Strength of 3/4" oak-veneer plywood...

Well, here's all you would ever want to know... :)

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shows that basically there's only about a 10-20% difference for same species as compared to ply--somewhat less than I'd have thought. I skimmed the (somewhat lengthy) report and if I got the gist right, it concluded for there testing the difference was within the statistical uncertainty. (Longitudinal to face sheet comparison)

I also found to my surprise that my impression that the laminating had a significant effect on the transverse bending moment was also mostly in error--there's an effect, but it's not nearly as large as I had expected. I suppose my perceptions were flawed owing to the fact that a

4x8 sheet is only half the width in the transverse direction so the impression apparent strength in that direction is amplified artificially.
Reply to
Duane Bozarth
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Actually, I found that

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you're a lot more nearly right than I thought, Mike...

Their test data shows neglecting the transverse plies gets pretty close to the right answer than I thought--although it's a long report and I haven't had time to read it thoroughly, there's one apparent inconsistency I don't quite see how follows because it also seems to say is essentially same as solid lumber of same dimension but seemed to refer to nominal dimension unless I somehow missed the nomenclature...

Reply to
Duane Bozarth

IMHO a far better method would be to double up on the plywood and reinforce with 3/4" solid wood around the perimeter. About 10 years ago I built an Oak veneer plywood cabinet double thickness at 1.5" thick total with 3/4" trim around the perimeter. Setting on top is an old Mitsubishi 35" tube type TV. Weight approximately 200#'s. No sag at all.

Reply to
Leon

IIRC that is for solid wood, not plywood.

Reply to
Leon

Correct, but follow the link I posted--their testing indicated on the order of a 20% or so discrepancy from solid material on a quick perusal...

Reply to
Duane Bozarth

Duane, from an engineering point of view if you take a xsection of a piece of plywood and assume the center ply to be the neutral axis [ the axis about which the plywood bends ] and then consider the plywood sheet as a simple beam then each of the plies running the same direction as the center ply will contribute to the bending strength.per the "engineers simple beam bending theory" The cross plies will contribute little to the bending strength directly, but indirectley they separate by varing degrees the contributing plies from the neutral axis there by acting as webs and allowing the contributing plies to act as caps . So in my view even though the separation is small some additional bending strengthis should be added.......mjh

Reply to
mike hide

moreso than that. even if the cross plies were made of air they would increase the stiffness of the panel- for the same reason a torsion box or hollow core door is empty inside.

Reply to
bridger

All:

I just wanted to take a moment to thank ALL of you who provided such good information and opinions on my project. Your advice was very helpful.

I modified my cabinet design to include a 3/8" dado for the TV shelf rather than the 1/4" I had originally intended. I've also added a vertical cross-section of plywood beneath the rear edge of the shelf.

I further added a vertical shelf support that subdivides the formerly open large area into two equally sized compartments. The vertical support should transfer most of the sag to the cabinet floor, and I'll also add an additional member under the shelf to transfer that load directly to the floor.

The cabinet went together better than I expected, and I'm down to a few niggling oops-shouldn't-have-done-that-so-I-hafta-fix-it items, then I can trim it out and prepare for finish. Inevtiably, I suppose, it's tending to twist a bit at the top, but I suspect that once it's in place that won't be as prevalent a problem (I hope). Suggestions for that welcome, too :)

Thanks again, all.

David

Reply to
intrepid_dw

Plywood was born to bow and twist. The secret is to screw, nail or glue it down before it gets started.

Reply to
Pat Barber

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