Panel Cupping

[Jerry Thompson]

I am in the process of building a "test" blanket chest using poplar. This is to gain experience and not waste expensive lumber. I am glade I chose this way first with the steep learning curve I have gone through.
Now I have two out of four panels that have cupped. The panels are oversized, two measure appox 22X26X3/4". The other two are approx. 38X22X3/4". They are all comprized of two 8'' boards with the remaining made up of approx. 2-3'' boards.
I first cross cut all the boards from 4/4 stock and jointed one side and let them sit for 2-3 days and then thicknessted planed them to 3/4''. All of this was done over many days due to other things in life needing done.
The lumber was also joined on one edge before planing. I ripped the other rough edge and again they all sat around for several days and showed no signs of becoming other than when I left them.
The boards were all glued up with clamps and cauls. All of them spent 24 hrs. clamped. When the came out of the glue up all was good.
Now after about 3 days two of them are cupped about 3/8-1/2''. I am working in my garage which has the same humidity as outside. I did use a RO sander to smoothe them all down and at that time, two days ago no cupping.
Due to lack of space they have been stored upright.
Should I have used narrower boards? Let the lumber acclimate longer after jointing? Could this be a humidity problem? I did bring two of the Panels in the house to see what happens.
I thank everyone for your help in advance.

[John Piwaron]

I can't say if 8" is too wide or not. What my experience has been is that when I use solid panels to make something, essentially a box of some sort, they stay flat best when joined into that box shape. Dovetails, finger joints, however you do it. The other thing that can help is to stack and sticker them with some weight on top. Maybe this is easier for me since my shop is in my house. It's climate controlled.

[Jerry Thompson]

I plan on using a D4R to dove tail the chest. I wonder if the cup would flatten in the jig clamp?

[Roy Harding]

I plan on using a D4R to dove tail the chest. I wonder if the cup would flatten in the jig clamp?
It might.

The force exerted may also crack the panel.

I don't have a solution to your problem - are you SURE the lumber was appropriately dry (6 - 8% MC) before you milled it?

When you say the lumber and/or panels "sat for several days" - did they "sit" directly on a cement floor?

[frank shic]

it's wood after all and very forgiving in that respect so you could just re-rip, joint and re-glue again unless you've already cut them to finish length and width.

[Jerry Thompson]

It occured to me that we had three days of rain and clouds, hence high humidity. I am going to leave them inside the house for a few days and see what happens. They did not sit on concrete. I do think the DT jig will take out the cup without splitting the panel. I can use a lot of muscle and push them almost flat on the table saw.
The first thing I always think is that "I screwed up!" I am looking at this as a learning experience.

[Carl Beckett]

I do projects in a non climate controlled shop

A LOT of wood movement, especially panels, as the outside humidity swings high low

See what happens after the humidity drops. Or bring them inside 2 or 3 days and see if they change

[John A langley]

We build panels just about every day mostly for doors. The shop is not climate controlled. We try to keep the boards between 2-3/4 and 3-3/4 wide and we alternate the growth rings. We have not had problems with panels cupping as much as you say yours are. But in the end it is wood and you just don't know what it is going to do. I think you do like Frank said and re-rip your boards and glue them back up. It will be easier for you to do your dovetails. D4R is a good dovetail jig but you want things as close to perfect as you can get for the dovetails to fit correctly. Good luck

[frank shic]

It occured to me that we had three days of rain and clouds, hence high humidity. I am going to leave them inside the house for a few days and see what happens. They did not sit on concrete. I do think the DT jig will take out the cup without splitting the panel. I can use a lot of muscle and push them almost flat on the table saw.
The first thing I always think is that "I screwed up!" I am looking at this as a learning experience.

jerry be very careful about pushing them too hard you don't want to get into a bind situation. every one of us who's done woodworking has had something cup or warp on us at some time. welcome to the club ;)

[Jerry Thompson]

Cupping Update: The panels, after being inside of the house, are now almost back to flat.
Thanks everyone.

[James White]

Jerry,

The panels need to be kept up off any surface with stickers. Otherwise the exposed side will gain or loose moisture with swings in humidity. While the side that lays on your bench, saw, etc will not gain or loose. This will result in cupping. Also after jointing you should have thickness planed. Fresh exposed lumber on the jointed side with conditioned/acclimated material on the unjointed/planed side. Do both operations then let the material rest for a few days with stickers between. Then you can do your final/light jointing and planing before assembly.

Finlay a conditioned shop space is a very big advantage when it comes to keeping your material stable. If you can afford to do it than you should. You need only control the humidity. For me this means running a dehumidifier in the spring, summer and fall and limited mild heat in the winter. Get a digital hygrometer and keep an eye on things.

James