Slightly cupped glueups

[Jared Cuneo]

Some, ok about half of my glue ups come out rocking a little (2-3 32's, sometimes a little more). I've made absolutely sure my edges are jointed and square, then ripped on a verified 90 degree sawblade but I sometimes still get slight cupping as if the jointed edges are off a degree or so.

Will I ever get it or do I just deal with this stuff as normal? I don't want to take any more thickness off of these boards as they are at 3/4 already.

Anyone have any words of wisdom? Oh, I am using Jet and Bessey parallel clamps on bottom alternating with pipe clamps on top.

Thanks!

JC

[Gary Keedwell]

How are you checking the ends for square? Do you have a real good square?
GK

[Jared Cuneo]

I have a Starret combo and a Crown try square, mostly use the Starret....

JC

[Jamie Baalmann]

I like to shim the glue up while it is in the clamps using a straight edge. It seems to help, the boards seem to always cup towards the clamp so it is easy to put a shim in the middle.

[Greg Cuetara]

Jared,
Are the boards cupped or are each of the boards straight with an angle at the joint line? If the problem is at the glue joint then you might want to try ripping to width and then jointing the edge then only glue up jointed edges.

If the problem is that the whole assembly is cupping then make sure the boards have alternating grain. Another problem could be the width of the boards. Depending on the species of wood and the width of sections if the boards are not dry enough they could cup. Also when planing the boards you need to make sure that you take equal material off each face. I have tried to plane down to a thickness and then put the boards back to dry and when I need them do a few final passes with the planer etc.

Another problem could be in the the way which the boards were first prepped. If they are warped or cupped you really should joint one face first before you put it through the planer. If you are just buying S3S stock then you may need to rip the boards down or make sure that they dry properly in your shop before you use them to glue up.

I'm sure many others will have opinions here.
good luck,
Greg

[Jared Cuneo]

I should be more specific. I am face jointing, then edge jointing. Then I run through the planer and rip to width.

The boards are not cupping individually, I think its more of a problem in the glue line itself as each board is 4 square at the time of glue up......

Hope that explains the problem better.....

JC

[Jamie Buxton]

That your glue-ups are cupped is evidence that your edges are not at exactly 90 degrees to the face. It doesn't take much to cause perceptable cupping; 90.5 degrees will do.

Setting the jointer fence to exactly 90 degrees is difficult. Fortunately, you don't need to. If the edge of one board is, say, 90.5 degrees, and the mating board is at 89.5 degrees, they'll glue up without cupping. So here's the process.... Lay out the boards in your panel. Select them for grain or color or whatever you like. Without moving them, put a mark on one end of the panel. That is, all the boards get a mark at the same end. Edgejoint both edges of each board, always leading with the marked end. In essence, this process cancels out any error in setting the angle of the jointer fence.

(The Neanderthals do the same thing while edge jointing with a handplane. There's no way a handplane is going to cut 90.00 degrees. They lay out the panel. Then they pick up two boards which will be a butt joint, and fold them like a book. They clamp the pair in a vise and joint them with the plane at the same time. This gives one board some angle, and the other board its complementary angle, just like the power-jointer process above.)

[frank shic]

thank you, jamie for that excellent suggestion. i noticed some cupping on my last glue-up as well and i was just trying to figure out how to emulate the neanderthal method on the my jointer.

[Peter Froh]

Rip the panel square the edges and try again.

This time make certain that you sticker the panel at all times until it's used in the assembly of your project.

I've had cupping problems in the past and it was all due to the fact that I left my panels lying flat with no air circulation underneath the panel.

Since I've stickered my panels/glue-ups I've not had a problem with cupping.

Good luck.

[nick brigg]

are you putting every second clamp on top to even out the clamping pressure?

[Tommy Emmons]

I was at a woodworking club meeting and Frank Klausz was the speaker. He said that if the boards are flat sawn, the upward curve of the grain should be the outside of the piece and that all boards should have the end grain curving the same direction. If you are getting cupping immeadiately after taking the clamps off, I defer to the previous advice.

[Denny Rice]

Some, ok about half of my glue ups come out rocking a little (2-3 32's, sometimes a little more). I've made absolutely sure my edges are jointed and square, then ripped on a verified 90 degree sawblade but I sometimes still get slight cupping as if the jointed edges are off a degree or so.

Will I ever get it or do I just deal with this stuff as normal? I don't want to take any more thickness off of these boards as they are at 3/4 already.

Anyone have any words of wisdom? Oh, I am using Jet and Bessey parallel clamps on bottom alternating with pipe clamps on top.

Thanks!

JC
I usually start with rough sawn stock close to one inch and take it to 3/4"

Wisdom passed down from my shop teacher 30 yrs ago:

1. Smooth the first face
2. Smooth the first edge
3. Rip to width + 1/16"
4. Smooth second edge
5. Smooth 2nd face planning to thickness
6. Square 1st end cutting off about 1/2"
7. Square 2nd end to lenght

I follow these easy 7 steps and 99% all of my glue ups come out great! What would the world be without shop teachers! My shop teacher would not get you touch a machine or a piece of wood unless you knew this by heart.

[Rick Thom]

If the jointing technique doesn't solve it, is it possible you are over-tightening the clamps? For a properly jointed glue-up you should be applying just enough clamping pressure to get uniform squeeze-out when the boards come together.
Some of us have bought the digital angle gauges, ie Wixey to help set up shop equipment where one surface must be set precisely relative to another. Seems to work well down to 1/10 degree or better.

[Jared Cuneo]

Lots of great suggestions to try, I'm definitely bookmarking this thread.....thanks!

Jamie, thats brilliant, I will give that a shot next time....

And as for overtightening, its possible....It doesnt take much pressure at all to get squeezout.....And yes, I am alternating clamps, top and bottom (parallels on bottom and pipes on top, every other one....)


BTW, I've only got 1/8" to spare on these glueups, and this is my first large project. I am going to plane them out a 'little', and try to pull them flat the rest of the way on assembly....(probably max of 1/16 or so)....Is this much pulling going to tear my project apart someday? IE, is everyone's glueups perfectly flat, or is it ok occasionally to be a little off (not preferred obviously)?





JC

[Lee Schierer]

Setting the jointer fence to exactly 90 degrees is difficult. Fortunately, you don't need to. If the edge of one board is, say, 90.5 degrees, and the mating board is at 89.5 degrees, they'll glue up without cupping. So here's the process.... Lay out the boards in your panel. Select them for grain or color or whatever you like. Without moving them, put a mark on one end of the panel. That is, all the boards get a mark at the same end. Edgejoint both edges of each board, always leading with the marked end. In essence, this process cancels out any error in setting the angle of the jointer fence.

Okay, I understand the theory of this, but how do you prevent the tear out when the grain angle is the wrong way for smooth jointing on one board when dealing with wavy grain. If the grain ends at the board edges are ////// on one board and \\\\\ on the other board you will get tear out on one of them when you joint them. I would suggest that with some time and a couple of pieces of scrap you can tune up a jointer to yield perfect 90's every time so that the jointing can occur to minimize tearout. Also a smoothly ripped board direct from a table saw with no visible tooth marks or burn marks is an acceptable surface for gluing with modern blades and a well tuned saw. I did it for years before I had a jointer.

If the boards are \/, where each piece is flat in and of itself, but the total is not, then the problem is the jointing. If the boards are U, where each piece is curved a little, then the problem is poor drying. Also clamping pressure can play a role here. If the piece is not flat when clamped, it will not be flat when the clamps are removed. You can also incorporate twist in the panel if the set up for gluing the panel is not flat. All the pieces should be supported on a flat surface while the clamps are applied, then rechecked for flatness before setting it aside for the glue to dry.

The older school for glue ups was to use narrow pieces and alternate the growth ring pattern on every other piece so that worst case you had a wavy board instead of a cupped board. I generally use this technique except when I am trying to get a particular uniform look on the grain pattern that will show and the altering won't work.

[Jim Becker]

Lee, very light cuts with the material moving slowing...and material that is over-length...should help you when you have the grain issues you describe. The careful sequencing of the pieces when edge jointing for "error cancellation" really does help thing come together, in my experience, so anything you can do to keep working that way even with knarly wood is desirable, IMHO. I mark the intended top of the sequence with a big "V" in chalk and then work across the sequence, alternating mark away/mark against the fence.

[frank shic]

anyone ever try using a tablesaw jointing jig? it seems like it would eliminate the tearout that lee mentioned.

[Jamie Buxton]

... Okay, I understand the theory of this, but how do you prevent the tear out when the grain angle is the wrong way for smooth jointing on one board when dealing with wavy grain....

I generally just ignore the tearout. I'm trying to make a structurally-strong joint. Tearout divots which would be unacceptable when visible on the board's face don't affect the butt joint quality.

If the tearout is really terrible, I turn the board around for one last pass on the jointer, but I don't use the fence to establish the board's angle for this clean-up pass. For these edges, I dry-fit the joint and check it for flatness before I glue it up.

[Jamie Buxton]

anyone ever try using a tablesaw jointing jig? it seems like it would eliminate the tearout that lee mentioned.

With one of those, you'd get the quality of cut provided by a saw blade. At least in my shop, that's rougher than what the jointer provides. I tolerate the saw's irregularities on plywood edges, because you can't edge-joint plywood, but I prefer the jointer on solid lumber.

[Gary Keedwell]

Really....wouldn't a dry run tell you how it may look? Simply lay the boards down in the most eye pleasing order and tighten them up. Place a straight-edge on top and check for straightness. Maybe look at the ends to visually see if there are any gaps.
Seems to me, a little practice run before you apply glue, would be worth the time spent?:)
Gary

[Jim Becker]

anyone ever try using a tablesaw jointing jig? it seems like it would eliminate the tearout that lee mentioned.

Well, I forgot to mention that now that I have the slider...well...I don't do a lot of edge jointing. The jigs like you mention can be quite effective as long as the blade is perfectly perpendicular to the table surface and as long as you can keep them absolutely against the fence for the whole cut without varying the speed too much or stopping. "Jointing" at the table saw is best with short pieces, IMHO, so you have the control necessary to complete the cut in one smooth swipe.

[Ron Hildreth]

Jared,
Just a thought, but I find that too much clamping pressure will make a glue-up cup. Back off and don't tighten the clamps so tight, or make yourself cauls to use top and bottom of the glued up panel.

Ron in Iowa

[Steve Schoene]

This don't put too much pressure myth just doesn't fly in the face of the significant amount of evidence that joints get stronger with more pressure than less. The glue manufacturers, Bruce Hoadley, the Forest Product Labs and researcher Roman Rabiej (author of the recent FWW story on the issue) can't all have it wrong.

If the joints aren't square (or complementary) then nothing with the clamping per se will get the glue up simultaneously flat and tight. If the boards have truely square edges then one side or the other can't be really tight, a consequence of unbalanced clamping that has let one face have thicker glue lines than the other.

Boards jointed properly to achieve a really fine panel won't pass light between them when one is stacked vertically on the other pushed together with only light hand pressure. This also gives a better reading of whether the edges are truly square.