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Flattening a large bowed piece of wood w/o losing thickness

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DTrak

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Discussion starter · #1 · (Edited by Moderator)
I am making a 100" table top and now have all my boards more or less flush on the sides (in case you saw my question yesterday about that). One of them is cupped and therefore rocks when it is laid on the floor with the others. It is 8"x100". Even if I had a joiner that could handle that, I cant remove any thickness because all the boards are currently the same thickness so this board would not line up. Is there some other method? Can it be bent somehow? If I put some heavy weights on the ends and then screwed it into the other boards, would it hold?

thanks
 
#2 ·
First off, is it cupped or bowed? Talking about weights on the ends makes me think you are actually referring to bow. Cup is warp across the face, while bow is warped down the length of the board.

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If you are really talking about cup, then the only success I've ever had with "fixing" a cupped board was to take a spray bottle and mist the concave face of the board, then lay it out with the convex side up for a while in a place where it'll dry-like out in the sun or a heated shop. The cupping is a result of moisture leaving the board unevenly. Doing this process helps to equalize the moisture.

No guarantees it'll work. I've had it work perfectly (then stored the board in its edge to prevent it from happening again) but more often the board tries to cup again because the grain structure in flat sawn boards allows moisture to leave from one face faster than the other.
 
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#4 · (Edited by Moderator)
Doesn't usually work for bowed. Nothing hurt by trying, but a lot of bow is the result of tension in the grain of the wood. How have you been storing the wood? If you've had it laying flat, try standing it on edge with at least an inch of air on both sides for several days and see if allowing the moisture to equalize gets it closer to straight on its own.

Sounds like the wood was not properly dried before you got it. A dry 8/4 board shouldn't move much.
 
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#7 ·
Doubt that anything short of flattening/jointing the board and its peers will deliver professional results. Sorry for the buzz-kill.

Is the heart of your question an unwillingness (inability? ) to flatten and then remill all of the boards in the top? Just asking because while I sympathize with the desire for an easy solution I'm also curious as to why flattening isn't the solution that you settled on, however reluctantly it may have come.
 
#10 · (Edited by Moderator)
If I hold it down flat with weights and then screw it into the adjoining piece with lots of pocket screws, would that hold it flat?

- DTrak
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Maybe. As the others mentioned, since bow can be dealt with easier, it could work, depending on how bad the bow is. It could also screw up the entire project. Depends on how much tension is in the bowed board and how much more it wants to move. You might also consider a cleat across the bottom, with the center screwed down tight and screws in the outer sections in elongated holes to allow for seasonal movement.

Doesn't really matter how many screws, glue, etc you use, wood will move. That is why we try to start with dry, stable stock to begin with. That wood has already shown how it wants to move.
 
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Discussion starter · #12 ·
The reason I can't flatten and remill all the boards is I don't have access to a joiner. And dont want to buy one just for this purpose. But even if I could, these boards are 8" wide and any joiner under $1k is 6" wide.

I can't replace this board because it is a live edge that matches the other live edge on the other side of the table. top.
 
#14 ·
If it's a very minimal bow, I'd do the glue up keeping the ends of the bowed board flush with the ends of the adjacent boards, and have the bow facing up. Then use a hand plane or belt sander to flatten that board flush with the surrounding area. If it's two inches thick you can remove quite a bit before you have to be concerned about anything.
 
#15 ·
I would recommend a hand plane. Get a #5 or a #7 - #5 will be cheaper, but not as easy to get your board flat as with a #7. For this scale of project and because it's a table top, I would go with a #5 because perfectly flat is not super important, it just needs to look flat and contact your underlying table support in all locations.

Now, I recognize that suggesting you go get a hand plane opens up a whole other can of worms - sharpening, flattening boards by hand, using a hand plane in general. But to be honest, there is plenty to learn with a power jointer as well, maybe more so because a jointer's operation is not always intuitive (I almost quit woodworking trying to get mine to work correctly).

Anyway whatever you decide, check back because we're here to help.
 
#16 ·
It all depends on how much effort (force) is required to bring it in line while it is being glued to the adjacent boards. It is normal in a glue up to have boards bowed slightly and to tap them in place while in the clamps at low pressure to even them so when planing the entire surface, you loose less thickness.

It is easy to figure, place the board bowed side up and press it down, if you can flaten it with your hand just pushing down, its fine, it will not distort the entire table top.

If you require standing on it to bring it down flat, then, if you absolutely want to use this board and the underside and edges are hiden, you could cut a serie of kerfs, evenly spaced along its length, say ay every 6 inches and 3/4 of the thickness and make it more flexible, once glued-up it will not weaken the table top and the entire assembly will be more stable.
 
Discussion starter · #18 ·
Thank you all! I dont think I want to plane it because all the boards need to stay the same thickness. Dont feel like getting into the steaming idea although it's great to know and will come in handy.
The bow isnt that bad, so I think I will try glue and lots of pocket screws. I have gotten very comfortable with a kreg jig.
thanks again
Dan
 
#19 ·
+1 for dhazelton's idea. The "thinner" part will be on the bottom, and will be in the middle, thus not open to inspection.

I think trying to bring it back with pocket screws & glue and holding it firm will not work over time. It will win out and bend another plank, and you will end up with a warp in the tabletop.
 
#20 · (Edited by Moderator)
With your parameter of all of the boards needing to be the same thickness, you are pretty much SOL. Even with a jointer and planer rework, you will lose some thickness. Steaming is a decent idea, but extremely hard to do with a 100" piece. Not wanting to replace the board, plane it down etc, you are pretty much out of options short of forcing it in plane with dowels etc. kerfing the bottom and/or putting cleats across the bottom at 12-18 inch intervals, but that is a short term fix only. The bad board will win out in the long run. I wish I had a magic bullet for you, but I threw mine out with my old board stretcher and a box of old chrome muffler bearings. :-( Sometimes you just have to say: " Well ********************" and move on with a complete redesign etc. Good luck, work safely and have fun
 
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