Might try The Foundry in Kendall Sq. It has a metalworking shop. (I can’t speak to whether it has a lathe.) Alternatively, if you have an electric drill that you can strap to a work surface, stick the bolt in the chuck and turn the head down with a metal file.

I checked their website and don't see a lathe listed. The Foundry is really just a community dance center and not an actual makerspace.

The bolt is hardened steel, so I don't think a drill and a file will end up being a workable solution.

Maybe I'll just find someone at Artisan's Asylum who will accept beer as payment.

For just two bolts can you put it in a vise and use a Dremel or something? Seems like overkill to use a lathe unless it needs to be really precise or something.

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What about an angle grinder or grinder blade on a drill? Those should go through hardened steel pretty easily.

I need some decent control on the final diameter. This is basically a shoulder bolt where I want to take the head diameter down to match the shoulder.

Artisans asylum is now in Allston.