I'm sure you can, but don't really want to. They're not made for the side load. I also wouldn't trust the chuck to be super precise tbh. You may also not be able to the the right rpm range you need. If its just uhmw you're milling, clamping a cross slide vise to the table and using a center drilling 2 flute end mill to drill out a majority of the material and basically clean it up by milling it should be ok, but wouldn't do a ton of it for sure.