Working on the eye stalk I found that making an iris that has a smooth action is hard to do. I actually made 3 designs, based on designs I found on the internet. In the end I chose to go the easy route.
I looked in second hand shops for an old 35mm SLR style camera but either could not find them or the ones I found were too pricey. I had an old Pratika MTL5 circa early 1980s which I chose to take apart. When all’s said and done the iris moved very smoothly.