Flatten a cupped panel

[javajake]

I am making a vanity with raised panels. In one of the panels I am working on, one or two of the boards are cupped. Any ideas on an easy way to straighten it? I can flatten it by squeezing it against my cabinet saw top with my hands, so I don't think its all too severe, but it's definitely a problem while I am routering the edges.

[Ben H]

This is a very hard thing to do, dare I say almost impossible. Are the cupped boards a part of the frame or panel?

[AceHoleInOne]

Try misting the wood with water from a spray bottle. The wood should relax and go flat again. Did the wood cup after you processed it? Frame and panel, I don't dilly dally with due to wood movement. Allow enough shop time to run the rail and stiles and door panel and get the things glued up. If you can't, place your wood in plastic garbage bags till you can get back into the shop. This helps slow the wood movement by preventing the air from drying your wood unevenly, which can make it cup.

-Ace-

[RenaissanceWW]

Are you saying that the panels are already at their final dimensions and then they cupped? Have you already cut the grooves that the panels ride in? If not then just re-flatten the panels and adjust your joinery to match the new thickness. If the joinery has already been cut you can still flatten the boards and use shims hold the panels tightly in the groove. Insert the shims from the back to press the panel up to the front of the groove so there is not visible gap. There will be a gap on the inside but it is unlikely anyone will see that. If it concerns you then insert a strip that fills the entire groove. The key will be to flatten the panels and get them into the frames as quickly as possible in an effort to control further movement. Also when you flatten them again, make sure you take an equal amount of wood off both sides to control moisture release.

[AceHoleInOne]

Oops..... to clarify my comment, misting the wood with water will allow the wood to go flat again, then further machine your door. Chances are the wood will twist on you again after the wood drys. If you pre-finish your raised panel (stain it or dye it) your panel will relax again (how much is depending on size and thickness of the panel)then you can lock it into the rail and stile.

-Ace-

[Rutabagared]

Oops..... to clarify my comment, misting the wood with water will allow the wood to go flat again, then further machine your door. Chances are the wood will twist on you again after the wood drys. If you pre-finish your raised panel (stain it or dye it) your panel will relax again (how much is depending on size and thickness of the panel)then you can lock it into the rail and stile.

-Ace-

I once saw Norm flatten a cupped board by cutting several kerfs in the back, flattening it against the bench, and filling the kerfs with epoxy.

Joe

[javajake]

Thanks everyone. I think part of the cupping was due to my leaving it flat on a table for 24 hours (maybe allowing more moisture in or out of one side than the other?). That, or the humidity is fluctuating pretty drastically in my shop... I stood the panel up on end for the rest of the day, and most of the cupping came out (enough that I can press it flat as I router it).

[Boatworks Today]

Future reference, this works pretty well..  Never ended up doing much with the WW channel (focused on the boat side of things) but it still works!

 

[JerrySats]

Nice tip thanks for sharing it , I like your vids .

[screwikea]

Future reference, this works pretty well..  Never ended up doing much with the WW channel (focused on the boat side of things) but it still works!

 

 

That seem like it's doing something similar to what steam bending does -- you're essentially using heat to make the wood's internal stuff soften up. It seems like a lot of effort to me for little gain, but I wonder if tightly clamping down a solid piece of wood or metal on top of it will further flatten the board. Then again, this could be useful if you have an interesting piece of stock that you're trying to salvage.