Table top cupping

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Forum topic by WoodNut82 posted 06-16-2018 04:07 PM 1251 views 0 times favorited 6 replies Add to Favorites Watch
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3 posts in 748 days

06-16-2018 04:07 PM

Topic tags/keywords: cupping joinery planing tip

Hello everyone,
I’m new to this forum and am fairly new to working with rough cut lumber. I am building a 6’ round dining table out of cherry. I bought the wood and let it acclimate to my garage for about a month before I started on it. I ripped the pieces to width and length before I jointed and planed the boards. After I finished planing them to 1.1875” thick I left them for a couple more days before I glued them together. After glue up I started flattening the back with my #6 hand plane. I got half of it flattened and came back to it a couple days later to find that what I had flattened has cupped. Is there something I can do? Should I let it sit and see if it gets better? Should I clamp it down flat and finish the rest of the back?
Thanks in advance.

6 replies so far

View Gene Howe's profile

Gene Howe

12169 posts in 4196 days

#1 posted 06-16-2018 04:50 PM

Had a similar problem on a large case lid. I wetted the concave side liberally and clamped it flat with some 2X2s and F clamps. Your thickness may not allow for flattening with clamps. At any rate, set the wet side down in the sun. I set it on concrete as it holds the heat. Then, about every half hour, wet it again. I left it in the Az sun for about 8 hours.
Your thickness may require longer and more wettings.
The article I read suggested using hot water. I just used cold. Your thickness might need hot.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View EricTwice's profile


248 posts in 1301 days

#2 posted 06-16-2018 05:16 PM

Make sure air can circulate all the way around your top. (have it up on sticks)
check your moisture content.

-- nice recovery, They should pay extra for that mistake, Eric E.

View OSU55's profile


2645 posts in 2757 days

#3 posted 06-16-2018 07:12 PM

I never leave a panel glue up flat after the glue sets, except to work on it. I stand them up after I finish a session, not knowing if Ill be back in an hour or a week. I also work both sides down together – work a while, flip over, repeat. I let them sit several days to a week after they are flat before smoothing. Removing the surface wood will change the stresses throughout, let it settle out. Has worked very well for me. Dry wood is a must – check in the center after a fresh cut.

View TheFridge's profile


10859 posts in 2254 days

#4 posted 06-17-2018 12:38 AM

It’s happened to much a bunch of times. Always cups away from the bench because the top loses more moisture than the bottom. Most times I can just stand it up for a day or so and it’ll fix itself most of the time or close enough to not matter.

I avoid stacking panels and laying them down. I always stand them up now. Far fewer problems.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View WoodNut82's profile


3 posts in 748 days

#5 posted 06-17-2018 03:27 PM

Thanks for the responses, it appears to mostly have gone away. It’s mostly the last 6” on both sides that are cupped, I can lift up on them and it goes away. I ended up finishing the rough flattening and cut out the rough circle. I stood it up and I guess we’ll see what it does after I get the pedestal done. I wouldn’t have thought that standing the pieces up would help that much, I’ll definitely start doing that. I don’t have a moisture meter but when I ripped them to width it seemed dry, I guess I should look into one. What brands would go with? Gene did that stay flattened after that? What would the chances be of it cupping the other way if there was to much moisture?

View Bishop78's profile


14 posts in 783 days

#6 posted 06-30-2018 04:23 PM

Take 2 strips of plywood slightly larger then your workpieces and sandwich your workpieces with clamps…thats the only way to reduce the cupping to basically zero. Of course you have to leave the pieces longer due to the fact that it drys on the ends which can cause cracks.

To keep the tabletop from cupping you have to follow the glueup rules. The tabletop should be made from 2-3 inch stripes alternating the growthrings, better yet take quartersawn lumber and build a skirt which is screwed on.To allow for expansion.

The most important rules if you want it to be flat are, do not stand it on its side and protect it from air. Put it into plastik or between big piecees of plywood on top and put weights on top of that or both. Just dont let the air reach it.

The thing i learn during my aprenticeship is if you build furniture like that out of wood, dont make all the parts and than start putting it all together. you never know what happens. Worst case is you get sick for a week and all or some of the pieces have warped in one way or another and are unusable. Build from the bottom up. Split it if you can into smaller projects that way you undergo less riskof something happening. Wood ain´t cheap

I am a cabinetmaker by trade and thats the professional standard in germany
I hope i could help

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