Q. re extracting really small tap

Marty Feldman · Sep 6, 2019

I don't usually break taps, but then I don't usually tap 2-56. Broke one today, in bronze casting, tapping manually with top pilot of tapholder rotating in jaws of mill chuck. Tap snapped right at workpiece surface. I have used extractors for size #4 and larger, but it looks as though there is nothing commercially available for #2. Or is there? Thoughts on methods to consider for tap extraction (not how-to's for general tapping) would be appreciated. Thanks.
-Marty-

Garwood · Sep 6, 2019

I think I would go straight to milling it out with a .070 carbide endmill or edm.

Rudd · Sep 6, 2019

If you can dunk the part in a solution of alum and water, maybe warm the solution up a bit, it will eat the tap but not the bronze. May take a few days.

Bill D · Sep 6, 2019

Chemical is the best most reliable way. Either acid or alum.
Bill D

CarbideBob · Sep 6, 2019

Garwood said:
I think I would go straight to milling it out with a .070 carbide endmill or edm.

I'd agree but be smaller than .070 as you just want to cut the core.
Don't know how deep.
Crudely ground left hand carbide spades are very useful for broken tap extraction but at this size it is a sensitive feel.
To just mill it a ballnose and gentle pokes and blowout but any endmill will be scrap when done.
Bob

Pathogen · Sep 6, 2019

I break them off in stainless steel. I use a sharp point cheap scribe. I am loosing my sight so I have to use a microscope. Using the point of the scribe I push the tap clockwise then counterclockwise. It can take 15 minutes but it will begin to move and it will back out.

If you are impatient you can use a tempered pin and whack the tap and either loosen it to make picking at it faster or you may get lucky and break off little chunks.

I use Tap Magic Protap cutting fluid and it has reduced my broken tap rate to almost nothing.

rons · Sep 6, 2019

I broke a tap in a tail stock ram. This part was not going to be easily replaced. A friend suggested I get it EDM'd out.
Took the ram to a good place and they did the operation in 1-2 hours. I re-tapped the same hole and it was like nothing happened.

That was for a 8-32 hole. I'm not sure about how it works for smaller holes than that but if you are interested then asking someone doesn't cost much.

john.k · Sep 6, 2019

Id try heat ,too...the bronze expansion may free the tap........otherwise chemicals.....try Rudds mix,or plain old nitric acid.....acid is hard to buy now,but I use a stain remover for stainless steel.....nitric and HF in a gel.....the gel dissolves in hot water ,making a good acid solution.....EDM is good too,if you have the machine.

Mud · Sep 6, 2019

Electro Arc tap disintegrator electrodes go down to .020, is there anyone near you with one of those? It's like a cheap EDM.

Can HSS be reliably welded? I took a 4-40 screw out last week by welding a tit on the end and loosening then unscrewing it with pliers.

Milland · Sep 6, 2019

In that second picture, you've made the world's smallest hip implant.

Rudd · Sep 6, 2019

Note on the alum method, I am believe this only works on carbon steel taps, not HSS taps.

gbent · Sep 6, 2019

Mud said:
Can HSS be reliably welded? I took a 4-40 screw out last week by welding a tit on the end and loosening then unscrewing it with pliers.

I've got the filler if you have the hands and eyes.

Cole2534 · Sep 6, 2019

Pathogen said:
I break them off in stainless steel. I use a sharp point cheap scribe. I am loosing my sight so I have to use a microscope. Using the point of the scribe I push the tap clockwise then counterclockwise. It can take 15 minutes but it will begin to move and it will back out.

If you are impatient you can use a tempered pin and whack the tap and either loosen it to make picking at it faster or you may get lucky and break off little chunks.

I've never had either of those methods work worth a fuck. What sort of punch are you using to delicately crumble up machine taps?

Sent from my SM-G973U using Tapatalk

Mud · Sep 6, 2019

Rudd said:
Note on the alum method, I am believe this only works on carbon steel taps, not HSS taps.

I did a hss tap in aluminum, took forever and made a mess of the part. I thought I screwed up, your statement now makes sense.

Mud · Sep 6, 2019

gbent said:
I've got the filler if you have the hands and eyes.

Yeah, seeing it was the hard part there.

G00 Proto · Sep 7, 2019

I used to take a nut and lay it over the top if the tap, then weld it in place with a Tig or Mig. The heat loosens the tap and the weld is usually strong enough to back the tap out.

Nowadays, I stop at my buddies shop with a twelve pack of his favorite IPA and use his hole popper (edm).

crossthread · Sep 8, 2019

You might want to make one of these. I did and it works quite well for what it is. I did not have a variac and they are quite expensive, so I just used a cheap light dimmer. I also found that kerosene makes a good EDM fluid. I guess an ammeter would be nice but I didn't use one. You can pretty much tell how it is working by the sound. I used a manual mill and just took my time on the down feed.

A Mini-EDM System

Cole2534 · Sep 8, 2019

crossthread said:
You might want to make one of these. I did and it works quite well for what it is. I did not have a variac and they are quite expensive, so I just used a cheap light dimmer. I also found that kerosene makes a good EDM fluid. I guess an ammeter would be nice but I didn't use one. You can pretty much tell how it is working by the sound. I used a manual mill and just took my time on the down feed.

A Mini-EDM System

Seems like a great use for a cheapo boring head, use it to arrive at a fairly precise diameter.

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Marty Feldman · Sep 9, 2019

CarbideBob said:
I'd agree but be smaller than .070 as you just want to cut the core.
Don't know how deep.

Bob is right about this when it comes to drilling out. The minor diameter of the tap is down around .060, so something in the 50's at the largest would be what's wanted. That's pretty delicate territory especially when applied to drilling out a broken tap.

I'm concerned about how well the other methods suggested, such as the homebrew EDM, would work in this small size. I don't own an ElectroArc (post #9) and am completely unfamiliar with it.

In answer to the question Bob raised about depth, the tap drill hole in the workpiece is .375 D and the broken piece of tap is roughly half that in length.

Thanks for all of the suggestions. Still thinking about how to proceed.

-Marty-

tdmidget · Sep 9, 2019

There must be a full moon judging by the replies.

Q. re extracting really small tap

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