In a similar vein, how do you make a more accurate machine tool using one that is less accurate?
I think the principle with screw cutting is that you start with a lead screw that is fairly good, and use a compliant follower (say, cork) that averages over several turns to cut another lead screw that is better than the first.
Somewhere I have seen what must be a simple explanation of this, but I can't find it on Wikipedia under Maudslay or Whitworth.