13.1 Introduction

Traditional surface finish is small when compared with dimension and the demands made on instruments have been extreme. This has required sophisticated mechanical design. This sophistication is not just for the instruments but also for investigating how surfaces function when in contact and moving.

The problem when investigating very smooth surfaces and measuring round and straight objects is that the instrument has to contain the reference from which the test surface is judged. So, the need to understand the surfaces has spawned the very shapes that were being examined, only much more accurately; hence the investigation of surfaces involved development of geometrics capable of providing flats, spindles etc. for the instruments. This involved the use of kinematics, and new materials.

Surface metrology instruments differ from machine tools because forces are small but accuracies have to be high. They vary from hand-held instruments to very large systems. They have to operate in environments that are relatively hostile: manufacturing is not the cleanest of operations. All eventualities have to be considered. Careful operation cannot be assured, so checks on performance and calibration are extensive as will be seen in this chapter and the next.

13.2 Capability

It is always the case that more is demanded of equipment/people/procedures than can reasonably be asked. One question often asked is whether an instrument's performance can be improved retrospectively i.e. after purchase and after use.

The quick answer usually is no, because the instrument has been designed to meet the specification and no more.