T-137
15.3 Running (Dynamic) Gear Testing
An alternate simple means of testing the general accuracy of a gear is to rotate it with
a mate, preferably of known high quality, and measure characteristics during rotation.
This kind of tester can be either single contact (fixed center distance method) or dual
(variable center distance method). This refers to action on one side or simultaneously on
both sides of the tooth. This is also commonly referred to as single and double flank
testing. Because of simplicity, dual contact testing is more popular than single contact.
JGMA has a specification on accuracy of running tests.
1. Dual Contact (Double Flank) Testing
In this technique, the gear is forced meshed with a master gear such that there is
intimate tooth contact on both sides and, therefore, no backlash. The contact is forced by
a loading spring. As the gears rotate, there is variation of center distance due to various
errors, most notably runout. This variation is measured and is a criterion of gear quality.
A full rotation presents the total gear error, while rotation through one pitch is a tooth-to-
tooth error. Figure 15-3 presents a typical plot for such a test.
Fig. 15-3 Example of Dual Contact Running Testing Report
For American engineers, this measurement test is identical to what AGMA designates
as Total Composite Tolerance (or error) and Tooth-to-Tooth Composite Tolerance. Both of
these parameters are also referred to in American publications as "errors", which they
truly are. Tolerance is a design value which is an inaccurate description of the parameter,
since it is an error.
Allowable errors per JGMA 116-01 are presented on the next page, in Table 15-7.
2. Single Contact Testing
In this test, the gear is mated with a master gear on a fixed center distance and set in
such a way that only one tooth side makes contact. The gears are rotated through this
single flank contact action, and the angular transmission error of the driven gear is
measured. This is a tedious testing method and is seldom used except for inspection of
the very highest precision gears.
Total (One Turn) Running Error (TCE)
One Pitch Running Error (TTCE)
One Turn
