Bike Chain Sprocket Generator – Blender Add-on

A parametric Blender generator for bicycle and motorcycle chain sprockets with five or more teeth.

Download the latest add-on ZIP

Unlike Blender's general-purpose gear generator, this add-on builds sprockets from roller-chain geometry:

• pitch circle calculated from chain pitch and tooth count
• circular roller seats
• C2-continuous quintic Hermite transitions from roller seats to tooth tips
• directional tooth-tip pitch with matching upper and lower contours
• optional straight tangential tooth-tip flattening
• closed manifold mesh with a circular center bore
• optional non-destructive edge bevel

Installation

1. Download bike_chain_sprocket.zip from the Releases page.
2. Open Edit → Preferences → Add-ons in Blender.
3. Choose Install… or Install from Disk…, depending on your Blender version.
4. Select bike_chain_sprocket.zip and enable the add-on.
5. In the 3D Viewport, choose Shift+A → Mesh → Bicycle Chain Sprocket.
6. Adjust the parameters during creation or reopen them with F9 / Adjust Last Operation.

Chain Size Presets

Chain Size Preset loads chain pitch, roller diameter, and a conservative starting thickness for the sprocket. The suggested sprocket thickness is intentionally smaller than the nominal chain inner width to preserve lateral clearance.

Preset	Pitch	Roller	Suggested sprocket thickness
Bicycle 1/8" – Single-speed/BMX	12.700 mm	7.750 mm	2.80 mm
Bicycle 3/32" – Derailleur	12.700 mm	7.750 mm	2.00 mm
Bicycle 11/128" – Narrow 10–12 speed	12.700 mm	7.750 mm	1.80 mm
Motorcycle 415	12.700 mm	7.770 mm	4.30 mm
Motorcycle 420	12.700 mm	7.770 mm	5.80 mm
Motorcycle 428	12.700 mm	8.510 mm	7.30 mm
Motorcycle 520	15.875 mm	10.160 mm	5.80 mm
Motorcycle 525	15.875 mm	10.160 mm	7.30 mm
Motorcycle 530	15.875 mm	10.160 mm	8.80 mm
Custom	user-defined	user-defined	user-defined

All individual values remain editable after loading a preset. Before manufacturing, always verify the dimensions against the exact chain manufacturer's data sheet and a physical chain sample. Roller and inner widths may vary slightly by manufacturer, product series, and O-ring/X-ring construction.

Recommended Starting Values

Parameter	Default	Meaning
Teeth	5	Geometric minimum; warning shown through 8T
Chain Pitch	12.7 mm	Standard 1/2-inch bicycle chain pitch
Roller Diameter	7.75 mm	Typical bicycle-chain roller diameter
Roller Clearance	0.15 mm	Additional radial clearance around each roller
Tooth Height	0.45 mm	Tooth tip above the pitch circle
Tooth Tip Pitch	1.5°	Upper and lower contours move together in one direction
Tooth Tip Flattening	0.0 mm	Radial depth of the straight flat cap
Thickness	2.0 mm	Match to chain inner width and manufacturing clearance
Bore Diameter	5.0 mm	Circular center bore
Scale	1.0	Uniform scale for every generated dimension
Profile Resolution	32	Profile vertices per tooth
Edge Bevel	0.10 mm	Non-destructive Bevel modifier

The supplied reference cassette has an outside diameter of approximately 45.98 mm for its 11-tooth sprocket. The add-on produces approximately 45.98 mm with the default 11T geometry.

Generated Object Data

The mesh is generated at real metric dimensions and respects Blender's Unit Scale. The object stores these custom properties:

• teeth
• chain_preset
• overall_scale
• chain_pitch_mm
• roller_diameter_mm
• tooth_tip_pitch_degrees
• tooth_tip_flattening_mm
• pitch_diameter_mm
• outside_diameter_mm
• profile_type

Tooth-Tip Controls

Tooth Tip Pitch

Tooth Tip Pitch shifts the upper and lower contour of every tooth tip together in the same tangential direction. This produces slightly asymmetric tooth flanks while leaving the circular roller seats unchanged. Positive and negative values reverse the direction.

Tooth Tip Flattening

Tooth Tip Flattening trims the rounded tip by the entered radial amount. The resulting cap is a true straight tangent line rather than a constant-radius arc. 0.0 mm disables flattening; approximately 0.15–0.30 mm is a useful starting range.

Important Notes

• Sprockets with 5–8 teeth cause extreme chain articulation and strong polygonal action. Five teeth is only the geometric minimum supported by the generator, not a recommendation for a normal bicycle or motorcycle drivetrain.
• Scale also scales chain pitch, roller seats, bore, thickness, flattening, and bevel. Keep it at 1.0 for a real chain unless the entire mechanism is scaled.
• The add-on does not reproduce proprietary shifting ramps, asymmetric shortened teeth, or Shimano/SRAM cassette spline interfaces.
• The center mount is intentionally a configurable circular bore. Add specialized shaft or spline profiles separately.
• Verify chain width, tolerances, material, mounting geometry, tooth strength, and the exact manufacturer specification before manufacturing or load-bearing use.

Development Test

Run the Blender API test suite from the repository root:

blender --background --python tests/run_blender_tests.py

The suite registers the add-on and verifies 5T–11T generation, all nine bicycle/motorcycle presets and Custom mode, manifold topology, positive volume orientation, target outside diameters, exact roller seats, Blender Unit Scale, uniform Scale, 6° directional tooth-tip pitch, a true straight 0.30 mm tip flattening, the evaluated Bevel modifier, and rejection of oversized bores.

License

This project is licensed under the GNU General Public License v3.0 or later. See LICENSE.