To all:
I glued-up a 30 x 36 maple tabletop about 1″ thick. After it sat for a day or two I have a slight cup, about 3/16 over 30 inches, higher in the center of the top. I am going to dye it with waterbased analine dye.
I used to know, and I have Bruce Hoadley’s book in front of me, but I forgot which side to apply the waterbased dye to first to eliminate some of the cup, and a couple of times I have put tops outside in the sun to achieve the same thing, but memory fails because I haven’t had this problem in many years.
It takes very little pressure to push the top to flat on my worktable and I think I can draw it almost flat when I attach it to the base but I would like to get it a little flatter before attaching.
Thanks,
John
Replies
John,
Water will swell the fibers, so wet the concave side first. If I understood correctly this is the underside of your table. If you can flatten it with hand pressure there's nothing to be concerned about. Whatever system you're using to attach to the base will be enough to control the cupping.
DR
Ring,Thanks, I appreciate it. I will dye the underside and seal it first.John
How was it setting when you left it. If it was flat on a bench then the cupping could be due to uneven moisture that would reverse itself if it is allowed to dry evenly on all sides, stickered to provide air flow. (a little weight on the top, but directly over a sticker would be a good thing too.) But, if this doesn't cure the problem, the cupping might be due to other stresses in the wood. These would reappear over time since the moisture level will even out, sealed or not. (No finish provides a complete barrier to water vapor.)
It was flat on my work table. I dyed and sealed the underside first and it removed a little of the cup, about half. Now I'm working on the topside and I'll just have to see how it does.
pins, I did a repair job on an old-timey maple school desk that was used to hold plants and warped due water damage. the top was a glue-up and the panel members were approx. 1" thick if my memory serves me right. I soaked the entire panel in a tub to relieve the glue and after seperation began to wet down the convex side of the individual members to stimulate movement to flat. One of our fellow workers mentioned doing the concave side and Iam not trying to cast doubt on what worked for him or be disrespectfull to a brother-worker. However any time I try to flatten a cup with water I wet the convex face and put it in the sun and treat it throughout the day. goodworkings. bufun
bufun,I did that once or twice before but I couldn't remember which side I turned towards the sun but now that I've started to finish the top I will just have to wait and see what I've got. I started out with about 3/16 cup over 30" so it's not too bad.John
"I did that once or twice before but I couldn't remember which side I turned towards the sun...." The concave side goes on the grass, the convex side stays up toward the sun (or other heat source). It's easy to remember once you get down the fact that the concave side has "shrunk" due to greater loss of moisture. I've used grass-and-sun, and damp-towel-and-heatlamp. forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
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