View Full Version : Cost of burning out a tap?

01-25-2008, 07:06 PM
Just curious,
What would an EDM shop charge to burn out a broken tap for me?
As luck would have it, I snapped-off a 1/4-20 tap, 1 inch deep... while working on my taper attachment for my lathe.
DAMN !!!
It was the last hole too. (of course). :mad:
I don't have access to a tap-zapper or EDM, or else I'd do it myself.

01-25-2008, 07:22 PM
If the work is made of non-ferrous material, you can use alum to dissolve the tap.

01-25-2008, 07:24 PM
HSS tap, 1018 part. :(

01-25-2008, 07:48 PM
I have drilled taps out a few times with carbide drills. it will squeel and spark and sputter but should eat it. Thats a hit or miss situation though.

Your best bet is to get on the phone and call around and see who has a tap burner. Even if a shop does not have one they might know who does.

01-25-2008, 07:57 PM
I have a tap burner that I have been refurbing, can't wait to try it:) Anyways, the shop I use when we have a bad day, charges 80 dollars, used to be 60:( Usually if they aren't to deep I can get them out with a small carbide endmill, 3/16" work best for 1/4-20 taps. Turn the rpm's way up, bring the endmill down so that it is centered as best possible, put some light pressure on the quill lock and slowly bring the endmill down through the tap,the locking of the quill helps you keep an even pressure on it., make sure to keep plenty of cutting oil on it and the hole, NO WATER BASED COOLANTS. It helps to retract the endmill every once in awhile when the swarf builds up in the hole and blow it out. This doesn't work everytime and can lead to more frustration, but it isn't to hard once you've tried it.

01-25-2008, 07:58 PM
1" of tap in the part or the top of the broken part is 1" down? I assume 1" worth of tap unless it's a extended tap. A couple of options besides burning it out.

- If it's not too far below flush, it is usually possible to MIG weld a nut to it and back it out.

-Like tattoomike said carbide drill or ball EM. On a Bridgie it helps to use the depth stop to only take a few thousandths at a time.

-If it's a through hole, shatter/push it on through with a punch and use a thread insert. I make my own Keen-style inserts by cutting the threaded portion from a SHCS and drilling and tapping it.

01-25-2008, 08:11 PM
The tap is 1" deep, into the part.
It's a blind hole, not a thru hole.
I tried welding a nut onto the remaining tap, but the tap broke off about .100 deep into the hole. :mad:
I think my next project will be a homeshop tap-zapper. :)

01-25-2008, 09:06 PM
Go to www.mcmaster.com and buy a tap extractor, its worth a try. They have fingers that fit down into the flutes and you tighten them up and back the broken tap right out. Well that's how it is suppose to work. We used them in the aircraft industry.

01-25-2008, 09:16 PM
An alternative may be to use a core drill equivalent to cut out a plug containing the broken tap, then Loctite or weld in a filler plug and drill and re-tap.

Herm Williams
01-25-2008, 09:22 PM
I normally charge 30 or 40 dollars depending on when they want it back and material that has the broken tap broken off in it. The unit (electroarc) that I have is not portable so item must be small enough to handle. You might check your local engine rebuilders, some have a disintegrator. if the hole has to have an insert or helicoil installed then the price is more.

01-25-2008, 09:23 PM
mo...why no water based coolants?

01-25-2008, 09:30 PM
I'm with Mochinist. I've broken bunches of 1/4" taps. 3/16 carbide endmill, run it at about 40-50sfm (800-1000rpms) wet or dry, it doesn't matter, your going to kill the endmill anyways. Feed it light, I've never done it on a manual, but on the CNCs, I'll run them in about .0001 per rev(.08-.1 ipm), its slow, but it beats scrapping a big dollar part. As for quill pressure for feed, I would say almost nothing, maybe hang a small bag of marbles(drill bits?) off of the quill handle(again, no experience doing this manually).

You will bust up a couple endmills doing this, but they are pretty darn cheap(TiALN coated(run these dry) at lakeshore carbide for $7.50, buy at least 3), I've always used square corner 4 fluters, and throw a little chamfer on them, a regular grinder works fine for that, you don't need a green wheel.

I'd stay away from the drills, the land in the middle will kill you, also, I've never tried this with a ball endmill, though, I don't think that the lack of chip clearance in the center will hurt you, especially if you are barely feeding, then again, plunging with a 4 fluter is not the brightest idea, but very little feed, so you should be OK. I'll take the 4 cutting edges on the 4 fluter vs. a 2 fluter for going into a tap, more economical, 2 almost free extra flutes.

Someone suggested pecking, from my experience, be careful, that is when pieces of the tap are going to fall into the bottom of the hole, make sure its clean before you go back in. I always used uncoated cheapies and flooded the crap out of them, with coated, just blast it with a bit of air, that should clear the tap dust out.

good luck.

01-25-2008, 09:37 PM
Well, I didn't do you any good at all, did I?:o Have you seen these TAP REMOVAL DRILLS (http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=359&PMT4NO=36642893&PMT4TP=*ITPD&PMITEM=77215606&PMCTLG=00). Masonary drills are similiar and may work in a pinch. Disclaimer: Whats worse than breaking a tap in an expensive part? Answer: Breaking a carbide endmill in a tap in an expensive part.:eek::mad: Carbide can be shattered into little pieces, though.

As far as quill pressure, it doesn't take much to shatter. i use the quill stop. Light pressure, ease up, move the quill stop a couple .001", repeat. CNC-pulse handle in .001" increments.

01-25-2008, 09:46 PM
mo...why no water based coolants?It jacks up the carbide, the hot cool action causes the endmill to breakdown and eventually fail.