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

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Forum topic by DTrak posted 12-24-2015 01:10 PM 1309 views 0 times favorited 34 replies Add to Favorites Watch
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DTrak

39 posts in 558 days


12-24-2015 01:10 PM

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


34 replies so far

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JayT

4772 posts in 1672 days


#1 posted 12-24-2015 01:42 PM

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.

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.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

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DTrak

39 posts in 558 days


#2 posted 12-24-2015 01:54 PM

Sorry, you are right, it’s bowed.
That’s an interesting process. This wood is 2” thick, so I am not sure it would work, but I can try it.

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JayT

4772 posts in 1672 days


#3 posted 12-24-2015 02:01 PM

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.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

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DTrak

39 posts in 558 days


#4 posted 12-24-2015 02:02 PM

I just updated the title of this post to say “bowed” instead of “cupped”

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johnstoneb

2143 posts in 1634 days


#5 posted 12-24-2015 02:03 PM

Your best bet is probably using dowels or biscuits and cauls in the glue up to get it straightened. This will work if the bow is not to bad. Your other option is probably replace that board.

-- Bruce, Boise, ID

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fuigb

403 posts in 2418 days


#6 posted 12-24-2015 02:03 PM

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.

-- - Crud. Go tell your mother that I need a Band-aid.

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DTrak

39 posts in 558 days


#7 posted 12-24-2015 02:04 PM

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?

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fuigb

403 posts in 2418 days


#8 posted 12-24-2015 02:06 PM

Ugh, OP updated from cupped to bowed while was hunting and pecking. A bow is more manageable than a cup for a hail Mary play, but I still expect the result to be frustration with the end product.

-- - Crud. Go tell your mother that I need a Band-aid.

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JayT

4772 posts in 1672 days


#9 posted 12-24-2015 02:12 PM


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

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.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

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bondogaposis

4024 posts in 1812 days


#10 posted 12-24-2015 02:12 PM

Your best bet is to get another board.

-- Bondo Gaposis

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DTrak

39 posts in 558 days


#11 posted 12-24-2015 02:15 PM

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.

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Snipes

94 posts in 1706 days


#12 posted 12-24-2015 02:25 PM

You could put some saw kerfs on the bottom side, maybe 3 then fill in with matching wood. this would work best if it bowes up.

-- if it is to be it is up to me

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dhazelton

2322 posts in 1757 days


#13 posted 12-24-2015 02:28 PM

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.

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Pezking7p

3097 posts in 1112 days


#14 posted 12-24-2015 02:33 PM

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.

-- -Dan

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ThomasChippendale

244 posts in 393 days


#15 posted 12-24-2015 02:37 PM

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.

-- PJ

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