On Tuesday, February 11, 2020 at 1:42:01 PM UTC-8, Leon wrote:
On 2/11/2020 1:21 PM, whit3rd wrote:
On Tuesday, February 11, 2020 at 6:39:07 AM UTC-8, Scott Lurndal wrote:
whit3rd writes:

Plywood
is weaker than solid wood (half the grain runs the wrong way).

Shelves need compressive strength in the top surface, and tensile strength
in the bottom surface (knots on top are less troublesome than on bottom, for instance).
Plywood has, on bottom surface, a very thin veneer of good high-tensile strength wood,
backed by a thicker layer with the grain running the wrong way.


Followed by grain running "in the right direction".

But that inner layer isn't on top (in compression) nor on bottom (in tension)
and its strength is largely wasted. That's why you can often get away with
strong/weak/strong sandwich construction (doors and aircraft panels).

It's also why a bow can be made of a broader stave, and get more power, but
if made of a thicker stave, it snaps in two. Enough stress to cause a bow, applies
very high tensile and compressive strain according to distance from the neutral centerline...