Question about high-precision granite blocks

[M30]

I'm not sure what these things are called otherwise I would just google it. We have a few granite blocks that I am told are very high-precision. We also have a granite slab and "high-precision" granite shims.

What are these things generically called and what would they usually be used for? Especially the granite slab. I was using it to make sure all the inserts on a face mill parallel while tightening them down. Not sure if that would be considered abuse.

Thanks.

[rustamd]

you talking about surface plates? Like this?

http://catalog.starrett.com/catalog/...?NodeNum=25399

[M30]

Thanks, that's it!

How are these used? It says for measurement and reference but what does that mean exactly?

No help from wikipedia either.

[toastydeath]

They're used as a reference straightedge for indicators and other measuring gear. Height gauges, indicator stands w/ dial test indicators, et cetera all need some sort of nominally flat reference surface to work from. The surface plate, granite parallels, and what have you all give that "reference" plane that can be assumed flat/parallel/perpendicular/whatever you need for the purposes of measurement.

For instance, you can check the wavyness of a long bar on a big surface plate. Take an indicator on a stand, and just slide the indicator base along the plate to get your measurement. Since the plate will be flat to some tolerance, you can get a accurate measurement of your flat bar +/- whatever the indicator and plate error are.

[rustamd]

also used for assembly, to have part square/parralel. With straight edge, some presion blocks you can assemble some high tolerence parts

[M30]

Should I not be using it for what I am then? Ensuring inserts on a face mill are parallel while tightening?

[lerman]

Assuming that you aren't scratching the surface plate, it shouldn't hurt. Small surface plates are pretty cheap, anyway.

It is NOT sufficient, though, that the insert edges be coplaner, though. You want the plane that they are on to be perpendicular to the axis of the tool.

Ken

[M30]

I was very careful to not scratch the surface plate.

It's interesting comment about the inserts being coplanar. How should one usually install inserts? I was told to that they align themselves but I was trying to be a bit more accurate using the surface plate.

Thanks.

[Mcgyver]

while its fair enough to say if it's a cheapo surface plate I'll do it anyway, none of this stuff should be used to align inserts in the sense that its precision inspection tackle you are talking about. surface plates can be cheap - the glued together Indian composites or expensive - the Starrett AA grade etc. the blocks and what you call shims (likely parallels) can be very expensive. price out Starrett's granite master squares and parallels for example - they should be treated with a lot care and used for inspection only to minimize exposure to wear/damage .

Point is, what you are doing is probably ok if its the cheap stuff, but i wouldn't do it with the good stuff