I picked up a SR Apex crank with 86 bcd chainrings from eBay. The crank and rings are in good shape but the crank bolts are seriously stuck and rounded out. Someone overtightened these. I reckon the best way to get them out is to drill them out.

Any better ideas?

Also what about replacement chainring bolts? There are plenty of chainring bolts for a double crankset but these need a longer chainring bolt as the same bolt is used for all 3 chainrings (unlike a 110/74 bcd triple). I take it that I'm going to have to look for used chainring bolts? The bolts are 12 mm in length and chainring bolts for doubles, which are readily available, are right around 8-9 mm in length.

I would douse them in penetrating oil and let them sit overnight, occasionally adding oil if they don't look soaked, and doing some gentle tapping - I can't prove it but the vibration always seems to help the oil penetrate. Then before actually drilling I would try using an appropriate size EZ out.
Good luck, that's frustrating... Regards, Eric

Maybe a Torx bit that's slightly larger than the bolt hole. Use a hammer to jam it in place, that should grip the bolt. Or, cut slots in the bolt with a Dremal and use a screw driver and vise grips to turn it.

Also, I may be able to help you out with chainring bolts.

I had same issue and just used a bit that was slightly larger than the hole in the Drive side. Once the bit "bit" into the metal it turned right out with a pair of vise grips on the shaft. Obviously be careful of the drill skipping an damaging your cranks or rings

...if the hex socket is rounded as you say, I would just bite the bullet and drill. As you probably have surmised, you need a bit about the same size in diameter as the inside of the receiver part of the chainring bolt ( I guess maybe it's a nut...but I've never heard them called that). I don't think it matters which side you drill from, but probably the clamping of the crank and rings to some fixed, flat surface will dictate which side is up.

It's something I've never had to do,but it looks like a job that would be so much easier with a drill press that I might try to find someone who had one. (assuming you don't)

Drill. Had to go this route a few days ago after all other methods proved useless. Took seconds to do.

EZ Out is a screw extractor.

For example: at harbor freight

I've never tried these on hollow hex bolts. It seems like the most reliable, least damaging method.

You can get longer bolts. Estimate the length you will need and type into a search engine.

I've used them on a frozen, broken seat post bolt, as well as chainring bolts.

Longer chain ring bolts are available here:

https://www.universalcycles.com/shop...hp?category=51