Bugga. Broke a tap

[Michael G]

I was tapping a blind M3 hole in some cast iron and broke the tap. It's part of a screw hole pattern for a cover strip to go on the mill table, so no moving away a few mm and starting again (and Murphy's law says it is always the last hole in the pattern that causes problems)

The standard textbook solutions don't/ won't work (I wonder have they ever?)


Grab the sticking out piece with some pliers and back it out - yeah, that breaks off too.
Using a centre punch, tap the tap on the flutes until it backs out - works until the piece being tapped breaks as well...
Weld a piece of rod to the end of the tap and wind it out - weld a rod onto a broken M3 tap below the metal surface???


To add a degree of difficulty, the hole is horizontal.
I think my only solution is going to be drill a couple of holes next to the tapped hole and wiggle the broken piece out then plug and re-tap in the plug. Any other less destructive suggestions before I get stuck in?

(Sigh. Last job of the day too)

Michael

[.RC.]

EDM machine :)

[KBs PensNmore]

Hi Michael, when I'm put in a position like that, I get the Dremel/die grinder out with a carbide burr and try to cut one of the flutes off, usually works. With a small tap like that, it might be easier to try to grind it out using a ball burr. As a last resort, a small masonry drill could be used, the end result will possibly be an oversized hole, requiring a plug and re-drilling/tapping.
HTH Kryn

[pipeclay]

When you tried grabbing it or hitting it with a punch did it move at all.

If it did move it might still be able to be removed with the use of either a pair of long nose pliers or fine point circlip pliers,it should be a 3 flute tap so it want be that easy to get a good hold,if either of the pliers don't work you may be able to use some small rods down the flutes,grab these and try to turn.

[alexm1]

I have had success with long nose pliers, put the "nose" between two of the flutes and back it out, needs to be a large enough tap to accommodate the pliers of course, I a not familiar with M3 so not sure if it is big enough.

[DavidG]

Buy a cobalt drill bit and drill it out.

[BigStick]

I have had success with long nose pliers, put the "nose" between two of the flutes and back it out, needs to be a large enough tap to accommodate the pliers of course, I a not familiar with M3 so not sure if it is big enough.
A carbide slot drill will drill it out

[DocBug]

https://www.youtube.com/watch?v=YbeKxFBZrF8

Easy with the right tools

Good luck

[Stustoys]

How much you want to spend?

http://omegadrill.com/wst_page2.html
http://www.ebay.com/itm/T-O-Broken-Tap-Extractors-Set-/321040191436

I've drilled HSS before, but it was a punch not a tap.

I've also seen but never used this sort of thing. (sure the pic is for an M16 tap but it was the only good picture I could find, you get the idea)

Stuart

[morrisman]

One of these may work

http://users.tpg.com.au/agnet/microgrinder.html

[Techo1]

Let's be realistic here guys, we are talking about an M3 tap buried in cast iron, the suggestions of drilling, milling or sticking something in the flutes just won't work unless the tap is loose, even getting it out with an EDM would be difficult without damage to the 2.5mm hole. I have removed broken taps and drills with EDM but never this small.

[DocBug]

What is the possibility of drilling oversize , filling either with metal or braze and re-tapping ?

[tinkera]

Hi Michael,
M3 is probably too small to remove with all the obvious tools. I would make hole saw from some silver steel 4mm id, 6mm od, harden drill out the tap & plug with cast iron. Quicker in the long run.
Ian.

[Michael G]

The hole is a horizontal one in the side of my mill table, so we are talking a hefty piece of CI here (I'd estimate 100kg upwards - this is not a mini mill here guys). I don't even want to think of taking that off and welding or EDMing. Apart from the distortion, brazing or welding would also take a lot of heat, so that is not really practical.
The pliers or extractor may work for a larger tap but this is M3 we are talking about and jammed in. No loose fit here. I may be able to use a burr on a dremel if I can find one small enough. Perhaps a diamond engraving tip if I can think how to keep it cool so I dont kill the diamonds (squirter bottle maybe). A carbide or cobalt drill may do the trick but apart from the size, they need rigidity and the only thing I'd have to drill with is a hand held drill - not the best of set ups.
A tap disintegrator may be the go but I've been looking for a cheap one of them off and on for many years and never found one. I have plans to make one but that's a long way down the list. The cover plate is for a job that I first thought about several years ago and got the bits for around a year ago. At that rate the home made EDM is due for completion in around 2017...

Michael

On edit - Ian's hole saw suggestion may be worth trying too.

[Pete F]

Before drilling out too much I'd hit it with some freeze spray and try to shatter it. The nozzle should be small enough to get in to an M3. I don't know how deep it is, but if it's too deep for a prick punch I'd probably sharpen up a pin punch to a point to help shatter it, alternatively turn up some silver steel to the appropriate OD, then grind a point on it, harden and temper it.

Put the nozzle in to the hole and flood the tap with freeze spray (available from electronics repair shop if you don't have some). Straight away take your punch and smack the tap well. It will either shatter or the combo of that and the freeze spray will loosen it up and you may be able to back it out.

After my haul of "hey these are cheap!" Indian taps you and Bob so liked to rib me about, I got pretty good at tap removal until I threw the last of them in the bin in disgust :rolleyes:

[RayG]

Hi Michael,

I'd be tempted to try a temporary edm setup, you need to build a dam around the area that will hold the dielectric, that could be plasticine, or putty or whatever... it just needs to stop dielectric from leaking away..... for dielectric you can use diesel, or I've got safflower oil that I'm going to try in the next little while.. then you need a power supply, 12v @ 2a is probably enough. an electrode that is say 1mm diameter, and some aligator clips and wires. Finally a means to control the distance from the electrode to the broken tap, since it's a one-off, you might jury rig something manual... ( I'm a little unclear on the power supply requirements, a bit of on-line research hasn't helped clarify things, some sources suggest a higher voltage with series resistance, more like a high impedance source. Others suggest 12V is adequate.)

Bring the electrode in until it arcs and then back off slightly and repeat until you burn the tap out. Might take a while, unless you can automate the electrode movement, but better than some other alternatives.

I am currently waiting for the Ben Fleming book "Build a Pulse EDM Machine next generation" to arrive and I'm planning on setting it up as a wire edm, might play with sinker edm as well, using the el-cheapo minitature chinese cnc.

Ray

[Pete F]

I don't think it's quite a simple as that Ray, I looked seriously at building an EDM a few years back (coincidentally shortly after my Indian tap bonanza) and you do need to set up a circuit to get the electrode to erode properly. You don't just go at it with a 12 V PS sadly. The simplest I can recall was basically a solenoid, with the "spark" forming a self-regulating feedback loop with the solenoid. Even then it's fussy from what I recall. When the EDM is running it doesn't actually touch the surface of the part, and if it does that brings bad juju to the whole works. The secret behind them cutting is getting the electrode to "float" just a wee bit above the surface, erode the part, be eroded itself, all the while feeding (normally down). Not so easy as you can imagine!!!

I decided it wasn't worth the effort and instead bought better taps :D

[RayG]

Hi Pete,

The idea I'm suggesting is along similar lines, but for a one-off job, the added hassle of automating the electrode distance can be replaced by patience and time..

A bit like what this guy has done... https://pico-systems.com/edm.html the power supply he shows is a 60V supply with a 30ohm resistor in series, so it's current limited to 2A into a short cct.

That said, I'm a novice at edm, I've played a bit but don't yet have a good enough grasp of the fundamentals, when the latest Ben Fleming book arrives, and I get the thing finished I'll be better informed.

For broken tap removal, it's sometimes the only way forward.

Ray

[soundman]

Short of a sonic screwdriver.....3mm is going to be tough.

break out your blue and white striped apron and try a couple of these ideas.

get a piece of 3mm mild steel rod...like a bit of fencing wire.....chuck it in your battery drill and see if you can get some traction on it.

did you try using the broken stub as a spanner to get it out...or is it all busted up now.

Again real blue & white apron stuff.....but try the above with a hammer drill....one that actually will hammer backward.

a bit of lube and the freeze spray from above may help

As some have sugested you might be able to smack it a bit with a punch.

If it does not break it up, it might loosen it and allow one of the other methods to get some traction.

try the idea of a bur, drill or whatever ...but run it left hand rotation....ya might luck it out.

you might try a left hand drill...it may not doo much drilling, but it might pick up enough traction......yeh you will wreck the drill

Inseatd of buying a left hand drill you could grind some reverse edges on a little masonay drill.


if its a blind hole...its quite possible you have bottomed the tap and it jammed in at the bottom......belting the stuffings out of it might just get you some wiggle room.....might just jam it tighter
too.


Now here is a bizare and entirely experimental butchery......improvise a stud welder and see if you can spot weld something to it.....you would probably have to grid the end flat first

Hell chum...you are between a rock and a hard place......if its going to come out at all.....persistance will be what does it.



if all else fails.......grind all but the head off a 3mm fastener that matches all the rest.....and glue it on with superglue.

cheers

[BaronJ]

Hi Michael,

I don't know whether it will work for you, but I have on a couple of occasions successfully extracted broken 2BA taps using a transformer arc welder, by sticking the rod to the tap and backing it out. Depending how deep the hole is you might have to wrap a bit of paper around the rod end to stop it arcing to the side of the hole before it gets to the tap.

Good luck.

[Steamwhisperer]

Hi Michael,
this probably wont help now as I fear the tap is too far below the surface but I would get a 3 mm flat washer and place it centrally over the hole and broken tap/bolt then find a short welding rod stub and weld the tap to the washer with the amps cranked up a bit higher than normal.
Then weld an oversize nut to the washer and back it out with a spanner.
The washer will protect the surrounding area, the short stub electrode gives you better aim and the higher amps will expand and contract a broken bolt or with a tap soften it a bit to give you a chance at not having it snap more off.
I think EDM on the horizontal could be a whole new world of pain unless you do it for a living.
Good luck.

Phil

[PDW]

3mm is huge if you're used to playing with guns.

One of the standard ways to remove a broken tap is to heat the end of it red hot using an oxy-acetylene torch then turn off the acetylene. The oxygen stream will turn the tap into iron oxide basically and it won't affect the hole.

Never done it myself but it's in Brownell's Gunsmith Kinks book and I'm quite sure it'll work - those tips & tricks were all submitted by practising gunsmiths and guns are expensive.

PDW

[simonl]

Hi Michael,

Sorry to hear about your predicament. Can't add anymore to the already long list of suggestions. As with anything like this, the hierarchy of solutions is always to start with the least destructive methods and work your way down. Freeze spray, as suggested by Pete is definitely the first place to start I would have thought.

Good luck,

Simon

[The Bleeder]

The hole is a horizontal one in the side of my mill table, so we are talking a hefty piece of CI here (I'd estimate 100kg upwards - this is not a mini mill here guys). I don't even want to think of taking that off and welding or EDMing. Apart from the distortion, brazing or welding would also take a lot of heat, so that is not really practical.
The pliers or extractor may work for a larger tap but this is M3 we are talking about and jammed in. No loose fit here. I may be able to use a burr on a dremel if I can find one small enough. Perhaps a diamond engraving tip if I can think how to keep it cool so I dont kill the diamonds (squirter bottle maybe). A carbide or cobalt drill may do the trick but apart from the size, they need rigidity and the only thing I'd have to drill with is a hand held drill - not the best of set ups.
A tap disintegrator may be the go but I've been looking for a cheap one of them off and on for many years and never found one. I have plans to make one but that's a long way down the list. The cover plate is for a job that I first thought about several years ago and got the bits for around a year ago. At that rate the home made EDM is due for completion in around 2017...

Michael

On edit - Ian's hole saw suggestion may be worth trying too.

Michael,

I'd try the freeze spay first and if that doesn't work Id go and hire a magnetic base drill to drill it out with.

Since the hole is horizontal you may have to make a jig to hold the drill.

If you need to drill it oversize I'd just heli coil it afterwards.

[DocBug]

Just fyi,

If you have a dremel, you probably have a 1.6mm collet. If you have a friendly dentist, see if you can buy a few high speed diamond burs off him. It may be sufficient to get in. If you cannto get any, let me know, i often get units in with burs inside, I can try to get a few together for you .

Regards
Alan

[rob streeper]

3mm is huge if you're used to playing with guns.

One of the standard ways to remove a broken tap is to heat the end of it red hot using an oxy-acetylene torch then turn off the acetylene. The oxygen stream will turn the tap into iron oxide basically and it won't affect the hole.

Never done it myself but it's in Brownell's Gunsmith Kinks book and I'm quite sure it'll work - those tips & tricks were all submitted by practising gunsmiths and guns are expensive.

PDW

Good idea, perhaps even a size 000 cutting tip. If the heat induced distortion is tolerable it should work. Cast iron won't be cut with OA. It may be a viable last resort.

[wheelinround]

Its been a log while since I boke one more due to not tapping much. Like most replies above i have drilled out or used long nosed pliers etc etc. I had broke one below the surface but could clearly still see the flutes I used a pair of dividers and set them to fit and slowly was able to retract the tap enough to once again grab with pliers and remove with no drama.

[Vernonv]

Another left field idea along the lines of the oxy ... how about using a plasma cutter?

[PDW]

Another left field idea along the lines of the oxy ... how about using a plasma cutter?

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

[Vernonv]

Might work but I wouldn't try it - might cut the CI.Yes you would need a steady hand and keep the torch perpendicular and centered.

[Pete F]

Hi Pete,

The idea I'm suggesting is along similar lines, but for a one-off job, the added hassle of automating the electrode distance can be replaced by patience and time..

A bit like what this guy has done... https://pico-systems.com/edm.html the power supply he shows is a 60V supply with a 30ohm resistor in series, so it's current limited to 2A into a short cct.

That said, I'm a novice at edm, I've played a bit but don't yet have a good enough grasp of the fundamentals, when the latest Ben Fleming book arrives, and I get the thing finished I'll be better informed.

For broken tap removal, it's sometimes the only way forward.

Ray

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.

Unfortunately it takes a bit more than patience Ray, in the link you provided the guy was using the slow jog function of his CNC machine to feed the electrode and maintain some semblance of constant gap as he matched the jog speed to the electrode/part erosion. I'm not sure how that could be done manually. You most certainly couldn't just hold an electrode there by hand and get it to erode, it would either not spark at all, or just weld.

The simplest tap erosion machines (it's too generous to call them EDM really) I recall consist of just a solenoid, it's not very fast erosion IIRC, and yes something like this could be jury-rigged to erode a tap (assuming the hole was vertical). It really would require patience however. Basically the solenoid is in series with the electrode and wired such that it retracts the electrode with current flow. Unlike proper EDM machines, the electrode actually contacts the surface, and the current flowing pulls the electrode off the weld, a spark occurs for a microsecond and a small amount of erosion occurs. The device will oscillate at it's natural frequency. It could definitely be worth looking at having something like that available in a workshop, for such a time as this type of thing happens, as they're not very complicated.

In fact I just did a search then to refresh my memory, and I think the above is reasonably accurate so I'll leave it as is. I think I'll go for a surf now so don't have time to search too much, but I did come across this site that looks quite good
http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html
http://mikesworkshop.weebly.com/a-spark-erosion-apparatus-mk-3.html

I just did a search under "EDM solenoid". I recall there's quite a lot of material available on the net for DIY EDM/spark erosion machines. I also recall that book Ray, I don't have it but remember it often being mentioned. However I think there's probably enough info out there to get started, especially with some of these simpler ones, to begin experimenting with this before the book arrives if you wanted to. I'm not sure if you're aware, but there's also the EDM Handbook available (legitimately) for free. I wasn't interested in wire EDM, but it's good to know what's possible, my interest was rather in sinkers, however it covers the whole area pretty well. Not really a DIY book, but a good overview of the commercial side anyway.
http://www.reliableedm.com/Complete-EDM-Handbook.php

[rob streeper]

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-AQAAMAAJ&pg=PA795&lpg=PA795&dq=annealing+a+broken+tap+to+remove+it&source=bl&ots=gP5hPLX7oW&sig=y7VXv5QBd5MOySSd83Dl3hE2oxE&hl=en&sa=X&ei=qABkVPOvFsKogwSgvIRw&ved=0CD4Q6AEwAw#v=onepage&q&f=false

[RayG]

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-EDM-Machine/dp/0976759624

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



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 :D )

Ray

[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.... :no:

Ray

[rob streeper]

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.... :no:

Ray

And the tap will anneal making it possible to drill.

[Techo1]

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.

[rob streeper]

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

[Pete F]

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 :wink:


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 :wink:

[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. The other common HSS like M-36 and M-43 are similar.

[PDW]

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

[rob streeper]

..... 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.

[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.
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

[welder]

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 :doh:

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 :?

[Oldneweng]

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

[Pete F]

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.

[variant22]

I had a similar problem with a broken small (m3 or 4) HSS tap. The way I got it out was wrecking a few fine Dormer carbide slot drills. It ended up coming out with a pick after hours of slot drilling. A ton stuffing about. I figured the pros used EDM but by the sounds of it maybe not. I have been meaning to get some small 3mm carbide drills for when this inevitably rears its head again. Blowing through expensive Dormer gear in a bind is not my favourite pastime.

[Michael G]

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.

... 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.

I tried with and without the nozzle/ tube but with a tap that small the flutes are mainly full of thread.

As for your second thought, I tried to plant a piece of filler wire on the end of the tap when I was mucking around with the TIG but the filler at 1.6mm just about fills the minor diameter by itself. I know what you mean though and if I could get something attached on there it would probably come out easily enough. I did think about using the spot welder but as it works on resistance there would be greater resistance tap to CI, so I'm just as likely to weld the tap in.

Tomorrow is another day (and attempt...)

Michael

[Pete F]

I tried with and without the nozzle/ tube but with a tap that small the flutes are mainly full of thread.

As for your second thought, I tried to plant a piece of filler wire on the end of the tap when I was mucking around with the TIG but the filler at 1.6mm just about fills the minor diameter by itself. I know what you mean though and if I could get something attached on there it would probably come out easily enough. I did think about using the spot welder but as it works on resistance there would be greater resistance tap to CI, so I'm just as likely to weld the tap in.

Tomorrow is another day (and attempt...)

Michael

Keeping in mind the full disclosure mentioned earlier regarding having never tried it, nor can I recall it ever being mentioned as a legitimate way to remove a tap, but what I'd do is switch from TIG to Stick on the welder and put it in the rod clamp. Then just jam the (insulated) fastener down the hole and on to the end of the tap. While I think I can honestly say I'm a pretty handy AC/DC TIG welder, I'm truly crap at stick. Abysmal in fact and I truly hate stick welding. One of the reasons is having to unstick rods, and at times I've had those suckers really well planted into my "weld" (to use the expression generously). I figured if I can do that without trying with a welding rod, it should be possible to do the same thing when I AM trying with a fastener!!! :D What the weld current would do to the threads in the hole I don't know, maybe they'd weld up ... or be disintegrated a little by the current? I genuinely don't know, but if it came down to having to grind/edm/etc the tap out, this is what I would try first and if it buggers it up more, well that's just the price of trying I guess.

[tinkera]

Hi Michael, Great thread, If you continue with the hole saw, I would turn up a plug of cast iron to a press fit in the hole, drill & tap 3.0 mm & screw in a SHCS so that the underside of the head was tight up against the plug face & drive it in with a hammer, remove SHCS, cut, file & polish level with table, remove screw & the job is done.
Ian.
P.S. I have made several hole saws over the years, fine for a one off.

[rob streeper]

There is nothing postive to report.

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.



You may try wrapping the TIG electrode with Teflon tape to cut down misdirected arcing to the sides of the hole.

[Michael G]

Keeping in mind the full disclosure mentioned earlier regarding having never tried it, nor can I recall it ever being mentioned as a legitimate way to remove a tap...

Understood, and worth trying as a potential solution


You may try wrapping the TIG electrode with Teflon tape to cut down misdirected arcing to the sides of the hole.

The arc comes off the point so unless the point is closer to the tap than the sides it will arc there. The tap end is currently around 1mm below the surface, so to establish an arc on the tap the electrode will need to be less than 1.25mm from the tap. Not much room. Having thought about it more I also wonder whether I'm making things worse - I was tapping dry so the hole will be clean as was the tap. Have I zapped the tap to the table?

Michael

[rob streeper]

How deep is the hole?

[eskimo]

I don't have an oxy, so can't comment on that one.




you could if I lent you a set

[sossity]

Not sure if this is a really stupid idea but could you try a dremmel and a carbide cutter to cut away the cast iron round the tap to lower the level of the CI wide enough to get a narrow pair of pliers onto the tap. Maybe if cutting the CI near the tap, you could swap to just a grinding stone so the carbide doesn't snap on the tap. I like the hole saw idea and this is jsut cowboy version of the same really but I think it could be realtively fast and easy if it was me, because i'm not sure i could make a hole saw. It would need to be drilled and plugged afterwards of course, with a bigger plug than making a nice neat hole saw, so not as good really.

[Michael G]

How deep is the hole?

Roughly 10mm


you could if I lent you a set

Thanks, but I'd need to borrow an operator too - I last lit up an oxy in around 1986.


Anyway, the prize today goes to Andre - His comment about a carbide drill twigged my memory. I was going to go for the holesaw thing but realised a guide would be needed to hold it one place, so before doing that I had another idea. I got a 4mm masonry bit, sharpened it up and managed to drill/ pick the tap out that way. If I'd had a third hand to apply coolant it would have been useful as at the end of it the bit was not in great shape.
331193
I then got a real drill and took the holes out to 5.5mm in the hope of neatening them up. I found a piece of scrap CI, turned up a plug the right size*, applied a liberal amount of bearing glue, pounded it home with a big hammer and dressed with a file. (The marks around the hole are from the TIG torch experiment)
331194 331195 331192

Anyway, I then refitted the cover strip, spotted through and have now retapped the holes**. That was a little nerve racking too.

*I bought a set of pin gauges around a year ago. It seemed like a good idea at the time and this is another use for them. In this case the pin was just fitting a hole at 0.216", so the plug was made a smidge larger.

**You know when you break a tap you think that you could grind it off and use it as a bottoming tap? Not always the best idea...:doh:

Michael

[RayG]

Nicely done. Looks pretty neat and tidy.

Now that it's done, someone should unravel this thread and weave it into a set of ideas for broken tap removal, for future reference.

Ray

[rob streeper]

Talk about snatching victory from the jaws of defeat. Congratulations - I bet you feel better now.

[welder]

Am Glad I could offer some inspiration Michael and really happy you got r done. I think a lot of people are overthinking the problem. Good job.

[Michael G]

I think a lot of people are overthinking the problem.

Yes, well I'd be one of them (or not thinking enough):B

Michael

[welder]

I hadn't heard about using the Tig till this thread. Considering the tap was below flush with the surface I would be to scared of welding the tap in the hole did you use a 1 mm tungsten?
But I will remember that for rusted bolts. One thing I have learnt working in a machine shop is that simple solutions are better.

[Pete F]

In my experience you will have zero chance of directing a TIG arc down into a small hole like this. The arc will instead get pulled to the bore of the hole.

[RayG]

In my experience you will have zero chance of directing a TIG arc down into a small hole like this. The arc will instead get pulled to the bore of the hole.

That's not what the idea was about, the electrode is shorted to the tap when the power is turned on. With the handpiece clamped in place, On my tig it just hums like it does with a stuck electrode. No arcing.

Ray

[simonl]

Nice work Michael. I will remember that idea.

Simon

[krisfarm]

Michael,
Good to hear that you have solved the problem.About six months ago a mate of mine arrived with a piece of casting that he had broken a 1/8" whitworth tap off in,below the surface just like your problem. I removed the tap by putting a short as possible length of soft steel (piece of soft tie wire around .080" dia) in a hammer drill,held it down firmly and gave it a very short burst,then while maintaining the pressure hit reverse and out it came.It was a HSS tap. The hammer effect had driven the soft steel just a little way into the flute grooves just enough to enable it to turn in reverse.
Bob

[Pete F]

That's not what the idea was about, the electrode is shorted to the tap when the power is turned on. With the handpiece clamped in place, On my tig it just hums like it does with a stuck electrode. No arcing.

Ray

Oh ok, but now I'm completely lost. So you take your TIG torch stick the electrode on the end of the tap and turn the welder on? What happens then? A genuine question BTW, not trying to be a smart-ass, as I don't follow this at all.

BTW a thousand apologies to BaronJ, I read back through the thread to see what I'd missed in terms of the TIG solution Ray pointed out, and instead found, to my complete horror, that BarronJ had already suggested essentially the same idea as I did, except that I proposed a fastener instead of the welding rod. Sorry 'bout that, there were a lot of potential solutions coming through pretty quickly and I missed that one. At least you know I think it's a great idea though :D

[Michael G]

So you take your TIG torch stick the electrode on the end of the tap and turn the welder on? What happens then?

I must apologise as well, as I misunderstood this idea too. Next time I get the TIG out I may have to try this. My TIG has all sorts of idiot proofing in built (probably just as well considering the user...), so if I started with a dead short it would probably not kick in (this one has an auto OCV reduction thing which effectively stops that when using stick. Not sure whether it is still in the circuit when using TIG)

Michael

[Pete F]

Ah ok, I found the post referring to that now, and understand why I couldn't get it. You must have an old School transformer welder Ray, as that won't work on modern semiconductor based TIGs, they have protection in to shut them down with a short. Mine won't do squat if you short the tungsten out. You can still scratch start them, but it's not great, they do however come to life as the short is removed.

[Oldneweng]

Great to hear Michael.

I used the masonry drill trick to drill a hole in an almost new ride on mower blade that I stuffed. It split about a third of the length and came off the bolt. I decided to fix it just to prove I could and for experience. Also it was on the weekend. The mowers get lots of use at this time. I drilled a hole to prevent the crack extending further. I managed to straighten the 2 sides as I mig welded it bit by bit. The blade has done quite a bit of work since.

I will try this trick on my broken tap tomorrow. I can easily tap the next size. It does not matter.

Dean

[RayG]

You must have an old School transformer welder Ray, as that won't work on modern semiconductor based TIGs, .

My TIG is a pretty basic smps model, but doesn't have all the bells and whistles that yours obviously does.

In any event the TIG is only the power supply to provide a current pulse, and also happens to have a convenient holder for a tungsten electrode.

No reason you couldn't try the same trick with just a car battery and a few wires hooked onto the tungsten electrode. The purpose is to apply a current pulse to the tap and heat it up enough to loosen it, not weld or erode it.

Ray

[Pete F]

Yeah I think it's a good idea Ray, I just couldn't grasp the concept as I was thinking of my own welder.

If using TC masonry drills, they strike me as something that wouldn't be too difficult to change to LH. The helix serves no useful purpose in this instance and it would likely just require a bit of a touch up of the TC tip on an appropriate wheel to change the clearance from RH to LH so they can cut. I've often found taps come out on their own when I'm trying to do something else with them, hence always try to run a drill etc in reverse if I can. I think masonry drills go down to about 3 mm IIRC, certainly 4 mm as I have some of those, so getting in to the useful territory for this type of thing.

[BaronJ]

Hi PeteF,



BTW a thousand apologies to BaronJ, I read back through the thread to see what I'd missed in terms of the TIG solution Ray pointed out, and instead found, to my complete horror, that BarronJ had already suggested essentially the same idea as I did, except that I proposed a fastener instead of the welding rod. Sorry 'bout that, there were a lot of potential solutions coming through pretty quickly and I missed that one. At least you know I think it's a great idea though :D

Thanks, but no need to apologise. :) Just thowing in a suggestion based on experience, been there, done that, got the T shirt.:U
Incidentally I've never had a TIG/MIG welder and only had, and still have a transformer based welder, not that it gets much use nowadays.

[Oldneweng]

Yeah I think it's a good idea Ray, I just couldn't grasp the concept as I was thinking of my own welder.

If using TC masonry drills, they strike me as something that wouldn't be too difficult to change to LH. The helix serves no useful purpose in this instance and it would likely just require a bit of a touch up of the TC tip on an appropriate wheel to change the clearance from RH to LH so they can cut. I've often found taps come out on their own when I'm trying to do something else with them, hence always try to run a drill etc in reverse if I can. I think masonry drills go down to about 3 mm IIRC, certainly 4 mm as I have some of those, so getting in to the useful territory for this type of thing.

I thought the same thing myself about left hand grinding of masonry drill tips. I think I have a 3mm one. You would need to take care with chips tho if you manage to drill to any depth and with 3mm diam this would not be much.

Dean

[Pete F]

The amount of chips you'd need to deal with would be minimal Dean, besides which, when drilling a tap I'd expect them to come out more like a powder. Just pull the drill, wipe it off, and reapply lube.