Henry wrote:
Imagine a rough table made of a single 4 x 8 sheet of plywood, with a
leg (4x4) at each corner. Imagine a weight placed exactly in the center
of this table.

The preliminary question is, how much will the plywood sag under the
weight? I should think that it would depend on (a) how thick the sheet
is and (b) how heavy the weight is. (Also possibly relevant might be the
area occupied by the weight; would a 100-lb weight on a 36 sq. in. base
cause more sag than the same weight distributed over, say, 324 sq. in.?)

My real question is this: is there a formula or rule of thumb to
calculate how thick the plywood sheet needs to be to support a given
weight without sagging beyond a certain limit?

This can be calculated fairly easily. I don't have time now but perhaps
this evening will. What is the type of plywood? The parameter needed
is Young's modulus, or modulus of elasticity. The remaining just
depends on the dimensions of the surface.

Phil


I know I could prevent sagging altogether by putting a fifth leg in the
center, but the space beneath the table needs to be completely open.

Thanks in advance for any insights you might have.

cheers,

Henry