I have been following RepRap and MakerBot for a long time now. I have seriously considered buying or making one. The major reason that I have not done so is I know that I would go wild making things with it, and most likely would go broke buying HDPE to feed the friendly monster.

This changes things considerably. Being able to effectively recycle HDPE so it is usable by a 3D printer is something that I have thought about in passing, but have never pursued. This would drastically reduce the cost of using one of these machines, and most likely make them more affordable to a wider range of people.

Keep up the great work!

Steve

But… what of the refund of the deposit on all those plastic milk cartons? Is the milk carton composed of more than $0.25 worth of plastic?

KnightFire: We don’t get that in NZ.

With regard to the strength: Having a cheap source of plastic for jobs where the extra strength is not required (cellphone stand, casting moulds, models, etc.) would be very useful.

Gee, Ben – first of all, “break[ing] some of the long polymer chains into shorter chains” does not equal depolymerization, and happens at lower temperatures (and also mechanically during the grinding process) than for HDPE. As for “Delrin” (DuPont’s trade name for Polyoxymethylene or POM), the melting point is much lower than for HDPE (the product in the OP) or PET (the product you’re citing). While depolymerization will be extensive at 450°F above the melting point (at standard pressure in the absence of catalysts), it begins far below that temperature.