Influence of square drive connections on the calibration of torque wrenches

Abstract

The influence of dimensional deviations in square drive adaptors on the calibration of torque wrenches is attributed to the effect of systematic eccentricities based on theoretical considerations. It is shown how deviations from the square cross-section, as they occur with commercially available adapters, lead to relative deviations in the calibration results of around 1·10⁻⁴. With the aid of an adjustable square drive socket of high precision, such dimensional deviations are specifically generated and investigated experimentally. The theoretical behaviour is qualitatively confirmed, and the consequences for the practical calibration of torque wrenches are discussed. A new parameter for characterising the quality of a square drive connection, the combined squareness, is proposed.