Shaft-to-shaft is just one form of machine alignment that is synonymous with just plain "alignment." The previous chapter on component alignment went internal to a machine's housing to discuss alignment on a smaller scale. This chapter will cover the most general and universal alignment methods used on a larger scale.

An optical line of sight is the most perfect straight line. The instruments and methods used here are borrowed from surveying practice, and the optical alignment task is best relegated to the civil engineering section. Optical tooling is extremely precise, and the methods are highly technical. The task requires a good knowledge of the instrument's errors and proper methods of nullifying those errors. There are many pitfalls waiting to snag the novice. The instrument operator must be a person of perseverance, perfection, and patience. This chapter is not large enough to teach proficiency in this subject. It is intended to expose the reader to the possibilities of optical measurements.

The key metrology feature of optical tooling is the most precise gravity-sensing devices that are available. These can detect an earth radian and establish a vertical line. With this vertical known, a telescope can be rotated on this vertical axis to sweep out a horizontal plane. Leveling is the most basic purpose for optical tools. Another feature of optics is to establish a perfect line of sight in any direction, and to measure that direction. In other words, angles can be measured very accurately. Therein lies the crucial aspect of...