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Reply by Dan Krager

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Posted on Are Most Benchtops Woefully Underclamped during Glueup? (probably not)

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Dan Krager

1573 posts in 900 days


#1 posted 12-06-2012 11:01 PM

...BTW Nicholas, 345,000/10,500 = 32.8 not 335. You might have said that tongue in cheek, but I’m a math major so… go figure!
There are a LOT of factors besides pressure that contribute to glue line failure. I have used a lot of exotic techniques for edge gluing and have so far not had a glue line failure that I noticed for any of those techniques. The most intriguing one is to plane the mating edges one at a time with a hand plane sharpened with a camber. This puts a tiny (almost microscopic) concave surface on the edge. When mated with another edge prepared the same way, there is a glue pocket formed that does not allow the joint to be starved for adhesive, and at the same time helps with closing the glue line reliably. This is not normally visible in exposed end grain.
Building tension into the glued panel that relaxes as the boards continue to age is done by planing the edges so that the center of the lengthwise joint is open when the boards are simply laid next to each other with both ends touching. We’re talking about a gap of under .005 for a six foot length. Pressure from glue clamping closes the gaps putting tension in the panel deliberately. This tension dissipates over time, but it tends to keep the ends of the panel from separating.
These two techniques have worked reliably for me over the years. I am skeptical of the research you refer to. It is possible to be so heavenly minded that you’re no earthly good. I have repaired more than my share of split tops that were poorly prepared…no glue could have held them together. I have worked with other panels that have not split and ring like a bell when tapped…still retaining some tension.
Don’t overlook moisture content. It is not necessarily uniform as one might assume. This could be a very long list if I tried to spell out all things that contribute to glue line failure. Not going to do it.
DanK

-- Dan Krager, Olney IL http://www.kragerwoodworking.weebly.com


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