We're making HDPE blocks by melting/fusing together bits of HDPE plastic. It's a little smelly and totally awesome.
Once you have a block of HDPE it can be milled, cut, and shaped similar to how you work with wood. I'm hoping to CNC some pieces soon.
BOM (Bill of Materials):
Cut up HDPE from milk jugs, cat litter jugs, etc. and place in baking dish, put in toaster over at 250 to 300 degrees for a bit… squish down… etc.
We're also using the “sawdust” and chips from HDPE that we've milled already, which melts down great!