a centrifugal jig has a container mounted for rotation about its longitudinal axis , separated into an axial region and a peripheral region by ragging material supported by a screen . the peripheral region is composed of a series of hutch chambers with reciprocating wall portions located radially outside the screen , for repetitively dilating the ragging . also disclosed is a hutch chamber construction applicable to both rotary and non - rotary jigs , having a reciprocating wall portion which includes convergent wall surfaces leading to the hutch chamber concentrate outlet .