Straighten warped Perform Ply?

[Jay Knobbe]

I bought a 4x8 3/4" sheet of PerformPly. Birch face, 11 plies.
It looked pretty flat when I bought it. Ripped it into 3 strips, 16"x96" So I could have 3 pieces of 1/4" mirror attached to it.
Now that it has been ripped it is obvious the pieces are bowed 1/4" over the 96" length. If a mirror is mounted to it I think its going to look like a fun house mirror.
My question is: Can I use my track saw to cut 1/8" or 1/4" deep grooves spaced 6-12" apart starting in the center and working out towards the ends for a distance of say, 3' and will this relieve some stress allowing the wood to relax and flatten?
I hope my explanation makes sense.
The darn sheet was $160 so I hate to waste it.
TIA

[Richard Coers]

How are you going to fasten the mirror to it? If you are going to use a mastic, then hold the strips flat and glue the mirror on. 1/4" bow over 8' will take very little force to flatten.

[Steve Demuth]

For that little bow, an alternative would be to cut grooves (maybe 1/8" wide by 1/4" deep) the long way and then glue long grain strips of wood into the grooves while clamping the plywood flat. I've taken both bow and wind out of plywood with that technique - as long as it's a shallow curve, the strips provide plenty of stabilizing power.

[John TenEyck]

Stack them on top of each other and clamp them together between some straight cauls for a couple of days. They may go back dead flat. Sounds improbable but it's worked more than once for me. It's failed, too, so no promises.

John

[Jay Knobbe]

How are you going to fasten the mirror to it? If you are going to use a mastic, then hold the strips flat and glue the mirror on. 1/4" bow over 8' will take very little force to flatten.

Glass Co is doing that with mastic.

[Tom Bender]

Presumably you don't want frames on the front but maybe you can add frames to the back. Maybe plane a little bow into them to counter the bow. And it'll make hanging the mirrors easier.

[Jay Knobbe]

Wanted to report back about what I did to resolve this problem. I cut a series kerfs along the width (16"), 8 all total, 1/4" deep. I then taped off the sides and using West System epoxy and their syringes I filled the grooves level to the surface. The West System 105/206 epoxy is quite thin and seeps into the entire area. Setting panels on my assembly table they remained perfectly flat and just as stiff as before cutting. Hope this helps.