Expectations of a granite surface plate ...

[arvidj]

I have in imported granite surface plate.

Sort of a two part question ...

Should there be an expectation that both primary sides (the 9 x 12 sides, not the 3 x 9 and 3 x 12 "sides" and "ends") will be flat? In other words there is not 'top' or 'bottom' to the plate.

Should there be an expectation that both primary sides be parallel?

Is so, any suggestions on how to check to see if my plate meets those expectations? I am guessing that a simple "measure it with a micrometer" might address the second one, but the first one has me stumped.

Thanks,
Arvid

[EdK]

Arvid,

There is a top and bottom to the surface plate so parallelism is not a feature. One side will be ground flat and the other is usually kind of rough. At least that's the case with the two granite surface plates I have.

Ed

[ETC57]

(03-06-2012, 01:21 PM)EdAK Wrote: Arvid,

There is a top and bottom to the surface plate so parallelism is not a feature. One side will be ground flat and the other is usually kind of rough. At least that's the case with the two granite surface plates I have.

Ed

Hay Ed,
If that is the case and I'm asking as one who dose not even own a surface plate, doesn't that make achieving level rather crazy?

Jerry.

[DaveH]

Jerry,

You may be confusing 'level' with 'flat'.

The surface plate has a very flat surface. You could still use a surface plate if it was inclined at 45 deg - except your beer will keep sliding off.

DaveH

[ETC57]

ROFLOL

OHH NOO we cant have that

So what your saying Dave is it's not a table?

No really, level is not important in it's function?

Jerry.

[DaveH]

Jerry,

You're right, level isn't it's function, it is it's flatness that is the important function.

DaveH

[arvidj]

I understand the difference between level and flat.

The parallel question would be related to “given that I have created a level surface can I set the surface plate on it and have an expectation that the top of the surface plate will be level”. The answer appears to be ‘No’.

Note that when I have had to level my surface plate I have used three screw jacks, my precision level and some time messing around to get the top surface level.

And as an example (not a useful one, just an example) of "parallelism" I would level the top surface of my surface plate and then put a 1-2-3 block on it and the top surface of the 1-2-3 block would still be level.

[ETC57]

Ok so why when I take a crew out to install a rather large (4'x8') surface plate in R&D type shops the customer always make me get out the machinist level when a carpenters level will do?

Jerry.

[DaveH]

(03-06-2012, 03:44 PM)arvidj Wrote: I understand the difference between level and flat.

Sorry arvidj - just Jerry and I having a bit of fun

DaveH

[ETC57]

(03-06-2012, 03:51 PM)DaveH Wrote:

(03-06-2012, 03:44 PM)arvidj Wrote: I understand the difference between level and flat.

Sorry arvidj - just Jerry and I having a bit of fun

DaveH

What good is a forum if it's not FUN!!!!

Jerry.