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Increase Tolerance Feature

In one sentence: Wrap a shape with a feature that increases its OCCT geometric tolerance to help boolean operations that fail on near-coincident geometry.

Overview

Workbench: OpenSCAD
Menu: OpenSCAD → Increase Tolerance Feature
Shortcut: none

Creates a Part::FeaturePython wrapper around the selected shape that increases the OpenCASCADE geometric tolerance from the default 1 × 10⁻⁷ mm to a higher value. The source object is hidden. Used as a last-resort repair technique when boolean operations fail because vertices or edges are just slightly outside the tolerance threshold.

Intuition

FreeCAD's geometry kernel (OCCT) uses a tolerance threshold to decide whether two points, edges, or vertices are "the same". If two vertices are 2 × 10⁻⁷ mm apart, OCCT considers them different; boolean operations then fail at that junction. Increase Tolerance Feature tells OCCT to treat a slightly larger distance as "the same", allowing the operation to succeed.

When to use it

  • A Boolean Union, Intersection, or Difference fails with "bad result" or "invalid shape" on geometry that visually looks correct.
  • You suspect near-coincident vertices or edges are causing the failure.
  • Other repair methods (Refine Shape Feature, ShapeHeal) have not helped.

When NOT to use it

  • As a first resort — always try fixing the geometry root cause first. Increased tolerance makes the shape less precise.
  • On high-precision parts — the tolerance increase degrades geometric accuracy. Document the deviation from nominal when using this on precision parts.

Step-by-step

  1. Select the Part::Feature that is causing the boolean to fail.
  2. Choose OpenSCAD → Increase Tolerance Feature.
  3. A Part::FeaturePython is created; the original is hidden.
  4. Retry the boolean operation on the new tolerance-increased feature.

Parameters

No task panel — the tolerance increase is a fixed default step.

Common mistakes and pitfalls

Increased tolerance makes the shape less precise

Cause: By design — this is a repair workaround, not a clean solution.
Fix: After the boolean succeeds, consider re-modelling the original geometry to avoid the near-coincident topology.

Python API

import FreeCADGui as Gui
Gui.doCommand("Gui.runCommand('OpenSCAD_IncreaseToleranceFeature', 0)")

See also