Types of Gears in FreeCAD FCGear Workbench
The FCGear workbench is a dedicated extension for FreeCAD designed to automate the parametric modeling of various mechanical transmission elements. This article provides a comprehensive overview of the specific types of gears you can model within the FCGear workbench, detailing the profile options, typical applications, and primary geometric capabilities supported by each tool.
Involute Spur and Helical Gears
The standard Involute Gear tool generates external gears based on the widely used involute tooth profile. Users can model standard spur gears with straight teeth or apply a helix angle (beta) to create helical gears. The workbench also supports double helical (herringbone) configurations to eliminate axial thrust. Fully customizable parameters include the module, number of teeth, pressure angle, clearance, and head/root coefficients.
Internal Involute Gears
The Internal Involute Gear tool models ring gears featuring teeth facing inward toward the center. These components are primarily utilized in planetary (epicyclic) gear assemblies. Like external involute gears, internal gears can be configured with specific modules, pressure angles, and tooth numbers, ensuring accurate meshing with standard external planetary pinions.
Involute Gear Racks
The Involute Rack tool creates linear gear bars designed to pair with rotary pinion gears to convert rotational motion into linear motion. Designers can set parameters such as pitch (derived from module), height, length, tooth count, and pressure angle, with support for angled teeth to mate with helical pinions.
Bevel Gears
The Bevel Gear tool models conical gears used for transmitting torque between intersecting shafts, typically oriented at a 90-degree angle. The workbench allows for the configuration of straight-tooth bevel gears as well as spiral bevel gears, which offer quieter operation and smoother engagement at higher speeds.
Crown Gears
Crown gears (also called face gears) feature teeth perpendicular to the plane of the gear's wheel, resembling a crown. In FCGear, crown gears can be generated to mesh with conventional cylindrical spur pinions, providing an alternative to bevel gears for perpendicular power transmission.
Worm Drives
FCGear includes capabilities to generate worm gear systems, consisting of two distinct components:
- Worm Screw: A threaded, screw-like shaft that drives the system.
- Worm Wheel: A specialized concave-face gear that meshes with the worm screw.
These gears are commonly utilized to achieve high-ratio speed reduction and non-reversible (self-locking) setups between non-intersecting, perpendicular axes.
Cycloid and Hypocycloid Gears
Unlike involute profiles, cycloid and hypocycloid gears utilize cycloidal curves to generate tooth geometry. The FCGear workbench provides dedicated generators for:
- Cycloid Gears: Commonly used in horology (clocks and watches) and specific low-friction mechanisms.
- Hypocycloid Gears: Essential for designing high-reduction, zero-backlash cycloidal speed reducers widely found in robotics and precision drive systems.
Lantern Gears
Lantern gears consist of cylindrical pins (rollers) arranged in a circle rather than traditional cut gear teeth. In FCGear, lantern pinions can be modeled to interface efficiently with cycloidal wheels or custom low-friction mechanical mechanisms.
Timing Pulleys and Sprockets
The workbench also features utilities for creating toothed timing belt pulleys (such as GT2, T-series, and HTD profiles). While technically pulleys rather than power transmission gears, they share identical parametric workflows within the FCGear environment for belt-driven automation projects.