Mirror¶

In one sentence: Create a mirrored copy of a shape reflected about one of the three standard planes (XY, XZ, YZ) or a custom plane.

Overview¶

Workbench: Part · Menu: Part → Mirror
Toolbar: Part Modeling · Shortcut: none

Mirror creates a new Part::Mirror object containing the reflection of the selected shape about a specified plane. The original shape is preserved; the mirror is parametric and updates when the original changes.

Intuition¶

Most mechanical parts have at least one plane of symmetry. Rather than modelling both halves, model one half and mirror it. The mirrored copy updates automatically when the original changes, keeping both halves in sync.

Part Mirror differs from Part Design Mirrored: Part Mirror creates a standalone mirror copy; Part Design Mirrored is a feature inside a Body that applies to the tip solid.

When to use it¶

Creating symmetric parts from a single half-model.
Quickly testing what the mirrored version of a design looks like.
Generating symmetric compound assemblies.

Parameters¶

Parameter	Type	Default	Description
Shape	Part object	—	The shape to mirror
Mirror Plane	XY / XZ / YZ	XZ	The reflection plane (passes through origin)
Base X, Y, Z	Distance	0, 0, 0	Position of the plane origin

Step-by-step walkthrough¶

Select the shape to mirror.
Part → Mirror.
In the dialog, choose the Mirror Plane (XY, XZ, or YZ).
Adjust Base X/Y/Z if the mirror plane should not pass through the world origin.
Click OK.

Python API¶

import FreeCAD as App

doc = App.newDocument()

original = doc.addObject("Part::Box", "HalfBlock")
original.Length = 20; original.Width = 10; original.Height = 5
doc.recompute()

# Mirror about XZ plane (reflect in Y)
mirror = doc.addObject("Part::Mirror", "Mirrored")
mirror.Source = original
mirror.MirrorPlane = "XZ"  # XY, XZ, or YZ
# Position the plane at Y=0 (origin) — default
doc.recompute()

# Fuse with original to get full symmetric part
fuse = doc.addObject("Part::Fuse", "Full")
fuse.Base = original
fuse.Tool = mirror
doc.recompute()
print(f"Full part volume: {fuse.Shape.Volume:.2f} mm³")

Common mistakes and pitfalls¶

Mirror plane passes through world origin by default

If your shape is not symmetric about the origin, the mirrored copy will be at the wrong position. Set Base to the position of your symmetry plane.

Mirror creates a copy — it does not flip the original

The original shape is unchanged. If you want to flip the shape (not copy it), use Placement rotation instead.