Drilling out a broken bolt ..... or so I thought

[Moody Blue]

Needed to remove the windshield wiper linkages from the van to get access to the upper strut mounts tucked back under the windshield cowling. Broke the head off a bolt fastened into a tapped hole in a casting. No problem I figure, I'll just drill it out and re-tap the hole. Done this numerous times before.

Well after an hour and countless drill bits I had drilled less than 1/4" into the broken bolt. I tried HSS, titanium coated and cobalt drill bits with no success. Finally I got out the carbide burr and die grinder and ground it out.

I don't know what material or hardness that bolt was but it was like nothing I've encountered before. It was only an 8mm (5/16") bolt, not real big. I've got another to remove and fear the same outcome. Any suggestions ?

 

[minuteman62-64]

Re: Drilling out a broken bolt ..... or so I thought

I've had some luck with hardened bolts w/this procedure:

1. Grind a dimple in the center of the broken off portion.

2. Chuck an old drill bit, that you don't care about destroying, and "drill" into the bolt at high speed until the smoke starts to show.

3. Switch to a good bit, preferably cobalt/titanium/etc. and try again to drill into the broken off stub.

Doesn't always work, but, the heat can reduce the hardness of the bolt to let you drill for an extractor and help loosen it in the hole.

 

[TilliamWe]

Re: Drilling out a broken bolt ..... or so I thought

Sorry I didn't get to reply to your first thread sooner. Or read this one first.

 

[bigdee]

Re: Drilling out a broken bolt ..... or so I thought

I have used a stick welder with “stud removal electrodes” works great, just place a nut over the hole of the broken bolt then poke the electrode through the hole in the nut and commence to fill the bolt hole with weld up to the nut then weld the nut to that and remove with wrench. The electrode has a special ceramic flux that will prevent it from fusing to the threads.