How are items manufactured with such precision, when it requires a machine with precise parts to manufacture the items (which presumably requires another machine to produce it’s parts)? Does everything eventually trace back to handmade parts or tools?
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Modern precision machinery traces back to a screw-duplicating lathe that was made around 1780, I believe. (Source: a series of videos by Jacob Bronowski on the history of science and technology, made for PBS.)
Early screw-cutting lathes were turned by hand. They have a screw that moves the cutting bit as the lathe turns. By using different gear ratios so that the screw turns at a different speed from the shaft being cut, different threads per inch can be cut.
The first such lathe, and the first screw, was made by hand, with files, etc. Once you have that very carefully made first screw, you can duplicate it indefinitely. You can also make screws with different thread counts, and nuts.
Once you have a reliable supply of screws and nuts, you can build precision measuring equipment. Say you have a 1/4-20 screw, with 20 threads per inch. One turn of the screw is 1/20 of an inch, or 50 thousandths of an inch. Put a pointer on top of the screw, and a wheel with 50 divisions evenly spaced, and you can now measure the thickness of a piece of metal to a thousandth of an inch. (You need to make the nut part of a c-clamp-like piece of metal, and have some way to set zero, but you get the idea.) (No doubt Metric screws were produced in the same way in France, as soon as the metric system was adopted.)
I have copies of old books from the 1800s on how to scrape and file metal surfaces with great precision, so there was still a lot of hand filing going on, through maybe WWI, but once you have some means of precision measurement, as standard screws provide, you are on the way to the modern world.
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