Minimum Allowable Dimensions for Controls Mounted on Concentric Shafts

A series of experiments was performed to determine the minimum allowable dimensions of circular, nondetent knobs mounted upon concentric shafts when frequent inadvertent operation of adjacent coaxial knobs cannot be tolerated. Both unshielded knobs and knobs whose front faces were shielded against inadvertent operation were investigated. A standard setting was used, and measures were taken of reach time, turning time and inadvertent touching of adjacent coaxial knobs. Manipulated variables were thickness, diameter and difference in diameter between the operated knob and the adjacent knobs.