Metric threads were obviously designed by somebody who had never seen or operated a screw machine. UNC threads (along with pre-metrification Whitworth threads, Italian threads, and yes even French threads) except for a few oddball sizes have pitches which are multiples of each other (2, 4, 8, 16, 18, 20, 24, 28, 30, 32...) or at least even numbers, so they can easily be made on a lathe with a single lead-screw with an even pitch. Metric thread pitches are completely arbitrary so there is no single lathe lead-screw which will work the same way; if you have a 2mm leadscrew on your lathe you can make 2mm threads the normal way but F you for most of the others. There was nothing stopping them from making metric thread pitches a regular series, but they didn't even know enough to do it. Ironically, it was probably decreed by some revolutionary who just finished overthrowing the aristocracy and replacing the arbitrary units system, who didn't even know better. So we all get to keep the famous 127-tooth lathe gear around for the rest of eternity so we can make metric threads. Way to make things better guys. Couldn't you have spent your energy elsewhere, like fixing your spelling?
Run the leadscrew with a servo and a rotary encoder.
But yes, metric threads are stupid.
