Position (True Position)

Position checks provide the ability to evaluate size, orientation and location. The number of datums specified, the number of measurements and the type of feature determines the way in which the evaluation is conducted. Here we will just consider a basic hole position check.

Evaluation Process within SA:

  1. The feature measurements are used to establish the center point or axis of the measured feature.

  2. The maximum point or axial deviation is minimized after aligning to the datums and using any degrees of freedom not locked down by the datums.

  3. The maximum deviation is doubled to define the measured deviation, any bonus tolerances are applied, and compared to the tolerance zone for evaluation.

Reporting

Tolerance Definitions Zones

Several Tolerance Zones options can be set for position evaluations on different features.

The geometry type has a direct influence on how a position check is evaluated. Cylinders can be evaluated as lines, circles, or full cylinders based on a user select. The extent of the evaluation is established by the extent of the measurements unless otherwise specified.

The offsets on points used in a position check on a line are ignored. The expectation as that measurements are on the axis.

 

 

Composite True Position

Composite Position Checks provide a means to evaluate the position of a pattern of features and combine that with a tighter evaluation of the position of each feature relative to each other feature within a single check. So for example, this allows you to check if a bolt hole pattern matches the correct location on the part at a lower tolerance while also verifying that the pattern is correct at a higher tolerance.

Evaluation Process within SA:

  1. The upper tier is evaluated following the position check guidelines above.

  2. The feature is then released to translate freely and rotate within the degrees of freedom not locked down by datums in the second tier and evaluated again.

  3. The check is passed only if both evaluations pass.