T-133
Figure 15-1 is an example of pitch errors derived from data measurements made with
a dial indicator on a 15 tooth gear. Pitch differences were measured between adjacent
teeth and are plotted in the figure. From that plot, single pitch, pitch variation and accu-
mulated pitch errors are extracted and plotted.
Fig. 15-1 Examples of Pitch Errors for a 15 Tooth Gear
15.1.2 Tooth Profile Error, ff
Tooth profile error is the summation of deviation between actual tooth profile and
correct involute curve which passes through the pitch point measured perpendicular to the
actual profile. The measured band is the actual effective working surface of the gear.
However, the tooth modification area is not considered as part of profile error.
15.1.3 Runout Error of Gear Teeth, Fr
This error defines the runout of the pitch circle. It is the error in radial position of the teeth.
Most often it is measured by indicating the position of a pin or ball inserted in each tooth space
around the gear and taking the largest difference. Alternately, particularly for fine pitch gears,
the gear is rolled with a master gear on a variable center distance fixture, which records the
change in the center distance as the measure of teeth or pitch circle runout. Runout causes a
number of problems, one of which is noise. The source of this error is most often insufficient
accuracy and ruggedness of the cutting arbor and tooling system.
15.1.4 Lead Error, fb
Lead error is the deviation of the actual advance of the tooth profile from the ideal
value or position. Lead error results in poor tooth contact, particularly concentrating
contact to the tip area. Modifications, such as tooth crowning and relieving can alleviate
this error to some degree.
Shown in Figure 15-2 (on the following page) is an example of a chart measuring
tooth profile error and lead error using a Zeiss UMC 550 tester.
20
15
10
5
0
–5
–10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A
B
C
Tooth Position Number
NOTE:
A = Max. Single Pitch Error
B = Max. Accumulated Error
C = Max. Pitch Variation Error
= Indicator Reading
= Single Pitch Error
= Accumulate Pitch Error
