Norton surface plate

[hms50]

Good morning gentlemen,

In mt travels I picked up a round ceramic disk about 6" in diameter and about 3/4" thick marked Norton surface plate. The surfaces are very highly polished and unlike a granite surface plate, the surface is "slippery" to the touch. Anybody know how flat this thing is and what it was for? It's so small it seems like it must have been for some special use.
Thanks,
hms50

[lalatheman]

That Norton surface plate type of tool has often been called a "Toolmaker's bench plate"
It's special beauty is that gage blocks can be wrung directly to its surface.
It's precision can be tested just that way , try wringing gage blocks to it , If they stick it's still in good shape.
The other way to check it is with an optical flat and a monochromatic light source, the bands seen in the flat should be straight.
I'd like to have one of them, espically a ceramic one.

[hms50]

Lalatheman,
Thanks for the info. I'll clean it with Starrett surface plate cleaner and see if a gage block will wring to it.
hms50

[Thrud]

Now, I have tool envy....

[hms50]

Goodmorning gentlemen,
After cleaning up the plate with Starrett cleaning solution, gage blocks do in fact wring to it. Does this mean that it is to be used for measurment set-ups? It's so small I just don't understand it's purpose. I guess if a cylinder square was placed on it, it would be good for checking shop squares? Not having worked in the trade, and being self taught, there is a world of knowledge I don't have. The other day I showed a real machinist a tool I picked up at an auction. I thought it was a stepped wedge-block for clamping work on a mill table. As it was covered with some type of dried up protective material I failed to notice that each step was marked for height. It turns out it's for use in setting heights quickly on a surface plate. After cleaning in mineral spirits it got real shiny and gage blocks will wring to it. The real machinist could not believe my ignorance! He thought i was pulling his leg. I didn't argue with him.

Thanks again
hms50

[lalatheman]

It can be used in any number of ways in measurement setups . Six inches dia is really a lot of turf to stack gage blocks on.
say you had three or four stacks of different heights spread out on that surface and the put the whole mess on a sin plate . . . or perhaps champed it sideways on your big surfface plate . . .or upside down or just made up a portable gage to take somewhere else to check somthing . . . the possibilitys are endless.
It's small size is a large part of its value and usefulness