What Kind of Carbide Drill Bit to Drill Out a Tap?

I don't think it is possible to drill out a tap. We always EDM them out.

Yep! Taps don't lend themselves to being drilled. Even if you can get a drill started, if it's anywhere near the edge and sees a path of lesser resistance, it probably won't stay in the tap. You're most likely to ruin your part if you try, and be out the cost of the drill, which will break much like glass. Your absolute best bet is to find a shop that has an EDM and hope they'll give you a hand. Who knows, you might find a kind hearted soul that takes pity on you and does it as a favor.

I'm curious how you're breaking taps in cast iron. It taps quite easily, so you might give some thought to what you're doing if you've broken two taps. If it's by bottoming, be sure to clear chips often and approach the bottom of the hole very cautiously, assuming you can't drill any deeper to get the depth of thread you desire. Let us hear how this turns out.

Good luck!

Harold

What size drill did you use for your tapped hole? Try a few thousanths bigger, it won't affect thread strength and will make your job easier. I have had luck making a forked tool to fit the flutes of the tap and back it out but that's SMALL, you'll need a jewler's saw, some O-1 drill rod heat treated just right, and a lot of luck. I think it helps if you burry some chicken guts in the back yard during a full moon.

I've removed some that small by "drilling", using a worn old carbide endmill (3/32 should do for a #5) in my milling machine. Setup over the center of the hole and raise the knee slowly up onto the endmill. By doing it gently, you should be able to core the tap, leaving it as bits to be picked out of the hole. It takes some patience to get through it, but it can be done.

Good luck. John Sullivan

Carbon steel or HSS? Carbon steel taps can often be shattered by striking with a punch. Depends on how much of the tap is in the hole, though.

John Martin

Great day, a 5-40 tap.. Heck I can't even see things that small anymore yet alone try and drill one out. Are you using a vise to secure the part your tapping or a tapping jig? I find myself breaking smaller taps (not as steady as I used to be) when in the sizes less than 1/4" so all my small tapping jobs go in a tapping jig if possible. No more holding it in one hand and working the tap wrench in the other.

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Skipping school, I decide to respond to what snipped-for-privacy@hotmail.com (Wally Blackburn) fosted 15 May 2004 16:09:46 -0700 in rec.crafts.metalworking , viz:

My limited experience drilling out taps (or screws) is to use a left handed drill bill and a reversible drill. What doesn't drill out may back out by it's lonesome. OTOH, it sounds like what you need more than anything else is a rigid setup and a slow feed to minimize the deflection. You may have some problems there with a hole too large for a 5-40 thread. In which case, drill and tap a larger hole, turn a nd thread a cast iron plug, insert it, and drill and tap the plug. (We did that with a lathe at the school. The shifting level for the speeds was worn "a bit" (gears were engaging only half way.) Shift the detent hole and violins: it's good for another fifty years!

tschus pyotr

may I suggest an approach that actually will work, and will cost you under $5 total?

go to a lapidary store and buy some diamond drills - they cost about a dollar each. Diamond will cut the tap just fine - you want the kind that looks like a toothpick with diamond dust all around it - use the to cut the flutes off the tap - power it with a high speed drill of your choice. if possible, put the assembly under water so the diamonds stay cool.

I know this works, I've done it several times - I usually destroy one diamond drill for every 1.5 taps.

bill

If you can score a lefthanded carbide drill bit, it tends to help as does use of a carbide lefthanded endmill.

Often times it will back out the tap after a certain point.

Gunner

That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell

These are commercially available, go down to #4, and have worked pretty well for me in the past.

Nobody has suggested that if it's a carbon-steel tap, you could heat the part & tap and let them cool, and the tap will be softer - if you're gonna drill it, softer is w-a-y easier...

No one mentioned that if the tap is broken off in an aluminum block (can't be that lucky) that the tap can be eaten out with acid.

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steam

I've

heat the

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You could us inductive heating to take the temper out of the tap.... Then drill it out...

Not if it's HSS.

Harold

Son-of-a-bitch!!! I didn't know, cool!!!

DITTO!

Harold

DITTO!

But with reservations. I am familiar with tap extractors, but they are also prone to failure, all depending on how or why a tap is broken. If you've broken a tap by loading the flutes with chips, you can pretty much forget an extractor. They also can let you down big time when you've bottomed a tap in a hole. They work very best for fools like us that break a tap by bending it. Ever notice how taps don't bend well?

Harold

EDM is the best way to do this, but a "christmas tree" carbide burr in a high-speed (at least 50K RPM) air tool will do the job.

Harbor Freight sells a small high speed grinder that is air driven. It is much like a dentists drill. I got a bunch of used dental drills from my dentist and have used them to drill out small taps. Not fast but it works. The little air grinder is cheap and the dental drills cheaper.

Dan