I'm trying to build a 18"x18" top. After glue up & sanding, the top cupped, I tried putting weight on to flated,but once removed cupped returned. I used maple any advise? Thanks Tommy
warping top(7 posts)
Tommy, it's possible the only way to solve this problem is by adding component parts, such as braces or aprons or edge trim attached to the top. ..Or, possibly, if the top is to be attached to a base, that could serve to straighten the cupping. If that won't work, you may have to re-rip the joints and re-glue.
It's usually a good idea to design in some kind of cross-bracing. Cupping occurs when all the grain of the wood is going the same direction.
Sharing a design sketch or description would help to come up with a good solution to your problem.
Thanks for the reply it's to be used as base for an old slot machine that has been restored. I think I may try to rip and re-glue I didn't think of that. Also I plan to make a stand for the machine to mount,and it will be attached somehow (yet to determined). I'm trying to keep as original as possible. Tommy
Sounds like a fun project! Sometimes this is a result of uneven exposure to moisture during the glue-up process (using water to wipe down the glue) and can straighten itself out to extent over a short period of time. If you suspect this to the be possible culprit, I would wait a few days before doing anything to see what happens as the boards normalize in moisture. When you are putting weight on, you might also wet the board on the bottom side of the panel (the side opposite where you put the weight). This will expand the fibers on the concave side of the panel, and combined with the pressure you are placing on the convex side, could help drive the panel back to a somewhat planer condition. If have had decent luck (not perfect) with this approach when moisture was the culprit. If the panel was distorted because of joinery problems (out of square table saw blade or jointer bed), then you can't fix it this way.
Also, be sure that when you are clamping you don't use excessive clamping pressure as this can cause distortions to occur in your panel as well. Use firm pressure but not gorilla pressure. :)
Here are my 2 cents.... A cupped panel is a cupped panel, and trying to force it back to flat isn't best long term solution to the problem.
Preemptively, be sure that material is acclimating to your shop environment before working with it. My material lives in an unheated building. I bring it into the shop at least 24 hours before I plan on working with it so it doesn't go kerflooey from temp and humidty swings.
When jointing edges, swap faces against the fence as you joint. I always do this. If your fence is a tiny degree out of square and you use 5 boards to make an 18" panel the cumulative effect will be significant. The result of swapping faces is that when you glue two edges together the face that was against the fence is up on one board and down on the adjacent board. Any deviation in the angle is offset.
Use boards that are 4" - 6" wide when gluing up panels.
Despite all this, sometimes wood reacts unpredictably. This happened to me just last week. I sighed over the time I was losing (of course I was behind schedule) and took the panel to the table saw to cut it apart and start over. Wood is a living thing, and can be unpredictable. Like they say, if you want it perfect use particle board and plastic laminate.
Depending on how bad it is cupped i have cut a 1/4 in deep slot in the bottom side from one side to the other and lay it upside down and flatten it and put a wood slat in there to keep it flat. you may need to do more than one cut to get if flat. i have done this to long boards i bought for a project only to find they cupped.
Provided the boards themselves are not cupped, I'd rip them apart, make sure my jointer fence is dead-on square, and joint all the edges. Then I'd alternate the rings on the ends. Some folks say it's not necessary. Norm Abrams always did it. Then I'd use cauls to keep the boards from cupping while they dry. Leave them in the clamps and cauls for a day or two. Hope that helps.
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