I don't understand what the advantage is to rotating the cylinder instead of the screw.,(reply>), @gjhard Thanks, that makes sense. I didn't catch that it can have an edge gap; no friction except that of the product.,(reply>), The Olds works brilliantly vertically. An Archimedes will not work well vertically and even then needs a tight (grinding) flight to casing gap. Olds can have 1/2", 3/4" edge gap and works better than perfectly. Big lift distances are possible with staging elevators too. Cascading them.  Low maintenance as no internal bearings.