DIYbanter - View Single Post - Strength of 3/4" oak-veneer plywood...

wrote:
All:

I'm trying to become better educated about the relative strengths of
different types of plywood, and right now I'm dealing with a 3/4" block
of seven-layer oak-veneer plywood.

I'm wondering what would you folks would consider to be the maximum
reasonable span that type of plywood should be expected to sustain for
a shelf holding a 27" tube TV? I'm presently planning a 36" span 22"
deep, secured to the sides of a cabinet via 1/4" dadoes in a solid oak
frame. The cabinet will be backed by 1/4" plywood, glued and screwed to
the shelf from the backside.

I think that unless the shelf is somehow supported in the front you're
going to have a problem.

I'm looking across the room at an entertainment center which we
purchased to house the stereo and a 35" tube type television. It's 3/4"
oak veneer plywood with solid oak face framing.

No sag in ~ 7 years BUT the width of the shelf is bisected by a vertical
support which forms one side of a cabinet beneath the television. The
other side (below the TV) is an open area with a shelf where the center
channel speaker is stashed. The whole thing, including the "shelf" the
television is sitting on is framed in 3/4 oak. There is no backing
behind the TV.

The reason I fear for your success as described above is the apparent
lack of support at the front of your 22" deep shelf. The weight of a
CRT Television is concentrated to the front. I suspect that left to its
own devices, your television may well wind up face down on the floor in
front of that cabinet.

Also, minor point, but any reason you're only looking at 1/4" dado
rather than 3/8"? I always thought the "rule" was the dado is one half
the thickness in 3/4 or 4/4 stock.

I've read some posts that say this type of plywood would be more than
adequate for even larger TV's, but a few others that say it will sag,
but none of the discussions I've seen have talked about how that sag
tendency varies with the number of layers in the plywood, so I have to
plead uncertainty.

Probably correct but by supporting it properly both front AND rear (with
maybe a center piece) you should be okay no matter what.