Feature of Size dimensions

Release Notes

This section reflects additions or changes that apply to Enventive Concept v4.2 and later. We strongly recommend upgrading to the most current version of Concept to take advantage of new features and bug fixes. If you are running an earlier version of the software, please open the Online Help for your version using the Enventive Concept Help menu.

Concept v4.2 includes the following position tolerance changes:

Parallelism FCFs are now stacked below their associated Position FCFs.
Position tolerances applied to rectangular Features of Size (FOS) are now modeled as standard Gaussian distributions rather than cylindrical Gaussian distributions. Previously, all Position tolerances applied to FOS were modeled as cylindrical Gaussian distributions, regardless of whether the FOS was rectangular or cylindrical.

The Cylindrical and Rectangular Feature of Size (FOS) dimensions simplify modeling specific types of parts in Enventive Concept.

Cylindrical FOS dimensions help to simplify modeling cylindrical features in a side or top view. These types of cylindrical features are common for turned parts or for holes or posts in molded or machined parts.
Rectangular FOS dimensions help to simplify modeling of wall and slot features in a side or top view. These types of features are common for molded or machined components. Rectangular FOS dimensions are automatically applied to the length and width of rectangles and the width of slots.

FOS dimensions and tolerance analysis

As derivatives of line-to-line dimensions, FOS dimensions that are contributors in tolerance analysis reports include size and orientation components. See tolerance analysis results for line-to-line dimensions for further information.

Unlike Length Equal constraints and Repetitive Size dimensions, FOS dimensions result in a single variable that provides symmetry in the part.

Note that in Enventive releases prior to v3, Length Equal constraints were recommended for simulating symmetry in some parts. With the addition of Cylindrical FOS and Mirror features in Enventive v3, this use of the Length Equal constraint is no longer recommended. Future releases of Enventive Concept will no longer provide a default tolerance setting for Length Equal dimensions and the tolerance will default to zero, with the ability to specify a User Defined tolerance if necessary (not recommended).

To place a Cylindrical FOS dimension:

Select the Cylindrical FOS Dimension tool from the Sketch toolbar.
Select two opposing lines on existing geometry in the sketch.

The Cylindrical FOS dimension is created, including a dot-dot-dash centerline between the dimensioned lines and a diameter symbol in front of the dimension value , as shown below.

To place a Rectangular FOS dimension:

Select the Rectangular FOS Dimension tool from the Sketch toolbar.
Select two opposing lines on existing geometry in the sketch.

The Rectangular FOS dimension is created, including a dashed centerline between the dimensioned lines (unlike the cylindrical FOS dimension, no special symbol denotes the dimension value), as shown below.

Note: Cylindrical (pin in hole) and Rectangular (tab in slot) FOS dimensions use two different formulas to compute the sigma value for a Side-View Floating Pin In Hole (SVFPIH) constraint. When the SVFPIH constraint is used to constrain a cylindrical pin within a rectangular slot, the rectangular formula is used. The SVFPIH constraint should not be used to constrain a rectangular tab within a cylindrical hole.

See Creating a Side-View Pin-In-Hole constraint for more information.

Applying datums to FOS dimensions

Datums can be applied to the Cylindrical and Rectangular FOS dimensions (described above).

To apply a datum to a FOS dimension, select the Datum tool from the Sketch toolbar, and then select the FOS dimension.

The datum symbol is positioned according to GD&T guidelines, as shown below, and cannot be repositioned.

Note: Per the ASME Y14.5 standard, when a datum flag is aligned with a diameter dimension, as shown above, it indicates that the center axis of the cylinder is the datum feature. (For Rectangular FOS, the center plane of the feature is the datum feature.)

Applying Position constraints to FOS dimensions

You can apply a Position constraint to a Cylindrical or Rectangular FOS dimension to specify the location and positional tolerance of the FOS dimension relative to the datum of another FOS constraint.

Note the following for Position FCFs:

Parallelism FCFs are stacked below their associated Position FCFs.
Position tolerances applied to rectangular FOS are modeled as standard Gaussian distributions rather than cylindrical Gaussian distributions.

To apply a Position constraint to a FOS dimension:

Select the Position Constraint tool from the Sketch toolbar.
Select the FOS dimension in the sketch that you want to apply the position constraint to.
Select the datum associated with a second FOS dimension (datum applied as described above).

A position tolerance FCF, a parallelism tolerance FCF, and an offset dimension (displayed as a basic dimension ) are applied to the FOS, as shown below.

Note: The basic dimension value should be set to zero whenever a FOS is supposed to be collinear/concentric with a datum. In other cases, a non-zero value may be used to specify the location of the center of the FOS with respect to a surface datum.

The parallelism FCF can be used to refine the orientation aspect of the Position tolerance.

Some drawings might specify an orientation refinement with respect to a different datum. For example, the position/symmetry tolerance would be specified with respect to Datum B, with a perpendicularity tolerance specified with respect to Datum A, as illustrated below.

However, due to the way that Enventive Concept handles constraints, it is not currently possible to define a feature’s location and orientation with respect to different datums. If you need to model this type of dimensioning scheme, please contact Enventive Support.