How to quickly learn ASME

Dimensional and geometric tolerances according to ASME Y14.5-2018

A dimensional and geometrical tolerance can not only be based on ISO-GPS standards, but also on the basis of "tolerance tools" and rules that are in ASME standards (ASME = American Society of Mechanical Engineers), in particular ASME Y14.5-2018. Since the ASME and ISO-GPS standards are increasingly being aligned, the actual (critical) difference today is less in the symbols used than in rules and principles that are not directly visible in the product specification (default rules). Typical examples include:

  • "rule # 1", a material condition comparable to the "envelope principle" for the relationship between size and shape of linear size elements. This rule applies as agreed with the reference to ASME Y14.5.
  • Partly different calculation of the effective maximum material dimension (MMVS) according to ASME and ISO (ISO 2692).
  • Different rules for the formation of reference systems. While according to ISO 5459 only secondary conditions of the direction between the situation elements of the associated areas are specified, it is based on ASME-coded specifications, secondary conditions of the direction and location. This largely unknown difference must be taken into account when setting up reference systems but also during later verification
  • Differences in the definition and evaluation of derived toleranced geometry elements (e.g. middle line and middle plane) between ASME and ISO GPS in the limitation of concentricity / coaxiality or symmetry deviations through position.
  • Blocking of rotational degrees of freedom of the tolerance zone through the specified references when using composite tolerances with position or profile tolerances.

A misinterpretation of ASME-coded customer product specifications or the widespread practice of adopting ASME-based customer-specific drawing headers in product specifications that have been created according to the rules of ISO GPS, as well as ignorance of the most important "default rules" (ASME Y14.5-2018, ASME Y14.5-2009 or ASME Y14.5M-1994), can very quickly lead to unnecessary discussions between the contractual partners, to non-functional products that do not meet customer requirements, to an incorrect quality assessment of the product and ultimately to problems in connection with product liability.