Q We are experiencing breakage in walnut cut-to-size chair legs, somewhat like honeycomb and straight across. Can you advise?
A What you have is “brash wood.” There are three causes. The first is due to the wood being much lighter in weight than normal. This is caused by very slow growth in porous woods. Light weight is also caused by the formation of tension wood (hardwoods) or compression wood (softwoods) within the tree.
A second cause of brash wood is decay, such as white rot. The third cause is if the wood is squeezed excessively, such as from a large clamp that was tightened excessively.
Q We are having trouble screwing into MDF. What should we do?
AThe lower the MDF density, the greater the chance that screws will not hold well without special procedures. The higher the density, the more likely that bulging will occur. The suggestion is to use a pilot hole. Use a drill bit diameter that is 85 to 90 percent of the screw’s root diameter; make the hole a little deeper than the screw’s length. Then, you can even put a few drops of epoxy in the hole prior to screwing to glue the screw to the MDF as well as achieve mechanical strength from the threads. Make sure to use special MDF screws.
Q We recently made a cabinet with stile and rail joints that were mortised and tenoned, then glued and finished. Now the joints are opening about 0.03 inches maximum, but the cracks are unsightly. Is there something we can do?
A Whenever two pieces of wood are joined with the grain of one piece running at 90 degrees to the other, you have the potential for problems. What happens is that the one piece doesn't move with moisture changes, while the other does. More precisely, along the grain, wood is stable, while across the grain, wood moves.
However, wood only moves if the moisture content changes. So, did you provide wood that was too wet or too dry? Was it stored or transported at a high humidity, or is the customer's environment too wet or too dry?
The only way we know for sure is if you measured the moisture content of the items when you manufactured them. You need to make some measurements - about 30 - on your finished pieces each day so you can guarantee that you are not shipping anything wet: over 7.5 percent moisture content in most cases. Then, you will know for certain that any moisture problems with your finished goods will not be your fault.
Source: Gene Wengert, “The Wood Doctor,” is extension specialist emeritus at the University of Wisconsin-Madison. He can be reached at [email protected]. Read past columns at WoodworkingNetwork.com
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