AlanB is correct.
I was bored last year and needed a project so I dicided I wanted to make a dubbing machine so that the platform would swing out of the way and then I could more easily make shaggier brushes. If the material stays in contact with the platform a more narrow and tighter brush is created.So those you see are prototypes I concocted out of materials I had around the garage.I wasn't very pleased with any of them and in talking to James Smith he shared with me one he built with a nice cam system so the platform would drop out of the way. Not being a wood worker like Jim I made one that works the same way and can be made very simply.
It is the one just above the drill in the picture. The base has two holes drilled in it that accepts two pegs that are attached to the under surface of the platform. That block is placed under the platform holding it at the correct level....material placed and trapped ...the block is pulled out and the platform drops down and twisting continued... I usually twist to breakage.
I may modify my original Jim Smith machine to do that.
BTW the one with the black platform is copied from the Nor Vise one.....not sure why I did that except I had material that would work.....I don't even have a Nor Vise.