Abstract: A compaction mill 10 comprises a rotary die plate 12 and a plurality of compaction rollers 14 spaced circumferentially along the inside of the die plate. Sprockets and chains provide a positive drive connection between the die plate 12 and the compaction rollers 14, ensuring that, in operation, there is substantially no relative slip between the outer peripheries of the rollers and the inner periphery of the die plate, where they are closest together. Guides 44 cooperating with sliding blocks 38, 40 constrain the rollers 14 against rotation about the axis of rotation of the die plate, whilst permitting guided displacement of the rollers in a radial direction with respect to said axis. Wedge members 46, 48, a screw threaded rod 50, and nuts 52 are provided to permit adjustment of the gap between the rollers and the die plate, and to make radial displacement of the individual rollers interdependent.