, and based on no particular experience or recommendations, is to stick a fastener in the welder's clamp and slip a piece of heatshrink or other insulator on it, and poke it down in to the hole and try to get it to weld to the end of the broken tap. Then try to use the fastener to work the remains of the tap back and forth with as much lube as I could get to flush around there. I haven't tried that method, have no idea of whether it would work, it's merely an opinion of what I'd personally be trying. The reason is two fold, firstly it puts heat IN to the tap temporarily (any any time you can get it to expand or contract is a good thing). The second reason is I've found once you can get the little suckers to move a little bit, they'll often keep moving .... if you can get a grip.