"Lapmaster" lapping machines were developed originally by the Crane Packing Company of Morton Grove, Illinois in the U.S.A. "Packing" is another word for mechanical seals, and in was in this field that the Crane Packing Company excelled.
Finding, after considerable research, that commercially-available lapping machines were unsuitable for their particular purposes, Crane set about developing their own. After considerable research and development a suitable machine was built and numbers of these, in various sizes, were employed solely in their own factory The lappers were capable of high rates of output - while also being accurate to better than one wavelength of light and capable of producing a surface finish from two to three micro inches. Satisfied with the results, Crane put the machines on the market and, wanting to expand sales into Europe, set up a subsidiary company in England, Payne Products Manufacturing International Ltd. Based in Hounslow, Middlesex. The history of the Crane company is both interesting and complicated - and can be found about here.
The working principle of a Lapmaster is simple: the jobs to be lapped are placed inside three or four "conditioning rings" that rotate on the lapping plate and entirely cover its surface. As the machine works, the items being lapped cause wear on the plate and attempt to upset its flatness. However, the action of lapping rings is designed to cause greater wear than the jobs and so continually "conditions" the lapping plate keeping it in perfect condition..