A modular rotary grinder, comprising: a rear power head assembly having a power head frame supporting a right lower power head wall, a left lower power head wall, an anvil, a rotor, a gear box, and a motor; said right lower power head wall and said left lower power head wall each having a rear mating edge, said anvil movably extending between said right and left lower power head walls (105, 107) proximate a portion of said rotor; a front compartment assembly having a front compartment and a ram assembly, said front compartment defined by a lower compartment plate and an upward extending lower compartment sidewall proximate each longitudinal edge of said lower compartment plate, said compartment plate and said compartment sidewalls being supported with a front compartment frame, said lower compartment sidewalls each having a front mating edge, said ram assembly having a ram with a lower edge proximate said lower compartment plate and side edges proximate each of said lower compartment side walls; said rear mating edges on said rear power head assembly and said front mating edges on said front compartment assembly being matingly engageable by slidable movement between a first closed position and a second open position, said anvil and said lower compartment plate being engageable, engagement in said closed position of said mating edges and said anvil with said lower compartment plate forms a compartment having said rotor in a rear portion thereof and disengagement in said open position of said mating edges and said anvil from said lower compartment plate provides for a man access-way between said rear power head assembly and said front compartment assembly; and a retainer assembly having a portion on said front compartment assembly and a portion on said rear power head assembly, each of said portions of said retainer assembly being cooperable with the other of said portions enabling said front compartment assembly and said rear power head assembly to be securely engaged in said closed position wherein said front and rear mating edges are mated and said anvil is mated with said compartment plate. a rear power head assembly having a power head frame supporting a right lower power head wall, a left lower power head wall, an anvil, a rotor, a gear box, and a motor; said right lower power head wall and said left lower power head wall each having a rear mating edge, said anvil movably extending between said right and left lower power head walls (105, 107) proximate a portion of said rotor; a front compartment assembly having a front compartment and a ram assembly, said front compartment defined by a lower compartment plate and an upward extending lower compartment sidewall proximate each longitudinal edge of said lower compartment plate, said compartment plate and said compartment sidewalls being supported with a front compartment frame, said lower compartment sidewalls each having a front mating edge, said ram assembly having a ram with a lower edge proximate said lower compartment plate and side edges proximate each of said lower compartment side walls; said rear mating edges on said rear power head assembly and said front mating edges on said front compartment assembly being matingly engageable by slidable movement between a first closed position and a second open position, said anvil and said lower compartment plate being engageable, engagement in said closed position of said mating edges and said anvil with said lower compartment plate forms a compartment having said rotor in a rear portion thereof and disengagement in said open position of said mating edges and said anvil from said lower compartment plate provides for a man access-way between said rear power head assembly and said front compartment assembly; and a retainer assembly having a portion on said front compartment assembly and a portion on said rear power head assembly, each of said portions of said retainer assembly being cooperable with the other of said portions enabling said front compartment assembly and said rear power head assembly to be securely engaged in said closed position wherein said front and rear mating edges are mated and said anvil is mated with said compartment plate.