Laminated Gunstocks: Grain Direction Considerations

Strength is gained when the wood grain direction of plies is alternated. Here's a discussion. August 15, 2012

I am aware plywood is made of alternating 90 degree layers. I am making some laminate rifle stocks, and all the grain is going in the traditional same direction... This is using powdered urea. My plies are about 1/8" each. Would there be any problem slanting some of the plies off the normal horizontal by a number of degrees, or is this looking for trouble? How much latitude is there in this sort of fiddling? The idea of a few slanted plies is nothing more than artistic effect, form, composition, direction - that sort of thing.

Forum Responses
(Architectural Woodworking Forum)
From contributor D:
I would think as long as the angled plies are sandwiched between other layers, all is good.

From the original questioner:
Hmm… I hadn't even thought of that. It was going to be several horizontal, several angled... Single slanted plies is interesting.

Just knowing wood and glue a bit, my guess would be there is reasonable latitude in shifting things around. You wouldn't think keeping things to a 15 degree shift, or so, there would be much opportunity for creep.

Thanks for putting the idea in my head. You of course don't know the work pieces, but it will fit in and read very nicely.

From contributor R:

If this stock were made from solid wood, you could certainly have some latitude about grain direction. In fact, in many cases, you would need to orient the grain to minimize the chance of breakage at the narrow point of the stock.

This does not change with a laminated stock if the laminations are all oriented the same. A part laminated with the grain all oriented the same will be stronger than a solid piece, but not nearly as strong as a lamination where the grains are crossed. In essence, what I think you are describing would still be weakest across the grains.

From the original questioner:
Okay. What would you think about stability and strength if every other ply was canted 15 degrees off the horizontal?

From contributor D:
Stability is gained with plies in more directions. Also, since the modulus is much stronger trying to crush end grain compared to side grain, multiple orientations add strength in different directions. Aircraft ply has plies oriented 45 as well as 90 degrees, and more plies over all. Cold molded boat hulls orient different layers of veneer at different angles, which are remarkably stiffer than a strip planked hull of the same scantlings.

From contributor R:
Anytime the laminations are not oriented the same is a net gain in strength. I am working with a client developing molded plywood furniture. We typically orient each layer 90 degrees to the previous, but have experimented with keeping them all the same. No question that the opposed grain is vastly stronger.