Meaning
Geometric requirements for motion transmission components define the permissible deviations from a theoretical tooth profile. The iso 1328 gear accuracy standard establishes the classification system for assessing the quality of cylindrical involute gears. This framework provides a common language for designers and manufacturers to specify the precision needed for a particular application.
It excludes other gear types such as bevel gears to focus on the specific meshing characteristics of spur and helical teeth.
Grade Classification
Numerical values ranging from 0 to 12 designate the level of precision, where lower numbers indicate tighter tolerances. Most industrial applications for moulded plastic gears fall between grades 8 and 12. Aerospace or high speed automotive components require the higher precision of lower grades.
Tolerance Specification
Deviations in profile and pitch are measured and compared against the limits set for each grade. A gear qualifies for a specific accuracy level only if all its measured parameters fall within the maximum allowable error for that grade. Designers select these levels based on the required speed and the noise sensitivity of the final assembly.
Higher accuracy grades necessitate more expensive tooling and more rigorous cooling control. Precise measurement of these errors requires specialized coordinate measuring machines or gear testers.
Moulding Variation
Shrinkage and warpage in semi-crystalline resins make holding tight accuracy grades difficult during high volume production. Tools must be cut with precise compensation to account for how the material pulls away from the cavity walls. Small changes in barrel temperature or hold time can shift a gear by several accuracy grades.
