# Edge Joining Woes - Cupping At Clamp Up



## LyttleBryan (Nov 18, 2013)

Everyone has something they just hate doing. For me, it's edge gluing boards for panels. I know why I hate it. It's because I'm terrible at it.

I'm working on Christmas presents. Making cheese trays for everyone since "wine and cheese" nights are a big thing right now. It's basically a cutting board, only face grain instead of end grain. I've got a variety of species of wood that I'm splicing into maple for nice contrasts.

My problem is that whenever I go to glue up the boards, they cup on at least one side, if not both.

I'm using an assortment of clamps right now that include:
3 - Bessy H Series Pipe Clamps (like pony clamps only they have feet)
2 - 36" Irwin Bar Clamps
2 - 12" Irwin Qwik Clamps
2 - 12" Bessy F Clamps

The boards have been run through the jointer and table saw. Comparing them against my machines square (one of those highly accurate ones) they appear square, but that's to the naked eye. Sitting on the bench, as long as the long boards aren't warped, they appear to make a nice seal.

I put them in the pipe clamps with clamps spaced every ~8" and then put cauls on each end that I clamp down with the F clamps. No matter what, after I apply even a little bit of pressure with my left hand (my far weaker hand) at least one of the boards in contact with the clamps will start to rise up and create a cup.

I created this highly technical diagram to explain the problem.










Things I've tried include:
- Using less pressure. Even with really good seams there is a lack of glue spilling out which tells me there isn't enough force to make the joint hold. On less good joints that need some convincing it's a no-go.
- Tightening the cauls with as much force as I can. Seems to work better with the Bessy than the Irwin clamps. Just can't get as much force on those. But still, the bessy side still rises.

I'm worried that it's the pipe clamps. Look at the clamp it appears that there isn't clamping surface touching all points on the boards, just the top. This acts to "tip the board over" if you will. This would be very disappointing as I can't afford a thousand dollars in new wood clamps right now, which is what it seems it would cost.


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## vikingcape (Jan 3, 2013)

Are you alternating your clamps top and bottom? As in put one clamp on and then turn it over and put another on, continuing to the end. I didn't do that and learned the hard way. I don't think it's the clamps, I think you just need to alternate them. Hopefully this helps


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## BigAL4160 (Nov 5, 2013)

Bryan, I feel your pain…edge clamping with pipe clamps isn't the most fun thing in the world. I have also noticed the phenomenon you display in your drawing of the pipe clamp not providing parallel pressure to the edge of the board. I have been getting success lately by alternating my clamps (one on top, one on bottom, one on top, etc.) and using very light pressure until all clamps are on, then alternately tightening each one slowly. Also, when installing each clamp, really press the boards onto the pipe, keeping them flat; I've been able to avoid using cauls most of the time just by doing this.

Its also possible that you could be using more glue than necessary causing the boards to slide around excessively. Just throwing that out there.

If all else fails you could pick up a couple new clamps. I got a 4 ft. black pipe at Home Depot for about $12 and the pipe clamps for about $14.

hope this helps,
BigAl


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## pintodeluxe (Sep 12, 2010)

The above suggestions are good, but here is the real key…

You need to compensate for any inaccuracy in the jointer setup/technique. Do this with the "I" and "O" method. 
Arrange your workpieces as they will be in the finished project. Label adjacent boards with an "I" and an "O." 
Continue this pattern for all boards… I,O,I,O,I,O etc. 
When you joint your boards, the "I" boards face inward toward the jointer fence, and the "O" boards face outward away from the fence. Middle boards will have an "I" and an "O". 
This compensates for any errors in your fence setup, and will result in a perfectly flat panels. 
Use your H style clamps, they are great for panel glueups. 
Here is a detailed walk-through of the process…
http://lumberjocks.com/pintodeluxe/blog/33797


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## djwong (Aug 2, 2009)

Did you try clamping your cauls down tight before applying pressure with the pipe clamps? You should be using 2 cauls on each end (top and bottom), and 2 clamps on each end. If you have enough clamps, you could put flattening cauls in the middle as well.

One other technique you can try is to use small blocks of wood as clamping blocks on the pipe clamp pads. The clamping blocks should be only as tall as your board stock. If you find that the board is bowing upwards as in you illustration, then you loosen the pipe clamp, and slightly raise the clamping block on the side closest to the bowing. This will have the effect of redirecting the clamping pressure to help straighten the boards. In use, I find this technique a real pain because it is difficult handling all the clamping blocks and getting them into position.


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## LyttleBryan (Nov 18, 2013)

Thank you for the info.

I am alternating the clamps yes. I may give the above post on alternating joiner pieces a try. Good reading.


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## Picklehead (Feb 12, 2013)

I recall a tip I read, although I confess that I haven't used it, that suggested using a dowel between the clamp pad and the edge of the boards being clamped, the thought being that it would prevent the angle of the clamp pad telegraphing into and tilting the outermost boards in the glue-up.


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## joeyinsouthaustin (Sep 22, 2012)

Much good advice and links already. Here is my advice.










Here is what you glue up can look like. Assuming properly joined and planed boards. Alternating the grain.. Look at the end grain and you should see smiles and frowns. Cauls over the top, alternating clamps top and bottom, not a ton of pressure, just the right amount.


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## LyttleBryan (Nov 18, 2013)

Joey, I could only hope to have that setup…and space…


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## joeyinsouthaustin (Sep 22, 2012)

One day right?!? It does work the same way on smaller scale


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## LyttleBryan (Nov 18, 2013)

One day!

For reference, below is an example of one I did about 20 minutes ago. It's pretty text book stuff. 

Wax paper on all the clamps
Packing tape on all the cauls.
Alternating over-under clamps.
Cauls on each end.

So where's the problem. Hopefully one day I'll find out.

Whoops, forgot the image.


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## joeyinsouthaustin (Sep 22, 2012)

IMO that quick grip does not have enough pressure to counteract the pressure of the two pony's below. Also.. your caul clamps should be moved out to the ends of the caul just at the outside edge of the outer boards. I can't see the endgrain clearly enough to eval if they are opposed. Also How are the cauls made. Do they have the slight curve in them? Other than that. Mostly get even pressure from more similar clamps. Two over, two under.


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## ClintSearl (Dec 8, 2011)

You're overclamping! Back off!


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## teejk (Jan 19, 2011)

I agree with Clint. Use a straight edge across the glue-up while it is still wet and tighten using your straight edge on your up side. Push down on the piece as you tighten using the straight edge as your bible. I love the pipe clamps but pipe is not engineered to be perfectly straight (it's sold for gas piping and absolute precision is not required).

Now the fact that you are not getting ANY glue squeeze out…I always hope to see little beads! I don't do cutting boards but seems to me that no glue means you have starved the joint and will have little Manhattan projects growing (I use TB II and view it much like a joint sealer…and yes it is FDA approved).


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## LyttleBryan (Nov 18, 2013)

Teejk, there is quite a bit of glue squeeze out in this photo, it's just hard to see because it blends so well with the maple. Starving the joint is not an issue.

Joey, I took your advice on the next one and moved things around like you suggested. I also made sure that there are the same number of over and under clamps.


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## OldRick (Oct 6, 2013)

+1 about over torqueing the clamps. I had the same problem with edge joining. Adding cauls and not torqueing the edge clamps made it a lot better. A fellow woodworker told me that you're just wanting to get the surfaces to bond together…not try to fuse them into a singularity. Leave extra thickness so you can send it through a planer when dry if possible.


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## carver1942 (Sep 25, 2013)

I have used the "*I*n and *O*ut" method that "pintodeluxe" suggests with success on panels for table tops. I don't like using cauls because if the joints don't match, pulling the boards down flat leaves a gap at the joint. This leaves a glue line that is difficult to hide on a table top or furniture panel. If care is taken jointing the boards so they are flat, and carefully joint the edges In and out to the jointer fence, they will glue up flat with out the need for cauls. Everyone has a method that they like to use for panel glue up, and you have to find what works best for you. As I said I have had success with the In and Out method. JMHO
regards
Ed


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## BinghamtonEd (Nov 30, 2011)

+1 on checking the cauls. Make sure they're straight, some people even plane a bit of a hit spot in the middle to make sure you get good pressure all across.
+1 to moving the caul clamps out

Maybe I've been starving my joints (but I've never had one fail) but that looks like a lot more squeeze out than I typically get. When you put your glue on, how much do you use and how do you do it? I run a bead along each surface, use an acid brush to spread it pretty thin, and rub them together while clamping. looks like a lot of uneven glue on the exposed edge of the second board from the right.

Maybe its the angle of the picture, and I don't have that style of Irwin clamp, but it almost looks like the face of the clamp near the grip is not square to the edge it's against.


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