Jun. 12, 09 - 09:43PM
Glad to hear you're making sure that the doors are square and flat as part of the gluing process. Sounds like you know it already, but I'll say it anyway. If the doors are not flat when glued, there's no fixing it.
Poplar should be fine for your doors as long as, like any other solid wood, it's properly dried. I'd expect kiln dried wood I'm using for doors to be about 6-8% moisture content. I've used poplar numerous times for projects, including for glass panel doors. You can check mc with a moisture meter.
From a handling perspective, if you're planing the door material, make sure that you remove equal amounts from both faces and work toward the middle. This helps with stability.
I'd like to know if the door is coming out of the clamps flat, and then "corkscrewing" gradually. If so, I'd point to unstable material. Not from the perspective of material selection, but from a moisture content perspective.
If the doors are already corkscrewed coming out of the clamps, your set up must not be as flat as you think.
George Vondriska, Editor