The first rule of plywood is that the grain of outer layers run in the same direction, so the sheet is structurally balanced.
Breaking this rule, I’m wondering if there are any instances at all in the woodworking world where only two sheets are laminated perpendicular to one another?
As a concept, is it downright crazy; destined to failure, or just bringing with it a slightly larger tendency for the finished laminate to warp?
In this particular instance, I’m thinking about laminating two pieces of 7mm thick softwood perpendicular to one another, to make a circular part around 200mm diameter. Although I’ve wondered about this point numerous times in the past.
In addition: would laminating two 7mm pieces with the grain running in the same direction have any advantages over a single 14mm thick piece, or would the properties be identical? Or how about a 45-degree angle between the grains?!
Thanks to anyone for taking my musings seriously!
EDIT: the above example wasn’t a very good one. Let’s say instead I want a thin sheet of say 5mm thickness, where a single ply would be too weak.
Replies
Why go through all that wood prep and glueing to make an eight inches disk, just plane an 8 inches board to 14mm and cut a circle out of it.
I suppose my example was bad. A 14 mm thick piece will be pretty stable anyway.
This is a better example: Another usage I’m thinking about is for a 5mm thick bottom for a box. 5mm non-laminated is too weak along the grain. So I want to laminate two sheets of 2.5. Two 2.5 mm is doable but any thinner is tough.
Consider trying both. Glue up the two softwoods at a perpendicular angle and cut into the circle. Then cut a a single thick softwood board into the circle. Clamp both on a bench at the equator with the showing grain parallel to the bench edge -- and then hit them with a hammer/mallet. The thick board circle will most likely fail while the laminated one won't.
Sorry, I should have made myself more clear: I know the 90 degree laminated will be stronger, it’s the long term stability I’m worried about. Warping etc.
Would two thin pieces glued up in the same grain direction be stronger than a single stable natural piece? I'm thinking not. So perpendicular. If you used a no creep glue like plastic resin, unibond, resorcinal ,westsystem epoxy or even hide glue you would probably gain some stability. Some people say titebond lll, for me the jury is still out on that. I do a lot of bent lamination and haven't had the guts to try titebond lll since I know other things do work. Some swear by it though.
How big is the box? Many small boxes have solid bottoms that thin.
The box is almost 200 wide and 600mm long. The grain is in the same direction as the box.
It’s probably functional as a single ply, however i’m imagining some rough treatment - when the box is full, dropped onto something hard, I can see it breaking easily.
Thanks for the recommendations. How about good ‘ole normal white wood glue (PVA)?
When you are laminating, do you ever worry about being sure to have the top and bottom of a lamination running in the same direction, or is it not a big deal?
This forum post is now archived. Commenting has been disabled