TABLE OF CONTENTS The unit event will also produce a sub-surface pattern that will follow the topography texture patterns given above. The example given in Figure 2.23 shows a burnished deep drilled surface where the feedrate was 0.13 mm.rev ?1. The sub-surface altered material regions are not constant within each unit event but they are repeated in a cyclic manner at a frequency corresponding to the feed. The hardness at a depth of 4 ?m fluctuates by 50% within each feedrate. This hardening is caused by a combination of plastic deformation and heating. The Figure shows a transverse photomicrograph that reflects a radial section through the hole. In 3D terms this sub-surface texture will be in a helical form corresponding to the helical motion of the drill passing through the hole. This corresponds to a texture class 1a. However, the main texture direction is inclined at an angle to the horizontal datum corresponding to the helix angle. If one wanted to be pedantic, one could say that such a helical texture does not actually fit into any of the texture classes. In this case it is irrelevant because the helix angle is only 0.1 . In other cases, it may be very significant. For example, the texture inclination is important on a file surface where the texture angle represents the angle of attack of the cutting teeth. The surface of a file would not fit into any of the texture classes because the lay is...
