A sanding or grinding tool has a drum provided with an abrasive cylindrical outer wall. The depth guide has a curved outer surface composed of a number of arcuate segments each having a radius which extends outward from the centre of the guide and which is of a differing defined length. The depth guide is rotatable in increments to cause each segment, in turn, to face the work piece. Each facing segment functions to define the depth of material removed from the surface of the work piece.