Screws are designed to be easily installed and removed. But they can become stuck for a host of reasons. Corrosion is one of the main culprits that cause a screw to become stuck. There are also several methods to remove stuck screws. Penetrating oils, vibrations and changes in heat describe some stuck screw removal techniques.Another method is to use a bolt extractor, which screws into the fastener. The bolt extractor is threaded such that tightening it will loosen the screw it is threaded into. But what happens when the extra-hardened bolt extractor breaks?
Weld a piece of stock metal onto the broken extractor bit. Use a piece of stock large enough to give you enough leverage to turn the broken bit out of the fastener it is stuck in.
Drip a small amount of nitric acid onto the broken extractor bit. The nitric acid will dissolve the edges of the extract bit. The smaller bit may be easier to pry out of the fastener. But be very exact. Nitric acid can damage other metals, such as fasteners and sheet metal
Cut the bit out with a plasma cutter. Plasma cutters use super-heated plasma to cut metals. If you have your own portable plasma cutter you can attempt this on-site. You can also bring the component with the broken extractor bit to a machine shop with a plasma cutter and have their trained technicians cut out the extractor bit.
Disintegrate the bolt with an electrical discharge machine (EDM). You can bring the component to a machine shop that has an EDM. The EDM will apply an electrical current precisely on the broken extractor reduce it to dust.
Take the part in question to a machine shop with a tap disintegrator. This works on the same principles as an EDM and is also called a metal disintegrator or spark eroder.
Be very careful with nitric acid, it is a very dangerous chemical. It can be harmful to your health, and it can also damage surrounding material.