Dealing with bowed boards

[Hoang N Nguyen]

Hi guys, I'm in a bit of a pinch right now. After jointing and planning some 8/4 soft maple, 5 out of 7 of my boards are slightly bowed. I assume it has to do with the 5 days of rain we've been having and the fact that I jointed one night, planned the next. The boards are 8' long and when I lay a 4' straight edge over the center of the board, I have about a 1/16" gap. The boards do straighten out if I apply a little bit of pressure in the middle. I plan to join 6 boards together to make a table top.

My question is, can I alternate the bowed boards (1 cup up the next down) and use dowels in between the joints, will it be enough to force the boards together and counter each other to keep it straight? I always use dowels when I join boards just to help with alignment. The table top will then be sent through a drum sander once all joined together. The table will also be attached to an apron so I'm guessing that will help pull the boards down as well. What are your thoughts?

Thanks,
Hoang

[John TenEyck]

I think you mean the boards are bowed end to end, not cupped across the width, correct. In any case, using wood that's not straight and true to build a table top with is just asking for more trouble. Your plan may work, but it may not and then you've got even more invested in it. Better to start over. But first, wait on your boards for a few days and see if they straight out on their own. If the problem was due to a difference in MC they may straighten out when they equilibrate.

John

[Hoang N Nguyen]

Yeah, I meant bowing end to end. Title and thread body fixed.

I could joint and plane them again but that would take off too much material and I would end up with a really thin table top. I'm guessing that would take me down to around 1.25" and I want at least 1.5" thick.

[lowell holmes]

I made a 7040 door for a bank conference room one time using 8/4 x 8 walnut that came to me bowed. I ripped each board down the middle and glued the pieces back together with bow's opposite each other.
I used dowels every 12" to align the wood. I joined the surfaces and you could not see the seam. The door is straight and still standing. The door had a large glass panel in it.

You might try straightening one of the board and see if it works. You could use biscuits to align the bowed boards.

I didn't know better in those days.

[Max Neu]

I think if you had just a slight bow that requires minimal pressure to flatten,you should be able to add a brace from underneath to keep it flat,assuming the design of the table will hide it.

[Larry Browning]

Ok, unless I am misunderstanding the problem, you are saying that the edges of the boards are not perfectly straight, 1/16 of an inch over an 8 foot length? That seems pretty minimal to me. It would not require much clamping pressure to close that small of a gap when edge gluing. I can see making a couple of passes on the joiner to straighten the edge as well, but why would you need to run it through the planer again? What am I missing here?

[Hoang N Nguyen]

dining table.jpg

I made a 7040 door for a bank conference room one time using 8/4 x 8 walnut that came to me bowed. I ripped each board down the middle and glued the pieces back together with bow's opposite each other.
I used dowels every 12" to align the wood. I joined the surfaces and you could not see the seam. The door is straight and still standing. The door had a large glass panel in it.

You might try straightening one of the board and see if it works. You could use biscuits to align the bowed boards.

I didn't know better in those days.

What you did is exactly how I plan to make my table in hopes it will fix the bow.

I think if you had just a slight bow that requires minimal pressure to flatten,you should be able to add a brace from underneath to keep it flat,assuming the design of the table will hide it.

Yes, the table will have 2 supports spaces out evening between the apron length wise. I plan to use http://www.rockler.com/table-top-fasteners these from Rockler to hold the table top to the aprons. From what I've read, they hold the table down really well while at the same time allow for wood movement. I will use the same hardware at the center supports to help pull the center down if needed. See attached picture for what I mean.

[Hoang N Nguyen]

Ok, unless I am misunderstanding the problem, you are saying that the edges of the boards are not perfectly straight, 1/16 of an inch over an 8 foot length? That seems pretty minimal to me. It would not require much clamping pressure to close that small of a gap when edge gluing. I can see making a couple of passes on the joiner to straighten the edge as well, but why would you need to run it through the planer again? What am I missing here?

Not the edge of the board but the face of it.

[Larry Browning]

Not the edge of the board but the face of it.

Ahh, my bad! But even that is is not much at all, especially over an 8 foot length. And, didn't you say it was to have an apron? Attaching the top to the apron should take care of such a minor bow. I just don't see this as a problem at all. Wood moves all the time. Who's to say that it wouldn't do it again even if you started over? That bow will probably disappear once you glue the boards together anyway.

[Robert Engel]

Funny, you would expect cupping, not bowing.

Anyway, my opinion? Thats not enough of a gap to worry about. I would be perfectly happy if that's all I had to deal with on a table top.
Yes is will pull down flat when you attach to apron.

Much bigger problem is cupping, both individual boards and after the panel glue up.
You won't know what you've got until the glue is dry.
If you experience this you'll be thankful you've got the extra thickness to deal with.

Just wondering, why such a thick top for a table? Is it a design preference?
1" would be fine if you needed to do more surfacing.

[Wade Lippman]

I vote with the "ignore it" group. 1/16" over 4' is pretty trivial. Good excuse to buy a biscuit cutter. (I would recommend a domino, but that might be a little overkill)

[Tom Deutsch]

Not worth worrying about. This is why folks make table tops out of plywood and band the edges - because they can't stand the slight irregularities that a hunk of a tree is going to have.

[Mike Schuch]

You have seven 8' boards all within 1/16" of each other with respect to bowing and your are complaining? I call that winning the lottery!

For a large table top like that getting boards as flat as you have is pretty fortunate. Yes, use dowels and alternate the bows and you should be fine. Try to keep the glue up as flat as possible while the glue is drying. Any bow induced in the glue up while the glue is drying will be very hard to straighten later.

[Davis Young]

I am with the others that it is not a big deal. However, I would not alternate the bowed boards. If the grain match allows, I would put the two straight boards on the outside and four of the bowed boards on the inside with the bow up (convex on top). If you can use cauls or whatever to flatten the boards at glue up, then fine. If you're worried about the bowed boards "corrupting" the straight boards, then you can glue up without flattening and then take out the convex afterwards in the drum sander. The edges and ends will still be at full thickness with the bottom being slightly dished.

[Mel Fulks]

I'm betting you faced with concave side contacting jointer. You will have better result with convex side down. Yes, you have to be careful. Hold down on infeed table til end of board is safely on out feed table then hold down on out feed side.Repeat as needed,many times you will see the board move straighter on the OTHER uncut side. Plane till other side is dressed then remove any extra wood from the side that was originally convex. The strong written instructions saying concave side down come from liability interests not woodworking.