Comment by contingencies

You can go up or down (probably sideways if you can account for gravity, eg. through rotary motion). Up is more common since you only need significant equipment on one side and access requirements mean that keeping the bulk of it 'down' is easier. No polishing is necessary. However, I recall reading that some polymers can be polished if you want, but IIRC it depends heavily on the polymer, the abrasive, intermediate fluids in use and result desired. Re: Source, I raided libgen for thermoforming over the last few months, visited about 10 equipment factories and studied their mechanisms and control systems, but actually learned this tidbit from 1000 Australian Inventions or some such book which I bought for my daughter before our family returned to China... to keep inventing ;)