Drilling out a tap

[Whiterabbit]

Let me start by saying I'm a numbskull and I know it.

I broke a tap and have not been able to extract it so far. I'm going to try to drill it out with a solid carbide bit, it's going to arrive in the mail today.

My question is about speeds. Should I spin the bit at normal speed for steel, or should I go faster or slower? I think youtube (that bastion of always-correct information) told me to run the bit faster than normal, but I want to check with the good people here to confirm.

[oldracer]

I doubt that you will be able to drill out a broken tap as they are way to hardened. The only way I have been able to remove one is with a tap extractor and you have to get the one with either 3 or 4 flues. I also had to add some heat along with some machine cutting oil and applying turning force very carefully. Good luck, John

[aspangler]

If you have an acetelene torch, use the #1 tip with a small flame. Get the tap up to a red or higher temp. Shut off the gas at the torch leaving the oxygen on and let the oxygen cool it quickly. Us a good HARD puch and small hammer and it "should" shatter. If it don't, try again or take it to a machine shop. Next time try using high carbon steel taps. They shatter well without the heat.
Ask me how I know. LOL

[country gent]

I have drilled them out with carbide drills or used a carbide end mill to plunge them out. The end mill works better for me as its easier to stay centered. A pointed drill in the fluted tap wants to wander due to the interupted cut. You want a very solid set up in a drill press minimum ( clamped down to the table solidly on location) holding it in a vise by hand wont do it. The drill will wander and vibration will break the drill. A mill set up is better still as it has a more solid spindle and better control. In a bridge port I locked the spindle and used the knee cranking it up to feed. You don't give the tap size so Its hard to give speeds. Carbide is hard but its also brittle, vibration and or flexing will break it quickly. Another needed bit of information is how deep the tap is and how much you have to drill out? The best for removing a broken tap is a plunger EDM it cuts with out touching the part an electric arc and die electric fluid flushes the material out but it dosnt actually touch. So no flex or wandering just removing the tap. In reality you don't need to remove the whole tap just the center web section and the rest can then be picked out or it may even fall out on its own. I did this with the edm made an electrode to just remove the web then pulled the threads out in strips with a pick and tweezers.

[Jeff Michel]

As a suggestion, you might consider the EDM option as Country Gent suggests. The carbide drill method does work but if you lack facilities to do the job properly, you will have a can of worms. Depending on the diameter, drill presses and most turret mills don't operate at the suggested speeds for carbide drills to work correctly. A good EDM operator can remove the broken tap and not even harm the threads. Good luck, they are a pain.

[W.R.Buchanan]

Yes, If the tap is broken is such a way that you can't shatter it or twist it out it is nearly pointless to try to drill it out. It will more than likely wander and completely screw up the hole and you'll be pissed.

In a machine shop when working of expensive parts that are too expensive to scrap and just do over, the standard method of removing a broken tap is to take it to an EDM shop or a shop with a Tap Blaster (less sophisticated EDM Machine) and have it burned out. This is the most cost effective method of safely and cleanly removing a broken tap or drill.

Most outfits that do this will even re-tap the hole after the fact to insure that you don't break a second tap in the hole.

This can be done but I assure you that after 35 years in business,,, You had better be much more lucky than good. When people come to me, depending on how bad it is,,, I tell them up front (Best Case) 40% chance I'll be successful. Worst Case,,, Zero. And I won't guarantee a positive result in either case.

I am both Lucky and Good at this and have been successful about 40% of the time,,, so act accordingly in your case.

If this thing actually matters to you have it burned out. That is considered the right way.

Randy

[Whiterabbit]

I have drilled them out with carbide drills or used a carbide end mill to plunge them out. The end mill works better for me as its easier to stay centered. A pointed drill in the fluted tap wants to wander due to the interupted cut. You want a very solid set up in a drill press minimum ( clamped down to the table solidly on location) holding it in a vise by hand wont do it. The drill will wander and vibration will break the drill. A mill set up is better still as it has a more solid spindle and better control. In a bridge port I locked the spindle and used the knee cranking it up to feed. You don't give the tap size so Its hard to give speeds. Carbide is hard but its also brittle, vibration and or flexing will break it quickly. Another needed bit of information is how deep the tap is and how much you have to drill out? The best for removing a broken tap is a plunger EDM it cuts with out touching the part an electric arc and die electric fluid flushes the material out but it dosnt actually touch. So no flex or wandering just removing the tap. In reality you don't need to remove the whole tap just the center web section and the rest can then be picked out or it may even fall out on its own. I did this with the edm made an electrode to just remove the web then pulled the threads out in strips with a pick and tweezers.

I will be using a mill, and my bit will be a 4-flute bottom-cutting short-length flat-bottomed endmill. The mill only goes up to 2000 RPM though.

The bit diameter will be 3/32, as the tap was an 8/32 and I thought 1/8" was a bit too big.

Depth of the break is a little over 1/8", the part a little under 1/4" thick, no protruding surface to get a handle on. I've chewed it up a little with a punch and hammer, but I have not been successful breaking the tap. Thus the desire to try a solid carbide bit to drill it out.

Does that change any of the suggestions? if I decide to go ahead and try this, what speed would you suggest running the mill at, 2000? with small pecks? if it meant reasonable removal from my part it would be acceptable if I destroyed the endmill in the process.

[JSnover]

I've burned a couple out by using the shank of a broken carbide mill or drill: mount it upside down so the flat end will touch the broken part. Run it FAST and feed it slow, let the friction do the work. It will take some time and it'll get HOT.
Probably not an option for a small tap like that, though. I'd go the EDM route if I was you.

[Moleman-]

I've used carbide endmills to remove broken taps. Go slow, use a collet to hold the endmill, remove any chips often and use a pic to check for any loose bits that could break loose and break the endmill. Smallest I've gone is using an 1/8" carbide endmill spun as fast as my drill/mill will go.

[country gent]

In the mill I would try 1200-1500 rpm and use the knee to raise the part into the work. You can lower and lock the spindle to get close and save cranking. Feed small amounts and clear chips often. These are going to be hard chips from the tap and if they bind will destroy the threads also. If possible get as many of the chips out as possible to save on their binding also. If you break the carbide off then your in real work. I have heard of the old electric pencils ( the carbide tipped that vibrated at high rates for marking steel) being used to shatter and break out taps by hand also.
Like it or not the end mill is going to be a one time use tool here. The corners will be rounded and it will be dull when you done. Go slow and pay attention adjust as needed. since the end mill is on the way this is after the fact but a left hand cutting end mill is the better to use here as its trying to back out the tap naturally. Keep the tool as short as possible for the added rigidity.

[Treetop]

Whiterabbit, I'm a retired machinist/tool and die maker. W.R. Buchanan wrote almost exactly what I was going to. Please read his post carefully. Treetop

[smokeywolf]

Even with a top quality solid carbide end mill and a Bridgeport it's a bit of a hit & miss affair. country gent, W.R. Buchanan and Treetop have offered solid advice. I too am a retired engineer and machinist.

All I can add is, good luck.

[oldracer]

I did not see what you were drilling and tapping in? If it is the top of a barrel for scope mounts such as two separate blocks like for a Unertl scope, why not just move the mount(s) to cover the hole with the broken tap. It will cause no issues and I have had several gunsmiths tell me they did this!

[John Taylor]

While I have drilled them out with carbide I forgot to say I use old broken carbide end mills. I sharpen the end like a cold chisel and run it at high speed. You don't want to break off a carbide end mill in a hole, might as well throw the part away. In some cases a carbon tap can be heated and allowed to cool slow which will make it softer. Most of the broken taps I run into are 6-48. The most common broken end mill I have has a 1/8" shank which is .005" over the drill size for the hole. So with an electric hand drill and a diamond tool grinder the diameter of the carbide can be taken down a little. When drilling out a broken tap or any other hard piece this way you need a ridged set-up, most drill presses will not work. EDM is probably the best way to go but finding one close by is not alway possible.

[Traffer]

Well I don't see it suggested so here goes. I broke one YESTERDAY. I usually just bust them up with the hardest pointy thing I have and pick the pieces out. However this was an 8-32 and it was in about 1/2" (quite deep for that small of a tap) So I tried a 2mm ball tip diamond burr on a dremel. I used cutting oil instead of water for cooling. I got it out in about 10 min and didn't ruin the threads. I would say if you wanted to try drilling one out with a carbide drill bit, you could grind a center depression with the diamond burr so it wouldn't wander into the flutes and should work OK. If you want to know where to get the burr pm me. Heck I could even send you a few as they are pretty cheap.

[bigdog454]

I'v taken out a few with a end mill in a bridgport. I use a ball end mill bit and have had good luck.
BD

[W.R.Buchanan]

You never said exactly what this tap is broken off in? is it a Receiver or barrel? or is it something else?

Randy

[JonB_in_Glencoe]

I did not see what you were drilling and tapping in? If it is the top of a barrel for scope mounts such as two separate blocks like for a Unertl scope, why not just move the mount(s) to cover the hole with the broken tap. It will cause no issues and I have had several gunsmiths tell me they did this!

I have experienced many broken taps (usually 6-32) in my field of work (not gun related) when drilling/tapping mounting holes for electrical components. When the hammer-punch method fails, as you state in your case, I would just cover it up as oldracer suggests.

I imagine that isn't an option here, but since you haven't posted what your tap is broken off in? I figured I'd just re-state the obvious.