I too, work as a machinist to a large degree. The most important part is having the set screw head super clean. Use a straight pick to dig out the crud, following all advice and tips shared to assure its clean so your wrench as the best chance for bite as it can. In many cases, this is how the screw could get rounded out.

A .22 caliber bore brush!
 

What a fantastic idea! I've been using a similar tool for years from my other "hobby", vacuum tube electronics. It's a hand held cylindrical brush made for cleaning the contacts of a vacuum tube socket , however it's not nearly as robust as a bore brush. I wish that someone still made an assortment of these style brushes. Just for the record, what is the size and thread pitch of these little set screws? Thank you, Paul

1/4 - 20 the inner three need to have a point, the outer three need to be flat, I was just at the hardware store yesterday.

Use a bottom tap or an old tap with the lead ground off to clean the threads above the screws.

Saw a video of a guy who got the hub red hot where the screws were and said they would drill much easier after that. Not sure if the temper gets taken out of them but I was going to try it one time as drilling them is beyond words as most know.

Jeff what do you think of that? I'm thinking the hub might warp with such heat from a Rose bud but maybe not.

That's interesting-- the set I got loose had the pointed one on top. I didn't remove the lower one, so I don't know what it looks like.

Localized heating at the set screw location would probably be fine. My main concern would be trying to face it afterwards because if it cools too fast, it becomes hard. ( difficult to machine)

I'm not sure if this is applicable, but I have spot annealed case hardened shaft to drill through it. I took a scrap piece of round stock the diameter of the desired hole, heated the end to red hot and held it to the shaft where I wanted the hole. Maybe you could try the same thing with the set screw and a piece of 3/16" rod. Heat the rod, stick it in the end of the set screw and let it transfer it's heat and anneal the screw. With all the mass around the screw it may take a few heating attempts to get the screw warm enough to anneal, but it should keep you from overheating the rest of the pto.

Bill

It's worth a try, maybe it'll save this project.