Straightening board that can't lose height

[Alan Lightstone]

I know this probably sounds stupid, but here goes. I've got a tabletop I'm getting ready to glue up. It's 1" teak, 28" x 48". Out of the 4 boards for the glue up, 1 has a slight cup, despite being jointed until I can't decrease its height anymore.

Is it possible to clamp the board flat for some prolonged period of time, and have the board assume the new flat shape without further machining? Or will it spring back the instant I remove it from the cauls and clamps.

The cup is a small amount, but it will be a work table in an art studio, so it really needs to be flat. It's possible that it may retain a flat shape after being glued with some cauls, but I also think it might crack.

[Frank Drew]

Alan,

If you can accept a slight loss of thickness, you might consider ripping the offending board in half lengthwise before re-flattening the two new boards, then running all your material through the planer just enough to even them all up.

If that's out of the question, you might try putting the warped board outside in the sun, with the high side up, cupped side down, maybe having lightly moistened the hollow (cupped) side. This might work to flatten the board, but no guarantees, and no guarantees the fix will last.

[fred marcuson]

it is going to spring back .. cauls may keep it flat ; but why take the chance .
if the thickness is an absolute , split the board , joint one edge pof each and add 1 of the ripped pieces to each side of the glue up .
yea i know , an extra piece in the top , but if the thickness and flatness is important .....

[Tom Rick]

I would buy another board.

~2.5 bf so a $50.00 board in these parts and the work produced has no problems- a bargain.

[James Baker SD]

+1 on Tom's suggestion. Turn the cupped board into a lamp for the studio or a frame for some of the art from the studio.

James

[John Coloccia]

my worthless opinion: fuggedaboutit. It's playing with fire.

Of course, I don't personally believe that the table will stay flat even if it starts out perfectly flat to begin with, so I guess you have to define what you mean by "flat".

Something else to consider: if you flatten it, and it's just a little thinner than the other boards, there's really no reason you can't still use it. Albeit, I've never had to do that, but I don't think of a good reason not to. Just put the lip on the under side. If there's trim around the edge, you'll be the only one that knows it's there. If it were just for my own home, that's probably what I'd do.

Maybe there's a good reason not to do that and someone will chime in.

[Frank Drew]

I would buy another board.

~2.5 bf so a $50.00 board in these parts and the work produced has no problems- a bargain.

If getting another board is an option, that'd be the path of least resistance, but, geez, teak is $20/bf??? :eek: !!

Mahogany, walnut, cherry, etc., etc., all cheaper... why does anyone use teak (except boat builders)?:confused:

[Alan Lightstone]

If getting another board is an option, that'd be the path of least resistance, but, geez, teak is $20/bf??? :eek: !!

Mahogany, walnut, cherry, etc., etc., all cheaper... why does anyone use teak (except boat builders)?:confused:
Actually, they were going to charge me $32/BF, but I talked them substantially down.

I've got many pieces of teak furniture in my house dating from the 1980's. Gorgeous stuff, impossible to find now. So matching pre-existing furniture has value to me. Unfortunately, it's not the easiest wood to work with, and costs stupid amounts of money.

The present cupped board is a great match in grain and color to the other boards. That's why I'm going through all of this.

BTW, which method do you all think is best if I do try one more thin pass to face joint the board. I've got a Laguna SCH 12" jointer/planer at home.

1.) Just use the jointer, and pray there isn't any snipe which would create a new problem.
2.) Build a jointer sled for the planer and run the board through the planer to face joint the board. Looking at the plans and article about one, I almost wonder if its easier to joint wider boards with the sled through a planer than with the jointer.
3.) Take John's advice and fuggedaboutit.

I thought about the clamping / cauls approach, thinking about how wood is steam bent into curves that take on the new shape. Of course, that's thin boards, not 1" teak. I knew it wouldn't work, but I had to ask.

[Bill Davis]

Is it possible to clamp the board flat for some prolonged period of time, and have the board assume the new flat shape without further machining? Or will it spring back the instant I remove it from the cauls and clamps.

The cup is a small amount, but it will be a work table in an art studio, so it really needs to be flat. It's possible that it may retain a flat shape after being glued with some cauls, but I also think it might crack.

I agree that gluing it with cauls it is not likely a solution unless you make the cauls a permanent part of the design. Wood moves with changes in the moisture content of the wood and that depends on the relative humidity of its environment.

"More than 90% of all problems with wood involve moisture."

When uneven shrinkage or swelling occurs distortion called warp is the likely result. In your case it sounds like the board is cupped and that can be verified by looking at the tree rings from the end of the board. Teak is one of the most stable woods as far as tangential and radial shrinkage but it is subject to dimensional changes - only less so than other woods. My guess is that the wood was not properly seasoned or dried before machining. But that is in the past and you have to deal with the result. You haven't stated what your average relative humidity is or what the RH at the location where the table will be actually used but even if you make it perfectly flat in your shop then move it to it's permanent home which has a different RH warp can re-occur.

IMO, one of the usual ways that are used in dealing with these problematic dimensional changes that might apply in your case - using mechanical restraint in the design/construction of the table. In other words using a stable material, whose strength is greater than the wood to hold the board flat and prevent it's shape from further changing. In other words attach the bent board firmly to a bracing material to hold it straight. To help minimize further dimensional changes (and they will occur with changes in RH) apply a finish that will slow down the moisture content changes in the table. The forces in shrinking and swelling wood are strong so be careful because spliting may occur.

If it is a critical job it might be more advisable to start with a new replacement board and be sure it is stabilized at the proper moisture content before machining it to the proper size.

[Neil Brooks]

I think both of my preferred options are pretty well covered: new board, or ... what about breadboard ends ?

There's ... some risk with that piece. My first thought WAS glue it, and then rip it NOT on the glue line, but ... to John C's point: playing with fire.

My $0.02.

YMMV :)

[Alan Lightstone]

I agree that gluing it with cauls it is not likely a solution unless you make the cauls a permanent part of the design. Wood moves with changes in the moisture content of the wood and that depends on the relative humidity of its environment.

"More than 90% of all problems with wood involve moisture."

When uneven shrinkage or swelling occurs distortion called warp is the likely result. In your case it sounds like the board is cupped and that can be verified by looking at the tree rings from the end of the board. Teak is one of the most stable woods as far as tangential and radial shrinkage but it is subject to dimensional changes - only less so than other woods. My guess is that the wood was not properly seasoned or dried before machining. But that is in the past and you have to deal with the result. You haven't stated what your average relative humidity is or what the RH at the location where the table will be actually used but even if you make it perfectly flat in your shop then move it to it's permanent home which has a different RH warp can re-occur.

IMO, one of the usual ways that are used in dealing with these problematic dimensional changes that might apply in your case - using mechanical restraint in the design/construction of the table. In other words using a stable material, whose strength is greater than the wood to hold the board flat and prevent it's shape from further changing. In other words attach the bent board firmly to a bracing material to hold it straight. To help minimize further dimensional changes (and they will occur with changes in RH) apply a finish that will slow down the moisture content changes in the table. The forces in shrinking and swelling wood are strong so be careful because spliting may occur.

If it is a critical job it might be more advisable to start with a new replacement board and be sure it is stabilized at the proper moisture content before machining it to the proper size.

Wise advice, I'm sure. Your mechanical restraint idea is intriguing. Not sure how I can work it into the finished design, however. Not sure how the LOML would respond to a table top with cauls and parallel clamps permanently attached to it. :)

RH here in Hot as Hades FL is about 53% indoors, and about 300% outdoors (actually, 80% outdoors in my woodshop, 60% with the AC on).

The equilibrium moisture content in the location that the table will be used is 9.6% (76deg, 53%RH). The teak is presently at 10.1% moisture content.

[Bob Direso]

I saw Norm Abrams flatten a board by cutting halfway through the board on the tablesaw at the center of the cuped area on the bottom side of the board. He then pressed down on the board to flatten it and completed the glue-up with the board in cauls. He then filled the saw kerf with epoxy so the board's strength was not reduced. Bob.

[Stephen Tashiro]

To use boards like pine 1x12's that I buy at the hardware store, I sometimes rout a channel about 2" wide and 1/2" deep down the entire length of a cupped board (on the side that is the peak of the cup). Then I "inlay" a strip of wood in this, at the same time clamping the board flat. I use a weak rubbery glue like Gorilla glue. As often as not, the board doesn't come out exactly flat but it comes out so limp that I'm don't worry about it resisting being held flat when it is screwed down to something else. Of course, this is just a technique for crude carpentry projects.

I've tried Norm's method on 1x12's too. But I find that I have to cut five or six parallel saw kerfs. Cutting and filling several saw kerfs is more laborious than dealing with one wide inlay and I don't think the results from saw kerfs are any better. It would be great If there was a saw blade that left a kerf narrow enough so that the bending would close the kerf. However even the very thin table saw blades leave a kerf that stays open.

[rick carpenter]

Easiest if you had enough thickness to the boards would be to saw a kerf lengthwise and glue and screw a section of small angle iron, possibly even routing the board bottom so that the a/i doesn't any sit thicker.

[lowell holmes]

I successfully straightened 8/4 walnut one time. I ripped the bowed boards exactly down the center. I dowelled the two halves back together and glued them. The halves doweled were from the same board and the bow in each half was opposite each other. They were straight enough to make a boardroom door.

[Eiji Fuller]

I didnt get how far from straight it was. If its just a bit cupped and the boards around it are straight you can just glue up the panel and align the boards during glue up. The straight boards around it will keep it flat. Im only talking at most 1/8" in 6'. Ive done countless glue ups and sometimes your boards dont stay perfect after milling. This method works.

Now if there's twist it is a different story.

Good luck

I went back and re-read the original post and if its only a slight cup you shouldnt have any problems. Just put it in the middle of the panel and the others should keep it straight. if there's an issue you can also add a cross piece to the apron and fasten the middle of the table top to that from under. If its not wanting to align without significant pressure then you could alway put a kerf about 1/2 to 2/3 thru that board to relieve the stress. Obviously on the under side and if place in the center it will never be seen and cause you no future trouble.