Each of the datum features referenced in a datum reference frame (DRF ) constrains one or more translational or rotational degree of freedom (DOF) of the DRF.
Poor Translational Repeatability
Ideally, an axial or planar datum feature is orthogonal to any translational DOF that it constrains. If that angle is too large or too small the DRF has poor repeatability. This message is displayed when the angle is greater than 150 degrees or less than 30 degrees.
The following image shows two similar examples in which datum feature B in DRF A|B constrains translation of the part along the X-axis of the DRF.
In the example on the left, the angle between datum feature B and the X axis of the DRF is 85 degrees. As that angle departs from 90 degrees, the repeatability of the DRF degrades.
In the example on the right, the angle between datum feature B and the X axis of the DRF is 25 degrees. This example causes the test associated with this advisor message to fail.
Poor Angular Repeatability
Ideally, a planar datum feature is parallel to the axis of rotation of any rotational DOF that it constrains. If that angle approaches 90 degrees the DRF has poor repeatability. This advisor message is displayed when the angle is greater than 60 degrees.
The following image shows two similar examples in which datum feature C in DRF A|B|C constrains the rotation of part about datum A axis.
In the example on the left, datum feature B and the rotational axis of the datum A DRF are parallel. As the angle between axis A and datum feature C approaches 90 degrees, the DRF has poor repeatability.
In the example on the right, the angle between datum feature C and the rotational axis of A is 65 degrees. This condition causes the test associated with this advisor message to fail.
