Parametric Sprocket

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How to Design a Sprocket for Bulldozer Drive

  • The sprocket generator in OpenSCAD creates a proportionally correct sprocket.
  • How do we know how to scale it to match our specific case?
  • We first design the track. We settled on pin spacing of 3", and XXH 1.5" pipe (see Pipe Chart) for the roller, with 1" pins. Thus: roller = 1.9" OD (1.5" XXH pipe), pitch = 3" (based on geometry of pins:


  • Ratio of 3/1.9=1.58. Ratio of pitch to the roller is constant.
  • Then we generate the sprocket using 5 parameters
  • 1 - Number of teeth
  • 2 - Roller (5 units)
  • 3 - Pitch - 1.58x the roller size as determined by our track geometry (looks sensible, and 3" pitch was selected as a convenient distance, and 1.9" OD roller was selected as a readily-available stock material
  • 4 - Thickness - that is the thickness of the plate material
  • 5 - Tolerance - play in the distance between rollers (pitch)?
  • To generate a correct sprocket, we can scale the resulting design in CAD - by superposing the track piece over the sprocket to make sure the track pieces fit in the valley-to-valley distance in the sprocket (which corresponds to the distance between rollers, or pitch)
  • See the File:Sprocketgeo.dxf for how the track pieces fit into the sprocket (example shows a larger sprocket than an 8 tooth sprocket)

Bulldozer 2015 Usage

HintLightbulb.png Hint: The bulldozer from 2015 used an 8 tooth sprocket, generated with sprocket(8,5,7.5,2,0.2); in the last line of the Editor

Exporting DXFs from 3D Objects in OpenSCAD

  • Exporting DXFs - [1] - essentially - load and flatten, then export DXF
  • Note: stock Export DXF does not work for 3D files - they need to be projected first.
  • To project - projection(cut=false) import("sprocket.stl"); STL file must exist in same directory
  • Sample file for exercise in OpenSCAD - the sprocket STL and the .scad file that loads the STL and does a 2D projection. Note that the directory must be correct.
  • Note: original srocket was generated using Parametric Sprocket Generator using sprocket(12,5,7.5,8,0.2);