Tolerances and Precision in Machining of Wood

Wood, a material of plant origin, is variable. These variations in wood affect the tolerances of manufacture. Manufacturing tolerance was studied by using micrometers to measure piece-after-piece processed by a S. A. Woods hardwood matcher. Flooring pieces of 2-1/4-inch nominal width varied from practically nothing to seven thousandths of an inch. It was postulated that variations could be due to variation in texture, variation in hardness, or peculiarities of cutter action. To test the hypothesis pieces of soft-textured and hard-textured white oak were alternately processed through a Woods matcher and carefully measured. All soft pieces measured approximately 2-1/4 inches wide, and all hard pieces measured approximately seven-thousandths of an inch wider than soft pieces. The conclusion was that cutters cut the soft wood but that the wood springs or gives as a result of the cutter action against hard wood. Hard pieces also create more friction which results in heat that expands the metal. The resulting increased thrust causes shifting of the oil film around the mandrel which may also cause an increase in the dimension of the product. As an outgrowth of the tolerance study, a moisture-meter gage was designed to indicate any changes in width created in hardwood flooring by absorption of moisture. With this tool one can check any change in hardwood flooring created by change in moisture content under warehouse storage. This tool gives an easy check as to whether or not anything is wrong with the flooring.

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