How do I enlarge a hole in hardened steel (or work around it)?

I have a new bike trailer, but my bike axle is a bit too large. Previously I drilled a hole out in a cheaper pressed metal bike trailer mount, but this one is way harder.

Does anyone know a machinist who can do this? I’m really not sure how to make a dent in this. In these pictures, you can see the old mount and the new one. I just need to make the hole 2 mm larger in diameter.

Will a metal file make a dent in the metal? If it will you can drill it with a regular drill bit.

Do you have a drill press handy? More than likely you’re spinning the drill bit way too fast and not applying enough pressure. You could use a hand drill but you’d want to clamp your part in a vise on a large table so you can push hard against it. If the drill bit stops making chips/cutting then stop spinning the bit otherwise you’ll heat up and work harden the part you’re trying to drill through.

Alternatively just use the file to make the hole larger, same deal make sure to clamp the piece in a vise.

I can look for a file and try it, although that sounds very labor intensive, so I’d rather make that a last resort.

I have a drill press available. I tried it, with no success. It barely scratched it. Would a sharper, harder bit get through it? The opinions in the room were mixed, leaning toward skeptical.

I just found this, and this guy makes a pretty compelling case for de-tempering it. Has anyone successfully done this? Rebuild: The Skill That Helps You Drill Through Steel - YouTube