Broken Carbide Drill bit in Pursuit Jig

Quote from Slingingsteel

I successfully drilled a shaft the other day with no problem, However, today i was drilling a little to fast and the carbide drill broke off in the jig and also half way through the shaft. So now I'm trying to figure out how to get the shaft out of the jig. The drill bit is acting like a pin keeping the shaft stuck. I don't think you can drill through a carbide drill bit can you? I'm a little stuck here, any suggestions?

Dylan

First what metal is the drill jig made from ? is it heat treated steel ? If so try putting the jig in a vice with the broken bit facing down. Then tap the end of the shaft lightly on the end with a hammer but not so hard as you deform any metal.. I need to tail some bugs and fire up the BBQ, back in a couple hr..

Cheers, Don

It's made from 12L14 steel.

Carbide drill bits are very brittle. Is there any part of the bit sticking up out of the jig that you can grab? If not I would clamp the shaft in a vice close to the drill jig, and give the jig a carefull solid hit with a hammer. With any luck the bit will break exactly at the point that will allow the shaft to come out, with some more tapping with the hammer. If you don't have a vice try supporting the shorter end of the shaft sticking out of the jig on the floor. This is just an idea, I've never done this before.

Nice!

Can you please describe in detail what you did? Did the bit piece just fall out from the vibration?

Quote from Slingingsteel

That worked!!

Thanks Don, you da man! :thumbsup2::thumbsup2::thumbsup2:

Cool mate, mechanical resonance and gravity can be your friend at times, it's good to start with nondestructive methods first.OK back to the tail....:D;)

Cheers, Don

U have to make sure the drill bit doesn't get to hot or it will shatter. You probably need to slow down a bit and maybe add some oil.

Should oil and slow speed really be used with carbide bits?

Once you start seeing lots of smoke, slow it down. That's what i do and it works fine. I also use a little bit of synthetic lubricant. I thought it was oil but its not.

Quote from Dan

Should oil and slow speed really be used with carbide bits?

On SS and carbide bit and drill press, I go slow and steady dry and keep the pressure on, if it is not cutting and just rubbing, heat will build up fast. I'm talking about a few spearshafts but not assembly line production .

Cheers, Don

I know I'm probably splitting hairs, but here's my take . . .

Different oils serve different purposes. In this case, you want the oil to reduce the heat due to friction, and to absorb some of the heat that is generated. But some oils (like motor oil) are formulated with additional additives that are intended specifically to prevent two metal surfaces from contacting. That's not optimal when you WANT the cutting edge to bite.

So while motor oil, WD-40, and many others will work a lot better than nothing, I find that pipe threading oil or a similar cutting oil works better still.

Quote from Tin Man

I know I'm probably splitting hairs, but here's my take . . .

Different oils serve different purposes. In this case, you want the oil to reduce the heat due to friction, and to absorb some of the heat that is generated. But some oils (like motor oil) are formulated with additional additives that are intended specifically to prevent two metal surfaces from contacting. That's not optimal when you WANT the cutting edge to bite.

So while motor oil, WD-40, and many others will work a lot better than nothing, I find that pipe threading oil or a similar cutting oil works better still.

What Jeff said You need the drill bit to bite, not burn. Slow and steady will get the job done. It take patience or a lot of broken bits to drill a shaft.

I bought an expensive carbide drill bit once. When I took it out of the package it fell on the floor and broke in half. I took one half and shaped it somewhat with a bench grinder. I then used it to drill a shaft that was too hard for a normal drill bit. That carbide bit seemed to work like an abrasive disk, grinding through the metal, making a hole very fast. The carbide bit I got from Greekdiver didn't work the same way. I was asking about oil because with a bit that's grinding into the metal using oil seems counter productive. I seem to recall that bit worked better at high speed. I haven't seen that kind of carbide bit since that time.

I know it seems a little counter intuitive. But I've been around some pretty big surface grinders in different machine shops, and they always use a heavy flood of liquid coolant to protect both the grinding wheel and the work piece from overheating. The fluid also helps carry the abraded particles away from the contacting surfaces.

Ah! thanks.