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Perpendicular Joint

In one sentence: Force two axes or face normals to be exactly 90° apart — for right-angle drives, orthogonal frames, and brackets.

Overview

Workbench: Assembly
Menu: Assembly → Joints → Perpendicular
Shortcut: M
DOF removed: 1 | DOF remaining: 2 rotations + 3 translations

A Perpendicular joint constrains one rotational DOF — the one that would change the angle between the two directions away from 90° — while leaving all other rotations and all translations free.

Intuition

A Perpendicular joint is essentially an Angle joint locked at exactly 90°. Think of a right-angle bracket: no matter where or how the bracket is positioned, the two legs of the bracket must always be at 90° to each other. The Perpendicular joint enforces this angular relationship.

When to use it

  • Right-angle drive mechanisms (bevel gears, worm gears) where two shafts must be 90° apart.
  • Structural frames and brackets where one member must be orthogonal to another.
  • Linkage constraints where an output member must always stay perpendicular to its input.
  • Assembly alignment when a part must be mounted at exactly 90° to a reference face.

When NOT to use it

  • Don't use Perpendicular for an arbitrary angle — use Angle instead.
  • Don't use Perpendicular in addition to a Revolute if they constrain the same rotation — the Revolute already removes all off-axis rotations; adding Perpendicular for the same axes over-constrains the system.

Step-by-step

  1. Press M or choose Assembly → Joints → Perpendicular.
  2. Click a cylindrical face, linear edge, or planar face on Part 1.
  3. Click the corresponding geometry on Part 2.
  4. Click OK.

The solver adjusts Part 2 so the two selected directions are exactly 90° apart.

Parameters

Parameter Type Description
Reference 1 Link Direction-defining geometry on Part 1
Reference 2 Link Direction-defining geometry on Part 2

Python API

Minimal example

import FreeCAD as App

doc = App.ActiveDocument
asm = doc.getObject("Assembly")

joint = asm.Joints.newObject("Assembly::JointObject", "RightAngleDrive")
joint.JointType = "Perpendicular"
joint.Reference1 = (doc.getObject("InputShaft"), ["Face2"])
joint.Reference2 = (doc.getObject("OutputShaft"), ["Face2"])
doc.recompute()

Common mistakes and pitfalls

Reference geometry must unambiguously define a direction

Select a cylindrical face (defines the axis), a linear edge (defines the edge direction), or a planar face (defines the normal). Selecting a vertex does not define a direction and will fail or give unexpected results.

Perpendicular leaves 2 rotations free

This joint only removes 1 rotational DOF — the one that controls the angle between the two directions. Two rotational DOF remain free. If full orientation is needed, add further geometric joints.

See also