“…the supporting structure can only withstand the forces if the interfaces between the ten individual segments of the central rings, which weighs several tonnes, are built with a level of precision of less than 100 millionths of a metre…” - and they found a small family business in the north of Italy capable of doing this!
1 meter = 100 cm = 1000mm.
So 1 millionth of a meter = 1/1000th of 1mm.
thus, 100 millionths of a meter = 0.1mm, or ~4 thou in American units. Easily achievable by hobbyists, let alone by serious, professional equipment.
Sure, that is a pretty exacting specification for what I suppose is a big machine, but I'm pretty sure very normal things like say, car engines get made to far tighter tolerances.
0.01mm is very difficult when you’re talking large custom objects with complex shapes.
> bei Toleranzen von teilweise nur 0,1 Millimeter
Keeping it all in the same units until the end here:
1 millionth of 1 meter = (1 / 1,000,000)m = (1e-6m)
1 millionth * 100 = 100 millionths => (1e-6m) * 100 = (1e-4m) = 100 millionths
(1e-4m) = .0001m | 1m = 1000mm => .0001m*1000 = .1mm
I am to used to people saying 100 millionth of a meter to mean 10 nm or 0.01 µm which would have looked insane if I had written that.
Aka 100 millionth vs 100 millionths
1 thou was achievable in routine shops in the 1940s and a tenth of a thou (2.54 micron) is a common accuracy to target these days. Obviously it depends on the context and the size of the object, at some point you move away from cutting to using grinding and lapping to achieve your results, which is ultra-timeconsuming.
Getting the same finish on a 120"/3m coil is 33 ppm. 100 ppm / 0.01% for any operation or process tends to be where things start to get really challenging. Deflection goes up by the length cubed, so increasing the size of all the tooling relative to the tolerance gets really challenging really fast.