I want to make a mold to press heated HDPE into 4x8 sheets.

Don't they normally use a screw to compress the pellets until they're molten then inject it into a mold? If you had a strong enough press you should be able to use the force of the press alone to turn the pellets molten.

>>1140906
Yeah I don't have any of that. I was thinking like C-clamps and some plywood

I've seen guys make little blocks of it, but to make a 4x8 foot sheet would be pretty ambitious. MDO plywood might give you a non stick surface if you sprayed it with some kind of release agent. Like Pam or something

>>1140944
Sorry guy, You're at least one order of magnitude off the pressure you'd need to mold plastic.

>>1140901
4x8 what? Feet, inches, cm?

If its on the smaller scale you could look at thick steel base, square sections welded to that to create the form and another steel section on the top. For pressure, I dunno, maybe something like a 2 tonne bottle jack

>>1140901

Realistically without the screw/pressure to get the heat, you'd need to heat the HDPE until it's workable, then form it. You don't get a lot of time to do that before it hardens, so your best bet would be to build a stove with your form in it, then run the stove while you have something heavy on top of the sheet forcing the hdpe into the shape you want.

>>1140967
Yap. I considered buying or building a large electric forge but my neighbor has one and it aint cheap to run