Avoiding Gaps in Your Glue Up - Question of the Week

April 23, 2008 by thewoodwhisperer
Filed under: Question of the Week 

This week’s question comes from Mike. He writes:

My most recent project as I’ve mentioned to you before is a baby crib for our first child. This crib will later convert to a day bed and then a full size bed. Therefore there are several legs that must be built first, 6 in total. These legs are built up of 3 pieces of 3/4″ maple laminated together. The center piece is planed slightly thinner to match the thickness of 3/4″ maple ply for the rails that will be mortised into the legs. Once I began to glue the boards together I realized I have some difficulty when it comes to clamping, more specifically knowing how to clamp properly.

I recently purchased some of Rockler’s F-style clamps. I love them and started with them however I quickly realized that they were probably not the right clamps to use for this application. I then grabbed some of my hand screw wood clamps. They seemed to give me a better spread across the boards which are 2 3/4″ wide. I supplemented with the f-style clamps using wood blocks to spread the clamping pressure evenly I do not own any small parallel jaw clamps or I would have used them for this job. What I ended up with was some of the legs went together well with no gaps in my glue joints while others has small gaps in the glue joints the full length of the legs that will have to be filled. How can I avoid this in the future? I’m not concerned that they will come apart because there will be some fasteners that go through the legs to attach the railings, but I would like to have tight glue joints when laminating several boards together so I don’t have to do so much gap filling before I go to finishing.

And here was my reply:
Hey Mike. Excellent question. Using “less than optimal” clamps is something many of use have to deal with. And there really is no big secret. It just comes down to lots of clamps and lots of pressure. I would recommend using cauls that are at least as long as the leg is wide. Then, I would use the F-style clamps to clamp down over the cauls. And since one clamp in the center of the caul may still not apply enough pressure at the edges of the leg, I would recommend putting two F-style clamps at the ends of the neighboring caul. So in effect you will alternate: one centered, two on the edges, one centered, two on the edges, etc… Do this across the leg every 4-5 inches (the closer the better), and you should have enough pressure. From your description, it really sounds like you had enough pressure at the center of the leg, but not at the edges. Of course this means you need a lot of clamps! But as they say, you can never have too many. And kust so you know, the way I do this: I use the parallel clamps and alternate the sides they clamp from. Then I actually reinforce the clamping with F-style clamps in between the parallels. Good luck.

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Comments

6 Comments on Avoiding Gaps in Your Glue Up - Question of the Week

  1. Chris on Wed, 23rd Apr 2008 6:56 pm

    2. Hi Mark, Mike,

    As a high school shop teacher I am asked this type of question a lot. What I’ve been taught is that the pressure from the clamping surface extends from the clamp in a 90 degree cone (45 degrees projecting from either side of the clamp face). The lines that extend out at 45 degrees should intersect each other prior to the first glue joint. If they don’t you need more clamps until they do. Thus narrower stock would require clamps closer together than wider stock.

    Alternating the sides that you are clamping from is definitely critical as well, and make sure you use enough glue and don’t starve the joint.

    Just thought I’d add my 2 cents.

  2. Jason on Wed, 23rd Apr 2008 7:24 pm

    3. Marc,
    I may be alone in this, but I can’t picture what you’re describing. Will you take a picture of this kind of glue-up.

    Thanks,
    Jason

  3. Quiglag on Wed, 23rd Apr 2008 9:52 pm

    4. I second what Jason said. I need pictures :)

    I will have to keep the 90 deg clamp pressure idea in mind next time I clamp something. It sounds like a good theory.

  4. Marcus on Thu, 24th Apr 2008 1:54 am

    5. Hello Mike,

    a siple thing would be to use a handplane with a cambered blade to create a verry slight hollow in the middle of your boards. That forces an enhanced pressure on the outside edges of boards.

    This is known as sprung joint for edge jointing but also works for face jointing like you did.

    Best regards

    Marcus

  5. Trent on Sat, 3rd May 2008 10:58 am

    6. What will you use to fill the gaps? I have a similar problem with a piece that has to be stained. Thanks.

  6. thewoodwhisperer on Sat, 3rd May 2008 1:22 pm

    7. I would recommend filling it with a stain-able wood filler. You can use epoxy or CA Glue to fill the gap, but the stain won’t penetrate and it might become an eyesore.

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