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Thread: Untwist plywood?

  1. #1

    Untwist plywood?

    About a year ago I cut cabinet shelves out of high quality euro-ply (baltic birch). They are 21" x 21". Now that I am ready to finish/install, I see they have all developed a twist. If you lay the shelf on a flat surface and push down one corner, the opposite corner lifts off the surface by 1/4". I've had big box store plywood warp many times but not baltic birch. Is there a fix for this? Thanks.

  2. #2
    Quote Originally Posted by Len Rosenberg View Post
    About a year ago I cut cabinet shelves out of high quality euro-ply (baltic birch). They are 21" x 21". Now that I am ready to finish/install, I see they have all developed a twist. If you lay the shelf on a flat surface and push down one corner, the opposite corner lifts off the surface by 1/4". I've had big box store plywood warp many times but not baltic birch. Is there a fix for this? Thanks.
    Not likely. You could try clamping out the twist but I'd be surprised if it works. I guess you could kerf it, fill with splines and clamp flat but it would not be worth the effort.

    I have used a few sheets of Columbia Europly Plus and had good luck with stability, but veneer core plywood can have a mind of its own and I have seen many a sheet of potato chip shaped baltic birch.

  3. #3
    Thanks Kevin. Maybe if I screw a piece of angle iron across the bottom back edge it will straighten out.

  4. #4
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    Go ahead and finish and install. Being a shelf, it will flatten out when the load is put on it.

  5. #5
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    Richard is correct.

    Also - I'm thinking you'll be anchoring it somehow? Or free-floating on cleats/ledgers? I would think there's an opportunity somehow for a surreptitious pin-nail in a back corner.

    The diagonal of 21" square is just shy of 30". 1/4" over 30" ain't that much, to be honest.
    When I started woodworking, I didn't know squat. I have progressed in 30 years - now I do know squat.

  6. #6
    Hi Kent. The shelves will be resting on brass shelf pins. 1/4" is enough to cause significant rocking.

  7. #7
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    Baltic birch can be really frustrating. Expensive per sheet but not necessarily flat. I'll have to ask if my lumber supply replaces warped sheets but I doubt it.

    From my experience they flatten over time if you keep them pressed flat.
    Yes, I have 3 phase!

  8. #8
    Quote Originally Posted by Len Rosenberg View Post
    Hi Kent. The shelves will be resting on brass shelf pins. 1/4" is enough to cause significant rocking.
    You can shim one of the pins. Noone will notice but you.

  9. #9
    If you are using the 1/4" pins (also called spoons) with a flat ground on one side where the shelf is suppose to sit, try rotating the pins on opposite corners 180 degrees so that the shelf rests on the round part. You should be able to pick up 1/8"+. You can also use those small silicone bumpers that are usually used for doors and drawer faces to keep them from banging when closed, as shims.

  10. #10
    Thanks Kevin and Rob. I know I can shim, but the item to go on the shelf is large and if I shim the shelf the item will not be on a flat surface, and will rock, so I would have to shim the shelf and the item. Last resort if nothing else works, but will try other solutions first.

  11. #11
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    Quote Originally Posted by Len Rosenberg View Post
    Thanks Kevin. Maybe if I screw a piece of angle iron across the bottom back edge it will straighten out.
    You need to run the untwister from corner to corner.

  12. #12
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    If the shelves are for a particular item and you don't need adjustability I would make wooden runners and screw them to the sides and screw the shelves to the runners.

  13. #13
    whats the untwister. Is it from Ktel?

  14. #14
    I've had a similar issue in the past and I was able to dampen the plywood on both sides, then clamp it with a twist in the opposite direction. I let it sit overnight with a fan blowing on it and the next day it was fairly flat, not perfect but close enough.
    - Mike

  15. #15
    Just came up with a simple solution. Instead of putting a shim between the shelf pin and the bottom of the shelf, which would prevent rocking but maintain the twist in the shelf, all I have to do is put a shelf pin in the hole right above the shelf, and put a shim in between that and the top of the shelf to force it flat. Only needed in two corners, and preserves shelf adjustability. Since the shelf pin holes are spaced 1" apart and the shelves are 3/4", given the width of the shelf pin the shims will be less than 1/4" thick. Thanks to everyone who responded, much appreciated!

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