Counter questions:<br>What is the advantage of rotating the zylinder vs. rotating the screw?<br>Because you haven't really covered any of that. Why couldn't they just use an elevator that rotates the screw? What is different when rotating the zylinder instead of the screw?,(reply>), @crazzilla These scoops could as easily(well to all intents and purposes) be driven by the central screw.,(reply>), It can also have several simple bearings along its length, keeping it centered and not touching the screw.,(reply>), @Lukas Graphen Does it explain why rotating the cylinder produces less dust? Also, at the time I assumed that that they were implying that that advantage was in comparison to conveyor style elevators, not in comparison to screw style elevators.,(reply>), It's easier to engineer. Because the moving section is on the outside, it can be belt or chain driven without any interference with the inside of the mechanism.,(reply>)," It’s explained from <a href=""https://www.youtube.com/watch?v=-fu03F-Iah8&amp;t=2m50s"">2:50</a> onwards. The biggest advantage is the reduced dust production."