I mill almost exclusively HDPE. Usually I’m around 1 or 2 on the DWP611 speed and I feed about 750mm/min with a two-flute carbide end mill. I find I can do about a 4mm maximum depth cut before I start having rigidity issues, but for roughing a full plunge slot at this speed I get significant chatter in the Y direction, where my SO3 is least rigid. I also opted for the standard size SO3 due to rigidity concerns.
To improve your cut, I would recommend the following:
- Play with feeds and speeds while cutting. Be very careful if you do this, but I actually feel the temperature of ejected chips to be sure they’re coming out fairly cool. As several have mentioned, often slowing down rpm or increasing feed can improved this as you’re cutting larger chips, minimizing heat put into the material.
- Utilize a 0.01in or 0.1mm finishing pass at full depth. This should cut your hairs off automatically.
- If you don’t have it already, I highly recommend buying a high precision collet set from Precise Bits. If you’re using it, the stock collet has high runout which could very well be causing uneven engagement of the cutter.