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I want to make table tops from left over 2"x 10" pine. I made an initial test one by squaring each side; then planning them to 1.25"(this was the width that allowed me to remove the board warp);then I routed a finger joint full length;glued and clamped together. When clamping together I also clamped boards crosswise across the top and bottom to stop it from bowing or warping. It turned out well, nice and flat, however, after finishing it has started to bow. I also noticed that the other boards I prepared, using the same technique as above, began to warp. I have seen tables done without framing that look great and are flat. What am I doing wrong, or what am I not doing to insure the top stays flat?

Thank you for any expertise anyone can share.
 

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I want to make table tops from left over 2"x 10" pine. I made an initial test one by squaring each side; then planning them to 1.25"(this was the width that allowed me to remove the board warp);then I routed a finger joint full length;glued and clamped together. When clamping together I also clamped boards crosswise across the top and bottom to stop it from bowing or warping. It turned out well, nice and flat, however, after finishing it has started to bow. I also noticed that the other boards I prepared, using the same technique as above, began to warp. I have seen tables done without framing that look great and are flat. What am I doing wrong, or what am I not doing to insure the top stays flat?

Thank you for any expertise anyone can share.
How old was the PIne? Years old? or fresh for the yard?

A few words to share on that... Usually when you join wood together for a table top, cabinet door, floor. etc. .. and do a glueup, you use woods that are a width or 1-1/2" to 4-1/2", depending on the wood. Then as you lay out for the glueup, you look at the grain at the cross-section and alternate between pieces how the grain is oriented...

If you orient all the wood one direction, it will cup towards the direction of the rings. If you go too wide a board with a glueup... wide boards, especially wiht soft wood, with open grain, the wider is is, the more it has a tendency to cup.

Especially with pine. In the spring, out a piece of pine out on some grass and watch it bend and twist. I know this seems strange to have a 10" wide piece, to rip it down to 3" wide strips to make a table top... but that is the why.


So don't dispair. You could rip it down again... flip the pieces to reorient the grain... to retool glue-edges, do another glueup and not loss that much width. Of course if the thickness was thicker, then it has less tendency to warp.
 

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+1 on Mike's solution:)
 

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All good input, but I would lime to add that milling twice can sometimes be a usefull approach.

The first time you mill it leave some on it to be milled to desired demensions later. This way you get a chance to see what the wood will do after being relieved of the stress removed on the first milling.

You don't have to use a bread board but wide boards can really be tuff to use without them. One reason is that wide quarter saw lumber is tough to fine "cheap". Check the ends and if you see two portions of the ring in one board and if you do you will likely have a hard time ending up with a flat board.

Of course all I've said is based on my novice experience and there may be much better input than mine here to be had ;)
 

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When you say 2x10, you must mean 1.5x9.5, therefore you only removed .25 inch. It sounds like you ran into a problem of uneven surface tension when you planed the boards. Planing releases surface tension. Also uneven moisture content. Sometimes I will turn a glue up or a board over, wet one side and leave it in the sun. Often it will flatten out. More narrow boards, as the other forum members have already mentioned, will help or eliminate the problem. The other important factor is applying the same amount of finish on the underside as the top, again, to balance the surface tension.
 

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Wood moves. Even bone dry and sealed it still has some movement. Look at the end grain. In most timber (unless it is quarter sawn) the end grain is arched (not parallel with the surface). To minimize warping (cupping) cut ""narrow strips and orient them with the end-grain arches alternating in direction "unununun" (this is intended as a graphic). Narrow is relative to the thickness of the timber and the arc of the end-grain. The appropriate width depends upon the arc of the end-grain (the more arch the narrow the strips), the distance between the hard and soft wood, and the type of wood in the grain. A bit of experimenting can help. Glue up a few samples, soak them in water for a few days and leave them in the sun until they thoroughly dry. Watch what happens. Select the arrangement that shows the least movement. Another solution in some timbers is to use narrow strips and orient the end-grain (alternated as before) laterally (side to side across the intended surface ()()()()(). The "downside" of this arrangement is the potential for the glue joints to be forced upon if the wood swells significantly. If stability is intensely critical use quarter-sawn timber which has a vertical grain. Quarter-sawn timber will shrink and swell but "cupping" is minimized. Quarter-swan timber is expensive and can be hard to find. Look to someone who sells timber for boat-building, steam-bending, or fine furniture.
 

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Discussion Starter · #8 ·
All this makes sense. To clarify, I am using dimensional lumber. It has been in my garage for over 1 year. I did alternate the grain, great use of computer keys by the way to illustrate, but I think using too wide of boards coupled with soft pine is my main problem. I did experiment and the wood I squared, planed, routed and glued in the same day, then began sealing 48 hours later did the best with respect to individual boards. However, I only sealed the top side, so the point about sealing the underside makes sense as I have some "cupping" across the entire 3 boards at one end. The boards I squared and planed then let sit, all cupped in the direction of the grain. Looks like my best solution is to rip boards into smaller widths and do more seams to achieve my desired total width. I am looking to make table tops 30" x 30".

Great experience, great advice. I hope I can one day returns some knowledge to everyone.
 

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One other thing that can help: when you are planing your material be sure to make a pass on the bottom side as well as the top. This way both sides will "breathe" the same amount. I am sure finishing both the top and bottom will cure your problem.
 

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To add to the notes on surface tension... If you are going to seal something, seal both sides.

Like has been said and experienced time and time again "here" on just router table tops... If you seal just one side, you create potential surface tension differences between the two sides... where one side is sealed and the surface more dense than the opposing side. The two sides will expand and contract (from various environmental and "other" factors) at differing rates... That in itself may cause cupping and warping.

That can also happen if you take old wood and plane only one side, exposing the fresh surface to changes, while the other side pretty much static remains static. Even if you only plane one side, if you just do a light side on the offside, that might even the tension between the two.

I hope those explanations make sense to you. Wood is an ever changing medium. We try to incorporate that into our plans and adjust for it.
 
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