Goes to outsourced finisher (an hour north of me) as a flat panel and arrives at jobsite in banana mode. We glue (TB1) and nail the 3/4" "furniture return" strip on the back and then glue and clamp the 1 1/2" nosing on (just like a built up countertop). Imagine this is an end panel capturing a fridge. This has happened with paint grade and stain grade. Material is usually 3/4" classic core and solid nosing. The curious thing is that sometimes the panel stays flat and sometimes not. Vas in ze vorld?

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We will make end panels like these when they are anchored to a box. If they are not, such as in the case of a refrigerator side panel, we will make these as balanced torsion boxes. I would expect this panel to warp with or without finish, in every type of sheet good. The reason is that it is unbalanced.

Is he back priming ? Priming the backs of panels are a must .

I'd narrow up those build up strips and see if that helps. What you don't know is how the finisher handled them. Does he prime and finish one side, then let it sit for a couple days? That allows moisture exchange on the unfinished side.

I have found that how a panel is supported post pressing and finishing is critical to keeping panels flat. Ifthe finisher sprays then leans the panels against the wall they will likely sag and set.
I have beams to layout panels on until full glue cure when pressing or until finish cures when spraying.
I would load them on edge for transport considering the extreme conditions in the back of a van.

Finishing has to be equal on both sides the panel has to be balanced.

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Thanks. The finisher being the issue hadn't occured to me.
- "Finish the back for a balanced panel"..does that mean finish paint or just a heavy prime coat on the back? - -
- Width of the strip of ply on back is usually 6" (as most fridge specs Ive seen say 4" furniture return... visible part back of panel when fridge door is open).
- As far as David's screen shot comment, we are talking plywood here (mostly), but just to get a little off topic, it seems a real problem in this line of work is IDENTIFYING "reaction wood" as 90% of wood deflects/opens/closes as it moves through a spinning blade releasing tensions in the wood. This is why sneak up on the rip. first wide, then to size before committing. Am I wrong?
- Lastly I was thinking if the panel is 3/4 glued to 3/4, it'd be more balanced than 3/4 strips glued to a 3/4 panel (surface tension?)
There should be a international technical woodworking handbook for dummies.
I used to work in Germany and they have one (though a little complicated cuz its german of course) but some info is wrong like glue ups should always growth rings up then down alternating. Having built many decks and table tops the results have been less than constant and thus a bit unpredictable. Sometimes things work in woodworking that shouldnt and sometimes things that should, don't. For example: I had a 24x80" plywood panel door with laminate on one side only adhered with contact cement) that was flat for 15 years before I threw it out. Similarly, a table top (1 1/8" thick plain sawn Maple/boards 5-7" wide/glue up was ~40 Wx 90"/connected with wooden table top fasteners in a groove (traditionally) cupped (edges pulled up). I'm secretively summoning you David, cuz I know you cant resist this one.
Love you guys! Sorry for the rant

The finisher needs to use the same materiel on the back and front.
A panel secured to the wall wouldn't need to be the same.

Other causes could be lack of support (laying on saw horses and drying overnight without proper support.) or sagging while finishing.

Applying the back coat the next day.

Your stiles could also be causing differential movement as well as you solid edge.

Hard to tell when you can't see what happens to it for 2-3 days.

Yep. I live in humid Florida now. Balancing humidity intake is always something that's discussed. I'm a builder, not a finisher or another. But we get a lot of problems with humidity. Pretty aggravating, really. Sometimes we get raised panels made in the north, dry winter and they come down here and the raised panels explode in the frames after acclimating.

Nobody does it but Jerry Metz used to talk about ripping and flipping boards with none being wider than 3"

Thanks guys,
Spoke to the finisher yesterday. He said they have heard of this issue before and thats what they hang everything and spray all sides at the same time. He said it could be that if they are slammed busy that someone did lean or stack a panel potentially causing it to bow. Maybe thats it.

Final verdict for future searches: INCONCLUSIVE

Seriously?

"....lean or stack a panel potentially causing it to bow" Nope - that will not do it.

"Final verdict for future searches: INCONCLUSIVE" Nope - that is inaccurate.

Prayers, crossed fingers, chicken blood under a full moon, black cats may all have their effects, but none as strong as moisture content change for a culprit.

It is the MC boys. Nothing more, nothing less. If it is going into a museum environment, with absolute constant temp and Relative Humidity, and you shop matches that, then you can ignore wood movement.

Other than that, and it moves, it is MC. No more, no less. You do want to keep the finisher on his toes for his part of the balancing act, but mostly it is your job to make it balanced.

So you're saying 1 or 2?

1. Plywood panel's MC was too high at time of machining and dried out in the 3 weeks they were at the finishers?

2. Plywood panel's MC was dry at time of machining and took in moisture in the 3 weeks they were at the finishers?

Also, TRUE OR FALSE?:

A. Glueing a 3/4" panel to a 3/4" panel is a balanced panel?

B. Glueing any other thickness panel to 3/4" panel is an unbalanced panel?

C. What you glue to one side, you glue to the other (3 layers and 2 glue lines) unless both panels are equally thick as in ex. "A" (2 layers and 1 glue line)

Thanks

I would look at how much finish is applied to the edges of the plywood rippers.

When sealing you need to think of all 6 surfaces. Plywood edges soak up moisture much faster than the faces. The faces typically get coated more so it makes the situation worse. You have 3 exposed long edges on one side that might not get enough sealing.

What is the 3/4” x 1 1/2” wood?

The order of construction can make a difference as well. If you edged the panel first, then glued the rippers on second is different than glueing the rippers on then bending the wood edging and/or thickened panel together.

I would ask the guys in the shop if they have been consistent in the manufacturing steps.

Brilliant ideas Adam. I never thought of any of those. Ply rips go on first then the solid 3/4x1 1/2" wood edge.
Anyone else care to comment om my last true or false questions?