Nyah

I snapped off a bolt while trying to remove it from a rear rack-mount. The frame is CrMo and the bolt is stainless steel. The bolt is 0.209" below the surface of the braze-on. The visible threads look undamaged.

Is there any way to safely remove it without employing a high amount of heat? I just had the frame powdercoated and would prefer not to spoil that.

Moe Zhoost

You can try to drill it for an easy-out, but stainless stuff is prone to galling, which effectively welds the metal parts, so you'd probably break the easy-out It may be better to drill the bolt out with a bit slightly smaller than the hole threads and then re-tap it. If you can't drill it precisely, then drill it and retap for a M5 bolt. It's a good habit to use anti-seize with stainless fittings.

Good luck

2_i 

You should use a carbide bit, smaller in diameter than the bolt, to drill through the bolt. At that stage, the bolt remnant will become an easily deformable tube that should be easy to take out. The carbide bits are fragile - do not tolerate bending - but they bite well into a bolt.

sch

A left handed drill is sometimes more useful for this purpose as it will back the screw out when friction increases.
Left hand drill sets are on amazon for under $20. A sharp pointed center punch to give the drill a starting point
is helpful as well. Most of the time the threads will not be damaged enough to matter, but worst case a retap
to 5Mx0.8 is feasible and that is a standard bike thread.

As the first responder noted, stainless can be difficult to drill because of work hardening, the drill starts off fine
but the stainless goes from relatively soft to very hard from drill heating which happens rapidly at the cutting edge
of the drill and before you know it the drill is chewed up. Slow speeds and oil lube help a bit, as do left handed
or carbide bits for this reason. Had this problem getting stainless screws ~3M size out of a Bosch stove awhile back. Chewed up
3 drill bits on one screw that would not come out. Cheapest carbide bit would be a 1/8" masonary bit.

FBinNY 

Breaking an old blot while removing it is a VERY BAD sign. When bolts break on installation, it can easily be from excess torque and the threads are still free turning within the hole. OTOH if the bolt breaks on removal it's almost always indicated a thread bound in the hole by corrosion (even with SS, since the hole isn't).

Start with a LONG soak in a product designed for freeing rusted together bolts and nuts. During the soak, try dislodging the rust bonds using a hammer and punch from both sides. You want more than a gentle tap, but you're not trying to punch the screw out.

Next (if space permits) consider trying to drill into the screw from the back. This way the drill's torque is also trying the turn the screw in the right direction. If no luck, drill from the right for an EZ-out. (do not compound the sin by breaking the EZ-out in the screw. If all else fails, you can try to drill it out and re-tap the hole, but staying concentric will be difficult. IF the eye has enough mead, you can re-tap for a coil type thread insert, and end up with a repair better than the original.

Last, and most expensive is to pay someone to disintegrate the screw with an EDM machine. This is most practical in farm country where there are machine shops that specialize in farm machinery repair, but a search of local machine shops may find one friendly to bikes.