Bowed Top Help!!

[Thomas Tukiendorf]

I spent two afternoons staring at a 90% done piece of furniture and can not make the next move, need help! It is for a customer who supplied the wood which came off his property, his only requests really was that it be made of his wood. The two boards I have for the top are a sweet match, the front one in the pic is jointed, plained and flat at one inch. The rear board is down to an inch and has even bow over its 68 inch. length, with the two boards ends lined up the back board crests at .210 of an inch in the middle. The board has an even bow, i can push it down in the center easy enough that has me thinking of doing some things that I normally wouldn't. The top will be attached using those z shaped things screwed to top and float in a groove in the aprons. Is my problem as simple as a stout spline? I am sure that it can force the two boards to except the spline, but what will happen later. Design wise i was hoping to keep the top as simple as just the two boards. The scale of the piece is big and the 1 inch is already a little thin. Any suggestions?
222936

[Andrew Pitonyak]

I have no experience, but, I thought that the prevailing wisdom is to use battens on the underside of the table. As an example, see Mike's response (#6) here: http://www.sawmillcreek.org/showthread.php?130827-table-top-warping

Elongate the holes....

Really like how the top looks (by the way).

[Conrad Fiore]

Thomas,
If you can put one or even two support rails under the table to pull down the bow, the boards will expand and contract along the width. You can use additional "Z" clips on those rails and the boards will expand and contract without problems.

[Mike Wilkins]

Must be something in the air, because I also was 90% complete with a project when the table top I painstakingly jointed, glued, and sanded to perfection decided to develop a nice potatoe-chip shape while I was working on other parts of the project. My problem was likely due to the wood not being dry enough, or sitting outside un-covered before I purchased it. I have to start over.
In your case, a couple of splined or battens screwed to the underside through elongated holes should do the trick. Good luck.

[Lee Schierer]

With that small amount of bowing, I would force the bowed board flat as I glue up the two pieces. There is no need for a spline if you can keep the surfaces aligned as you apply the clamps. Place the bowed board at the front so that your z-clips will hold the front against the face frame which will work to hold it flat. You could even use screws to hold the front to the face frame and let the seasonal movement happen at the back with the flat board.

[Thomas Tukiendorf]

It's the El Nina torture test, one week shop doors and windows open, next week heat blasting, so on and so on.

[Mike Cutler]

Thomas. I think a spline along with the other supports will be fine.
.210 can be alot, but over 68" is not that great of lever force.

[Todd Burch]

I'm in the Mike Cutler camp. I would glue them up, aligning with your preferred flavor of a spline if you want. Once they are glued, they will move as a single unit, and no one is going to notice 1/5 of an inch (and it won't be that much, I think at max, 1/2 of 1/5") over 5 1/2 feet. Just remember to not mention it to your client!!

Did you stack your top pieces on top of each other, and the one that is bowed was on top? If you did, you can't be doing that. Always cover the top board in a stack of boards (or even a stack of ply), even for short durations of periods. ("Too long" to stack and not cover, in my shop rule book, is > 15 minutes!)

[Edward A Miller]

A batten or a couple of them should resolve the issue, This/these will also serve to stabilize the lower support frame. My suggestion however would be to securely fasten the batten(s) to the frame, but leave a small gap, even as much as 1/4", between the top of a batten and the underside of the top even after it is pulled flat. This space should allow for eventual lateral movement (float) of the substantially thick solid-wood top.

This will enable your top to be a smooth plane on both sides. If a heavy duty connection is needed into the underside of the top, threaded inserts could be inserted so machine screws could be used as fasteners.

From a purists perspective, a butterfly/bowtie spline(s) could be inlayed into the top at the wood joint seam and have a shaft that extended downward into the frame cavity. The lower end of the shaft could have a rectangular mortise thru which would pass a slightly tapered wedge that when pushed further into the slot a downward pull on the top would be created. If the joint design is such that a compound taper is used, it would not only serve to draw the boards together, but provide the downward pull from below; it would be possible for this wooden feature to be independent of the top so it could be taken in and out (showoff!).

Occasionally, I have installed butterfly splines where a larger timber has checked in order to halt further wood separation and also give the project a 'handcrafted' look. FYI: This also says to the viewer, "Yes, I know about the check!" I admire good butterflied grain, but it can resemble veneered plywood! This concept is rather extreme, but if one likes to showcase wooden joinery, brew another pot of coffee and go for it!

Whatever your choice of remedy will be, your project will be beautiful because you care!

[Bill Wyko]

I read somewhere to lay a board down on the moist lawn curved side down. That was suppose to take out the curve in a plank that's showing signs of curve. Once you got it straight you could join the two and clamp it flat until it cures.

[Neil Brooks]

Must be something in the air, because I also was 90% complete with a project when the table top I painstakingly jointed, glued, and sanded to perfection decided to develop a nice potatoe-chip shape while I was working on other parts of the project. My problem was likely due to the wood not being dry enough, or sitting outside un-covered before I purchased it. I have to start over.

+1

In the "notes to self" column, I need to add ... check stock with metal detector AND moisture meter, before machining (in addition to letting it acclimate AFTER machining !).

I've got a bowed lodgepole (beetle-kill) pine leg, on my Shaker Hall Table, now. It bowed about 3-4 days after glue-up, even though I thought I gave it enough time to acclimate.

I decided to live with it. Will probably regret that decision, over time, though ;)

Near right leg. It's not that noticeable, in the pic, but you can see that the leg bottom doesn't sit flush. That's the warp :(

https://lh3.googleusercontent.com/-Nb_uyO9S6QM/TysXUqghkXI/AAAAAAAACeM/aUOiNlDbSfg/s640/P1050421.JPG

[Todd Burch]

...It's not that noticeable...

:D And I don't have a drinking problem - I can stop any time I want. :p :p

[Neil Brooks]

:D And I don't have a drinking problem - I can stop any time I want. :p :p

Okay. It's THAT noticeable, and ... I'm currently raising a glass of red TO your drinking problem :p

[Stephen Cherry]

I wouldn't worry for two minutes about this- just remember that in clamping, worry about flattness, together will take care of itself.

Also, an apron in a normal table will hold it flat. I like Kreg screws and elongated slots better than anything else for holding a table top on- you can get some real down force with a screw that is not very tight.

[Thomas Tukiendorf]

thanks all, will post some photos when done.