Start with a smaller drill bit and work your way up. It takes awhile but usually works.

Heat, WD, and use a smaller new bit. Then go larger till you get to the thread. You may need to re tap/threads, depending how straight you are. Take your time

Small bits to start, and I have found Cobalt drill bits make a massive difference. I had a broken bolt that I tried drilling out with titanium drill bits for over 30 minutes and made virtually no progress. Bought some Cobalt bits and I drilled all the way through in about 2 minutes. It really does make that much of a difference.

As others have said, use a smaller drill bit to drill a pilot hole (make sure you're centered and straight) and go up incrementally in size until you're getting somewhat close to the threads, but not drilling into threads. Use plenty of penetrating oil, even let it soak overnight. If you have to buy a new sharp drill bit, get a left hand bit so it helps work it loose as you drill. If you're lucky you can use an 'Easy Out' to remove the remainder after drilling through most the bolt. Be careful not to break the easy out or you will have a really tough time getting that hardened steel out too (same goes for the drill bit).

greddy_1700 said:

Small bits to start, and I have found Cobalt drill bits make a massive difference. I had a broken bolt that I tried drilling out with titanium drill bits for over 30 minutes and made virtually no progress. Bought some Cobalt bits and I drilled all the way through in about 2 minutes. It really does make that much of a difference.

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Thank you, I got 2 cobalt drill bits one 1/4in and one 27/64 in and was able to go right thru it with no problem. Cobalt makes a huge difference.

One thing I do is buy reverse bits... often the constant heating and cooling of stepping up bits will have the bolt eventually back out as youre drilling.

Sean30z said:

Thank you, I got 2 cobalt drill bits one 1/4in and one 27/64 in and was able to go right thru it with no problem. Cobalt makes a huge difference.

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Glad to hear it worked out! Yes, they make a huge difference when drilling hard metals. They're kinda expensive, but worth every penny.

My preferred method is to use left hand threaded drill bits, start with the smallest bit and work bigger.

Eventually you will either have the second hole bite enough to back the rest of the bolt out, or weaken the intergrity of the bolt enough for a left threaded extractor to work