Well I tried it out yesterday on molding some HDPE. Here is what I learn and passing on.
I used all kinds of jugs that were HDPE. Folgers Coffee cans, Gain laundry soap jugs, and Clorox fabric softener jugs. Of course some milk jugs. I used my home oven that is gas range. 350 on the dial wasn’t enough so I bumped it to 375 and worked well however the thicker stuff from the first three items were hard to form but the milk jugs work a treat. I made a 3×5 inch plank for the Z axis for the CNC. The molted plastic was placed onto a piece of plywood with paper on it so the plastic would not stick to the plywood. I then placed a second sheet of paper onto the plastic with another plywood board on top and used every clamp I had to secure it and squeeze the plastic. Waited a hour and removed the plastic. The plastic isn’t smooth and has ruff edges so I took it to my router and squared it off. The plastic didn’t shrink much and the overall thickness is 3/8inch thick.
I tried cutting it to the proper size I wanted but luck would have it I snapped the last hacksaw blade I had. Cutting it isn’t too hard by hand, it’s about the same as if you were cutting a mid grade pine 2×4.
Also a few extra tips. Wear some nice think gloves. I used a pair of Mechanic gloves and you can feel the heat real quick. Also use aluminum foil on a cookie sheet and some Pam cooking spray as a release agent. Just lightly mist the cooking spray onto the foil covered pan. Instead of foil you could use Reynolds parchment paper and skip the cooking spray. Also just use Milk jugs. The plastic is a lot thinner so the thermal contact is better so it becomes easier to work with.