I can understand your desire to make your own. But there are some major issues that you have to solve to make this work. The first is the FFL of your lens. If the helical is too long you can't focus to infinity. And if it too short you will also have a focusing problem in that you won't be able to focus to infinity unless you make an extension for the lens board to make the helical the correct FFL when it is fully retracted. How will you calibrate DOF and distance settings? Then the helical has to be large enough so the rear element fits inside it. These would eliminate nearly all MF helicals and most "junkyard" helicals.
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