Q. I have a recently made table top that is now cupping—Why and what can I do? The doors that left our facility were flat, but now are warped…Why and what can I do? We are seeing some open glue joints at the ends of our edge-glued panels…Why and what can I do?

A. At least one quarter of the questions and requests for assistance that I receive are concerned about a problem or defect that developed after the product was manufactured. In response, perhaps we (you the reader and I) can formulate as list of basic wood processing principles. How about we call them “The Wood Doctor’s Commandments,” unless someone has a better idea for a title. So here we go with #1. #2, #3 and #4. These are not “written in stone,” so we can change them to make them better.


The Wood Doctor’s Commandment #1. Wood does not move, shrink or swell, (including warp) unless the moisture content (MC) changes. Therefore, it is critical to match (within 2 percent MC) the MC of the lumber used in manufacturing to the expected MC when the final product is in service. Obviously, maintain this MC during manufacturing, shipment and storage.


The Wood Doctor’s Commandment #2. In dry wood products, a glue joint is 1-1/2 times stronger than the wood. So any glue joint failure is the result of improper gluing procedures. Surface flatness, joint pressure and wood MC are critical when gluing wood. However, almost all gluing failures are related to incorrect MC.


The Wood Doctor’s Commandment #3. The best electronic moisture content meter is one that is used by the employees. In most cases this means used at least several times every day, with readings recorded and graphed so that operating decisions can be made. Pin-type or pinless is OK. Just make sure you know the limitations of your meter. For ease of repairs, I suggest “Made in USA.”


The Wood Doctor’s Commandment #4. When cutting lumber into parts, the ripping operation is usually where most volume is lost. Therefore, to maximize yield and minimize cost, use the most sophisticated scanning system for the rip operation that you can afford. Serious attention given to efficient ripping is well worth the effort.


Proposed: The Wood Doctor’s Commandment #5. Most wood businesses are profitable. However, most wood businesses have cyclical income, month to month. Therefore, a wood business must have adequate cash reserves to cover the slow months. This also means: Do not spend cash reserves for equipment, but get a loan.


Gene Wengert, [email protected]

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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