I have done that many times. :tango_face_grin:I've never had to try it, but I've read that you can make a thread-chasing "tap" (just to clean up threads, not cut them from scratch). You start with a grade 8 bolt, then cut relief grooves lengthwise, with a grinder. The relief grooves provide room for stuff that the tap is scraping loose, so it doesn't just bind up the threads.
Interesting sounds like a good idea to try.I've had some success by feeding a light gauge copper wire down through each flute of a broken drill bit and then twisting the two pieces of wire together like a twist tie to wind the drill bit out.
It works often enough that it's always my first attempt for broken drill bit removal.
If you drill, it is critical that you drill very carefully, and be certain the initial drill is centered in the broken off bolt. I think the block is likely aluminum, and those threads can be easily wrecked by a wandering drill.
Can you face the end of the bolt with a file or small grinder to make it as flat as possible, then use a punch to be sure your drill starts in the center? If you get a good starter hole, soak for a day or two with penetrating oil or home brew to increase the odds of it breaking loose if and when you try the easy out.
In all cases, don't be in a rush. Take your time and be very deliberate with the drill.
Note that light gauge means small enough to fit down the flute, but still large enough to almost fill the space in the flute. If the wire is too small, it will pull out as you twist them together.I'ne not heard of doing that before, but you can bet that the next time I break a drill bit off I'll give it a try.
It serves as a heat shield and weld spatter protection. Most broken bolts are into machined surfaces.Welding to it is good too. I don't know why the washer is always mentioned. I guess because it is almost flat. I have just welded a little to the top of the bolt that's in there and then sat but on top and weld the inside up. Then let it sit for a minute or two. The steel cools and the aluminum heats and expands. Then slowly apply pressure with wrench.