Dimensions and Tolerances for Machined Furniture Parts

If wood is machined very accurately, the expensive hand-fitting of parts in furniture assembly can be eliminated. Research at North Carolina State College indicates that it is possible to machine wood to very close tolerances with the aid of statistical quality control techniques. The practice of precisely specifying dimensions and tolerances on working prints has not been extensively adopted by the furniture industry. Dimensions are usually specified in the form of a model piece of furniture. With most types of wood machining equipment, such as rip saws, planers, molders, and tenoners, there are two sources of variation–machine variation, which reflects the precision of the equipment, and setup variations, which depend on the skill of the operator. Machining to dimension is an operation ideally suited to the use of control charts X and R. These charts can indicate graphically when the operation is under satisfactory control. The best opportunity for improving wood machining operations lies in obtaining better machine set up. When the machine is set, a series of pieces are measured until a decision is made either to run or to reset the machine. Using woodworking machines to their potential level of accuracy and using good quality control techniques to fix precise tolerances can lead to decreased waste, decreased reworking, and increased uniformity and quality of the product.

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