Corrected capability studies with asymmetrical tolerances

Journal article, 2019

The quality assurance of dimensions with asymmetric tolerances is as important as for dimensions with symmetric tolerances. A number of methods for calculating corrected capability indices for dimensions with asymmetric tolerances have been suggested, of which all but one involves reassigning the tolerances to become symmetric. As tolerances should be specified in the design phase, not the quality assurance phase the logic of this is flawed. The methods suggested in this article result in the same values for corrected capability as the previously suggested method that does not change the tolerances. This does not mean that one of the two methods are redundant; depending on preference and to some degree the form the data is presented in suggest one is preferred over the other. This article explains how the method suggested was derived and validates the result with computer generated data.