I'm looking to make some enclosures for my servo drives. They're currently bare PCBs and while they have mounting brackets I'd like to make sure no stray conductive swarf gets in. Enter HDPE. It's cheap, easy to get in sizes thick enough to make enclosures out of and people say it's easy to machine. But from my research I'm seeing conflicting information. My favorite feeds and speeds calculator - FSWizard - doesn't list HDPE, but lists Delrin. When I put in a 1/2" HSS end mill it's telling me 4k RPM at 40" per minute. With a .875" DOC and a .15" WOC. But from what I'm seeing online is to go full DOC, full WOC at much higher feed rates with low RPMs. Who is right?

Because this is going to be an enclosure milled out of solid bar I'm looking for what will get me the most material removal, but also what will get me a nice surface finish for that finishing pass. Another thing I saw mentioned is that you should use pristine end mills for plastics in general and only use them for plastic. I have some pristine smaller 2 flutes and an entire set of pristine 4 flutes. I'll probably be machining more HDPE in the future because it's so damned cheap. Should I be getting a set of plastic endmills and if so, which ones? Would they work for most plastics? (Delrin?)