scored a surface plate

[bedwards]

I scored a 3x16x30 piece of polished granite that had another use in another life. Its flat within .0015 over most of it with one spot .002 that I can mark and avoid. I realize its not AAA or AA or probably even B but is this good enough for home work?

Thanks for what might be a dumb question

Bryan

 

[Tony Wells]

Sure it is. For most layout work, since you will be working off of scribed lines wider than that variance, no reason it won't be good for that. Plus, if you use it for support of Vee blocks to assess runout, that's not all that important either. One man I worked for years ago (very successful, I might add) started out using a blank tombstone. I doubt it was that flat.

If you have the means of measuring flatness, why not lap it in?

 

[bedwards]

ok, how do you do that? With a piece of plate glass and compound?

More dumb questions

Bryan

 

[8ntsane]

Cant help on the lapping the surface plate in, but for all intended purpose in a home shop, it should serve you well. All I have is a import surface plate, and havnt seen a need for anything more, for what I do

 

[Tony Wells]

Well, lapping a granite plate isn't easy, and isn't cheap to have done. You typically use an autocollimator and a Repeat-o-Meter to measure your progress. A heavy cast iron lapping plate is used with different grades of diamond dust. And lots of elbow grease. I don't think i would bother for that small error. If you needed better accuracy, plates that size aren't that expensive. I'd say cheaper than having it lapped, or buying the stuff to do it with.

 

[bedwards]

Thanks for the replies guys. Free stuff is always fun. I didn't mention that it has a 1/2" hole bored right in the center, but that is easier to work around than a high spot.


Bryan