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Cylindrical Joint

In one sentence: Allow a part to both rotate and slide along a single axis simultaneously — the joint for splined shafts and telescoping drives.

Overview

Workbench: Assembly
Menu: Assembly → Joints → Cylindrical
Shortcut: C
DOF removed: 4 | DOF remaining: 2 (rotation + translation along one axis)

A Cylindrical joint aligns two axes and keeps them co-linear while allowing both free rotation and free axial translation about that shared axis. All off-axis translation and off-axis rotation are locked. It is the combination of a Revolute and a Slider on the same axis — but with the rotation and translation completely independent of each other.

Intuition

Imagine a pen cap sliding onto a pen barrel: the cap can both rotate around the barrel's axis and slide along it — two independent DOF on one axis, with no motion permitted in any other direction. A Cylindrical joint models exactly this.

The key distinction from a Screw joint is independence: in a Cylindrical joint the part can rotate without advancing and advance without rotating. In a Screw joint, rotation and translation are rigidly linked by a pitch ratio.

When to use it

  • A splined shaft that can both spin and slide axially in a splined bore (e.g. telescoping drive shaft, sliding gear selector).
  • A telescoping tube where both rotation and length change are independent.
  • Any mechanism where rotation and axial translation on one axis must be independently free.

When NOT to use it

  • Don't use Cylindrical if rotation and translation are linked by a ratio — use Screw instead (a Cylindrical joint with a fixed pitch coupling).
  • Don't use Cylindrical if the shaft cannot slide — use Revolute to lock axial translation.
  • Don't use Cylindrical if the shaft cannot rotate — use Slider to lock rotation.

Step-by-step

  1. Press C or choose Assembly → Joints → Cylindrical.
  2. Click a cylindrical face or circular edge on Part 1.
  3. Click the mating cylindrical face or edge on Part 2.
  4. Optionally set an Offset (initial axial position) and Rotation (initial angle) in the task panel.
  5. Click OK.

Parameters

Parameter Type Default Description
Reference 1 Link — Cylindrical face or circular edge on Part 1
Reference 2 Link — Cylindrical face or circular edge on Part 2
Offset Length 0 mm Initial axial offset along the axis
Rotation Angle 0° Initial rotation angle

Python API

Minimal example

import FreeCAD as App

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

joint = asm.Joints.newObject("Assembly::JointObject", "SplinedShaft")
joint.JointType = "Cylindrical"
joint.Reference1 = (doc.getObject("OuterTube"), ["Face2"])
joint.Reference2 = (doc.getObject("InnerShaft"), ["Face1"])
doc.recompute()

Common mistakes and pitfalls

Cylindrical vs Screw for lead-screw mechanisms

Both allow rotation and translation on the same axis, but a Cylindrical joint makes them independent — the part can rotate without advancing. A lead screw requires a fixed ratio between rotation and advance. Use the Screw joint for that.

Cylindrical removes only 4 DOF

If your mechanism count shows more residual DOF than expected, check whether a Cylindrical joint was intended to be a Revolute (5 DOF removed). The extra free axial translation may be the source.

See also