how do I glue boards together well?

[Adam Herd]

I am making a coffee table and have the same problem i always do when glueing boards together, they never come out perfectly flat. I bought the boards pre planned so they should all be the same thickness. When I glued the 4 boards for the top together they are all just slightly higher or lower than one another. How do I improve this to save time sanding and planning? I used some scraps as cauls but still didn't achieve a perfectly flat top.

[Matt Day]

That’s usually considered glue creep, but could also be improper clamping techniques.

Adding biscuits to align the boards will help, but they have to be cut properly and be tight fitting to work their best. Dowels or Festool Dominoes work too.

A easy beginners mistake is too much clamping pressure which will make the boards want to be misaligned.

Gluing up 2 boards at a time can be helpful too, so you have time and can disused on one alignment at a time.

Lots of possibilities. Any chance you have a pic of what the panel looked like with the clamps on?

[Dan Hahr]

You really can't glue two edges together without something holding them in place. Glue is slippery until it sets up and clamps generally do not exert force precisely in line with the boards. Any offset and the boards slide out of alignment.

If small enough, Ill just put a small clamp on the ends across each glue line to hold them parallel as I tighten the clamps across the width. If larger, I'll use cauls across the surface. The cauls can't really be just scraps; they need to be machined either dead flat or equally curved on each side.

If it has to be very close, I'll sometimes cut splines instead of using biscuits for alignment. Biscuits don't really fit well enough to ensure perfect alignment.

Dan

[johnny means]

Cauls are one way. A deadblow is also very handy for banging boards into submission after clamping. I typically like to skip flatten on side, square the edges, than glue up panels to my maximum planer width, then plane to thickness. This way I at least get fewer seams to flatten and the resulting panels are much less squirrely.

[Phil Mueller]

Adam, you’re not alone. Happens to all of us. If I’m dealing with a glue up that can’t afford to be much thinner, I do as Matt suggests and start with just two boards. You have a good 5 mins before the glue sets up, so take your time to align them well when clamping. Start with a clamp in the center and tighten it while checking that the boards are aligned. Then add clamps from the center to the ends, tightening enough to hold and making sure the boards are aligned. I’ll then add clamps over the top in between the lower clamps. After an hour, I add another board and continue this way until all boards are glued up.

I also add clamps to the joint at the end just until the glue sets. Even after all this is done, I still may have a bit of misalignment, but at least its fairly minimal.

[Art Mann]

Dowels will work if you have a good doweling jig. The self centering kind is not good enough. You need the kid that references the top surface instead. You really only need perfect alignment on the side that shows.

[Edward Dyas]

If when you first snug the wood together in your clamps you would use a small sledge hammer and a block of wood you can hammer the boards flat. Unless they vary in thickness it should end up flush on both sides. Cauls just hold the overall panel flat if some of the boards are warped or not jointed square.

[Jim Becker]

There are many ways to get a better glue up and many have already been mentioned. Dowels/Dominos/Biscuits to help align one surface; using cauls (preferably with a slight curve to get pressure to to the center of the panel, clamps that help support the panel all at the same height, such as parallel clamps, etc. It's a dance...

[Edwin Santos]

Cauls are one way. A deadblow is also very handy for banging boards into submission after clamping. I typically like to skip flatten on side, square the edges, than glue up panels to my maximum planer width, then plane to thickness. This way I at least get fewer seams to flatten and the resulting panels are much less squirrely.

+1 on this.
A variation on the same theme is to do your glue up in stages - i.e. instead of gluing up four boards, glue up two and two, and then glue the two pairs. In this way you are only wrestling with one seam per glue-up.

[lowell holmes]

I make them a bit over thickness, glue them together, and then plane them to thickness on my thickness planer.
I have good luck with this procedure.

[ChrisA Edwards]

Do many of you ever use a glue line router or shaper bit to prepare the edges prior to glue up of boards to make a panel?

I've had all the same issues in the past, I've had fairly good success with Dominoes, but just wondered if my initial question might be a better approach. Although, I think, board thickness has to be exact for the glue line bits/cutters to be beneficial.

I would use these either on my router table or shaper.

Thoughts.

[Mike Henderson]

I'd recommend cauls, also.

Mike

[Mark Hockenberg]

It sounds like you bought S4S lumber. If so, you still have to ensure that the edges are 90 degrees to the face (and straight). If not, you'll have flatness issues during glue-up.

When I glue up boards, I alternate which face is against the jointer fence. This method allows a slight out of square error in the jointer fence to be "cancelled out" in the glue joint. Here's a great YouTube video that demonstrates this: https://www.youtube.com/watch?v=bbAYBtR7BYA. Even though I set my fence at 90 using a good engineer's square, I've seen small errors creep in.

The alternating jointing method, along with dominos, allows me to get dead flat glue-ups. With a couple of passes with a finish sander with 80 grit I get flat panels.

[Mike Cutler]

Adam
How are you preparing the edges? Any deviation from 90 degrees to the face is going to cause issues. A tried and true technique irsto run them through a jointer, and alternate the face of the board on the fence. This way any deviation from 90 degrees, will be nulled out.
I have always found that working alone always causes people a little trouble with panel glue ups. You just don't have enough hands.
I always use epoxy for panel glue ups. It cost quite a bit more, but you have a long, long, time to fuss about, and you only have to apply enough pressure to get the material to touch.

[Dylan Wyatt]

+1 on alternating the faces on the jointer. I skip plane the board to ~15/16", rough out stock plenty wide, run all edges through the jointer alternating faces against the fence to cancel out errors, glue together using #20 biscuits for alignment, then run through the planer to final dimension and cut the panel to size.

[Robert Engel]

I bought the boards pre planned so they should all be the same thickness.
This is the source of your difficulty. My approach to gluing up panels is "keep 'em big and thick as long as you can".

Obviously this doesn't apply to your situation, just thought I'd mention it.

That said, there are various alignment aids that will help such as biscuits, dowels, Dominos.

If you don't have the tools for that, a slot cut with a router to accept a spline will work quite well.
Another way is a tongue and groove joint.

[Mel Fulks]

IF you have an old beefy jointer with a wheel adjustment outfeed you can raise outfeed a thou or two .That will make
a "sprung" joint, (slightly open at middle area). Then with one clamp at each end you can press down any piece that's
too high and clamp middle of length. Used to be a standard architectural millwork technique demanded by management.
Much easier with wheel adj outfeed since it's easy to calibrate adj wheel to know where you are going and how to get
back. Yes...I post this every year

[Mark Daily]

415130415131

Some helpers like like these might be beneficial, but some sanding is almost always necessary to get a perfectly flat surface.

[Mel Fulks]

MORE: I also had a standing offer of $20.00 to anyone who found an open end ,interior or exterior, on any panel I made.
Never had a claim. Lots of jobs had over 100 panels.

[Jim Becker]

I bought the boards pre planned so they should all be the same thickness.

I missed this in my original read of the thread. There is pretty much zero chance that purchased pre-surfaced boards are all going to be the same thickness. They will be close, but chances are they all came off a machine at different times or are from different trees or are at slightly different moisture content, etc. You will always need to pick a surface for each board that will be "top" and then either index on that surface or the opposite one for your glue up. One surface can be reasonably flat, but the opposite side will most likely have more noticeable variations in thickness. In full disclosure, the same holds true for stock one prepares in their own shop from rough. It's extremely unlikely that eery board will be perfectly the same thickness.

[Kevin Beitz]

I give up trying to get them flat. I built a 12 ft x 8 ft router plane.

[Lee Schierer]

Before gluing, I arrange the boards the way I want them, draw a large V across all the boards with chalk. This gives me the order I want and the orientation when I begin gluing. I used to try gluing up 3 or more boards all at once and found the same problem Adam is asking about. Through experience I learned that I could glue up two pieces at a time and work the boards working from right to left by aligning the end to the right at the joint with a C-clamp, then working to the left tightening the bar clamps one at a time while also leveling the surface that would show right at that bar clamp. I would glue up four board panels two boards at a time and then glue the two board pieces to each other. I have far less sanding to do on the final panel assembly which makes up for the time lost only gluing them two at a time.

[Jerry Olexa]

Biscuits help a lot initially in alignment.....Your concern is common but biscuits eases much of that.

[Allen Arin]

Its better to glue in pairs instead of gluing one by one and there must be some issue with the clamping technique check with that too.

[Mel Fulks]

Only once did I have a problem with panels. Boss had a customer who made it clear to him that she wanted good
panel matches. With picky customers I've always been the panel guy. When the job was done he told me she had
tears in her eyes as she gushed about their great beauty. Then they hired some hacks to do the finishing. They looked
like they had dark varnish stain. Lady was in shock. Panels were then soaked in a bath tub to remove the "finish".
They used ACETONE Several weeks later he told me all the panel glue joints were coming loose and I was never again to
use sprung joints. I boogied out. Never work for a dim bulb

[Will Blick]

you got some great advise here
this thread will live on, as everyone struggles with this... some less than others...
In addition to many of the comments above...
when I thickness plane my wood, I am assured all boards are the same thickness, this helps a lot.
I clamp up lightly, then install in the same direction of the clamps, my massive alum. beams I purchased for this purpose, they are almost 2x4 size, and heavy, no flex. I clamp those to keep the boards from creeping...once in place, I tighten the glue up clamps, then re tighten the alum bars down, a bit of a dance to get there, but FLAT!! Its hard to get cauls to give you enough pressure in the middle as these boards want to dance!
I also used to use dowels, with a Dowelmax, yes, it works very well, but what a time sink, and its easy to mis align one. Dominos are easier and work good, but also time sink. Never had great success with bisquits, too loose, although, they are better than nothing. There is also 90 deg male / female edges you can put on your boards that will assure edges are aligned, but the entire panel can still bow, hence the benefit of the two at a time process...

lots of options, pick and chooze based on your project details...


BTW, did everyone notice, woodpeckers recently offered a one time tool to address this issue, but IMO, the force on the cross members is NOT downward enough. Other makers have provided similar clamps for years. If you follow the glue manufacturers recommendatoins of approx. 100 psi at the glue joint, that is a lot of clamping pressure, the boards will always follow the path of least resistance and creep unless they are constrained. Or, as others suggested, you provide waaaay less clamping pressure than recommended. In most cases, less pressure will work if your boards are jointed well....and they are thicker. the tinner the wood, the less glue area.