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

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Perhaps a lot more safe than you imagine. Bending strength is proportional to the square of the thickness. Deflection is proportional to the cube of the thickness.
Why not just consider it to be the same as "regular" wood at least in the strong direction? That would be a lot more accurate.
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I made a cheapo TV entertainment center, with pine ply. Only want to see how it holds up thru the years. Also, it would serve me a better idea to what I really want out of it when I make the next one, with RED OAK. I have a Sharp 27". The plywood (that the TV is sitting on) is measured as 21"x37"
What I did was use biscuits on the sides (probably three each 2 sides). The back was straight glued to the back. The front has a 1"x1" (pine).
The real reason I use 1"x1" in the front was to cover the front of the plywood (those layer lines), but also see if it will support the TV as well. You are asking the exact same thing on what I did. I made that thing about 5 years ago and upon reading your remarks, I took a good look at my thing now, it has NOT sag a bit!
Regarding how I did with the 1"x1" (it is actually 1-5/16", so it may be a 1-1/2" x 1-1/2"?), I cut 1/2" off (top view), leaving 7/8" for the front, and 1/2" off (back view), leaving 5/8" for the bottom support (but really it's the "whole" "L" piece that supports the front). I hope you understand my English.
The pine plywood was from Home Depot. The next red oak ply will be from Alpine Plywood. But I might end up getting the red oak ply from HD if the Alpine Ply is *way* overpriced. The ply will only serve as shelfing, the rest (largely viewable) will be solid red oak (raised panels).
(Sorry to run on) I am also thinking about using 1/2" ply for the sides and back only to help with the weight. But a WW professor at my UWM said it will be same thing, either (with 1/2" or 3/4" ply) both will end up heavy! He suggests to stick with 3/4", but I don't know yet.
My comment about you plan using dadoes, I would refrain from do that because it could lead to breakage when moving it around? But thats me being a "biscuit guy" (even I do use dadoes rarely).
So, to answer your question, YES, it will support it fine!
In fact, I am planning to make the new one this summer (which is why I was asking about raised panels issues :P ), I am looking to do 36"x24", to play it "safe" in case I get a 32" TV. I don't want a larger tube TV. I was also thinking about "what if" I get a HDTV (or whatever is out there today), it will have to have something different (they are so wide, like 48").
Chuck

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You can try the "sagulator" - a calculator for determining wood deflection. For your dimensions (36x22), red oak sagged .04". They didn't have oak plywood. Maybe someone can tell us how oak plywood compares to solid oak strength-wise.
Here's the URL for the calculator: http://www.woodbin.com/calcs/sagulator.htm
...bob
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BobN wrote:

Well, here's all you would ever want to know... :)
http://www.fpl.fs.fed.us/documnts/fplrn/fplrn059a.pdf
It 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.
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IIRC that is for solid wood, not plywood.
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Leon wrote:

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...
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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
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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
intrepid snipped-for-privacy@hotmail.com wrote:

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