Surface plate

[bazmak]

I used my 9" faceplate from the lathe for tramming.Amongst other things

 

[Cogsy]

I didn't think about my brake disk. Good old ebay got me a brand new one for about $35 delivered and it gives me a nice big 360 degree swing for tramming. I forget what flatness I measured it at when I got it (by taking tram readings then rotating the disk and repeating), but it was good enough that I didn't mark it for future orientation.

I agree the glass will flex a lot on its own. It needs to be backed by something reasonable flat as well, but it's not flexible enough to conform to the underlying shape of an object. So placed on top of a granite block would be as close to perfect as I could expect to get in my shed. If I remember I'll try and take some measurements at some point.

 

[bazmak]

Your defeating the object of the excercise.If you need to put flat granite under glass why bother

 

[Herbiev]

We have a company here that make headstones. Their bin is full of good offcuts

 

[Cogsy]

Baz - it doesn't have to be flat granite, just flat-ish to support the flat glass so it doesn't flex.

Herbie - that sounds like a very good idea. I might just head off to the mason works near the cemetery next time I'm out that way.

 

[Rudy from Norway]

Many good alternatives to make a surface plate here. Anyway, this is what I ended up with. A “big” slab og granite. After searching the net for plates no suppliers could send such a heavy (56kg) item within reasonable costs. This one however, is coming from Chronos Ltd Engineering Tools in the UK and shipping cost to Norway was £48 (+VAT). And this is the whole point. The price of the plate is also reasonable at $66 +VAT.
I guess this will serve me even long after I have gone. Just carve my name to it and put it upright. Talk about investment beyond life! (I actually might like that thought 😊.
I opted for a plate with known flatness since I’m very interested in high accuracy. I’m already stressing my machines accuracy capabilities. Having confidence in the measurements is there for something I find valuable. This stone is 40x40x10 cm and comes with a map showing max deviation of 2,2um. That is probably good for any model engineering. Chronos also have a 45x45cm at about the same price, but it was out of stock so I got this one.
Credit to Chronos for having a very reasonable and fast shipping method nobody else bothered to arrange for.

Rudy

 

[Ghosty]

Hi All,
I used to have a 18" square X 1" thick ground glass plate, It got "lost" in one of my moves, I had it for almost 30 years, I ended up going to the kitchen build/supply place and got a 400mm x 400mm x 20mm marble tile, only cost $40, and is polished on both sides

Cheers
Andrew