Fixing a cupped board tabletop - Woodworking Talk - Woodworkers Forum
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post #1 of 5 Old 08-21-2015, 10:09 AM Thread Starter
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Fixing a cupped board tabletop

Hello everyone,

I built a farmhouse style table about 6 months ago from this build.

I wanted it to be rough and simple, however
One of the 2x10 boards have developed significant cupping (as shown in pictures attached). I was trying to research how to fix this and I am somewhat confused on the best way to go about it. It seems I could try a few different things that may or may not work permanently.

The boards (2x10) that comprise the table top are horizontally joined with pocket screws.

I have concluded that my options are
1)Wet the concave surface (in this case the top finished side) and try to clamp it flat and allow it to dry

2)Heat the convex surface (in this case the bottom unfinished side) and clamp

3)Do a combination of #1 and #2

4)Make kerf cuts on the bottom of the board, fill with a spline or other wood filler and clamp flat


I would appreciate any advice, I really do not want to replace the board because we used a vinegar steel wool stain that would be hard to replicate the exact color.
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post #2 of 5 Old 08-21-2015, 11:38 AM
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Heating the material to straighten it is a temporary solution. Sealing all sides of a project does help considerably regarding moisture absorption but supplies no help in seasonal heat expansion regardless of a ply/lam mat or solid wood.

Regarding the 2nd video, I would have kerf cut the flat sawn wood on the inside of the ring pattern as opposed to the outer. The number of kerf cuts would depend on my method of fastening the mat to the project. In all the remods I've been involved with, one thing I always found regarding door frames and thresholds the back and bottom sides were always kerf cut to prevent cupping. I also would not have cut as deep as the man in the video, that weakens the mat at the cut enough to possibly cause a split during a shrink stage.

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post #3 of 5 Old 08-21-2015, 10:24 PM
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Remove the pocket screws first.

Recut along your existing gluelines, rejoin and reglue after checking for proper fit.

Hard to tell you the best / easiest way to fix it without knowing what sort of tools you have available to use.

How you fix it if all you have is a router and circular saw is different from how you fix it if you have a tablesaw and joiner with long tables. Also depends on the clamps you have available.

On projects like the one you pictured - I generally like to clamp down against a flat suface while clamping things together at the same time.
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post #4 of 5 Old 08-21-2015, 10:34 PM
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When you finished the table top did you finish the underside of the top too? You should always finish both sides. Normally to flatten a cup warp you wet the cup side to raise the moisture contact to that side of the board. Since the cup side has a finish on it I think the best fix would be to cut the warped boards out of it and do the top over.
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post #5 of 5 Old 08-22-2015, 01:59 AM
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no coffee in that cup....

That is typical of plain sawn or flat sawn wood. Here the arcs face down the wood cups upward:

I doubt if kerfing from the bottom will work all that well, since the joints want to spring open. Kerfing on the top won't look right if you fill the kerfs with wedges. so, now what?

A. use a different type of wood milling process, quartersawn is best. In other words, replace the board(s)

B. Resaw the wood into 2 thinner planks, flip one over and glue the opposing halves together so they will counteract one another. You can still have your stain on the top and keep the look you want. You will loose some material from the kerf, but it can be replaced with a thick veneer in the center.

C. They will always want to re-cup, if you try to un-cup them. I have run out of other ideas....

one other idea:

another other idea:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 08-22-2015 at 02:34 AM.
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