Abstract
The parameters of microtome sectioning are defined, and the use of the diamond knife ultra microtome for metallurgical studies is described. The effect of cutting stresses on the formation of sections is discussed. It is reasoned that vibration of parts of the cutting system would only be excited by the first impact of the specimen or the knife and not by the forces acting on them throughout cutting. Vibration is shown to produce smooth variations in section thickness, the thickness being constant all along any normal to the direction of cutting, and varying along the direction of cutting. Knife marks are shown to be due to variations in cutting stress associated with knife edge defects; these produce variations in the thickness and structure of the section, even when the mechanism proposed by Farrant cannot apply. Some folds and wrinkles are explained as being due to variation in cutting stress due to variations in knife edge quality. All the above defects can be avoided by a proper choice of experimental conditions, but it is shown that there is a shear stress imposed on the section during cutting which in the majority of cases permanently deforms it, producing a surface structure characteristic of the material being cut.