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InternalInvoluteGear

CycloidGear

FCGear

Description

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.

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

Usage

1. Switch to the FCGear Workbench.
2. There are several ways to invoke the command:
   • Press the Involute Rack button in the toolbar.
   • Select the Gear → Involute Rack option from the menu.
3. Change the gear parameter to the required conditions (see Properties).

Properties

An FCGear InvoluteRack object is derived from a Part Feature object and inherits all its properties. It also has the following additional properties:

Data

base

• Dataadd_endings (Bool): If true (default), then the total length of the rack is teeth * pitch. If false, then the rack starts with a tooth-flank.
• Dataheight (Length): Default is 5 mm. Value of the gear width.
• Datamodule (Length): Default is 1 mm. Module is the ratio of the reference diameter of the gear divided by the number of teeth (see Notes).
• Datateeth (Integer): Default is 15. Number of teeth.
• Datathickness (Length): Default is 5. Height from the tooth root to the lower side of the rod.

computed

• Datatransverse_pitch (Length): (read-only) Pitch in the transverse plane (see Notes).

fillets

• Datahead_fillet (Float): Default is 0 mm.
• Dataroot_fillet (Float): Default is 0 mm.

helical

• Databeta (Angle): Default is 0 °. With the helix angle β a helical gear is created – positive value → rotation direction right, negative value → rotation direction left.
• Datadouble_helix (Bool): Default is false, true creates a double helix gear (see Notes).
• Dataproperties_from_tool (Bool): Default is false. If true and Databeta is not zero, gear parameters are recomputed internally for the rotated gear.

involute

• Datapressure_angle (Angle): Default is 20 ° (see Notes).

precision

• Datasimplified (Bool): Default is false, true generates a simplified display (without teeth).

tolerance

• Dataclearance (Float): Default is 0.25 (see Notes).
• Datahead (Float): Default is 0. This value is used to change the tooth height.

version

• Dataversion (String):

Notes

• 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

See FCGear InvoluteGear.

Scripting

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
App.ActiveDocument.recompute()
Gui.SendMsgToActiveView("ViewFit")

InternalInvoluteGear

CycloidGear

FCGear