A Photographic Study of Veneer Formation

Quality of veneer depends on what happens at the edge of the knife. Structural deformation and types of failure were analyzed under magnification and through motion pictures of the cutting action. Test blocks of cottonwood, silver maple, and sugar pine were fed against a stationary knife of known angle by using a milling machine. Two major types of failure are lathe checks and compression tearing. Although possible shear failure was observed, most lathe checks appear to be tension failures resulting from a combination of stress components that depend upon properties of the wood, veneer thickness, cutting angle, knife sharpness, and friction between the veneer and the face of the knife. The resultant maximum tensile stress at the knife edge is not necessarily perpendicular to the cutting plane. Compression tearing results from resistance to severance at the cutting edge, causing groups of cells to be pulled out of the veneer surface. By increasing the cutting angle, stresses that cause lathe checks can be reduced. Under certain conditions, failures in the face of the veneer may be caused or accentuated by the action of the nosebar. A double-surfaced nosebar was found to give added control over the cutting action.

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