On Sat, 2014-03-29 at 15:02 -0400, John Kasunich wrote: > > On Sat, Mar 29, 2014, at 12:01 PM, Jon Elson wrote: > > On 03/29/2014 03:39 AM, Jeshua Lacock wrote: > > > > > > > > > > > > My 1080 pound 4x5 foot granite surface has a glass cut looking surface > > > that I bought surplus. > > > Anyways, do you think the reason it is shiny is because it is grade A, > > > while the grade B should be matte? > > > > > > > > It is most likely an optical bench, made to be extremely > > stable and free > > of vibration, and probably had air bellows supporting it. > > It is probably > > NOT a surface plate, ie. one that is ground with diamond > > paste to > > be flat to within some insane tolerance for inspection purposes. > > The fact it has a mirror finish means it was polished, not > > lapped > > against other plates, in the time-honored 3-plate method of > > automatic generation of flats. > > > > I'm inclined to agree with Jon. When I saw the photo I > thought it looked pretty thin to be a surface plate. A little > googling says a 48x60 surface plate is typically 6 or 8 > inches thick and weighs over 2000 lbs. A thinner plate > will sag from its own weight. Not a problem for an > optical bench, as long as it is stable. Big problem for > a surface plate. > Some years ago when Boeing Surplus - Kent was still open they were selling a base for a CMM. Maybe 1.5 m square and 30 cm thick pink granite with another maybe 1 m square by 30 cm thick granite centered under it and I assume epoxied to it. Good buy if you needed one .. $400 or so and they would load it for you. ;-)
Dave ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
