Recommendations
- Rotary tables and precision axes: glass encoder disc — flat, low thermal expansion, clean photolithographic lines.
- Spindle speed measurement: incremental discs with A/B and Z index are usually sufficient.
- Accuracy budget: resolution is not accuracy — graduation error, eccentricity and interpolation error dominate. See line count vs resolution and eccentricity error.
- Environment: oil and dust on the tracks affect any disc type; sealing requirements are the same for glass and metal.