Originally Posted by
BCRider
It'll be a fussy bit of work and likely use up more than one of the little grinding stones that fits in there. The hardened allen ball will not allow you to use any cutting burrs so stick with the grinding points. A hard lesson to learn isn't it.....
Small grinding stones will take forever . . . and many of them. A single 1/8" tungsten carbide burr with a point, mounted in a die grinder [or Dremel type tool] will do the work in about 1 minute. The piece of broken allen wrench will definitely come out.