Abstract: A manually operable herb grinder features a housing assembled from a plurality of detachable sections, including a drive section for housing drive components and one or more product chamber sections for containing a product. The product chamber is divided into input and output chambers for initially receiving unground product, and catching ground product falling from a grinding area intermediate the two chambers. Blades carried on a shaft in the grinding area are rotated by a planetary gear system, whose input is a rotatable cap installed over the drive section at a top end of the housing. The grinding area is situated between a spoked divider at an upper end of the input chamber, and a perforated divider at the upper end of the output chamber. The cap is rotatable by hand, or by frictional rolling contact against a surface.