I had the need for parametric pulley dxf's so I could import them in Fusion 360 and other software.
With this scad file you can choose the 3 parameters you'd like.
- shaft diameter
- tooth profile
- number of teeth
after you set the values you'd like press F6 to render and than export to DXF.
for more instructions check my instructable: https://www.instructables.com/id/Design-a-Parametric-Pulley-DXF-STL
UPDATE: there is a file called V2 which is a little faster.