I am building a desk and recently glued together a panel for the top. The panel is 4 boards of 7” wide quarter sawn white oak, rough length is 60”. The individual boards were flat, and the butt joints were tight and smooth.
During my dry run of the process I decided to glue the middle two boards first as I found it easier to control cauls on the center joint, after that was dry I added the two outside boards. I was happy with the final result as the full panel ended up flat.
Then… I had other commitments and had to let the panel sit a couple of days in my workshop, my garage, and when I returned to it I found it cupped a fair amount. I live in NC and my garage is subject to humidity, although lately the humidity has been lower
My questions:
Is the cupping a result of the humidity exposure and/or was my process part of the cause of cupping?
I’m going to work on flattening it with a #6 plane per a FWW article; once I’m done is the panel susceptible to cupping again?
I may add Breadboard ends to help control future movement, any other ideas?
Thanks
Replies
Cupping is often caused by uneven moisture from side to side of the panel, was the panel left with even air circulation on both sides?
Flip it over and wait...or better yet put it on stickers inside somewhere. It will probly return to true. With Qsawn stock it almost has to be differential absorbtion.
If you mean the top and bottom, actually no; one side was lying on my workbench with no air and the other was up. I can stand it on end but will that matter now?
I too would get it somewhere stable and wait before I started removing material. If it was on end touching concrete, that can be trouble. If it was laid flat on a surface the exposed side and contacted side would behave differently over time.
I generally have my "top" boards selected early on but, I mill them and make / install the top close to the finish of a piece. I guess if I think about it, I make and sub-assemble or assemble most of my parts. Loose parts left laying around look for trouble ;-)
The above advice to expose both sides to the air and await a reduction or elimination in the cupping is right. Quarter sawn planks will not easily cup and if a glued-up desk top has cupped it's likely to be differential moisture content in one face compared to the other. Being laid down on the workbench will reduce the moisture loss or gain on the downward-facing side compared to the upward face.
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Personally I try to keep stock somewhere with a stable atmosphere identical to that where the finished piece of furniture using that stock will eventually reside. In Blighty that's somewhere where the measured moisture content of the wood will be between 10 and 12%. Making something in a damp basement or garage then taking it indoors is almost certainly going to lead to wood movement issues of some kind.
It would be best if you could let your desk top stabilise (and un-cup) in part of the house with an indoor atmosphere rather than the typically damper atmospheres of a garage or basement.
If you do take it "indoors" to lose moisture, be wary of potential splitting at the ends where the end-grain shows. If there is significant moisture to lose from your desk top to stabilise it, the boards can separate at the ends because end grain dries out much faster than face grain. (This is one reason for making such glue-ups with a spring joint between the boards). Cover the end grain with tape or something similar to inhibit rapid moisture loss.
Lataxe
Thanks to everyone's advice. I've moved the panel inside and have it raised so both sides are exposed. I'll wait a few days and see what happens.
I will get back and advise the results
Thanks again
I had this happen recently on a cabinet I was building. Left it sitting on my table saw after glue up and the bottom panel warped. I elevated the cabinet for a couple days and it went back to flat.
I never glue up a top until the rest of the project is done. Then I can glue it up and install it next day.
If you can't do that, never leave a glue up living down, even if there is some air underneath. Leave it in the clamps, with the panel standing on the clamp ends. Both sides get equal air movement until your ready for it.
As others said, it should flatten. Give it a day with the other side down, then stand it straight up on one side, not the end grain. Never keep wood on top of or too close to concrete. Too much moisture,
All deference to JohnC2 the woodworking god but you didn't do anything that bad. I build tables of various sizes, all made from edge-joined different species. I glue the tops from left to right (superstitition) with lots os cauls. I use hidden battens underneath. Meaning I rout 2" wide dados, 1/2" deep on the long ends and glue good hardwoods in them. If the customer doesn't like the look on the underside, I add cherry or hickory plywood to hide the battens.
Oh forgot, I don't like breadboard ends. Like others I agree with leaving both sides to the open air.
Mikaol
Sorry, but I've never once needed battens, breadboards, or any other shenanigans to keep a panel flat. But I don't glue up panels and leave them sitting flat, either. Pretty clearly, that was the issue. We work, we learn. Not a big deal.
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