Form Tolerances

Abstract

It is possible to control four form tolerance types: straightness, flatness, roundness and cylindricity. The chapter covers all the concepts necessary to define specification operators (according to ISO 17450-2) and some procedures to establish the reference elements in order to define the deviation errors. Some terms related to form parameters are described such as peak-to-valley, peak-to-reference and reference-to-valley deviations. The ASME standards use the envelope requirements or Rule #1, according to which form tolerances are contained within the dimensional ones, and these tolerances are therefore only used with the purpose of limiting the error when the workpiece is produced with dimensions close to the least material condition.