Panel Glue Up, what do I need to watch for?

[Bill McCarthy]

I'm making a couple of boxes to store some of my chisel sets in. I figure that this will give me some practice for making drawers latter on. I'm using left over off cuts from 2x4s, nothing fancy. I'm resawing the 2x4s to 1/2" thick, then gluing them together to make the top and bottom of the boxes.

So I can begin good habits, what do I need to pay attention to when gluing up panels? The one that I can think of, is to keep the grain all going in the same direction, so I won't have problems latter when planing. What else? Is there a general "maximum" width of each board (I'm thinking about expansion)? Along those lines, is there a suggested maximum width of a panel? Is there some kind of configuration of the boards to mitigate future cupping? What do you guys know about that I haven't even considered?

I'm not ready yet, but I do have future plans for making some kitchen cabinets.

[Jim Koepke]

Making sure your edges are square will help save a bit of time after gluing.

You may also want to make some cauls to clamp across the panels being glued so the clamps for the edge gluing do not deform your panel.

jtk

[steven c newman]

363301
Something like this...
363302
Use a lot of clamps, and alternate which face they are on.

[Bill McCarthy]

363301
Something like this...
363302
Use a lot of clamps, and alternate which face they are on.


Steven, is there a reason you arrange the stock vertically? I never would have considered doing that.

[Leo Graywacz]

While it's being glued up and in the clamps put a straight edge over the width of the glue up. If there's a cup it'll stay that way. Flatten it out while the glue is wet and things will be better.

[steven c newman]

One very good reason...space. Did not have the room to lay it down. One bonus....leg vise made a nice third hand. Easier to access both faces, in case I needed the cauls on either side.

[David Eisenhauer]

For me, it seems that the thinner the panel, the more it pays to ensure that the edges are truly square. If the edges are not square, the panels tend to cup or bow when clamped even though the panel appeared to be flat when not in the clamps. Cauls are important to prevent cupping or a general bowing of the entire assembled panel during clamping and I find that watching my clamp pressure also helps to prevent bowing. Clamp tight enough to get some glue squeeze and stop rather than clamp as tight as you can. I don't think there is any panel width restriction, just have to plan for panel expansion in accordance to the width of the panel. Certainly no issues with panel width in typical kitchen cabinetry. If you have not used cauls before, go ahead and try it out as there are some positioning and juggling things to figure out when using cauls while glueing/clamping and the clock is running. This is definitely a time to do the dry run before the real event.

[Robert Engel]

1. Grain direction
2. Grain matching (forget about alternating rings, etc.)
3. Edges square (joint alternating faces to create complimentary >'s and cancel any error.
4. Do not clamp too tight. A common error with thin panels.
5. Do a dry fit first!

[Pat Barry]

For me, it seems that the thinner the panel, the more it pays to ensure that the edges are truly square. If the edges are not square, the panels tend to cup or bow when clamped even though the panel appeared to be flat when not in the clamps. Cauls are important to prevent cupping or a general bowing of the entire assembled panel during clamping and I find that watching my clamp pressure also helps to prevent bowing. Clamp tight enough to get some glue squeeze and stop rather than clamp as tight as you can. I don't think there is any panel width restriction, just have to plan for panel expansion in accordance to the width of the panel. Certainly no issues with panel width in typical kitchen cabinetry. If you have not used cauls before, go ahead and try it out as there are some positioning and juggling things to figure out when using cauls while glueing/clamping and the clock is running. This is definitely a time to do the dry run before the real event.
This is counter-intuitive, at least to me right now. I would have thought it to be much more important for thicker boards to be perfectly square on edges before glue-up. This purely a geometry problem the way I see it.

[Leo Graywacz]

If you are using a jointer to square up your edges just make sure that you put one side against the fence and the other board has its side away from the fence. Then if your fence is a bit out of square the complementary angles will add up to 90 anyway. Since I've learned this trick my glue ups have been much flatter and true.

[Simon MacGowen]

1. Grain direction
2. Grain matching (forget about alternating rings, etc.)
3. Edges square (joint alternating faces to create complimentary >'s and cancel any error.
4. Do not clamp too tight. A common error with thin panels.
5. Do a dry fit first!

+1 and plus this:

Get rid of the glue squeeze=outs (with whatever method you find effective) BEFORE they are cured. Don't listen to those who tell you to scrape off the hardened glue squeeze-outs UNLESS they are tiny ones or you don't care about the underside. Or unless you want to learn the hard way.

Simon

[Leo Graywacz]

Yup, once the glue is hard on the squeeze out it's best to sand it off. Scraping it off may pull wood with it.

[Simon MacGowen]

This is counter-intuitive, at least to me right now. I would have thought it to be much more important for thicker boards to be perfectly square on edges before glue-up. This purely a geometry problem the way I see it.

I am with you on that point...but why take any risk? Start with edges that are darned square or at complementary angles so they are 90 degrees. Don't be a lousy woodworker at the stock prep. stage though I have seen many who are, while trying to be a good one after that -- with mixed results, of course.

Simon

[steven c newman]

363338
Test fit before a glue up...the only "clamp" used..
363339
Boards are just 3/4" pine.
363340
Couple of clamps and a bead of Elmer's.....nothing to it....:D

[Pat Barry]

+1 and plus this:

Get rid of the glue squeeze=outs (with whatever method you find effective) BEFORE they are cured. Don't listen to those who tell you to scrape off the hardened glue squeeze-outs UNLESS they are tiny ones or you don't care about the underside. Or unless you want to learn the hard way.

Simon
Agreed - get it before its hard. Note - it is easier to remove squeeze out after the glue dries enough to be more of a gel / rubbery, before it gets hard. I don't like to wipe off wet glue because then you smear it into the wood and make it difficult to remove - not important if you are painting anyway, but really important if you are dyeing or staining on open pore woods.

[andy bessette]

...What do you guys know about that I haven't even considered?...

Start with quality wood.

[Bill McCarthy]

Start with quality wood.

Andy, you're right of course and I did not consider that for this particular project. I'm trying to get in a little practice at making something, while at the same time finding a use for the leftover off cuts from the 2x4s. But yes, for something serious, quality wood would go without saying; except...

I love your signature line, that fits me to a Tee. If I don't know that I can't or not supposed to do it, I go ahead and do it. Sometimes it works, sometimes it doesn't.

I appreciate everybody's advice. I glued and clamped everything earlier. Its 22" x 15 1/2" which I'll cut down to the size I need. I used 5 boards to make it. I used 3 clamps and 2 cauls, with the center clamp being on the opposite side of the other 2.

I did try to clean up the glue squeeze out as best I could, but I'm sure I missed something, probably on the underside and what is being hidden by the cauls.

I used 3 pieces of 2x4 to resaw and come up with the 5 boards used. Before resawing them, I jointed one face and one edge on each 2x4. The jointed edges that came from the same 2x4 were glued together. For the others, I did place them together and jointed those edges so they would have the complimentary angles.

I'll remove the clamps and cauls tomorrow and find out what happened. Thanks for all the help guys.

[Todd Stock]

Not mentioned: space clamps to provide adequate and consistent glue line pressure. This is an application of Saint-Venant's Principle, and in practice means that clamps should be spaced such that they produce overlapping pressure fields at the glue line. If we were gluing up a 12" wide panel from equal width boards, our clamps would need to be no more than 12" apart to get relatively constant glue line pressure, while if we were gluing a thin edge strip to that same wide panel, we would need to use more clamps or a relatively deep caul to ensure constant glue line pressure.

[Patrick Chase]

This is counter-intuitive, at least to me right now. I would have thought it to be much more important for thicker boards to be perfectly square on edges before glue-up. This purely a geometry problem the way I see it.

From a geometry perspective it's equally important for thick vs thin boards.

I think that the reason it *seems* more important for thin boards is because it's harder to detect a thin board that's out of square by a given angle, so you need to be more vigilant to achieve equivalent surface flatness.

[steven c newman]

Thin boards flex more than thicker boards when clamped up....they need the cauls to keep them flat..

[Patrick Chase]

Thin boards flex more than thicker boards when clamped up....they need the cauls to keep them flat..

True, but that argument cuts both ways. Because thin boards flex more and *can* be trued with cauls, that should in theory allow for more angular slop in jointing.

It doesn't work that way in my experience, though. A degree is a degree either way, but it's a lot harder to spot with a thin board.

[steven c newman]

I'll be doing a couple thin Poplar boards, to make the bottom panel on a desk....thin as in 3/16".....they will bow if I even add a clamp to one board (BTDT) let alone a couple. Sometimes, just a "rubbed joint" will be enough.

3/4" Curly Maple..
363419
Needed cauls on both faces..
363420
This was a 3 board glue up.

[Pat Barry]

From a geometry perspective it's equally important for thick vs thin boards.

I think that the reason it *seems* more important for thin boards is because it's harder to detect a thin board that's out of square by a given angle, so you need to be more vigilant to achieve equivalent surface flatness.
Right, the geometry (angle of the dangle coupled with the width of the mating boards) is what is driving the fit up. However, the thin boards are more forgiving g with regard to the resulting gap being less noticeable. No one is arguing that it's ok to have mating edges that don't sum up to 180 degrees, although some do advocate a slight angle can be managed as long as the mating angle is complementary, resulting in the 180 degrees.

[Kees Heiden]

For thin boards I routinely use the match planing technique. Planing two boards at the same time, so any error in the angle cancels out. Of course you still need to prevent twist and you still need to get them straight.

[Todd Stock]

Any out-of-square not matched by the mating piece of stock will show a glue line if clamped in plane, or will not be flat. Without all those square inches of excess gluing area to rely upon to keep things together, a nearly perfect joint is a functional requirement if the panel will carry any sort of load.

[george wilson]

WHY GLUE THE PANELS IN ? Get some of those little neophrene balls from WoodCraft. They are called "Space Balls". Leave about 1/8
of clearance all around where the panel fits into the slots. Place 2 or 3 Space Balls in each rebate. They will squeeze down some,but will hold the panel so that it does NOT RATTLE,but can breathe as needed,without risking glue being pulled out by the roots(:)) while the panel shrinks in Winter,or swells in Summer.

REMEMBER,WOOD NEVER STOPS MOVING. The larger the panel,the more trouble it will be. I think the Space Balls are a great idea.

[Todd Stock]

Huh? I don't recall that coming up...

On Space Balls...good idea. I see they label them as "...tested by NASA astronauts" now...what is THAT about?

[george wilson]

I am frequently not a great fan of the most modern stuff. But,those panels WILL continue to move over the seasons,even when varnished. Space balls are a great way to keep those panels flat and just let them move.

Otherwise,just drive a small finishing nail in the back side of each panel,through the surrounding wood. That,if there is clearance all around,will also keep the panels on center,but allow movenent,if you don't mind filling the small nail hole. I'd recommend drilling an undersize hole before nailing. I just put a masking tape flag around the drill bit. Then,drill till the flag just touches the wood. You don't want to go clear through,and out the front!:) Anyway,that's the way they have done it for ages,without attempting to glue them in.

[Leo Graywacz]

Yup, I usually use a 23ga pin in the top and bottom to keep it centered so it can move. Bigger panels I use two pins on top and bottom spaced about 1" apart.