anyone make a table to hold a granite slab?

[EricKeller]

I'm in the middle of fabbing a table for a granite slab, and I was wondering how to support it.

[Curtis D.]

Just built this welding/fabrication table. Although not specifically for a granite slab, I believe it would hold up a truck. 3" channel, 2" angle and 2 1/2" square tube. I think with a little modification a similar design would work for a slab.

[EricKeller]

that's pretty nice. I actually have the structure almost done, sometimes it's good to have a big junk collection. I'm just interested in the interface between slab and metal. I got some good input off-board.

[Archibald]

Three points of contact using rubber mat between your stand and the plate.

[Alistair]

that's pretty nice. I actually have the structure almost done, sometimes it's good to have a big junk collection. I'm just interested in the interface between slab and metal. I got some good input off-board.

Eric,

here's a rough and ready Sketcthup I did of a granite plate support table I'm planning to build. Using three mounting pads at the "Airy" points seemed to be the most important aspect of getting the interface between the table and plate right (from the research I did anyway). I made three discs cut from cork flooring tiles, which I'm using with my current table (an old deli meat slicer table, no, really). Don's link to the rubber anti vibration mat looks like a much better idea though.
Here's a link to what Starrett has to say about Airy points, and how to calculate their location,
Surface Plate Calibrations - The L.S. Starrett Company (go to the bottom of that page).
Hope this helps

Alistair.

[EricKeller]

this is the advise I got from my local metrologist

The 3 point contact advice below is 100% correct, but it's an incomplete picture of working with so-called kinematic mounting. Although the description is correct, I do not recommend it. Three points of contact is repeatable and deterministic, but also very tippy. I can't imagine that a couple thou (worst case) is a big deal. A better way would be to use many little rubber pieces between the granite and the table. Elastic averaging with many points of contact on a semi-compliant buffer will maintain good flatness and will never fall over onto your head.

[Alistair]

Well, I'm not going to question the advice of someone who measures things for a living. I was just relating my own experience and observations with my own setup.
I had no issues with tipping. The height of the three contact pads isn't significant enough to let the mass of the plate generate much of a sideways component when you're cold setting a frame (ie. the pads don't deform very muich at all).
Like your guy there says, this kind of hair splitting isn't necessary for checking bike frames.
I followed the Starrett advice since it wasn't any more difficult or expensive than any other way I could think of, and I figure that their advice on something like this would be pretty good. If there was some risk of the plate falling off the table then I would be concerned, but I've not experienced anything like this happening.

My 2 cents.

Alistair.

Alistair.

[dbohemian]

So when are we going to have some slab races?

[EricKeller]

I like to see pictures of what others have done, although the expert I cited above offered to help me get the slab up on the table so I couldn't ignore his input in any case. At this point, I'm planning on doing the actual straightening with a different setup off of the granite slab

David, I think you would beat me for sure, my casters aren't anywhere near that nice.