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Understanding Point and Curve Tolerances in Fibersim

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Community Manager

Clicking Tools > Options > Fibersim Options brings users to the Fibersim Options dialog box. The bottom section of this dialog, called “Part Options”, features three tabs. Clicking the “Tolerances” tab, then double-clicking the entry below will bring up the “modify Fibersim Options” dialog:Tolerances1.jpg

Advanced Curvature Mode will be explored in another article, but before we explain the other options, it is important to point out first that the entries for Chord Tolerance, Coincidence Tolerance, and Non-Tangency Angle are initially greyed out by default. Changing the “Tolerance Setting” from “Automatic” to “Customize” will allow users to modify those three values.

Non-Tangency Angle:

Any non-tangencies between adjacent curve segments smaller than this angle will be ignored. Non-tangencies larger than this angle will be preserved.


Chord Tolerance:

Defines the maximum chord height between the true 3D curve boundary and the Fibersim tessellated curve boundary. The value is 3mm by default, unless the NX modeling tolerance* is increased above .0254mm, in which case, the Chord Tol becomes 12 times the modeling tolerance.Tolerances3.jpg

Coincidence Tolerance:

Maximum distance between two objects for them to be considered coincident (e.g. curve on surface, connected curves, etc.). It is recommended that this value NOT be lowered in order to avoid severe performance degradation.

Constant Gauge Overlap Tolerance Factor:

This value controls the tolerance Fibersim uses when computing constant gauge regions for surface offset utilities such as the Parametric Surface Offset (PSO). It is meant to reduce the effect of “slivers” generated at the corners of constant gauge regions when the offset curves of adjacent Zone Transitions aren’t perfectly parallel. Typically, such problems should be resolved by repositioning the Transitions such that their curves are parallel to one another, but when this is not possible, this tolerance factor can be increased.


Actual Tolerance:

This value accompanies the Constant Gauge Overlap Tolerance Factor and is presented for informational purposes only (it cannot be edited by the user). The value is equal to Constant Gauge Overlap Tolerance Factor times the CAD modeling tolerance.

Curve Offset Accuracy Factor:

Controls the density of points used in tessellating offset curves for Zone Transitions and other functions that involve offsetting curves. If greater curve refinement is necessary, the value can be lowered, but the computation time for such offsets (for example, when highlighting Zone Transitions) will increase.

 * When working with NX in particular, the modeling tolerance can be set as desired, but it is STRONGLY recommended to avoid changing modeling tolerances on a feature-by-feature basis. Doing so can produce unexpected results for downstream features, particularly when generating curves on surfaces with differing tolerances. This effect is exacerbated when using a complex application such as Fibersim, as we work primarily with curves on surfaces.