Surfacing of the Western Pines and Associated Woods

Monetary loss due to planing degrade is of prime importance to every mill operation. Of equal importance is surface quality. The purpose of this research was to study planer operation systematically, and at the same time to record the machining characteristics of the western pines and associated woods. The variables tested related to machine design and operation–feed speed, knife angle, and knife heel. Moisture content and rough material thickness and width were held constant. The controlling of rough lumber dimensions had the effect of controlling depth of cut. The finished surfaces were analyzed for surface quality and degrade. All of the testing was performed with one machine. Various feed speeds were obtained by using different size pulleys on the feed motor. Eight species were used; the lumber was of common grades, Nos. 1 through 4, of uniform size, at 10 to 16 percent moisture content. Knife angle, the angle formed between the face of the knife and a line drawn through the center of the cylinder and intersecting the cutting circle at the point of contact of the unjointed knife, was set at 20?, 25?, and 30?. Knife heel is the area of the knife edge increased with continued jointing; the heels studied were minimum and maximum. Feed speed in inches per knife is related to the number of knives in the cylinder, revolutions per minute of the cylinder, and feed speed of the material in feet per minute; speeds studied were 0.087, 0.100, and 0.120 inch per cut. The characteristics of wood which cause difficulty in machining are knots with the diagonal grain and clear wood having diagonal grain. Variables in the planer offer the best opportunity to improve the finished product. Trained operators and machine maintenance–including replacement of worn bearings, alignment and adjustment of the machine, and maintaining the sharpness of the knives–are important. Though knife angles have slight effects upon degrade loss, various degrees of surface quality can be produced with different knife angles. Low knife angles cause raised grain due to scraping. Increasing the knife angle may cause torn grain due to the lifting action of the knives. Feed speed is the most important factor. An increase in feed speed causes an increase in chip thickness, and as thick chips resist bending, the material shears along the grain and causes fibers to break off below the surface. With all other variables controlled, feed speed can cause the greatest deterioration of surface quality and degrade loss. Since speed is related to production, it should be understood how it can be used to the fullest extent so that maximum production of high quality products can be achieved. Recommendations for optimum planer settings for the eight species used are given.

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