Grinds your herb. can scale down to 70% successfully, perhaps lower. this model is currently about 75.70mm in diameter.The lid is spun, which transmits power through a planetary gear set, rotating the grinder mechanism within the grinder.The lid can be modified as you please, there is an example of an alternate lid, an alternate lid blank, and a standard lid.If you have issues getting gears to fit properly, try the over or undersized gears. Print 1x of each, and 3x of the planet gear.Crappy video of my hastily printed grinder, at 100% scale: http://youtu.be/Nk74DxlVplI