Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

 To create the helix a template needs to be made. The calculations for this template are calculated like this. You have a shaft with a diameter that corresponds with the pitch diameter of the gear. You have a particular helical angle. From a point on the diameter if you created a line equal to the helical angle and rolled it around the diameter until it came back to a point in line with the starting point this would give you the advance of the helix in one revolution.
Attached are the PDF's that Chuck Fellows drew up laying out the creation of the fixture and the development of the helical templates.