FCGear TimingGear

TimingGearT

LanternGear

Gear

Description

The FCGear TimingGear command creates a timing gear.

The purpose of timing gears is to allow the camshaft and crankshaft to turn the timing chain. The crankshaft turns to move pistons up and down inside the cylinders. The camshaft turns to allow intake and exhaust valves on the cylinders to open and close. These components are important for proper engine timing.

Timing gears are connected to a timing belt or timing chain.

Above: Timing gear

Usage

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

Properties

See also: Property View.

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

Data

base

• Dataheight (Length): Default is 5 mm. Value of the gear width.
• Datateeth (Integer): Default is 15. Number of teeth.
• Datatype (Enumeration): Default is gt2. Type of timing gear – profile pitch for timing belts (see Notes).

computed

• Datah (Length): (read-only) Radial height of teeth.
• Dataoffset (Length): (read-only) X-Offset of second arc mid-point.
• Datapitch (Length): (read-only) Pitch of gear.
• Datar0 (Length): (read-only) Radius of first arc.
• Datar1 (Length): (read-only) Radius of second arc.
• Datars (Length): (read-only) Radius of third arc.
• Datau (Length): (read-only) Radial difference between pitch … diameter and head of gear.

version

• Dataversion (String):

Notes

• type: The pitch of the timing belts (distance from tooth centre to tooth centre of consecutive teeth) is specified in types. GT2 has a pitch of 2 mm, GT3 of 3 mm, GT5 of 5 mm etc..

Useful formulas

• addendum diameter = pitch diameter + 2 * module
• belt length = 2 * axle base + belt tooth pitch : 2 * (teeth 1 + 2) + belt tooth pitch² : 4 * pi² * axle base * (teeth 1 - 2)²
• axle base = belt length : 4 - belt tooth pitch : 8 * (teeth 1+2) + ¼ * sqrt [belt length - ½ * belt tooth pitch * (teeth 1+2)² - 2 * belt tooth pitch² * (teeth 1+2)² : pi²]

Scripting

Use the power of Python to automate your gear modeling:

import FreeCAD as App
import FreeCADGui as Gui
import freecad.gears.commands
gear = freecad.gears.commands.CreateTimingGear.create()
gear.num_teeth = 12
gear.height = 5
gear.type = "gt5"
App.ActiveDocument.recompute()
Gui.SendMsgToActiveView("ViewFit")

TimingGearT

LanternGear

Gear