kaysiebke-cell/gates-cdx-kettenspanner-ritzel-generator-brompton

This project is a FreeCAD macro that generates a custom guide sprocket, also called an idler pulley, for the belt tensioner on a Brompton folding bike that has been converted to a Gates Carbon Drive CDX belt system. It is not the main drive sprocket on the rear wheel, but the smaller ball bearing wheel that keeps the belt properly tensioned. Users have two ways to get a sprocket. The simplest is an online web configurator where the tooth profile, mud ports, belt guide, and bearing seats can be adjusted and previewed live in 3D, with ready made STL files available for common sizes between 12 and 18 teeth, or a custom STL that can be dragged straight out of the browser. For more control, the project can also be run directly as a macro inside FreeCAD, where a dedicated panel lets a user preview the tooth profile quickly, build the full solid model, and export a clean finished part for printing. The generator is fully parametric, meaning tooth count, pressure angle, pitch, and tooth depth can all be adjusted, and the tool remembers the last settings used along with working fillet values so recalculating after a failed attempt does not start from scratch. The README includes detailed guidance for 3D printing the part in PA12-CF, a carbon fiber reinforced nylon filament, covering nozzle type, infill, print speed, bed and chamber temperature, drying, and which printer models are compatible. It also covers optional post-processing steps like filling layer lines, wet sanding, and sealing the surface, along with safety notes about the irritating dust produced when sanding carbon fiber parts. This project is aimed at Brompton owners who have converted their bike to a Gates belt drive and want a replacement or upgraded tensioner sprocket, and it assumes some familiarity with 3D printing or FreeCAD.