Best drill bit to remove broke cobalt bit?

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Mad Dart said:
Put a nut over the hole the bit is in and build up a weld up off the bit and out of the hole and weld it to the nut then back it out with a wrench. Tig would be best but it can be done with a mig also. I have done this technique several times on bits, bolts, ez outs etc. Never once has it failed me.

You can do the same technique on the bolt that's broke off. The heat from welding will loosen it up and it too will come out. The whole process takes about 10 min. As soon as the weld is not cherry red, start going after it with your wrench. Do not let it cool all the way off.
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Mad dart stated the proper way.
This is the best way, glad you got the bolt out.

Most people do not have a welder, I say you did a great job with using what you have.
Next time it you don't have a welder try a left hand drill bit and heat......before you break any drill bits trying to drill it out.

Also if you are going to remove the studs on the end of the heads, heat the head, lightly rock the stud back and forth, it is in a water jacket and most like is rusted worse than what you just dealt with.
 
Well, you did have to grind it out like I said.
But my prediction of a Helicoil was off.
Good work with the girder.

Hum, this is just one more reason to buy the TIG I've been thinking about for body work.
MIG IS clumsy.
 
Glad to see you got that bastard out. snapped off bolts in places on cars is a "always happening" thing....Some can remove them one way, others not so much and then some doesn't have the same tools as one giving the advice, it turned out well, GREAT work with a die grinder thats for sure! AMAZING you didn't take out the threads originally in the head from factory, NICE work! AND......... one things for certain. you got a seriously steady hand!
 
inertia said:
IIRC .. In a post not long ago,, a member swore by using a carbide(?) masonary bit..

hope it helps..
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Yep a carbide bit will get the job done. Just regrind the lead edge of a masonry bit
to cut steel

Oh well I see you got it out good deal
 
Same deal on a slant head. Your hole is open, so you can drill it through and retap. I used a wire guage drill on a dremel. Went right through it, but keep a very steady hand so you dont greak it, keep going bigger until you are up to a 5/16 bit. Now all you are left with is the shell or threads of the old bolt, pick them out or pound them through into the water jacket. Chase threads or tap to next metric size and stud it with a brass stud
 
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