Machining plastics

I cut a few small sheets of HDPE in my CNC router and it cut really easily. I was using a 2 flute 1/8" endmill at 16000 rpm and 40-50 ipm. Cut depth was 0.08" per pass. It could have easily handled a more aggressive cut. It produced small chips, no strings.

The only slight issue was a few drill holes where the drill pecked, but didn't completely raise out of the hole between steps. A small amount of melting occurred here.

The end mill had probably seen 10 hours of use cutting cherry, so it was not very sharp. Most people recommend sharp tools.

Steve
 
My application is Gravoply. I'm certain it is not Delrin or nylon. I have a sheet 0.375 thick that I need to make precise shapes in. Do you all have any experience in shaping this stuff? Should this be a separate thread?
 
I've cut quite a bit of nylon. The chip tends to be an unbroken string that wraps around the part being machined and can be time consuming to clear. I found that if I just reversed the feed at the end of the cut the tool would push the strings ahead of itself and right off the end of the part.
 
If you're just trying to teach kids basic machine skills, I wouldn't waste money on plastic.......start em out on scrap wood. Then progress to aluminum.
 
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