AGMA (American Gear Manufacturers Association) and ISO (International Organization for Standardization) both define gear tooth accuracy, but they differ in metrics, tolerance grades, and application focus.
- AGMA standards (e.g., AGMA 2015, AGMA 2000) use “quality numbers” from 3 (coarsest) to 15 (finest). AGMA 9–10 is typical for general industrial; AGMA 12–14 for precision servo and aerospace. Key parameters: pitch variation (FP), profile deviation (fα), helix deviation (fβ), and runout (Fr). AGMA also includes tooth thickness allowance and backlash classes (A, B, C).
- ISO 1328-1:2013 uses grades 1 (loosest) to 12 (tightest). ISO 5–6 equals AGMA 9–10; ISO 7–8 equals AGMA 12–13; ISO 9–10 equals AGMA 14–15. ISO breaks down deviations into single pitch deviation (fpt), total cumulative pitch (Fp), profile (fα), helix (fβ), and tangential composite (Fi”).
- The main difference: AGMA emphasizes functional composite testing (double flank roll test) which is faster for production; ISO emphasizes individual flank parameters which better predict noise and high-speed behavior.
For custom gears, specify both standards to avoid confusion. Example: “AGMA 12 (equivalent to ISO 1328 Grade 7), with fα < 6 µm, fβ < 5 µm, Fr < 10 µm.” ISO is more internationally recognized for automotive and general machinery; AGMA is preferred in North American heavy industry, mining, and wind energy. For plastic or powdered metal gears, use AGMA because its composite testing tolerates slight part-to-part variation. For instrumentation or robotics, use ISO grades 4–5 (very fine) with full flank measurement.
How to specify: On your drawing, state “Gear quality per AGMA 2015-A01, Class 12” or “Tolerances per ISO 1328-1:2013, Grade 7.” Ask your manufacturer for the measurement method – a gear analyzer (Klingelnberg, Gleason) can report both simultaneously. Avoid mixing: “AGMA profile with ISO pitch” because calculation radii differ. Cost escalates with tighter grade – moving from AGMA 10 to AGMA 12 increases price ~40% due to grinding, special fixtures, and slow inspection. Unless your application (e.g., surgical robot, jet engine gearbox) demands sub-2 µm errors, stick with AGMA 10 or ISO 8 for cost efficiency.