warp in table top

[fred henkin]

Just built a table top 72" x 45". The boards run lengthwise. I built it in the garage and brought it in the house last week planning on finishing it this week. Unfortunately, after a few days in the house it warped (widthwise). Over the 45" width the warp is about 3/16 at the max. Any suggestions on how to get it out. The table is made of 5 boards. The outer boards are walnut and the 3 inner boards are maple. All have been kiln dried. I was thinking of setting the board warp side down and placing a humidifier under it for a while then screwing boards to the under side width wise, to help stablize it. What do you think?

[Brian Loran]

I had a table top warp on me like this. I bought some angle iron and screwed it to the bottom allowing for wood movement with elongated holes. Flattened it right out and you can't see the angle iron unless you crawl under the table. I painted the iron real nice just in case someone does though ;)

[Stephen Cherry]

Over the 45" width the warp is about 3/16 at the max. Any suggestions on how to get it out. ?

Attatch it to the table apron, it will straiten out. I like to use pocket screws for this using a Kreg jig. There should be about 3-5 screws on the end aprons, with the center pocket made normally, and the other pockets elongated by drilling a few holes side by side to form a pocket slot. You may want to throw in a screw or two on the side aprons, but not near the leg so that the apron can flex to accomodate the expansion and contraction of the wood.

If you are not using traditional aprons on the table, you will need some sort of battens screwed to the bottom. Or if the aprons are not ready, clamp some heavy wood crosswise to the top to keep it flat, or clamp it to a flat surface. I have some thick fireproof doors that I have used for this purpose.

[Jim Andrew]

I have had some wood pieces, which went crazy after being moved, straighten back up after a while. Also planed some wood, which when I checked it was dry, but after planing went crazy. Just left it alone, and after 2 or 3 weeks it came back straight. Personally, wouldn't get in a hurry.

[Nick Canzona]

Sounds like the individual boards are cupping. Not surprising for 9" boards. Assuming plain-sawn lumber, a cup will develop on the side of the board that was closest to the center of the tree. Look at the end grain. If the growth rings are oriented the same way on all of the boards, the individual cups are accumulating across the width, creating a "crowned" top. One (tedious) solution would be to re-rip, and reglue with alternating growth rings. You would be left with alternating cups and crowns on the top, but the maximun deviation should be less than 1/32", which you could plane or belt sand out. If you use battens underneath, make sure you don't attach them all the way across, or the top will split as it tries to shrink and expand in width: A pair of screws into the middle board might suceed in pulling the crown down. Before doing this, I would estimate the top's resistance to this stress by standing or sitting on the table, to make sure my weight was sufficient to flatten it. If it isn't, the batten idea probably won't work, and you risk having the screws pull out. If it were me, I would just finish the bottom of the table top with a waterborne finish--two or three coats--which should remove most of the cupping, then fasten the top to the apron or trestle, then re-examine the crown. If it's 1/8" or less, I would finish the top and live with it.

[Howard Acheson]

What did you rest the table on when you brought it inside? Was it in a position where air could by equally to both surfaces? Was it under a heat vent?

If any of these apply, sticker the panel up off any surface by 5-6 inches and give it a few days. See if it flattens out.

[Peter Quinn]

IMO it's a table top, it doesn't have to be flat like a door would. The frame will hold it flat enough for use typically. I would sticker it in the space for several weeks if possible to let it acclimate before finishing. If it rocks too much while finishing you could screw battens from below to keep things flat on e you have a seal coat on the bottom. You could leave the battens if the design allows. Just make sure the screw holes let the wood move.

[scott vroom]

For the past 2 years I've been using a hollow core interior door with 1/4" hardboard for a (reversable) top, on sawhorses, as my work table. Decent quality hollow core doors are made using torsion box technology and tend to remain very flat. The table has served me well for glue up and assembly work (and, of course, for piling junk on top of when I'm too busy or too lazy to put it away :))

In the past, I've used angle iron to straighten warped wood, as another poster suggested.

[Pat Barry]

Once it has acclimated, wouldn't the best solution be to take a little off the top and bottom, equally, thats about 3/32 on the top and 3/32 on the bottom and get it flat again? Surely 3/32 wouldn't be missed would it? Once it is flat, then get the support structure attached, and quickly before it has a chance to change its mind. Also, once it is flat again, be sure to finish the top and bottom equally to prevent a on sided moisture uptake and subsequent warpage.

[Chris Tsutsui]

I'm with Nick on his suggestion.

I was always told to alternate boards like he mentioned, if you didn't do that then I would just attach the table to the aprons and maybe use figure 8's and this will allow movement in case the table decides to turn flat again, etc...

Plus I think if the table is slightly cupped then it's a good thing because if you have spills then it can be contained in the "cup". :)

One question I have is did you use a good glue and perhaps a spring joint for the boards? With all this movement I'd be more concerned with the glue seams.

Pics would be nice too, I love walnut and maple. :)


Sounds like the individual boards are cupping. Not surprising for 9" boards. Assuming plain-sawn lumber, a cup will develop on the side of the board that was closest to the center of the tree. Look at the end grain. If the growth rings are oriented the same way on all of the boards, the individual cups are accumulating across the width, creating a "crowned" top. One (tedious) solution would be to re-rip, and reglue with alternating growth rings. You would be left with alternating cups and crowns on the top, but the maximun deviation should be less than 1/32", which you could plane or belt sand out. If you use battens underneath, make sure you don't attach them all the way across, or the top will split as it tries to shrink and expand in width: A pair of screws into the middle board might suceed in pulling the crown down. Before doing this, I would estimate the top's resistance to this stress by standing or sitting on the table, to make sure my weight was sufficient to flatten it. If it isn't, the batten idea probably won't work, and you risk having the screws pull out. If it were me, I would just finish the bottom of the table top with a waterborne finish--two or three coats--which should remove most of the cupping, then fasten the top to the apron or trestle, then re-examine the crown. If it's 1/8" or less, I would finish the top and live with it.

[Peter Quinn]

I'm with Nick on his suggestion.

I was always told to alternate boards like he mentioned...

I was taught to avoid that at all costs. Or at least to ignore it and orient for asthetics, because it was a futile effort anyway. And none other than Tage Frid also recommended against that too. The argument against alternate orientation is if you alternate boards, they still cup. But one cups up, the next cups down and so on. This creates the "waves on the ocean" effect for which there is no real cure. You can flatten it this year, it will return the next until you have scraped or sanded the top to nothing. With all the boards oriented the same way relative to heart wood you get one deep consistent cup which can easily be removed in practice with battens and stout rail structure. Most tops are 7/8"-1" thick, and over a typical 40"+- table width there is enough flex to easily correct the situation.

With panels made of rather narrow pieces, like stave cores or butcher blocks, I do orient alternatively, and it does seem to keep things pretty much in balance. But when a wide top is made up of a few wide plain sawn boards, it may not actually be the best strategy. Food for thought anyway?

Fred, I presently have a 6' long counter top on my bench at work made from two 18" wide pieces of walnut which are book matched. Its got at least 1/2" of warp to it corner to corner, its around 1 1/16" thick, and I can easily pull the warp out on install. Some times when you change environmental conditions it helps when acclimating to actually flip the entire top over several times every couple of days to allow both faces to be the "up" face for a while even if well stickered. I have seen maple tops warp back and forth in opposing directions several times before coming to a rest, if only temporarily, in just a few days time. And given we have just started heating season in much of the country RH is in a great state of flux presently. This is where science takes an advisory role and art takes a lead role. Or at least a little English?

[Rick Fisher]

I build a lot of sofa tables .. the tops are usually 19" x 55" ish.. The tops are usually not perfectly straight by the time I attach them.. 3/16" is a lot however..

I always pocket screw the top to the aprons and the slight curve just disappears.. A hand screw clamp between the apron and the top while the screws go in is more than enough..

If you can push it flat with your hands, it should be fine to screw down.. If you have to use clamps to flatten it .. it could likely crack after installed.

[fred henkin]

Thanks for all ther advise. I have flipped the table over and the warp is almost gone after 2 days. I plan to continue to flip it back and forth for a few more days before attaching the aprons and putting on the finish.

Thanks again

[Lee Schierer]

Thanks for all ther advise. I have flipped the table over and the warp is almost gone after 2 days. I plan to continue to flip it back and forth for a few more days before attaching the aprons and putting on the finish.

Thanks again

Good plan. When you go to finish the top, be sure to put equal amounts of finish on bot the top and bottom as it is mounted and allow the table top to move as it will continue to change seasonally. I like to put a slot in my aprons and use L shaped blocks to secure the table top to the aprons and the slots. This will help hold it flat and still let it move.