bowed/cupped tabletop

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Forum topic by Unionwood posted 12-11-2011 08:26 AM 2055 views 0 times favorited 8 replies Add to Favorites Watch
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7 posts in 2072 days

12-11-2011 08:26 AM

Topic tags/keywords: warp cupping bowing how-to fixing

I built a solid, vertical grain fir table top in my shop a couple of weeks ago. It was 7’ x 42” wide so it was quite large. 3×3” legs with a short 1 1/2” apron and a 1 1/2” thick top as per the customers requests. They wanted a parsons-styled table. I secured the top to the frame/apron by screwing through the apron into the table top. In my unheated shop (its winter here, just above freezing) the table was beautiful and sat perfectly flat. 3 days later the customer calls and the table has cupped and the ends(lengthwise) have raised about 1/4” from the apron/leg frame.
Anybody have any experience fixing this problem? my shop still has little-no heating and wont for a few weeks! Please help!
thanks, as always

-- Support your local

8 replies so far

View pintodeluxe's profile


4824 posts in 2231 days

#1 posted 12-11-2011 08:38 AM

To prevent problems like this, I really recommend using kiln-dried lumber that is very near the indoor moisture content. This will ususlly be 8% or less. Also, alternating the growth rings up, down, up, down etc. will help. Better yet, use quartersawn stock for the top.
I would try elongating the holes in your apron, and snug them down again. This will allow for more expansion and contraction with seasonal wood movement.

Best of luck

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Bob Cox Jr's profile

Bob Cox Jr

4 posts in 1776 days

#2 posted 12-11-2011 07:21 PM

You might want to google “uncup the cup” by Charles Neil. Several other articles will come up in the search.

-- Hoot Owl Creek Wood, Hoot Owl Creek, Indiana

View Sawkerf's profile


1730 posts in 2486 days

#3 posted 12-11-2011 08:33 PM

Although moisture may have made a contribution to your problem, I suspect that the temperature change from your cold shop to their warm house was the major culprit.

Since it took three days for the table to twist out of shape, you might try removing the screws that hold the top and let the table sit for a couple of days – it might move back to where it needs to be.

I would also use figure eights to secure the top to the leg/apron assembly.

-- Adversity doesn't build reveals it.

View Unionwood's profile


7 posts in 2072 days

#4 posted 12-11-2011 09:18 PM

Thanks all for your help! Sawerf, I agree with you and think that the temp change is the big problem. Also, wondering what exactly is it that the figure 8’s do that differs from actually screwing it in?

If i bring this back to my cold shop, i will let it sit for a couple days and then slowly heat our shop up to a closer room temp then fix the problem.

I have also made saw kerfs in the apron for Lee Valleys Tabletop Mounting Clamps but cant figure out how that differs from screws either?,41306,41309&p=40146

Thanks again!

-- Support your local

View Sawkerf's profile


1730 posts in 2486 days

#5 posted 12-11-2011 10:45 PM

I wouldn’t bring it back to a cold environment – that may just cause the cycle to repeat itself. I would separate the top from the leg/apron assembly and leave it at room temperature for a few days to see if it might stabilize like it should. I suspect that the leg/apron assembly will be ok, but the top might need to be rebuilt to get rid of the cupping. If so, make sure that the growth ringd alternate up and down, and don’t overtighten your clamps. If you’re introducing stresses during glue up, they’ll show up later.

I use figure eights because I find them easier to install, and they’re designed to allow a bit of movement. I don’t work with the temperature differences you do, but 20 – 30 between my shop and inside the house isn’t uncommon.

-- Adversity doesn't build reveals it.

View Dallas's profile


3599 posts in 1905 days

#6 posted 12-11-2011 11:12 PM

Those Lee Valley clips are meant to allow sideways movement, not to retard up and down movement.

I did a small desk for a grand daughter awhile back and the top warped after sitting in the house for a week. I took it home and after three more weeks nothing had changed so at the risk of ruining it, (at that point I didn’t care), I locked it in a closet with a warm air humidifier for about 4 days.
Once I removed it, I covered the top with a piece of laminated MDF and stacked enough cinder blocks on it to mash it completely flat. After putting it back in it’s detention closet, (solitary confinement) with a small electric heater, and leaving it for 4 more days, the top has stayed flat for the last 4 months.
What I think happened was that there was residual moisture in the wood and as it was acclimating to the new environment it dried faster on one side than the other. Putting it in the closet with the humidifier added some moisture back and then using weights and heat allowed it to dry evenly the next time.

Good Luck, I hate when things like that happen.


-- Improvise.... Adapt...... Overcome!

View 404 - Not Found's profile

404 - Not Found

2544 posts in 2387 days

#7 posted 12-12-2011 01:40 AM

Did you apply equal coats of finish to both sides? I noticed a cup come into a walnut frieze rail that I only sprayed on the face side.

View doncutlip's profile


2832 posts in 2974 days

#8 posted 12-12-2011 01:47 AM

Yeah, if moisture can get in one side and not the other it can allow a board to cup. I’ve made that mistake many times using water based finishes. It will cup upwards on the dryer side where the wood fibers are contracting compared to the other side. I also noticed this with some cheap plywood, it cupped really bad. I read about the dry side wet side condition so I clamped it down and brushed water on the dry side – and it straightened out somewhat.

-- Don, Royersford, PA

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