2.1 Visualization

The biggest problem with surfaces is that the machining marks are very small. Until the late 1920s, no attempt was made to measure the surfaces. They were examined by eye or by touching with the fingernail. These very subjective tests provided a means of comparison between good and bad surfaces. Providing that these methods were confined to within one factory they could be satisfactory, but if outside checks were needed then such an arbitrary evaluation would be insufficient.

One possibility is the use of standard comparison specimens [2.1]. These are metal plates upon which standard processes such as grinding and turning are represented by a number of roughness values. These standards are made by replication from real surfaces. The surfaces of the specimens are usually chromium-plated for wear resistance. A test surface i.e. a surface under examination can usually be identified by comparing it with the comparison standards by eye and by scratching.

These standards are useful in cases where high accuracy is not needed. Incidentally, some idea of the variety of surface properties can be obtained simply by scratching each specimen with the fingernail. An even better estimate of surface variety can be obtained by viewing the image of a strip light in the standards and varying the angle.

2.2 Profiles and roughness - understanding the measurement routine

In order to be able to make sensible estimates of roughness by either stylus or optical methods, it is necessary to define all stages in the measurement procedure. Perhaps...