On my side, when I turned Nylatron (I know it's not the same density of the HDPE but...) I use a round HSS drill rod which I shaped a very sharp tool that I mount on a tool holder. I stoned the tool front and side face to polish it to make very clean cuts. And using a round drill rod will allow me to rotate the tool if my chips doesn't go where I want. Also I make a ONE pass turning at full speed with a very aggressive feed to make a thick chip. This way, the chip goes 15 feets away of the chuck with a great loop. Also, I make a pause of 1 second when I'm at the end of the pass to seperate the chip from the blank.
The Nylatron part is a 5" bushing. The worst part is to turn the inside of the tube. I use a small boring bar with a TCGX AL insert. Again, I make a ONE pass turn with an agressive feed at full speed. The chips came out of the blank and fall again at 15 feet of my TL-2
