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What to do about cupped tabletop

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Forum topic by Rob263 posted 09-20-2021 04:40 PM 224 views 0 times favorited 4 replies Add to Favorites Watch
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Rob263

5 posts in 1738 days


09-20-2021 04:40 PM

Topic tags/keywords: tabletop walnut cupping warp

I am in the process of building a dining table out of solid walnut. I don’t have the skills or equipment to make the tabletop myself, so I got my wood supplier to do it for me. The tabletop is 6/4 walnut, 7’ long by 40” wide, and is made up of 6 smaller boards glued together. The shop is reputable and seems to know what they are doing. I received it about a month ago, and since then, it’s been standing behind my living room couch leaning against the wall (long side on the floor). It was leaning at maybe a 10 degree angle, with the underside of the piece facing away from the wall.

Anyways, now that I’ve completed the base, I’m paying attention to the tabletop, and I notice that there is some significant cupping. The concave side (the underside) goes in about 3/16” in the middle down from the edges.

Unfortunately, I didn’t check for cupping when I initially received the piece, so I’m not sure if it came like this or if I caused it myself somehow. Regardless, the damage is done, so what are my options now?

I’ve seen some articles/videos where they dampen the concave side of a cupped board and let it sit overnight to straighten it out, but will that work on my 6/4 tabletop? I tried applying this technique yesterday evening, but this morning I don’t measure any difference in the amount of cupping.

Any advice would be greatly appreciated.

Note: I don’t have a table saw, thickness planer, or jointer (I mainly use hand tools)


4 replies so far

View controlfreak's profile

controlfreak

2929 posts in 851 days


#1 posted 09-20-2021 05:50 PM

Since it has had time to acclimate I would have it re-milled prior to glue up. I wouldn’t even think about doing anything until I knew the exact moisture level of the wood in question. We are going into a change in seasons so it may not be done moving yet.

View Rich's profile

Rich

7471 posts in 1839 days


#2 posted 09-20-2021 08:26 PM

3/16” over 40 inches isn’t a huge amount. Since all the pieces are sitting there, why not see if you can pull it flat when you attach it? You can get an idea of the force needed by just setting it on the base and pressing it flat with your hand.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View HokieKen's profile

HokieKen

19440 posts in 2388 days


#3 posted 09-20-2021 08:30 PM

I’m with Rich. Any board, or glueup, is liable to cup like that if left unconstrained and leaned against a wall. And 3/16 isn’t that much over that width. I would assemble your table and see if it pulls flat. And if not, is it even noticable?

-- I collect hobbies. There is no sense in limiting yourself (Don W) - - - - - - - - Kenny in SW VA

View splintergroup's profile

splintergroup

5892 posts in 2472 days


#4 posted 09-20-2021 08:30 PM

6/4, 40” wide with only 3/16” is quite small, but you’d probably have trouble forcing it flat with whatever top mounting method you are going to use (could try however).

A uniform cup (not just a single board in the glueup) seems like a moisture imbalance. You could initially try flipping the top around and see if it begins to move the other way.

Another run through a wide belt sander means you’d lose 3/8” in thickness minimum which may/may not be acceptable.

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