Exact analytical solutions to obtain transmission errors with radial eccentricities of involute cylindrical gears are derived. Transmission errors including eccentricities of a pair of spur gear are measured and compared with analytical results. The measured and calculated transmission errors agree with each other and the proposed analysis is verified accurately. The influence of phase angle differences is investigated under no load. It is quite small but is not negligible comparing to the amount of transmission error caused by tooth flank topography and tooth deflections. In addition, transmission error of a micro gear system is calculated. The result shows that if the system is similar in shape, the calculated results are exactly the same. That means it will be quite difficult for the micro gear system to keep smooth engagement comparing to the conventional one.
