as I have set out in the MS 'Coronation' thread
I drew it up in Illustrator by tracing a high resolution image kindly sent by cycles gitane, the key measurement is the PCD of 50.4 for the cranks. The teeth are taken from a free online creator using standard bike chain measurements of pitch and roller size, with my preference for 44 teeth. The file generated is exported as a DXF file, then converted with an online DXF to PDF converter, then the PDF was taken into Illustrator and resized to fit the size required. The Illustrator file can then be exported out as a DXF file which can be used as the input to generate the G code required in the laser cutting/engraving. Surprisingly, the laser cutting company was happy with the drawing and all I need to do now is to send the file so they can do the quote.
My dxf file was then prepared by the laser cutting company
and it was laser cut and lightly engraved using 3mm stainless steel.
the path with the little ovals was lost but I think I know how to overcome that if I have anything else engraved.
The five mounting holes fit the crank arm position and need to be enlarged and sleeved, and threads tapped like the Williams chainrings, another project for a mate.
Running it along a 1/8" chain sees the teeth mesh smoothly.
very happy with the price and the result.