Panel Gluing and Clamping

      To keep staves in a panel from slipping as they set, use moderate amounts of glue and clamping pressure. May 20, 2006

I am looking for some help on resolving an issue I am having while gluing up large panels of maple. When laying up a panel in our clamp carrier the staves move and create an uneven surface. We have a Doucet clamp carrier and are running the hold down bars and clamp pressure at the exact manufacturer’s specification, yet the staves slide past each other. We end up loosening the clamps and tightening them up to 5 times per panel before the panels stay flat. This only happens with our maple panels and not with our oak panels. The staves are cut square, at least as far as I can measure. Our adhesive shouldn't be the problem either as it happens with fresh glue and with glue that has been in the pan for an hour or so. We are applying the adhesive at the recommended rate or slightly higher and are getting adequate squeeze out. The panels are flat when the clamps are tightened, but as soon as the hold-down bars are retracted, the staves start to slide past each other.

Forum Responses
(Adhesives Forum)
From contributor A:
The slipping problem is probably the result of too much adhesive, too much pressure and too short an assembly time. Minimize the adhesive spread consistent with adequate coverage. Only a very small amount of squeeze out is required to assure good coverage.

Reduce the edge pressure as much as possible while, of course, assuring that adequate contact is being made. Don't be concerned with the manufacturer's suggested pressure because pressure required is determined by the precision of the machining and preparation of the edges. If this is as good as indicated you should be able to back off on the edge pressure and still insure the intimate contact required to get a good bond.

The adhesive will become tackier and less slippery as water dissipates it, and this will happen faster as the spread pieces are allowed to set in open assembly (before layup on the clamps) and also before pressure is applied. If maximum production is required, this option will have to be ruled out, but if quality is a bigger concern perhaps a delay of a few minutes while letting the adhesive tack up will alleviate the slippage.

Forum Responses
(Finishing Forum)
From Gene Wengert, technical advisor Sawing and Drying Forum:
Contributor A gives an excellent response. Let me add that the stickiness or instant tack of an adhesive varies from formulation to formulation. You may wish to explore using a little stickier glue, but watch the spread rate and squeeze out, as mentioned previously. Although it may not pertain to your situation, it is also critical to make sure that the edges that are being glued are both 90 degrees to the surface - in other words, that they are parallel to each other.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor J:
You should consider the use of some JLT panel flattener clamps. They have a long flat straight edge on the top that goes against the wood across the glue up, and a bar below that engages the bottom of a pair of adjacent clamps. They are engaged with a "vise grip" like handle that forces the stock against the rails of the clamps, holding them flat while clamping. I put just a small amount of clamping pressure on the clamps - just enough to engage the wood, then add the panel flatteners, and then finish adding clamping force on the panel. They stock always stays flat against the clamp rails. It is also very quick, and very easy to apply the panel flatteners.

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