Desirable Dimensions for Concentric Controls

Abstract

A series of experiments was performed to determine the minimum allowable dimensions of circular, non-detent knobs, mounted on concentric shafts, when frequent inadvertent operation of adjacent coaxial knobs cannot be tolerated. 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. It was concluded that if three knobs are to be concentrically ganged and if the middle knob is about 2 in. in diameter, (a) the diameter of the front knob should be at least 1 in. smaller and that of the back knob 1¼ in. greater than that of the middle knob, and (b) the front and middle knobs should each be ¾ in. thick, whereas the back knob may be as thin as ¼ in.