T-131
SECTION 15 GEAR ACCURACY
Gears are one of the basic elements used to transmit power and position. As designers,
we desire them to meet various demands:
1. Minimum size.
2. Maximum power capability.
3. Minimum noise (silent operation).
4. Accurate rotation/position.
To meet various levels of these demands requires appropriate degrees of gear
accuracy. This involves several gear features.
15.1 Accuracy Of Spur And Helical Gears
This discussion of spur and helical gear accuracy is based upon JIS B 1702 standard.
This specification describes 9 grades of gear accuracy – grouped from 0 through 8 – and
four types of pitch errors:
Single pitch error.
Pitch variation error.
Accumulated pitch error.
Normal pitch error.
Single pitch error, pitch variation and accumulated pitch errors are closely related with
each other.
15.1.1 Pitch Errors of Gear Teeth
1. Single Pitch Error (fpt)
The deviation between actual measured pitch value between any adjacent
tooth surface and theoretical circular pitch.
2. Pitch Variation Error (fpu)
Actual pitch variation between any two adjacent teeth. In the ideal case,
the pitch variation error will be zero.
3. Accumulated Pitch Error (Fp)
Difference between theoretical summation over any number of teeth
interval, and summation of actual pitch measurement over the same
interval.
4. Normal Pitch Error (fpb)
It is the difference between theoretical normal pitch and its actual
measured value.
The major element to influence the pitch errors is the runout of gear flank groove.
