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. -- John Kasunich [email protected] ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
