Grinding head assembly

A grinding head assembly, comprising:

• an abrasive grinding element having a grinding surface and a generally annular opposed top surface;
• a rigid, generally annular backing plate having a generally annular first surface operably coupled to and esentially covering said grinding element top surface, said first surface comprising an annular, generally planar face and a plurality of radially spaced concentric ribs projecting outwardly from said face and an opposed, second surface spaced apart from said first surface to define a backing plate width;
• a generally cylindrical attachment boss projecting outwardly from said second surface and spaced apart from said grinding element by said backing plate width, said boss defining a boss diameter extending across at least two of said concentric ribs, and including structure defining an internally threaded boss channel;
• a backing plate holder adapted to be drivingly connected for rotation with a drive shaft, said backing plate holder including an attachment surface including structure defining a cavity for receiving said boss in a complementary fit whereby the rotational energy of said backing plate holder is transferred to said boss and distributed along said rigid, generally annular backing plate, through said backing plate width, to said grinding element;
• and
• attachment means extending through said cavity and receivable in threaded engagement by said boss channel for detachably coupling said backing plate to said backing plate holder.