Straightening Bowed Plywood

[Anonymous]

Dave:

Thanks for all your ideas!! I'm going to be lavish with the drywall screws where I can, and where I can't , I'll use your stiffener idea.

Bob Muilenburg

[dknelson]

I used some pretty badly warped 1/4 pine for some of my benchwork (I use the David Barrow "domino" approach so my benchwork is a sequence of identically sized 2 x 4 foot dominos) and basically what I ended up doing was make the wood work against itself -- that is, I was lavish with drywall screws, forced the sides and ends to be exactly even with the edges of the exactly cut 2x4 foot plywood tops, and used a frame holder to make all corners exactly 90 degrees. This meant using lots of clamps during the screwing process. And often I wished I had a buddy to assist when I needed a third (or fourth!) hand. That is where the frame holder is a lifesaver by the way. It holds wood at exact angles while screwing.
Wood is stubborn stuff with "memory" but in my experience it can be tamed with enough drywall screws -- which I never thought I'd be buying in packs of 500. And now I am on my third pack.

When storing my plywood I have it face down, never on edge, and never leaning against anything, piled up for weight, and do not leave it on the floor where it can leach moisture. On a regular basis I reverse it to try to avoid bowing. But even then there is slight bowing. The reason I think is that the different layers of plywood absorb moisture differently.
Also before using lumber for benchwork I try to have it in the basement for one full change of seasons first rather than immediately build from it. This calls for advance planning!
I only buy wood from a place that stores it indoors under cover. I found the plywood that bowed was stuff I stored on its edge, so i don't do that. I also found that plywood ripped from a 4x8 sheet seemed to bow more readily than the handi-panels already cut to 2x4 foot size. I think it has to do with the way the stuff is shipped and stored.
One idea might be, if you buy your plywood and it looks pretty straight, to coat it with wood hardener or shallac to keep the moisture out, if you think it might be a while before you use it.
Now none of that answers your question does it? All I can recommend I guess is to place the plywood face down (so the center bows up) and pile really heavy stuff on it for a good long time. Maybe even clamp it. But frankly I suspect it would quickly bow back.
if you are in serious danger of totally wasting some expensive birch plywood there IS one more idea that might work, but adds complication. That is to screw and glue a stiffener of say 1x1 inch furring strip at the back for the full length of each 1x4 inch strip. Do you understand the concept -- sort of like a "T" But make sure that wood is not bowed too!
Somehow I suspect I have not been of any particular assistance here. Sorry!
Dave Nelson

[Anonymous]

I'm going to rip 3/4" birch plywood into 1x4s and use them for my layout benchwork. My benchwork plan is pretty dependent on reasonably straight lengths of 1x4, and unfortunately, the plywood I have is seriously bowed. The pieces I have are 7 and 1/2 inches by 5 feet and are cut with the grain. I'd appreciate any ideas on how to straighten them out.