The Per Unit check box appears for flatness and straightness dimensions. It lets you specify a flatness per unit area or a straightness per unit length:

Per Unit check box

When you select the Per Unit check box, PC-DMIS changes the Feature Control Frame Editor area, adding an additional line where you can enter a tolerance value as well as the unit area or unit length values:

Feature Control Frame Editor (per unit flatness)

Feature Control Frame Editor (per unit straightness)

PC-DMIS now automatically uses a step increment that ensures that the "per unit window" will include maximum overlap as it "slides" over all the point data.

Once you enter in the desired information and create the Feature Control Frame, PC-DMIS also applies the flatness per unit area or straightness per unit length in the Feature Control Frame:

For example, a flatness FCF with an overall flatness tolerance of .05 and a per unit tolerance of .01 per unit area of 10 x 10 would look like this:

Example of a Finished Per Unit Flatness FCF

For example, a straightness FCF with an overall straightness tolerance of .0254 with a per unit tolerance of .012 / per unit length of 10 would look like this:

Example of a Finished Per Unit Straightness FCF

Form Only Profile: A Form Only list appears for profile FCF dimensions if you do not specify a datum for the dimension. Whenever this list appears it signifies that the dimension is a "form only" profile dimension. A form only profile dimension determines how close the profile dimension matches the same form as its nominal. Form only ignores whether or not the location of the profile is outside of acceptable tolerances. For a Form Only dimension, pay attention to the measured values in the generated dimension.

PC-DMIS 2009 and later support the Form Only Profile of a Line when the considered feature is a constructed curve based on a linear scan. The theoretical points are projected onto the theoretical curve to determine what theoretical points and vectors to use in the profile calculation. Curves can also be used in the FCF per unit length profile of a Line.

The Form Only list contains these two items:

- Single Segment - This is a single segment overall "form only" profile (as compared to a composite or two segment profile).

- Per Unit - This behaves the same as the Per Unit check box for flatness except that for straightness and line profile, the "Per Unit" distance is a linear distance along a line (for straightness) or along a line, scan, curve, circle, or ellipse (for line profile). This item only applies to line profile, not surface profile.

Form and Location Line Profile: If you do choose a datum then a "form and location" profile is implied, and the Form Only list is replaced by the Composite check box, allowing you to determine whether or not the dimension is a composite line profile dimension. See "Composite check box" below. Form and location dimensions let you determine if a particular profile matches the same form and the same location as its nominal. This differs from the Form Only option, because the location of the profile must also be within acceptable tolerances defined by the Plus and Minus tolerances. For a form and location dimension, pay attention to Max / Min values in the generated dimension.

- A single segment "form and location" line profile:

- A double segment "form and location" line profile:

- A composite "form and location" line profile:

The Composite check box controls whether or not the primary dimension row and secondary dimension row should use the same symbol in a single merged cell that spans both rows. When you select this check box, the symbol displays like this:

If you clear the check box, the primary and secondary rows display with separate symbols, even if the symbol represents the same thing.

The ASME Y14.5 – 1994 Geometric Dimensioning and Tolerancing describes the differences in interpreting these conditions.

#### FCF (Plan) Dialog Box - Feature Control Frame Tab

FCF (Plan) - Feature Control Frame tab

The Feature Control Frame tab helps you construct a Feature Control Frame (FCF). It provides you with the tools to define datum features, select the features used in the FCF dimension, an editor to define the specific symbols, tolerances, and datums used in your FCF, and a preview area to see the current state of the FCF as you build it. For information on the various items in this tab, see the list of controls below:

ID - This box displays the name for the FCF. You can edit it if you want something different.

Features - This list displays available features for the particular FCF type. Some features may exist in the part program, but are not available to the feature control frame. For example, a plane feature is not available to Circularity. Planner updates this list after you select the first feature. This ensures that when you create a pattern of features for the FCF, those features are compatible features.

Datums - The Datums shows all the datums in the Plan. It lists datum features above the current cursor position in the Plan window. It also lists datums it will create to satisfy this FCF.

Leader Lines - This list shows the same features that you selected from the Features list. Each feature has a check box associated with it. When you select a check box, Planner draws a leader line in the Graphics Display window from the FCF to that feature. By default, Planner initially displays all possible leader lines, but you can clear check boxes to turn off leader lines as well.

Feature Control Frame Editor - This area lets you apply changes to the FCF. You can select fields with the mouse or by pressing TAB and then ENTER to place the field into edit mode. If the field is editable, it will either display a drop-down list of available options, or it will display a box into which you can type text. When finished editing a field, press ENTER, TAB, or click on a different field to exit the edit mode. Pressing SHIFT + TAB will move backwards to the previous field.

When a field is empty a short description is displayed with brackets around it for identification. These descriptions correspond to these fields:

<MC> - Material condition

<D> - Diameter

<Dim> - Dimension or feature control frame type

<PZ> - Projected zone

<num> - Number of features

<nom> - Nominal of feature size

<+tol> - Plus tolerance

<-tol> - Minus tolerance

<tol> - Tolerance

<dat> - Datum

<sym> - Dimension symbol

<add notes here> - Note field in the first line

<add optional design notes> - Optional design notes in the last line

Spherical Zone - You can use a spherical tolerance zone if you have a True Position FCF for a point or sphere feature. To enable a spherical tolerance zone, select the feature to dimension, then in the FCF editor, select the diameter symbol
and change it to the spherical zone symbol as shown here
:

Planar Zone - This button appears in the Feature Control Frame Editor area of this tab if you are defining a True Position FCF dimension or one of the orientation FCF dimensions (Perpendicularity, Parallelism, or Angularity) and the tolerance zone is set to a planar zone. To enable a planar zone and display this button, select the diameter symbol
from the FCF editor and set it to blank as shown here
:

Once the Planar Zone button appears, you can click it to open the Planar Zone Direction dialog box
.

The Planar Zone Direction dialog box lets you specify the direction vector for the planar zone in one of two ways:

- Choose an axis in the current active alignment. Select the Axis option. Then from the Axis list, select an axis from the list: X, Y, or Z.

- Input the IJK of the direction vector directly. Select the Vector option. Then in the I, J, and K boxes, type the direction vector.

This direction vector will be given in the current active alignment.

Datum Definitions - This button provides you with easy access to the Datum Definitions dialog box, allowing you to define datums for your current FCF dimension.

Feature Control Frame Options - The options in this area change based on the type of FCF dimension you are creating.

Per Unit check box

Form Only / Form and Location options

Composite check box

Actions and Procedures - This section displays hints and instructions to assist you in building valid FCFs.

Preview - This section displays a preview of the FCF with the current settings. It will not include any of the empty fields or empty descriptions that appear in the Feature Control Frame Editor section, for example fields that have brackets, such as
"<dat>".

Notes on the Feature Control Frame Editor

In the Feature Control Frame Editor area be aware that some of the icon fields, if they are not supported, will not appear for certain dimensions. For example, if you have a Circularity dimension, Planner displays the tolerance field, but hides any datum or modifier fields.

Form dimensions (Circularity or Roundness, Cylindricity, Flatness, Straightness, Profile with Form Only) - These don't support datums or modifiers, so these fields will not appear. Profile in some cases will fall in this category when checking for "Form Only". But "Form and Location" for Profile dimensions allows the display of modifiers.

Orientation dimensions (Parallelism, Perpendicularity, Angularity) - These allow datums and modifiers.

Location dimensions (True Position, Concentricity, Coaxiality, Symmetry, Profile with Form and Location) - These allow datums and modifiers.

Runout dimensions - These must have datums.

Also, only these dimensions can have multiple lines in the editor:

- True Position

- Parallelism

- Perpendicularity