Extracting a broken screw or stud

To center a drill on a ragged broken stud I machine a drill guide for a center drill. The drill guide should fit snugly in the hole and the end of the guide is as close to the stud as possible. Once the center hole is drilled I use a LH drill to drill through the drill guide and drill out the bolt as close to the minimum diameter as I can, then use a Proto 4-sided extractor to back it out. This, plus a lot of lube, usually works.

The Mig technique works well, especially if the stud is sticking out of the work.
 
I spent what seems like a life time removing broken screws and taps the first thing you have to do is remove the reason it broke. If it is rust I always heated it up red and rapidly cooled it in water the rapid cooling breaks the rust bond turns the rust into carbon and the rapid expansion and contraction helps,, also I have even done this on cast iron I have never had one casting break. Then I put a washer over it and if it is a small bolt I tig the washer on followed by a piece of key stock so I can get a wrench on it. I have never failed in 25 yrs of not being able to remove a broken bolt. One time I had a fella that broke off three studs and broke off three colbalt drill bits in the studs in a cast iron chevy block. I setup with a bunch of masonary carbide drill bits and started in with a lot of pressure you can drill through them with carbide but everytime a chip breaks off or when you break through you lose a bit but it does work and I saved the block it was still in the car!! .. Ray
 
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