Abstract: An apparatus for rotating a seat relative to ball in a valve lapping machine includes a seat spindle assembly, an airbag assembly with a first and a second airbag, and a linear compensator affixed to a frame of the seat spindle assembly and to the seat tooling adapter plate. The airbag assembly is adapted to apply contact force between the seat and the ball. The linear compensator has a top plate, middle plate and a bottom plate. A first set of rails extends in a first direction so as to allow movement between the top plate and the middle plate, while a second set of rails which extends in a second direction perpendicular to the first direction allow movement of the bottom plate relative to the middle plate. A ball valve lapping machine utilizing this apparatus is also provided.