What is the ISO 1940 Standard?

The ISO 1940 standard is a globally recognized reference used to define the permissible unbalance levels for rotating parts. This standard establishes different quality grades (G-classes) based on the part's rotational speed and application. For example, a G2.5 grade is used for high-precision shafts and motor rotors, while a G6.3 grade is suitable for lower-speed and less-sensitive parts. This classification provides a clear guideline for engineers and manufacturers on how well a part needs to be balanced. It ensures that critical components operate safely and efficiently, while avoiding unnecessary costs and time spent on achieving excessively high precision.

ISO 1940 is an essential guide for ensuring quality and consistency in balancing processes. Choosing the correct G-class for a part's intended use extends bearing life, reduces vibration, and improves a machine's overall performance. At MBS Balance, we design all our industrial balancing machines and services to comply with these international standards. Working with our customers, we determine the most appropriate ISO 1940 quality level for the specific needs of their parts, providing solutions that are both reliable and cost-effective.

ISO 1940-1 has been updated since 2003 and is in force under the name ISO 21940-11; the content and the G grade logic have been preserved. The core of the standard is that it defines the permissible specific unbalance with the relation e_per = (G × 1000) / w, where G is the quality grade (mm/s) and w is the angular operating speed in rad/s. This formula explains why the same G grade corresponds to a much smaller gram-millimeter tolerance at high speed.

Common G Quality Grades

• G0.4 - gyroscopes, precision grinding spindles
• G1 - recording spindles, precision grinding spindles
• G2.5 - gas and steam turbines, electric motor rotors, compressors
• G6.3 - fans, pumps, general machine parts
• G16 - drive shafts, cardan shafts
• G40 - automobile rims and wheels

MBS Balance selects the correct G grade together with the part's speed and mass to calculate the permissible residual unbalance and configures its balancing machines in full compliance with this standard.