Granite suface plate capacity?

I'm in a pinch for space and I have a 6' x 8' x 9" Rahn grey granite plate.
Because of the footprint I would like to put a couple of 1500 lb. machines on the table with load spread out evenly on 4 x 4 timbers.
I would probably have to leave the machines on the granite for up to a year until I get my new building done.
Does this sound like to much weight for the granite and or the length of time for the storage.
The plate has a factory stand if that makes a difference.
Any help would be appreciated.
Thanks, Kevin.

50 pounds/ft^2

The federal spec for surface plates says 50 pounds per square foot for deflection within the stated tolerance for the plate.

This would give a value of 2,400 pounds for your 6' x 8' plate.

- Leigh

Ref: Fed Spec GGG-P-463c section 3.2.3 Thickness and stiffness. on page 4.

The plate is about 6000 lbs. Add machinery, you've got 9000 lbs. If your floor load bearing capacity is ok, then it depends upon the machinery, too. The plate mass will dampen some vibration, but a mill will give you different reaction forces and live load than a shaper.

I'm conservative. Would go for 8x8s vertical posts supporting your plate. Several. Maybe a 4 x 3 matrix of them underneath your plate, with 2x10s as rails on a crossbraced pattern. I like the 8x8s because I feel that they are more resistant to tipping. They spread out the load. 4 x 3 x 8 x 8 = 768 square inches. 9000/768 = about 12 psi floor dead loading. This is greater than the usual 10 psi dead loading (usually require the floor to support 10 dead and 40 psi live load. My design might be enough to support a locomotive, though.