Online Calculator Size at Reversal Point
There are different instruments to inspect the size over/between two balls. The most simple instrument is based on the rocking method. These hand-held instruments are equipped with measuring inserts and a dial indicator. The nominal size is adjusted by gauge blocks. Afterwards, the operator needs to find the reversal point to receive the relative deviation.
Special case of helical gears with odd number of teeth
The reversal point will not coincide with the required measuring plane (perpendicular to the gear axis). As a consequence, the operator detects a deviation that is too large.
To use the available measuring instrument anyway, it must not be adjusted to the nominal size but to the dimension at the reversal point. This can be calculated online with following tool, just enter your gear data below.
FRENCO held a presentation at GETPRO 2015 about this topic.