Removing a broken bolt or stud is never easy, but it can be made easier by using certain tools. One of the best tools is a left handed drill bit, these bits need using in a drill that is in the reverse gear, sometimes when drilling a broken stud the drill bit bites into it and removes it from the threaded hole!
If the broken bolt is going through the hole in the material you can use a right handed drill bit to try and drill the broken part out, in some cases the drill but will bite into the bolt and push it right through the material. If the hole is a blind hole (does not go right through the material) a left handed drill but can be useful.
A left handed drill bit is the reverse to a normal drill bit and so you use it in reverse, so if the drill bites into the material there is a chance that the drill bit will remove the broken portion of the bolt.
This is the left handed drill bit that we are going to use. To start off with the bolt needs to be as flat as possible so file or grind the bolt if it is not already flat.
Then centre punch the centre of the bolt and drill it with a centre drill first.
Now you can put the left handed drill into the chuck and then drill the hole in reverse.
If the drill bit bites it will extract the screw and remove it from the hole. If it does not remove the damaged bolt you can use a screw extractor or easyout.
You could also try - Remove a broken bolt using a welder
