I've used this method more times than I remember of as a tool and die maker.First start by drilling the head of the bolt dead center .The trick is to use a left hand drill bit .Yes they do make them.manny time befor the head has fallin off the bolt has turned between the heat and the left hand friction.If not you continue with the proper drill size for your thread left hand.That way if it hasn't unscrewed by itself you just have to clean up the thread with a tap.Hope this helps it's never failed me
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