Q. When edge gluing, what will provide the better edge prep, a moulder or a rip sawblade? We rip now, but….
A: I am reading between the lines and suspect that you are having some gluing failures. Appreciate that the strongest glue joint is made when the edge surface is made no more than about 15 minutes before gluing. At the same time, often we only need a joint that is 40 percent of the maximum possible strength, so we can be a bit sloppy and still be happy…until your needs change and nobody tells the gluing people that you need a stronger joint…maybe 80 percent of the maximum. In short, aged surfaces are not a good gluing surface.
We also need a gluing surface that is not burnished, that does not have loose fibers and that does not have squished or damaged fibers. That is, we need a clean cut. A dull moulder blade or a dull saw will both make terrible surfaces.
One quick test for a surface to be glued is to put a water droplet on the surface. The droplet should be absorbed within a minute if the surface is ready for gluing. This droplet test does not tell you, however, if the fibers have been damaged.
A sharp moulder blade or cutter creates an ideal surface. However, you do need to pay a lot of attention to keeping the cutter sharp. Sloppiness in sharpening will mean poorer joints.
Concerning rip saws, let me ask you “What part of the saw tooth touches the surface that you will glue?”
The answer is “The sides of the tooth” and not the "sharp" part of the tooth. Therefore, you need a ripsaw blade that has the correct tooth design and then has sharp sides on the tooth. The process of sharpening is called side-dressing. A good saw shop will know this and can do it. Many shops do not do it. With proper saw side-dressing the surfaces will be "clean" and not smashed or crushed.
Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.
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