I scanned a gear at 600 dpi, adjusted contrast in Photoshop, selected the white area, then created a work path. I exported that as path.ai, and used it as the cross-section of a spline object (a gear) in Carrara. As you can see in the above image, the results are poor, regardless of whatever smoothing or tolerance I used in Photoshop. Is there a way of generating gears with a good tooth shape and specific number of teeth, in such a way that they are much more mathematically perfect than the above?