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post #1 of 6 Old 06-13-2012, 04:32 PM Thread Starter
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birch plywood grain question

Might be a stupid question...is baltic birch plywood just as strong wether the grain is going with or against the piece?

I have a 1/4" ply 40" L x 4" W piece and the grain is going against the length. Would it be just as durable without flexing or breaking where the grain is parallel with the length?

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post #2 of 6 Old 06-13-2012, 05:33 PM
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Usually plywood is an odd number of plies. Sometimes the outer plies are much thinner than the inner plies, so it's going to vary according to how the plywood is constructed.

So, let's say your plywood is three plies. That means only the center ply is running with the grain. If yours is five plies then two of the five plies are running with the grain.

In thicker sheets it matters less because the plies are thicker and there are more of them. In thinner sheets, the odds are stacked against you so I'd say yes, it's weaker than if the grain were running with the length.
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post #3 of 6 Old 06-13-2012, 07:23 PM
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Quarter inch Baltic Birch is a 5 ply board. The center and two outer plies are laminated in the same direction. On a narrow strip, it would be marginally stiffer if the grain was oriented in the direction of its length.




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post #4 of 6 Old 06-14-2012, 02:30 AM Thread Starter
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The center and two outer plies are laminated in the same direction.
That makes sense, 3 plys in the same direction is better than two.
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post #5 of 6 Old 06-14-2012, 11:20 PM
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Quote:
Originally Posted by aaronhl
Might be a stupid question...is baltic birch plywood just as strong wether the grain is going with or against the piece?

I have a 1/4" ply 40" L x 4" W piece and the grain is going against the length. Would it be just as durable without flexing or breaking where the grain is parallel with the length?

Aaron
Think of it this way: If you take a piece of veneer and pull on it with the grain, you can pull on it with all your strength and not break it; now take the same piece and pull across the grain, it will readily.

Now get a piece of 1/8-inch styrofoam, and glue two sheets of veneer to it. After it drys try flexing the sandwich. It will readily flex in the cross grain direction, but will be much stiffer in the long grain direction. This is directly related to the strength of the wood, and the distance from the center of the section.

This holds true in plywood. But in plywood the layers of veneer in between the two outer layers adds a great deal of sheer strength to the sandwich. The two layers of veneer on the surface dominate the structure and their wood grain has the greatest influence on how stiff the plywood is in which direction.

The more plys and the less voids the stiffer the plywood is.

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post #6 of 6 Old 06-15-2012, 02:47 AM Thread Starter
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