Camera Adapter Ring

Hey, what can I say but that I'm proud of what I've achieved here. I have 3 lenses for my Yashica Fx-7, 28mm, 42-75, 80-200. The 28mm has a 52mm filter ring while the other two take 55mm filters. Faced with a request for indoor fotos under tungsten lighting I investigated the required filters. Quite apart from none of the local shops having the right things in stock, they also have no adapter rings. I casually considered making the adapter and mentioned making it to one of the shop owners.

He Laughed

I made it

Stubborn, yup. (-: Took a weekend of puttering around. Much of the time got absorbed in making the required small tools. 2 'real small' threading tools, one inside and one outside, and one narrow grooving tool to make the run out groove and clean up the flange surface. The tools are shown below. The internal tool was made from an old file which was heated red to bend, then heated red and quenched to harden, followed by tempering at yellow/brown. The other tools were made from a piece of HSS 2.7mm thick that came from a leather cutting machine.

Since my Myford is imperial, and filter threads are 0.75mm pitch, I had to turn the spindle using a hand crank, which takes a while even on such short threads. (For the full technical explanation of this do a web search on metric threading in an imperial lathe - the only way to do it dead accurately is using a 127 tooth gear wheel which won't even fit on my lathe, biggest I have is 90 teeth)

Technical details:

The gears for the threads

The common camera filter pitch is 0.75mm.
The gears I used were
Drivers 35 38 40 Driven 55 63 65 ratio 0.236208 error 0.005180%
Any driver can drive any driven so you just need to swap them around until you find a way that it fits the banjo.
I usually start with the smallest driver driving the smallest driven and so on and it usually fits.
So that would be
   35 on the spindle
   55 and 38 on stud 1
          63 and 40 on stud 2
                 65 on the leadscrew

I calculated the gears using my program from
which I now have to run in a virtual machine because it will not run under 64bit Windows.
I must try to rewrite it in something more universal like Python so it can run anywhere.

Turning the part

To turn the part itself means that you need to turn the threads on one end and then turn it around to do the other end. Being so thin it will distort if you hold it in the chuck so what I did was to mahcien one end and then part it off. Then I could machine temporary matching threads in the remaining stock so the part xcan be threaded onto that so that the other side can be machined.

I don't think it matters which side you do first and I cannot recall which way round I did it.

I think I did this:
  1. - mount the stock and do the basic turning and boring so the small end is facing outward
  2. - thread the small end (the outside threads).
  3. - part off a few millimeters too long.
  4. - bore and inside thread the stock that is still in the chuck so the small end of the adapter fits into it.
  5. - thread the adapter into this temporary mount
  6. - face to length,
  7. - bore and thread the large inside threads.

Note that you do need to make the threads a loose fit since if they are tight the aluminum will stick or gall to the lens. You also need to leave space for the black paint (or anodizing if you can do that).

So, here are some pix of the finished product for you to admire. <-;

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Last modified: January 28 2019 11:22:24.