Fix a panel warp

[David Huston]

Just glued up a 18x30 panel last night. It is made up of about 10 pieces. I glued up 5 pieces into two panels and then those together. Now the big panel has about a 1/16 to 1/8 bow. I know I can rip and reglue but was wondering since it isn't a huge bow if there was any other way to maybe fix it? The panel is only about 3/4 thick so I don't have much room to sand it flat.

[John TenEyck]

Simple put, no. If you can't afford the loss in thickness from planning/sanding it flat, then the only permanent fix is to rip and reglue.

John

[Andrew Seemann]

A bow like that is common after a glue up. Even a small change in humidity can cause bowing, and that is nothing compared to the seasonal moisture changes the panel will experience. The design of whatever you are making the panel for will need to accommodate and restrain the movement. Also, don't forget that the panel will move between 1/4 and 1/2+ in width summer to winter, so you will need to allow the panel to move despite fixing it in flatness.

[Marc Jeske]

David - Did you leave it laying flat on the bench, or like one side flat against anything overnight?

Uneven acclimation to the ambient humidity highly possibly caused the warp.

If you found it this morning convex on top, it gained moisture.

If you found it this morn concave on top, it lost moisture.

Rip, re joint, and glue can be a solution, but only after you have determined that the panel will "always" stay warped in that direction.. otherwise, if that is not checked first you may be creating a permanent reverse problem.

Put the panel convex side up exposed to sunlight, or heatlamp, etc - KEEP an eye on it over a few hours.

Use your straightedge to gauge progression toward flatness.

You may very well find it straightens out... If so, store it on edge w air movement exposed to both sides equally.. NOT flat against anything...and out of sun or drying furnace blower heat, etc and/or tightly wrapped in poly till you secure it in final use.


I work w edge glued 3/4 pine panels up to 28" wide x 7' long and fight this alll the time.

They are used as plain frameless flat lids on budget Caskets .. NEVER stay flat, constantly moving.

And even if I observe my suggestions above during processing, once it is installed on the box, and the lid is closed.. is when it all starts.

I do lacquer both sides pretty evenly, but still.. only one side is exposed to more rapidly changing ambient than the closed up interior.

I have tried glued on battens which I know are wrong (cross to long grain direction)

Have not yet tried slotted screwed non glued battens like the tabletop mounting methods.. probably my next step.

Not anxious to try breadboard ends as this is a budget priced piece I make.

I maybe should try T+G NON glued edges w non glued battens, although the non one piece look will severely change the look of the piece.

Comments on that ?

Quartersawn is way out of budget for this product.

Not to hijack thread, but any help on my problem may also be helpful to the OP.

Marc

[Andrew Seemann]

David,

If you just need the panel to be flat for assembly, you can do the adjustments as Marc noted, they should work for adjusting the moisture content on one side to change the bow. Note that they are only temporary, when the moisture content in the board goes back to equilibrium, the panel will move back to whatever shape accommodates that equilibrium --until the humidity changes and the panel needs a new shape to accommodate the new equilibrium

[David Huston]

It dried overnight flat on a glue up rack made up of two PVC pipes screwed to some 2*4 pieces. The piece is going to be used as a tray for a friend's coffee maker so I doesn't stain the marble countertop. I will flip it over and let it sit for a while. I was going to just put some non skid pads on the bottom of it but now I might put some rubber feet and that should make the warp less noticeable.

[Marc Jeske]

Yup, like Andy said... That's why it's SO important to have the individual boards "Equilibriumed" within themselves before milling and edge gluing.

So, you really need to start out right, and THEN, as I explained. do everything you can to KEEP it right.

The above is all in a perfect theory world, pretty tough to really accomplish all considered.

Certainly can be done, but may REALLY slow down the project waiting for the wood to settle down.

And after alllll that, then it will go to someone's home in AZ, or maybe coastal LA, and again the problems will start.



Marc

[Lee Schierer]

You should also check your jointer (or table saw) to insure that the edges are in fact square. A 1/2 degree error on a jointer can give you the type of bowing you are seeing. Check the angle of your jointer fence on the out feed table.

[andy bessette]

It dried overnight flat on a glue up rack made up of two PVC pipes screwed to some 2*4 pieces...

I would throw that drying rack away, as PVC will easily bend under load and not provide flat support.