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### Position Feature Control Frame Dimension Information

This topic displays notes and other information about the Position Feature Control Frame (FCF) dimension.

Rules on Position FCF

See the "Rules for Using Feature Control Frame Dimensions" topic where Position rules are discussed.

The Size Symbol

When choosing circular features to dimension (circles, cylinders, or spheres), you can determine the type of size symbol used on the line that defines the size tolerances for the FCF. By default, the diameter symbol is used:

However, if you want to dimension a feature's size based off its radius instead of its diameter, you can instead choose the radius symbol: R

When you click Create, PC-DMIS creates the dimension, calculating the feature's nominal size value and any tolerance values based on the type of symbol in the selected dimension:

- If you chose the diameter symbol, PC-DMIS uses the nominal diameter of the feature.

- If you chose the radius symbol, PC-DMIS uses one half the nominal diameter of the feature. The tolerance values are the radius tolerances (one half of the diameter tolerances).

For example, this table shows the exact same four circle features dimensioned using the same nominal size and tolerance values, but with different calculations due to the size symbol selected:

Using Diameter for Size | Using Radius for Size

These values are then used in other areas of PC-DMIS such as the Edit window and the Report window.

Reporting Format

The major changes in the reporting format for Position are that PC-DMIS 4.0 and later now reports the following in the Report window:

- The deviation of each feature in a set and not just the deviation of the entire set. This will help you better determine which feature is out of tolerance in a pattern of features.

- The shifted position of the datum as a result of the datum fitting (with datums of size).

- The total datum shift in X, Y, Z and rotation in U, V, W done by the fitting algorithm.

When reporting a Position FCF there is a lot of information available. To avoid confusion, and to see how the FCF affects the calculations, PC-DMIS has split this information into four parts.

1. Size information. This gets evaluated separately from the position of the feature.

2. Bonus tolerance information of the main feature or set

3. Datum information including the datum shift and datum rotation

4. Feature or set position information.

The additional information is much more useful than in versions prior to 4.0. For example, the datum shift information was not output previously, but it can be a big factor for an out of tolerance Position dimension. Now, you can tell whether the feature or datum is in the wrong place.

See "Feature Control Frame Reporting Tables for some visual examples.