Designing & 3D Printing Helical Bevel Gears in OpenSCAD
Description
How to use the OpenSCAD Helical Bevel Gear Generator
This is an experimental parametric bevel gear generator written in OpenSCAD for creating printable straight bevel and helical bevel gears.
The script is intended for:
- Hobby projects
- Robotics
- Educational demonstrations
- Motion systems
- DIY gearboxes
- Experimental mechanical design
The tooth geometry is an approximate printable form designed for FDM 3D printing and rapid prototyping.
Getting Started
Open the .scad file in OpenSCAD and edit the parameters in the example section at the top of the script.
After changing the settings:
1. Press F5 for preview
2. Press F6 for full render
3. Export as STL
Main Parameters
teeth
Sets the number of teeth on the gear.
Example:
teeth = 24;
module_size
Controls tooth size and gear pitch.
IMPORTANT:
Meshing gears must use the same module_size.
Example:
module_size = 2;
thickness
Sets the overall gear thickness.
Example:
thickness = 12;
bevel_scale
Controls how much the gear tapers toward the top.
Smaller values create a steeper cone.
Example:
bevel_scale = 0.45;
twist
Controls tooth spiral angle.
Example:
twist = 0;
Straight bevel gear
Example:
twist = 15;
Spiral/helical bevel gear
Positive and negative values create opposite twist directions.
IMPORTANT:
Meshing helical bevel gears should use opposite twist directions.
Example:
Gear A:
twist = 20;
Gear B:
twist = -20;
twist_slices
Controls smoothness of the helical twist.
Higher values improve appearance but increase render time.
Example:
twist_slices = 32;
bore_dia
Sets the centre shaft hole diameter.
Example:
bore_dia = 5.2;
Hub Options
add_hub
Enables or disables the hub.
hub_dia
Sets hub diameter.
hub_height
Sets hub height.
Grub Screw Hole
add_grub_screw
Adds a side hole through the hub.
grub_dia
Sets the grub screw hole diameter.
Backlash
backlash_mm
Adds tooth clearance for smoother meshing and better FDM printing tolerance.
Typical values:
0.10 = tight fit
0.15 = general use
0.20 = loose fit
Tooth Shape Parameters
tooth_top_ratio
Controls tooth tip width.
tooth_root_ratio
Controls tooth root width.
Most users should leave these at default values.
Recommended Print Settings
Material:
PLA for testing
PETG for improved durability
Layer Height:
0.2 mm
Walls:
4 recommended
Infill:
40% to 60%
Orientation:
Print with the large face downward on the bed.
Supports:
Normally not required.
One advantage of this geometry is that the bevel shape naturally tapers inward, making it very FDM-friendly.
Suggested Starting Values
Straight Bevel Gear:
twist = 0;
Helical Bevel Gear:
twist = 15;
More Aggressive Spiral:
twist = 25;
Notes
This script creates an approximate printable bevel gear geometry and is not intended to replace precision industrial bevel or hypoid gear design.
However, it works very well for:
- Educational demonstrations
- Robotics
- RC projects
- Experimental gearboxes
- Mechanical prototyping
- Maker projects
The design also allows experimentation with spiral bevel and hypoid-style concepts by adjusting the twist direction and shaft positioning.