Making plastic sheets needs a big, flat press. I don’t have a fancy press, but I am able to fashion a press out of old, used stuff. A friend of mine works in commercial construction, and they’re doing a remodel, which means lots of old stuff on the way to the landfill. So, he snagged a sheet of old duct work for me and I was able to make a new set of plates to press the single use plastic cups I use for my lampshades.
Here’s a quick (5 minute) video of me making the new plates and a quick test run pressing plastic cups into a new sheet.