JIS B 1704 regulates the specification of a bevel gears accuracy. It also groups bevel gears into 9 grades, from 0 to 8.
There are 4 types of allowable errors:
1. Single Pitch Error.
2. Pitch Variation Error.
3. Accumulated Pitch Error.
4. Runout Error of Teeth (pitch circle).
These are similar to the spur gear errors.
1. Single Pitch Error, fpt
The deviation between actual measured pitch value between any adjacent teeth and the theoretical circular pitch at the central cone distance.
2. Pitch Variation Error, fpu
Absolute pitch variation between any two adjacent teeth at the central cone distance.
3. Accumulated Pitch Error, Fp
Difference between theoretical pitch sum of any teeth interval, and the summation of actual measured pitches for the same teeth interval at the central cone distance.
4. Runout Error of Teeth, Fr
This is the maximum amount of tooth runout in the radial direction, measured by indicating a pin or ball placed between two teeth at the central cone distance. It is the pitch cone runout.
Table 15-5 presents equations for allowable values of these various errors.
Table 15-5 Equations
for Allowable Single Pitch Error, Accumulated Pitch Error and Pitch Cone
Runout Error, mm
| Table
15-6 The Formula of Allowable Pitch Variation Error (mm) |
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Besides the above errors, there are seven specifications for bevel gear blank dimensions and angles, plus an eighth that concerns the cut gear set:
1. The tolerance of the blank outside diameter and the crown to back surface distance.
2. The tolerance of the outer cone angle of the gear blank.
3. The tolerance of the cone surface runout of the gear blank.
4. The tolerance of the side surface runout of the gear blank.
5. The feeler gauge size to check the flatness of blank back surface.
6. The tolerance of the shaft runout of the gear blank.
7. The tolerance of the shaft bore dimension deviation of the gear blank.
8. The contact band of the tooth mesh.
Item 8 relates to cutting of the two mating gears' teeth. The meshing tooth contact area must be full and even across the profiles. This is an important criterion that supersedes all other blank requirements.
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.
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.
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 inspectiop of the very highest precision gears.
