FCGear InvoluteRack

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FCGear InvoluteRack.svg FCGear InvoluteRack

Menu location
FCGear → Create an Involute rack
Default shortcut
Introduced in version
See also
FCGear InvoluteGear


Gear racks are used to convert a rotary motion into a linear motion or vice versa. The following examples show the different applications:

  • A rack with gear on at a retaining weir.
  • Various rack systems of rack-and-pinion railways.
  • Rack and pinion steering in a vehicle.
  • Rack and pinion winch as mechanical hoist (e.g. car jack).
  • Pneumatic rack and pinion drives used to control valves in pipeline transport.

Involute-Rack example.png

From left to right: Spur gearing, helical gearing, double helical gearing


  1. Switch to the FCGear workbench icon.svg FCGear Workbench.
  2. Invoke the command several way:
  3. Change the gear parameter to the required conditions (see Properties → Data below).




  • DataPlacement: Placement is the location and orientation of an object in space.
  • DataLabel: User name of the object in the Tree view.


  • Datatransverse_pitch: Pitch in the transverse plane – not changeable, is calculated automatically (see also the information in Notes).


  • Dataadd_endings: If True, than the total length of the rack is teeth * pitch, otherwise the rack starts with a tooth-flank.
  • Databeta: With the helix angle β a helical gear is created (positive value → rotation direction right, negative value → rotation direction left).
  • Dataclearance: Default is 0,25 (see also the information in Notes).
  • Datadouble_helix: True creates a double helix gear (see also the information in Notes)
  • Datahead: Default is 0,00. This value is used to change the tooth height.
  • Dataheight: Value of the gear width.
  • Datamodule: Module is the ratio of the reference diameter of the gear divided by the number of teeth (see also the information in Notes).
  • Dataproperties_from_tool: If helix angle β is given and properties_from-tool is enabled, gear parameters are internally recomputed for the rotated gear.
  • Datasimplified: True generates a simplified display (without teeth).
  • Datateeth: Number of teeth
  • Datathickness: Height from the tooth root to the lower side of the rod.


  • Datapressure_parameter: Default is 20 (see also the information in Notes).


The parameter descriptions of the View tab will be found in Property editor, further below at Example of the properties of a PartDesign object.


  • transverse_pitch: The value is the result of multiplication of module * pi. This means for the standard involute rack of FCGear: 15 (teeth) * 3,14 (transverse_pitch) is 47.12 mm. See also module further below.
  • clearance: At a gear pair, clearance is the distance between the tooth tip of the first gear and the tooth root of the second gear.
  • double_helix: To use the double helical gearing the helix angle β (beta) for the helical gearing must first be entered.
  • module: Using ISO (International Organization for Standardization) guidelines, Module size is designated as the unit representing gear tooth-sizes. Module (m): m = 1 (p = 3.1416), m = 2 (p = 6.2832), m = 4 (p = 12.566). If you multiply Module by Pi, you can obtain Pitch (p). Pitch is the distance between corresponding points on adjacent teeth. The result of the multiplication is displayed in transverse_pitch
  • pressure_parameter: Only change the parameter, if sufficient knowledge of the gear geometry is available.

Useful formulas

For more information see FCGear InvoluteGear.svg Involute gear.


Use the power of python to automate your gear modeling:

import FreeCAD as App
import freecad.gears.commands
gear = freecad.gears.commands.CreateInvoluteRack.create()
gear.teeth = 20
gear.beta = 20
gear.height = 10
gear.double_helix = True

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