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So I'm planning on making a table top with 2x10s, glue and pocket hole screws. I'm worried that when I clamp everything together, the boards will bow when I put pressure on them. Am I over thinking this, or should I do plan on doing something to minimize bowing. Thanks for any advice guys.
 

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I made "H" supports out of 3/4" plywood and used ratchet straps. I alternated them above and below.
This picture is terrible, from an old cell phone but maybe you can see what I did.


If you're using clamps you can make cawls and alternate the clamps above and below.
 

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So I'm planning on making a table top with 2x10s, glue and pocket hole screws. I'm worried that when I clamp everything together, the boards will bow when I put pressure on them. Am I over thinking this, or should I do plan on doing something to minimize bowing. Thanks for any advice guys.
The start of your problems would be to use pocket screws. IMO, don't use them. About your glue up. You should first do a dry fit to see how the mating edges look. If they were jointed and fit without any gaps, you can proceed to the glue up.

Have all your parts, glue and clamps all ready, and laid out. You don't want to be hunting for something at the last minute. It seems at this point it's a simple matter of applying glue and just setting the clamps and cauls and tightening them up.

Clamps, like pipe clamps for instance have a closing pressure from the clamp ends that can exert more pressure on an upper or lower edge of the board other than the center, if not positioned properly. Many of those clamps the ends do not close under pressure absolutely parallel to each other.

When tightening one of those its a good idea to see how the mating edges are reacting as the clamp gets tight. Alternating the clamps position on top of the boards and the bottom of the boards help in creating a straight line of pressure to bring the boards together.

As an example of an improper clamp attachment, lets assume that there is slightly more pressure along the top portion of the edges versus the bottom. As the clamps tighten, the pull can make the combination of boards bow, or curve into a "U" shape. This would be indicative of all the board edges (that may be flat to each other) and the faces take a shape other than horizontal. The other side...meanwhile...will show that the glued edges are not tight but slightly separated allowing the board to tip away from its mating board. Over clamping (too much pressure) can do this.

The whole point to this drawn out description is when setting clamps to the outer edges of a group of boards, insure that they are set to exert centered pressure to the boards.





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+1 with C'man. I would not use pocket screws.

The 1 1/2in thick edge is more than enough surface area for glue. If the joints have no gaps without clamping, the glued edge should be stronger than the wood.

You should be concerned about any clamp causing the boards to bow so you need to prevent this.

Examples to prevent.
a) Use cauls. The "H" support in earlier reply is an example. Something stiff.
b) Apply clamps alternating top and bottom so that any tendency for bowing is equalized.
c) Use a clamp like this one. Mix of clamp and caul.
http://www.woodcraft.com/product/2000321/1858/woodriver-clamping-system.aspx
d) Glue two boards at a time. The more boards you clamp in one go, the greater the tendency to bow due to width.
 

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Something like what Sarge did would work for alignment also. But instead of doing that, I just used biscuits to keep the boards aligned
 

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Discussion Starter #7
Thanks for the advice, but I've got a few questions.

Why do you guys say no to the pocket hole screws? Do they pull the boards out of alignment when you tighten them down?

Would you recommend dowels instead of pocket screws, or skip all of those and just glue?

Any particular glue that you guys like for this type of glue up?

If I were to use cauls or H-brackets during the glue up, how do I keep excess glue squeeze-out from gluing the cauls/H-brackets to the table top?

If it means anything, I don't have a jointer, just a table saw. Also this will be a distressed farm table.

Thanks guys,

WV
 

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Thanks for the advice, but I've got a few questions.

Why do you guys say no to the pocket hole screws? Do they pull the boards out of alignment when you tighten them down?
The pocket screws will not really help with alignment, and will not add strength to the joint. I feel they are used to join pieces at right angles in lieu of a wood joint and glue.

So not a good use of your money in the screws and the time to drill and insert.

Would you recommend dowels instead of pocket screws, or skip all of those and just glue?
If the board are all flat i.e. no bow along the length, then you may not need dowels

If the boards have a bow, you can try and have the boards correct by gluing one with an up bow to one with a down bow to try and get flat. This is best done with cauls or dowels. I would use dowels, but it is more of personal preference.

If you do not use cauls, then I would use a few dowels for alignment. You will still need to alternate clamp on top then bottom etc, to prevent the boards for bowing.

Any particular glue that you guys like for this type of glue up?

If I were to use cauls or H-brackets during the glue up, how do I keep excess glue squeeze-out from gluing the cauls/H-brackets to the table top?
Any brand of yellow glue should work assuming there are no gaps. Yellow glues are not going to fill a gap.
I use Titebond III. Titebond I or II will also be fine. Slight difference in strength, water resistance and set up time with III having best strength, water resistance and longest set up time.

You prevent the excess glue from sticking to the cauls either by putting masking tape on the cauls, or cut strips of plastic bags to go under the cauls.

I also put masking tape on the clamp bars/pipe around where the glue lines will be. I just prefer to not get glue on my clamp bars/pipe.
 

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Glue

Just put some clear packing tape on the cauls. I use Titebond liquid hide glue for almost everything except ouside stuff. No creep and a good open time. I leave table top glue ups in the clamps/cauls overnight @ normal temps and 24 hrs if colder.
 

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Walleye,

Couple of ideas based on my experience. To make a glue up like that go a bit easier I always use a a few dowels to keep the boards aligned. That glue is darn slippery!..Mark the boards, use a dowel jig, then test fit to make sure all the holes line up. That way when you are clamping them up you will be able to concentrate on keeping them flat and not have to worry about the alignment.

If you are using big box 2X lumber it is eventually going to dry out and all the knots are going to stand proud. I made a "dining" table for my daughter's first apartment after she graduated from college. Needed to be an odd size it fit the space available and knew it was short term set up so I made it out of 2X6 material. Planed it, jointed it, let is sit a week or two then glued it up. Maple stain, lacquer finish, 2 extra leaves, came out quite nice. After she was done with it she stored it for awhile then passed on to my younger daughter. By that time it had lived in some places that were very dry and all the knots stood proud. Daughter wanted to take it to Florida with her so I leveled the surface, re stained and re lacquered it. That 2X stuff is tricky for furniture use because of the moisture content.

Have fun,
Don
 

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I took a 2x10, cut a through mortise slot on each side, slid a pair of 2x2 oak turning squares they the slots, stood the boards up and clamped them together. I clamped back, front, back, equally spaced on the mortised boards, pulling them evenly together. I used a 36" framing square/ level on the top and bottom as the boards were stood up to ensure even pressure and alignment.

The oak 2x2s allowed for "racking" to be noticeable to adjust uneven pressure. It came out perfectly straight, no bows or uneven sections. I was careful not to put too much clamping pressure, which helped a lot. Sometimes we go apesh:?t on the clamping, so mindful of the pressure.
 

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So I'm planning on making a table top with 2x10s, glue and pocket hole screws. I'm worried that when I clamp everything together, the boards will bow when I put pressure on them. Am I over thinking this, or should I do plan on doing something to minimize bowing. Thanks for any advice guys.
If you tighten the clamps so much that the boards bow then you have tightened too much. Do away with the screws: they add nothing to a good glue job.

George
 
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