A material processing apparatus comprising: a material processing device; a rotary operating device coupled to said material processing device for the operation thereof; a primary drive system coupled to said rotary operating device and being operable to rotate said rotary operating device; an auxiliary drive system having a rotary drive member, said auxiliary drive system being operable between a driving state, in which said rotary drive member is coupled to said rotary operating device and is operable to rotate said rotary operating device, and a non-driving state in which said auxiliary driving system does not rotate said rotary operating device, wherein said processing apparatus is operable in a primary mode in which said primary drive system rotates said rotary operating device and said auxiliary drive system is in said non-driving state, or in an auxiliary mode in which said auxiliary drive system is in said driving state and operated to rotate said rotary operating device, and wherein said auxiliary drive system is operable to impart rotational movement to said rotary operating device in either rotational direction and in that, in said auxiliary mode, the auxiliary drive system is operated to rotate said rotary operating device alternately in both rotational directions, characterised in that said rotary operating device comprises male and/or female formations for engagement with corresponding female and/or male formations provided on said rotary drive member, said male and/or female formations being spaced apart around a circumferential surface of said rotary operating device or rotary drive member respectively, and in that said formations (44, 46) comprise respective mating surfaces at which respective male and female formations engage and by which rotational movement is imparted, said mating surfaces extending obliquely to and/or parallel with the rotational axis of said rotary operating device and said rotary drive member. a material processing device; a rotary operating device coupled to said material processing device for the operation thereof; a primary drive system coupled to said rotary operating device and being operable to rotate said rotary operating device; an auxiliary drive system having a rotary drive member, said auxiliary drive system being operable between a driving state, in which said rotary drive member is coupled to said rotary operating device and is operable to rotate said rotary operating device, and a non-driving state in which said auxiliary driving system does not rotate said rotary operating device, wherein said processing apparatus is operable in a primary mode in which said primary drive system rotates said rotary operating device and said auxiliary drive system is in said non-driving state, or in an auxiliary mode in which said auxiliary drive system is in said driving state and operated to rotate said rotary operating device, and wherein said auxiliary drive system is operable to impart rotational movement to said rotary operating device in either rotational direction and in that, in said auxiliary mode, the auxiliary drive system is operated to rotate said rotary operating device alternately in both rotational directions, characterised in that said rotary operating device comprises male and/or female formations for engagement with corresponding female and/or male formations provided on said rotary drive member, said male and/or female formations being spaced apart around a circumferential surface of said rotary operating device or rotary drive member respectively, and in that said formations (44, 46) comprise respective mating surfaces at which respective male and female formations engage and by which rotational movement is imparted, said mating surfaces extending obliquely to and/or parallel with the rotational axis of said rotary operating device and said rotary drive member.