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Mirror (Symmetry Transform)

In one sentence: Create a mirrored copy of selected sketch geometry about a chosen line within the sketch, adding the mirror image as new geometry in the same sketch.

Overview

Workbench: Sketcher · Menu: Sketch → Sketcher tools → Mirror
Toolbar: Sketcher Tools · Shortcut: none

The Symmetry transform tool (Sketcher_Symmetry) copies selected geometry and reflects it about a selected line (or sketch axis) within the same sketch. Unlike Mirror Sketch, which produces a separate sketch object, this tool adds the mirrored geometry inside the current sketch as additional edges.

Intuition

Think of folding a piece of paper and pressing hard: the ink on one side transfers to the other, giving you an exact mirror image on the same sheet. Symmetry transform does this in the sketch — you draw one half, select it, pick the mirror line, and the other half appears immediately in the same sketch.

When to use it

  • You are drawing a symmetric profile and want to draw only one half manually then mirror it to complete the sketch.
  • You want to add a symmetric feature inside an existing sketch without creating a new sketch object.
  • You need a reflected copy of a set of construction lines.

When NOT to use it

  • You want to mirror a whole sketch as a new object — use Mirror Sketch.
  • You want the two halves to remain parametrically linked by a Symmetric constraint — use the Symmetric constraint on the key points instead; Symmetry transform creates independent copies.
  • You want a 3-D mirror of a solid feature — use Part Design Mirrored.

Step-by-step walkthrough

  1. Select the geometry to mirror (the geometry to be reflected, not the mirror line).
  2. Ctrl-click the mirror line (a line in the sketch, or the sketch's horizontal/vertical axis).
  3. Activate Mirror via Sketch → Sketcher tools → Mirror or the toolbar button.
  4. The mirrored copy appears on the other side of the line. Both the original and the mirror are in the sketch.

Tip

To mirror about the sketch Y-axis, Ctrl-click the vertical axis line before activating Mirror. The sketch axes (horizontal and vertical centre lines through the origin) are always available as mirror references.

Parameters

Parameter Type Description
Geometry to mirror Selection The edges and points to be reflected.
Mirror axis Line selection The line about which to reflect. Can be any line in the sketch or the sketch axes.
Delete original Toggle (Off) If on, removes the source geometry after mirroring.

Common mistakes and pitfalls

Mirrored geometry has no constraints and adds extra DoF

Cause: Symmetry Transform copies geometry but does not copy constraints. Each mirrored element adds its DoF to the sketch.
Fix: Apply Symmetric constraints to key points, or apply Coincident and Equal constraints to ensure the mirror geometry tracks the original.

Python API

# Mirror/Symmetry is invoked via the GUI command.
# The underlying operation uses SketchObject symmetry helpers.
# TODO: verify whether a direct API call exists for the in-sketch mirror.
print("Use the Mirror tool interactively.")

See also