Q. When our crosscut or chop saws cut the end of oak strips, the end has many small splinters. Do these affect or cause the joint failure we see?
A. First, the chop saws need a plate, maybe wood, at the back of the saw to hold the fibers against the wood piece as the saw completes the cut. It needs to be very close to the saw blade itself. Sometimes this is called a backer. In a planer, it is a chip breaker. When this is not done, the saw will break them off instead of cutting them, which is what you see.
Second, it is likely that they will affect gluing very slightly with oak, but less so with softer woods. However, the effect is only at the very end. If the failure goes beyond the last 1/8 inch, then there is a bigger issue with the surface preparation, pressure or other factors. As you know, the joint should be 150 percent stronger than the wood itself. So, you need to look for why your joints are not full strength.
One of the most common causes for a weak glue joint at the ends is that the strips are cut one day and then, because the moisture in the air is not in equilibrium with the moisture in the wood, the wood changes moisture, especially at the ends. The ends absorb moisture at least ten times faster than the faces, and if in a tight stack, the difference is even greater.
With a moisture change, there is a size change that occurs, so the two pieces of wood being edge glued are not within 0.002 to 0.006 inch. This effect is greater when we are in the heating season, which means drier air in the plant, so the ends dry and shrink. You may need an outside person to come and examine the situation closely.
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.
Have something to say? Share your thoughts with us in the comments below.