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Old February 15th, 2010, 10:40 AM   #1
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Default Broken Drill-bit, how to drill out?

Drilling a pilot hole in a grade 5 3/8" bolt in our bronco frame when suddenly the 5/32 pilot bit snaps inside the bolt. What to do now? It was a cobalt bit. Can't seem to drill through it with another bit and there is no visible fluting to get a bit extracter in. The bit broke with nothing hanging out either...
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Old February 15th, 2010, 10:41 AM   #2
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Torch.
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Old February 15th, 2010, 10:42 AM   #3
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small burr.
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Old February 15th, 2010, 10:45 AM   #4
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sol ........fire stick
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Old February 15th, 2010, 10:48 AM   #5
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carbide bur. or carbide drill. Half to find something harder the the cobalt drill. But be careful carbides brittle.
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Old February 15th, 2010, 10:50 AM   #6
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Weld a nut to the bolt, use socket to extract.
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Old February 15th, 2010, 10:52 AM   #7
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drilling through a cobalt bit will be very tough. got access to a plasma cutter or cutting torch. just burn through it. then re-tap the hole to bigger size or weld a nut on the hole.
perhaps go all the way around the broken bolt and bit with a good hole saw. plate over the hole then re-drill and tap.
just a few thoughts. good luck
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Old February 15th, 2010, 10:53 AM   #8
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Try a left handed drill bit sometimes it will back out
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Old February 15th, 2010, 11:08 AM   #9
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Quote:
Originally Posted by Plato2k5 View Post
Weld a nut to the bolt, use socket to extract.
Works really well, if you can get to it with welder.
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Old February 15th, 2010, 02:45 PM   #10
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Works really well, if you can get to it with welder.
The remaining bolt shaft is behind the surface of the frame so no access to weld a nut. Plus the bolt is seized so not sure that would do a whole lot of good. The original bolt head snapped off.

Will see if I can find a carbide tip. If not I may have to buy a $300 oxy-ace torch
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Old February 15th, 2010, 03:02 PM   #11
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Take a punch and break it up into pieces and dig them out.

I have had to do this too many times but luckily it has been a while since.
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Old February 15th, 2010, 04:21 PM   #12
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Take a punch and break it up into pieces and dig them out.

I have had to do this too many times but luckily it has been a while since.
A punch is going to break up a cobalt bit? I suppose if the punch were harder than the cobalt.
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Old February 15th, 2010, 04:25 PM   #13
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Quote:
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A punch is going to break up a cobalt bit? I suppose if the punch were harder than the cobalt.
it could be, they're designed to be struck, so they need to be harder than what they are striking, so they do not deform, or shatter.
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Old February 16th, 2010, 03:30 PM   #14
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at my buddies machine shop I have seen him use small endmills on die grinders to eat out busted drills or taps.
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Old February 16th, 2010, 03:33 PM   #15
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i've done this several times, .250 carbide end mill chicked in a die grinder will chew at it, SAFETY GLASSES! i don't have much more than that as normally any broken drill bits i've done have been on a machine, not on the vehicle.
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Old February 16th, 2010, 05:23 PM   #16
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A "B F H" and a center punch works.
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Old February 22nd, 2010, 09:38 PM   #17
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Wanted to follow-up with the solution. The punch did not work. Any new cobalt bit just got dull as it rubbed against the stuck bit. No local stores had carbide bits in stock.

In the end I took a die grinder to it. Now the hole is a bit bigger than the original 5/16 hole (it's a 3/8 bolt); so I ordered a weldnut from mcmaster carr and will try to make that flush with the frame with a combination of mig welding and jb-weld.
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Old February 22nd, 2010, 09:44 PM   #18
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Quote:
Originally Posted by amc78cj7 View Post
Wanted to follow-up with the solution. The punch did not work. Any new cobalt bit just got dull as it rubbed against the stuck bit. No local stores had carbide bits in stock.

In the end I took a die grinder to it. Now the hole is a bit bigger than the original 5/16 hole (it's a 3/8 bolt); so I ordered a weldnut from mcmaster carr and will try to make that flush with the frame with a combination of mig welding and jb-weld.
If you have a welder or use of one Just weld it dont mess with the JB-weld.
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