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Phisherman
 
Posts: n/a
Default questions: strength of plywood

On Tue, 12 Aug 2003 14:57:24 +0300, (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?

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


To take a 3/4" ply sheet and add 4 legs would be a poor design of a
table. The table that size will certainly sag under its own weight.
What is lacking is an apron let into the legs, and for a 4x8' sheet,
at least six 2x2" legs or possibly some angle iron.