Bowed/warped Baltic Birch Plywood

[chris weir]

I picked up 4 @ 5' x 5' x 18mm sheets of Baltic Birch plywood from a local supplier for a cabinet project in my dining room. I didn't notice that the plywood wasn't completely flat until I got it back to my shop. When I hold a 6' straight edge across the diagonal I get about 1/2" bow from the center to each corner on the worst piece (1" from corner-to-corner). Is this acceptable or should I return the warped/bowed pieces for flatter pieces? I need to make 3 cabinet boxes at 40" width x 31" height x 14" depth. I'm concerned the bow in the plywood will make it difficult to square up the boxes. I should have looked more carefully at each piece of plywood before purchasing, but didn't think this type of plywood would be like this.

Thanks for any comments,
Chris

[jack duren]

Frame or frameless cabinets?

[Marc Fenneuff]

I first started working with my local supplier’s “Russian Birch,” 12mm thick and 5x5 sheets, last year. I was surprised to find that it was in fact not dead flat, had footballs and voids, and occasionally the kerf would start to close up when ripping to size (I too am making drawer boxes). My only other supplier is an hour away so I’d also like to know if my expectations were not in line with reality.

[jack duren]

You can get it without footballs but it can be flat when purchased learned in a truck or shop and won't stay hat way...

[chris weir]

Cabinets will have face frames

[jack duren]

It should pull out with face frames and a back. Just a little difficult to cut...

[Erik Loza]

What Jack said. As long as you can get a truly square cut, making the carcase should bring it into flatness. This type of ply seems to be more the norm than the exception these days. Good luck,

Erik

[Mark Daily]

Personally, I would take it back. I’ve never had good luck relying on a face frame to flatten a bowed side.

[David Stone (CT)]

IME, even good quality Baltic Birch purchased from a speciality supplier that stores it reasonably well is not going to be dependably all that flat and some of it is going to be sufficiently bowed that you need to work with awareness of that fact. The piece you describe sounds worse than some, but not wildly unexpected. I recently built a kitchen's worth of cabinets with prefinished maple ply for the carcases and BB for the drawers, and many, if not most, of the longer parts had some detectible bow (as in, like a 1/16 +/-) along their length. As others say, use the back and, if there is one, the face frame, to straighten things out. And measure the diagonals to ensure squareness at both the front and rear faces. (Don't trust a square since that will be thrown off by even a modest amount of bowing.)

To another question on this thread: All the Baltic Birch I've encountered is subject to having some patches on one face, with the other side patch free. Voids are very rare and I've never had it close up on the kerf. None of it is as flat as a sheet of MDF, which would be my definition of dead flat.

[Kevin Jenness]

I've never cared much for baltic birch aside from applications where the exposed edge is a feature- it's rarely flat and the thick faces are usually badly checked. I would not use it behind a face frame. For what it is good for Columbia Europly-plus is a better (though more expensive) alternative.

[Mark Rainey]

same problem https://sawmillcreek.org/showthread.php?278444-Baltic-birch-plywood-with-twist&highlight=

[Andrew Seemann]

As noted above, Baltic/Russian birch, contrary to popular belief, does not always stay flat. Birch is an unstable wood. Slicing it and cross laminating it makes it more stable, but it still will be slightly unstable. That said, it still is one of my favorite materials; I just use it in a way that doesn't require it to stay perfectly flat on its own.

[roger wiegand]

Is there such a thing as consistently and forever flat plywood? It's not something I've ever run across in pushing 50 years of woodworking.

[Chris Fournier]

If you google "Baltic birch grading or grades" you'll see that not all BB is created equal! That will address the voids/football issue interior and on the faces. Flatness? Plywood? It's a relative thing, never been a problem for me in my shop in my projects. When sanding prior to finish I find that the "checking" is taken care of. The "checking" is a product of the veneer slicing process.