When the Delrin Melts on to the End Mill

You really cannot belt sand it away very

 easily 

what I have done is the past is melt it off with this lens which was surpluses from some DoD project many years.  (A parent with a DoD contractor whose name I have forgotten handed it off to me in the 1970s.)

It works well.  It is about 6 inches diameter and I can hand focus those 10 square inches of sunlight to a circles a fraction of an inch in diameter.   It melts it off very nicely,  at least on days with no cloud cover.

How much energy is that?  In Mr. Burkhardt's physics class in 12th grade, he sent us outside to measure actual received energy by measuring how quickly a plate of aluminum warmed up.  My group eventually reported a bit more than 1000 watts/square meter.  There is a lot of power there if you can apply it usefully. 

UPDATE: Another technique that worked was putting it in a vise and crushing the delrin until it snaps off.  I would never do this with a carbide endmill because they are so brittle.