A:When a glue joint is formed, there are two components to
its ultimate strength. One component is the mechanical strength
that results because the two pieces of wood are full of nooks
and crannies. The glue fills these spaces and then solidifies.
(Analogy: Think of a puzzle that has interlocking pieces. This
interlocking provides some strength.) If you try to slip the
one piece that has been glued past the other, the solid glue
that fills the nooks and crannies will resist this shearing
movement very well.
However, if you try to pull this joint apart (that is, put
it under tension), these small nooks and crannies are not very
strong in tension and so the joint will fail easily. What
builds up tension strength (or pulling apart rather than shear
strength) is the chemical bonding between the wood and the
adhesive. So, the second component of a strong glue bond is
Unless the surface to be glued is very fuzzy or is damaged,
or if there is a lack of glue or adequate pressure, the
mechanical bonding will occur 100 percent of the time. The
chemical bonding will occur only if the wood is receptive; that
is, if the bonding sites are not oily, occupied with dust or
moisture, and so on.
(In all the years I have worked in troubleshooting, I have
seen a gluing problem related to the adhesive only twice; all
the other times, the problem is related to the wood itself.) If
I were you, I would be interested in this tension strength of
my joint, as this is what is failing when you have a weak
joint. The shear test is not what you need. Instead, use a
Q: We are getting a lot of cupping in some of our lumber. What is causing this and what can we do to fix it?
Getting the most from a widebelt sander and abrasives is a matter of balancing your budget with proper features to perform the work needed.
Proper heat treatment is as important as the selection of HSS for tooling.
The companies in this directory are making investments to make sure that you have the tools and products necessary to develop successful products with lightweight panels.
Q: I have read every Wood Doctor column you have written and have gained a lot of practical information. But here is a question I have not seen addressed before. As background, our fairly large company has really gone into JIT, just-in-time, manufacturing, which means in-process materials cannot sit around very long at all. Well, this has recently translated into machining our glued up panels (edge-glued on a clamp carrier) within 24 hours after they are glued, or sometimes less. Of course, you know what the problem is: sunken glue joints that are obvious after finishing. My suggestion of waiting three days after gluing, as we have always done, has not been well-received. I am hoping that you have some help for us.
Avian has reported that its lightweight board meets and exceeds the CARB 2 standards making it one of only a few suppliers of CARB 2 standard boards.
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