Full definition
The precision process of positioning two coupled rotating shafts so their rotational centerlines are collinear (or at a precisely defined offset for specific coupling types), minimizing the forces that cause premature bearing, seal, and coupling failure. Methods in order of precision: (1) Straightedge and feeler gauge — crude, ±0.2 mm, suitable for initial rough alignment only. (2) Dial indicator (rim-and-face or reverse indicator) — ±0.02 mm, traditional precision method requiring skilled technician. (3) Laser alignment — ±0.001-0.01 mm, fastest, most accurate, with thermal growth compensation; the modern standard. Tolerances per API 686 and coupling manufacturer recommendations: typically <0.05 mm offset and <0.05 mm/100 mm angular for general industrial machinery; tighter for precision equipment. Misalignment is the #2 cause of rotating machinery failure (after contamination/lubrication), responsible for up to 50% of premature failures. Even 0.1 mm of offset can reduce bearing life by 50% and increase energy consumption by 2-5%. Per API 686 (machinery installation and alignment), ISO 10816 (vibration severity), and coupling manufacturer tolerances. Tools: SKF TKSA, Fixturlaser NXA, Pruftechnik Rotalign.