When a datum feature is referenced at a material condition other than RMB (i.e. MMB or LMB), the datum feature simulator is a fixed size. 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. The movement that can occur (datum shift) is movement through any degrees of freedom that the datum feature constrains. 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). Once the cylinder is referenced at a condition other than RMB, the related tolerance zones can be optimized in rotation and translation.
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.
You can get the report to omit datum shift information by removing material modifiers on your datum feature references. You can also modify the rule tree of the report template, but I wouldn't advise it. Lastly, you can update to a version of PC-DMIS after, or including, 2020 R2. 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. This third option would be my suggestion as the newer command is much more stable than XactMeasure was with non-standard GD&T.
When a datum feature is referenced at a material condition other than RMB (i.e. MMB or LMB), the datum feature simulator is a fixed size. 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. The movement that can occur (datum shift) is movement through any degrees of freedom that the datum feature constrains. 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). Once the cylinder is referenced at a condition other than RMB, the related tolerance zones can be optimized in rotation and translation.
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.
You can get the report to omit datum shift information by removing material modifiers on your datum feature references. You can also modify the rule tree of the report template, but I wouldn't advise it. Lastly, you can update to a version of PC-DMIS after, or including, 2020 R2. 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. This third option would be my suggestion as the newer command is much more stable than XactMeasure was with non-standard GD&T.
