Dealing With Cupped Panels – Including Door Panels


I was reading an article about an individual that glued up some 1/4 inch door panels to make doors for his cabinets. He worked on these for a cabinet he was building.

He put the project aside for a week and when he came back the panels had cupped 5/16 of an inch. He tried bending them back with clamps, it helped but didn’t fix it. So if you ever run across this issue, here is the solution:

First identify why the cup happened. If you leave the panel out on the workbench, especially with wood stock that thin, one side is going to be exposed to the air’s elements and the other side isn’t. Changes in humidity are likely to occur, affecting both sides differently since one side is face down.

If there is more moisture in the air, it will cup on the downside, looking like an upside down U. If the air is drier, it will cup upwards, looking like a U.

Reversing the cup is possible by putting the cupside upward and putting weight on top, then give it some time to let the moisture content to equalize. You can try spraying water on the concave side as well.

If the panels are resawn, they are more prone to cup because of the tension on the interior of the panel that will be created from the process of exposing the resawn material’s insides to the elements, elements that wouldn’t have penetrated as deeply into the material until it was cut open and exposed.

Also, whenever the wood is resawn, it will act as a rubber band does when it is in a stretched position and then let go. It will loosen and create cupping in the wood. There is another thing to try as well.

You can lay the panel on a table or level surface with the cup side down, with a wet towel underneath. It works better with a little weight on it. If you have a heat lamp, this will help it to cup the other way, but you need to monitor it so that it won’t cup too much the other way, but it will level out.

You won’t really know exactly when to stop the process until you take the lamp off of it and then let it cool off for say, half a day or so…

This can be done for about any panel, not just 1/4 inch thick. Of course, you would have to have a sizable lamp, almost tanning bed size, in order to take care of a 4×8 sheet of wood. But I don’t think I would do this to a panel this size because once you cut it up you may not have such a problem with the pieces.


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Ted Leger –


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Updated: February 16, 2017 — 11:57 pm
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