I have broken about as many screw extractors, as bolts.
Have had better luck at drilling a series of holes (tiny pilot,
followed by thread-root diameter). It wants some good
hand-eye coordination (or a proper jig) but then you'd be
left with just the threads to pick out, easy enough (after
the first few, a tap might handle the rest with due care).
On cheapo pencil irons I used to just go buy brass bolts
of proper thread and file the tip to suit. Adequately close
to copper thermal conductivity, at least on a cheesy 40W
pencil.