I could use 36" or 48" surface plate, but no one makes one that's 8" or 12" wide. A wide plate of that length would be too heavy for my uses, such as guitar fretboard truing.

Can a surface plate be cut the long way without destroying its accuracy? Are there internal stresses that would just ruin the accuracy?

I had thought it could be cut by a water-cooled diamond blade in gravestone or counter top shop.

I was also thinking that splitting a 24" plate into three would yield 3 plates that could, hypothetically be trued together, if need be. The pieces would still be over a hundred pounds but could slide on find grinding compound or cerium oxide, such as the telescope people use.

I wouldn't imagine that cutting a block of granite would ruin it's flatness.

Scott

Find a place that does granite counter tops. Go around back, and get a few scraps from their dumpster. Get a roughly matching pair, and play around with lapping them a little bit if they need it. How flat do you really need it?

Flatness, for instance a guitar fret will buzz if it's .002 off. I would like to make other straightedges from the surface plate too.

Both require only a small portion of a large surface plate. I've seen granite straightedges before, which would be ideal, but I could probably have a surface plate cut for less.

I'm surprised that long aspect ration plates aren't common.

Checkout this E-bay store.
http://stores.ebay.com/Discount-Machine-Shop
Larry

If it were me I'd go out and get the ElCheepo Grizly surface plate and find some one with a Water Jet cutter. I know the one at the shop I use to cut stuff can cut up to 5" think Marble.

How about a nearby memorial marker (gravestone) shop? I'd think they could cut a piece of granite or marble the size you want and probably grind it as flat as you require. I bet you could have it surface ground at a grind shop if the memorial shop couldn't.

Just a thought.

if you did that, could you then say it was "dead flat"?

I believe you're "dead right".

good, i was afraid i was "gravely" mistaken..

I'll bet it would be deadly accurate!

Scott

I suspect these comments will be terminated. That is, of course, unless they are resurected by someone who believes in reincarnation.

You have to know some one will give these comments a second life (http://www.secondlife.com/)

Anyway back to the thread topic.

I can't believe that no one makes a long narrow surface plate. There are a lot of thin narrow things that could be measured without taking up the whole shop with a stone two people couldn't move by hand.

Seriously, they are available. The problem is your required size isn't a common standard size. Consequently, it's a "special" which will cost more. I've seen many off-sized granite blocks at auctions, but that would be leaving it pretty much to chance.

You could purchase the nearest to the size you want and have it cut down to your requirements. Probably could be done by a local tile / terrazzo mechanic for less $$$$ than ordering a "special".

Check that catalogue that lgalla posted a picture of. On page 19 of their current catalogue, there are some granite parallels listed, and black granite straight edges.
Something like 2 x 4 x 24" for $160
2 x 6 x 36 for $390

Flatness grade A .00005" /foot

The website is www.shars.com, but they are also known as discount machine on Ebay. I don't know if everything they sell is on Ebay.