--Not sure if Google would be the place to search it, but many moons ago there was an article in the Amateur Scientist column of Scientific American about constructing a "ruling engine", a device for making optical gratings. It used a principle called a "differential screw" to get reeeeeally fine divisions using fairly simple components. You might want to see if you can find a copy of the article.
Take this to heart. It's much easier to position something to within .0002 than to lock it there. Several times I've had to design and build both manual and automatic mechanisms to do this and it's never as easy as you might think.
Read, not skim, the section "Screw Thread Systems" in Machinery's Handbook. It's many pages of dry material, but worth the effort if you need to understand screw threads.
Ned Simmons
Edmond Scientific specializes in optics. I bought my first 6 inch reflecting telescope mirror kit from them many years ago.(1957) They are located in New Jersey.
John
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