Why vertical? Warping mill . . .
I have been giving a lot of thought to the design of a warping mill, as it seems it should be a lot faster than a warping board.
I want it to be easily dismantleable, and am thinking of using broom handles and slats for the rotating part, with a longer broom handle for the pivot. If I make it horizontal, AFAICT apart from the legs, which will be fine as individual units kept intact, it should be possible to assemble it simply by poking the broom handles through the appropriate holes. If I was to try this vertically, I would have to fix everything into place, or the broom handles would slide down and out. Being vertical also makes balance a bigger problem, and you'd need to make a better bearing, and how would you actually support it upright in the first place?
All in all, it seems horizontal would be so much easier, that I can't see why anyone would even try to make one vertical. I must be missing something . . . ?