Edge-gluing problems

[Chris Oakley]

I can't seem to ever edge-glue two or more boards without creating a bowed board. Am I applying too much clamp pressure, or doing something else wrong? I run both boards through my jointer then use I bar clamps, one on one side of the board, and two on the other (for about 48 inch long boards).

Any help that you experts could give a rookie rookie would be much appreciated.

[Jim Izat]

I'm not exactly sure what you mean my bowed but with a 48 inch glue up I'd use at least four clamps, one on each end and two in the middle. If the panels are coming out uneven, you could try using clamping cauls. One at each end and one in the middle ought to keep everything flat.

Jim Izat

[Daniel Rabinovitz]

In the past dowel rods were used to align the boards and now the use of biscuits has won over us woodworkers.
Without going into great detail, maybe you're putting too much pressure on the clamps on one side.

[Richard Allen]

Hi Chris

It could be you jointing. Joint one board with the face towards the fence and the other board with the face away from the fence. That way any tilt out of perpendicular the jointer might have is mirrored on the other board.

You most likely are doing that already. So using a lot more clamps with less pressure would be good.

I like to use waxed paper between the clamps and the glue line to keep everything clean. I need to remove the clamps and waxed paper in a few hours (whatever the instructions and weather tell you) so that one side of the panel doesn't absorb more moisture than the other.

My shop has a lot of natural light. I make sure the glue-up is out of direct sunlight.

Before I walk away from a glue-up I inspect the piece to be sure the clamps have an even pressure and everything is as flat as I expect.

I hope some of this helps.

Thanks

[Lee Schierer]

Which way is the bow, along the length or across the width?

Make sure the boards fit tight when dry on the edges. If you see gaps, they should be corrected before glue up. Check the edges for square.

Make sure you put clamps evenly spaced on top and below the boards being glued up.

Make sure you work on a flat surface and that the piece stays flat.

Work left to right or right to left. Tighten all clamps lightly, then go back and make them tighter. If you are bowing the clamp, it is probably too tight.

Leave the glue up flat or stand it up straight if you can.

[Todd Burch]

I second Richard Allen's suggestion for flipping faces of your boards against the edge jointer fence. I learned this from a Kelly Mehler video several years ago, and it was like a weight being lifted from my shoulders every time I used my jointer.

Another thing to consider is your wood. I use a lot of pine; it's cheap; easy to cut; occasionaly has interesting figure (I hunt out birdseye grains a lot), and it's cheap, but I said that already.

One thing I RARELY do with pine is use a full width 1"x12", as I KNOW that eventually, it will cup. So, I rip it in half, flip one side, and glue it back together. Or, I rip the center 2" out and throw out the middle, then flip and reglue. Only when the piece demands full grain continuity will I not rip and reglue. The pith wood in pine, and other woods, is commonly referred to as reaction wood, and/or juvenile wood, and pith wood does not have the same grain structure, movement behavior or chemical makeup as the rest of the wood. So, what my point is, watch your use of boards when you include the pith.

Also, are you using flat sawn boards, or quartersawn? Flat sawn will tend to cup more than a quatersawn board; it's a function of how wood moves in relation to moisture absorbtion.

Finally, (pant, pant), how are you storing your glued up panels? If you are laying them flat on your bench overnight, and the next morning it has cupped - then you screwed up by causing one side to be able to absorb more moisture than the other side. Keep an even air flow to both sides until you are ready to use it.

Todd.

[Ted Shrader]

Chris -

Good suggestions, all. Mine are
Too much clamp pressure. You just have to hold the boards firmly in place, not squeeze the dog snot out of them. And tighten the clamps gradually in steps.
Edges may not be perpendicular. Reverse the face sides against the jointer fence. That will compensate for any out of square condition of the jointer fence.


Those suggestions assume the panel is not twisted. Are the clamps on a flat surface when you are assembling the panel?

Good luck,
Ted

[Chris Oakley]

I think I found that I'm doing alot of things wrong. I haven't been paying attention to the way I run the boards through the jointer, leave the glued up board on the tool bench overnight (which isn't the most flat surface.....I think that's my next project a new workbench).

I use biscuits (I use it for almost all my joints, since it's so easy). It's my understanding that the biscuits are mainly for aligning the board, and serve no structural purpose?

Also, would pipe clamps help, or does it matter?

[Richard Allen]

Hi Chris

Sometimes procedure can solve a lot of problems. But sometimes there isn't a procedural solution. Sometiems the solution is arrived at by discovery.

As for clamps. pipe clamps work fine as do many other clamps. There is some sort of ROT about clamping that goes something like:

one clamp for the distance from the clamp to the glue joint. So if you were clamping 2 6" wide boards to make a 12" wide board you would need a clamp every 6" with the clamps at the end no more than 3" from the ends.

One thing you can do, which is of questionable value, is to joint your boards so there is a gap in the middle. The gap should be no bigger than a sheet of paper is thick. You can do this by pressing down harder on the stock as the middle of the board passes over the cutter. The theory being that the ends of the panel are more liekly to spread open than the middle. As evidenced by some OLD tables being cracked at the ends but never having seen old tables chracked in the middle while intact at the ends (unless by some trama).

I tend to use this "daylight" procedure when jointing. But I am fairly sure that modern glues will out perform the wood when it comes to the ends of panels cracking.

Thanks

[Keith Outten]

Here's my procedure;

1- Lay the boards flat on a table and align them for color, grain, etc.
2- When your satisfied with the layout use a pencil and strike two marks in the shape of an arrow across the glue joint or joints.
3- When you go to the jointer remember that the pointy side goes toward the fence the open side is joined away from the fence.
4- When all of the boards have been through the jointer lay them back on the table, align the arrow marks and check the fit, it should be perfectly tight...no gaps.
5- Setup your pipe clamps at the appropriate spacing intervals, I don't have a rule of thumb, I always SWAG the spacing.
6- Tighten your clamps in stages and keep the pressure as consistent as possible, use several passes to get to the final pressure but never use excessive force. If the joint is tight it doesn't take much pressure.
7- After 30 minutes in the clamps remove the boards, never leave them overnight or any longer than 30 minutes.

I have never had a glue joint fail in 25 years using this procedure.
That's my story and I'm sticking to it!

[Howard Acheson]

As many have said, unless your jointer fence is exactly 90 degrees, you will get a bowed glue up. Alternate faces against the jointer fence and any difference from 90 degrees will be cancelled out.

Second, use cauls for panel glue ups. I use cauls on both ends and in the middle for longer panels. The cauls stay on until I am ready to work on the panel.

Next, after glue up, either sticker your panel if you lay it on another flat surface or stand it completely on edge. Air must be able to circulate freely to both sides or you will have warping.

Finally, total clamp pressure is generally not the problem but it is a good idea to alternate clamps top and bottom. It is almost impossible to put too much pressure on a glue joint. A good glue joint in hardwood needs about 200 psi. That means that a 3/4" board will need 1800 pounds of pressure every foot or so. A 3/4" black iron pipe clamp will get to 2,000 pounds just before bending so a clamp every foot or so is what you should aim for.

[John Christiansen]

Chris,
You said; leave the glued up board on the tool bench overnight (which isn't the most flat surface.....I think that's my next project a new workbench).


In my shop, and I have to pressume any where else. If you leave any board laying flat on a solid surface, (meaning without stickers of some sort) that board's going to cup. You've created an unequal surface moisture situation, and the top side is going to concave, since the top side is drying out more and faster than the bottom side.

[Tom Gattiker]

What kind of clamps are you using.? 2 factors to consider

If the bar bows it is going to exert bowing pressure on your glueup

If you use clamps with a deep reach, that's also going to exert bowing pressure. Avoid "joiners clamps" or deep reach clamps that apply the pessure at a point that's 2.5 inches or more from the bar. Use something like the standard pipe clamp, which allows the board to sit on the clamp bar (perhaps with wax paper separating them).

[Ron Meadows]

Somthing that I do, which I don't think has been mentioned yet, ist to apply downward pressure at the joints when tightening the clamps. Seems to help keep everything flat in the middle and is very easy to do.

Ron

[Malcolm Timbers]

Before applying glue, I put the two boards one on top of the other on edge and sight down them to see if they are sitting square. Sometimes I clamp the bottom one in the vise and use a square to sight one end and the other to see if the mating board on the top is out anywhere.

I usually glue up my stock in the rough and hand plane the high spots after the glue sets and then run it through the planer. Of course, that won't work on stuff that is wider than the planer. In that case I just hope and pray that they will come out okay.

One note: don't glue up any boards with tight rings! Those rings near the centre of the tree. They will always cause the glue up to warp.

[Howard Ruttan]

Excellent suggestions from all.

I just have one thing to add, especially since I am still not clear how the boards bowed exactly.

Did you test the moisture level of the wood? Is it actually dry enough to work? Also, did you let it acclimate to the humidity in your shop before working it? I always let lumber acclimatize in my shop for at least a week and a half to two weeks before I even think of cutting into it.