Abstract: An apparatus convertible between chopping or shredding operations and grinding operations. The centrifugal grinder or chopper includes two opposed plates with at least one plate rotating with respect to the other. A plurality of shearing plates are rigidly but removably secured to one mounting plate while a plurality of grinding segments or chopping and shredding knives are rigidly but removably secured to the other mounting plate. Each shearing plate includes a curved rib extending outwardly toward the other mounting plate. When one of the mounting plates is rotated with respect to the other, material is forced centrifugally outward into spaces or grinding chamber segments and chopped or ground before passing out of the spaces or grinding chamber segments and into an outlet. An automatic gap adjustment mechanism is further disclosed for setting the desired gap between the ribs of the shearing plates and the grinding segments or chopping and shredding knives.