![]() NOWHERE within the standard does it say to "simply add" the MMB to the feature bonus as this would be wrong, resulting in the acceptance of bad parts. In contact with the datum feature simulator, and datum 4-31, illustration (c), then the feature must remain Such as rotating away from the datum feature simulatorīeyond the established boundary limits, as shown inįig. Such that it does not fully limit or constrain the feature If the datum feature simulator geometry is The datum feature shift/displacement shallĪlways be limited or constrained by the datum feature The datum feature simulator and not the datum features. The datum reference frame is established from LMB, or surface of the feature and the datum feature The applicable (unrelated or related) actual mating envelopeįor MMB, actual minimum material envelope for In an amount that is equal to the difference between Reference will allow the datum feature to shift/displaceįrom the boundary established by the datum feature simulator MMB or LMB modifiers applied to the datum feature PC-DMIS calculates datum shift in accordance with ASME Y14.5 (see extract from Y14.5 - 2009 below - a similar statement appears in Y14.5 - 2018 section 7.11.11). ![]() This is not the first time you have made such unfounded assertions which is why I am stepping in now to prevent the spread of mis-information. ![]() Unless you can provide concrete evidence to back up your assertions, please refrain from stating that PC-DMIS is calculating datum shift incorrectly. This third option would be my suggestion as the newer command is much more stable than XactMeasure was with non-standard GD&T. The GD&T library was overhauled, the XactMeasure command was replaced with the Geometric Tolerance command, and all information on datum shift was removed from the report. Lastly, you can update to a version of PC-DMIS after, or including, 2020 R2. You can also modify the rule tree of the report template, but I wouldn't advise it. You can get the report to omit datum shift information by removing material modifiers on your datum feature references. The rules for determining the size of the MMB or LMB are considered more complex than introductory GD&T, but they are written in Y14.5 and I'd encourage you to go read through the standard to determine the rules. Once the cylinder is referenced at a condition other than RMB, the related tolerance zones can be optimized in rotation and translation. For example, a cylinder will constrain two degrees of rotation and two degrees of translation (if no other datum feature references of higher precedence constrain those particular DOF first). The movement that can occur (datum shift) is movement through any degrees of freedom that the datum feature constrains. As the datum feature departs from the fixed size, it is allowed to move around/within the datum feature simulator by an amount that corresponds to the amount of departure. MMB or LMB), the datum feature simulator is a fixed size. When a datum feature is referenced at a material condition other than RMB (i.e.
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