On Apr 19, 8:26 pm, Orval Fairbairn
wrote:

Isn't aircraft ply made with the plies on a 45 degree bias for
bending?
** Posted fromhttp://www.teranews.com**

Some is 45; others are 90 -- you can specify when ordering.

I think it's the face plies that are either 90 or 45 to the cut
edges, and the core plies are at 90 degrees to the face plies. I
haven't seen plywood with the cores at 45 to the faces.
45 degree faces are for places where the design calls for
angled grain across some structure (like a box spar) to closely align
with the stress forces, while avoiding so much waste.

Baltic birch (or Finnish birch, if you prefer) will bend most
readily across the face grain (grain 90 degrees to the bend line) if
it's dampened. I used to spray water on the faces and run a hot
clothes iron across it, turning that water to steam and driving it in.
Doesn't hurt the resorcinol ply glue. I once cut a 3/4" wide strip of
1.5mm ply, face grain running the long way, steamed it, and wrapped it
around a pencil spiral-fashion without it buckling or breaking. Tied
it that way and when it was dry it pretty much held that shape.
Trying to bend it with the grain (grain parallel to the bend
line) will usually fracture the core plies, since it's pretty hard to
get moisture that deep.

Dan