Flattening warped table top

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Forum topic by Bradb7888 posted 05-22-2017 04:04 AM 721 views 0 times favorited 4 replies Add to Favorites Watch
View Bradb7888's profile


13 posts in 1139 days

05-22-2017 04:04 AM

Topic tags/keywords: table walnut finish warping humidity

I’m working on a walnut coffee table top and have a question about keeping it flat.
I have done some reading and talking to friends since I made the table top and now realize I should alternate the grain pattern so one board grain cups up, one cups down, etc. I will probably use bread boards in the future as well..
Unfortunately on this project I did not and my table top has a 1/8” bow on both ends. I currently put the long sides on some walnut 2×2s and put a few pieces of railroad in the middle to weigh it down and over the last few days it has flattened out. It’s actually perfectly level right now but I’m curious if this will last long. I’ve already put a few layers of tung oil and waited several weeks for it to dry and built the bottom and painted it so I would hate to add bread boards and have to oil them and rebuild the bottom..
I don’t know much about relative humidity but it’s in my non air conditioned/minimal air flow garage in Tennessee if this helps. I plan on adding a few coats of wipe on poly and bringing it inside. Does any one have any insight as to if it will warp again or what I can do to prevent future warping?

4 replies so far

View TheFridge's profile


10859 posts in 2097 days

#1 posted 05-22-2017 04:07 AM

Battens. Or if it’s a typical table the aprons will do it if it’s not too bad.

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

View Woodknack's profile


13026 posts in 2991 days

#2 posted 05-22-2017 06:31 AM

Depends on why it warped. 1/8” isn’t much, it could just be a fluke of the wood but generally tabletops cup because moisture is moving in or out of one side more than the other. Did you finish top and bottom equally? Did you lay it flat on the saw/table/floor cutting off air flow to one side? Did you finish one side and leave it for a few days before finishing the other side? I agree with Fridge though, that the aprons will probably keep it flat if it was only 1/8” out. Or battens if you won’t have aprons.

... I should alternate the grain pattern so one board grain cups up, one cups down, – Bradb7888

Myth, don’t bother. It doesn’t prevent cupping. Arrange boards for best appearance.

-- Rick M,

View bondogaposis's profile


5610 posts in 2962 days

#3 posted 05-22-2017 12:41 PM

Should be fine. 1/8” isn’t much across a table top, depending on the size of the table of course. I should suck down when you attach it to the base.

-- Bondo Gaposis

View Robert's profile


3605 posts in 2091 days

#4 posted 05-22-2017 01:05 PM

It depends on how thick the top is, but if 3/4’ you should be able to take out most of that bow with the breadboads & the rest when you mount to aprons. You may have to make the overhang short, like 1”. Keep a batten clamped the whole time you’re doing it & make the tenons as long as possible for maximum strength.

Like RickM, I also don’t alternate growth rings for panels. Grain matching/grain direction is far more important to me. Nothing worse then hand planing a top with grain direction going opposite ways from board do board.

Everything depends on wood being acclimated and how you are storing your panels after glue up. This is HUGE. After glue up, keep your panels in clamps and stickered or wrapped in plastic to minimize movement. One big mistake I used to make was keeping glued up panels in an non-climate controlled shop. Disaster & frustrated used to await me the next morning!

-- Everything is a prototype thats why its one of a kind!!

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