called "stusplate"(is it the done thing to put a direct link here?) As you can see from the reflection of newpaper, the surface has a very fine finish like no surface plate I have ever seen. It comes in a felt lined lockable box. Does anyone have any idea what this sort of plate is?
Most optical flats are glass or quartz. I have a 6"dia x 1/2" glass flat. Although your flats are opaque, bearing in mind the polish, the thickness and the careful packaging, I still think they are likely to be flat to optical precision standard
Stu has a couple of toolmaker's flats. They're made with a surface that allows a gage block to be wrung to the surface, so that clamps aren't needed. It's frequently used in gage labs for qualifying and certifying instruments. Standard sizes are 2" and 4", so Stu's are something pretty special. I've seen them that big, though, in Mitutoyo's qualification lab.
If you keep that surface scratch-free, there's no better way to set up a stack of gage blocks to extreme, certifiable, transferable accuracy.
If you have a set of certified blocks, you can make transfers from them to something else (a custom gage, a height gage, an electronic indicator, etc.) and rely on the transferred dimension -- with the allowed tolerances of the first set of gage blocks plus that of the plate.
The surfaces of these plates are lapped similarly to the gage surfaces of gage blocks. You can apply the certified flatness of the plate, add the cert. range of the gage blocks, and then document that height (assuming you'd done scheduled certs. on the gage blocks) for reporting to a customer; even a very demanding one.
A big plate like the ones that Stu has may not be in the 2 - 4 millionths range of the smallest ones, but whatever it is, you can apply that certified accuracy to your gaging.
There are a lot of links on Usenet, many I wouldn't click on if I didn't know the target. If I can be as bold as saying this, we tend to trust the metalworking.com Dropbox. Most of us are not link happy newbies just experiencing the Internet so adding the full link to that site is just fine and saves a bit of time.
Thanks Ed (and others) There are some light scratches in the small one, just behind the person it the photo. I didn't do a very good job cleaning the block as I wasn't sure what to use. I'm yet to clean the large one, I'll try to get onto it this evening, but what to use? I'm guessing "kero and a rag" aren't the done thing.
I believe you are right about the "production manufacturing ", they have a name plate from a wire company where I am guessing they were used, but they have no other name on them.
I'm try and get some more info on here tonight. thanks again
Kero and a rag isn't bad at all. Don't use anything the least bit abrasive or corrosive to steel. No Windex. Then lightly oil it with a rag and put it away. Wipe the oil off before using. If you're going to try wringing gage blocks against them, clean with a solvent on the working surface, really well, first. Paint thinner should do it.
You're welcome, Stu. They're interesting tools and they don't take up much room. With scratches, you probably won't get much for them, so you'd might as well keep them.
You may or may not have a need for them, depending upon the kind of work you do. I don't think most hobbyists need a full set of gage blocks, but I do find use for a few very good ones, to check my mikes, calipers, and height gage.
But those plates you have are not something any of us would really need, either. They're nice to have. You can get some use out of them, but it's unlikely you'll be qualifying gages or making production gages.