5 ms·

My favourite fact about it comes from https://phys.org/news/2016-02-plasma-physicist-discusses-wendelstein-x.amp https://phys.org/news/2016-02-plasma-physicist-

My favourite fact about it comes from https://phys.org/news/2016-02-plasma-physicist-discusses-wendelstein-x.amp https://phys.org/news/2016-02-plasma-physicist-discusses-wen... “…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!

dale_glass 3y ago
Odd units. 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.
- Retric 3y ago
  You messed up at your last step 1 millionth = 1mm, 10 millionth = 0.1mm, 100 millionth = 0.01mm 0.01mm is very difficult when you’re talking large custom objects with complex shapes.
  - dale_glass 3y ago
    Oh, English fail on my part then. I had assumed that 100 millionths of a metre == 100 * 1/1000000.
    - eis 3y ago
      The german site of the source speaks of 0.1mm so you were correct > bei Toleranzen von teilweise nur 0,1 Millimeter https://www.ipp.mpg.de/de/aktuelles/presse/pi/2020/01_20 https://www.ipp.mpg.de/de/aktuelles/presse/pi/2020/01_20
    - Retric 3y ago
      No your correct, I just read it wrong. Really needed to pay attention to the s.
  - starkrights 3y ago
    I think the original commenter is right- correct me if I missed what you’re getting at. 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
    - deleted 3y ago
      [deleted]
    - Retric 3y ago
      Ops, 100 ( 1 millionths of a meter) is a much more reasonable tolerance here than 1 / (100 millionth) of a meter. 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
- dekhn 3y ago
  millionths of a meter are known as micron so most people would call this '100 micron' (or '100 micrometers') which is indeed close to 4 thou, as you calculated, and is the level of accuracy of my ~$500 3d printer. 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.
- kortex 3y ago
  What usually matters more than absolute tolerances is relative tolerance, aka ppm. 100 micron / 4 thou tolerance can be achieved with hand tools and a bit of patience on the benchtop scale, say a 4" part. That's about 1000 ppm, or 0.1%. If I gave you a meter stick, you could probably eyeball marking something +/- 1mm. 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.

dale_glass 3y ago

Odd units. 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.

Retric 3y ago
You messed up at your last step 1 millionth = 1mm, 10 millionth = 0.1mm, 100 millionth = 0.01mm 0.01mm is very difficult when you’re talking large custom objects with complex shapes.
- dale_glass 3y ago
  Oh, English fail on my part then. I had assumed that 100 millionths of a metre == 100 * 1/1000000.
  - eis 3y ago
    The german site of the source speaks of 0.1mm so you were correct > bei Toleranzen von teilweise nur 0,1 Millimeter https://www.ipp.mpg.de/de/aktuelles/presse/pi/2020/01_20 https://www.ipp.mpg.de/de/aktuelles/presse/pi/2020/01_20
  - Retric 3y ago
    No your correct, I just read it wrong. Really needed to pay attention to the s.
- starkrights 3y ago
  I think the original commenter is right- correct me if I missed what you’re getting at. 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
  - deleted 3y ago
    [deleted]
  - Retric 3y ago
    Ops, 100 ( 1 millionths of a meter) is a much more reasonable tolerance here than 1 / (100 millionth) of a meter. 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
dekhn 3y ago
millionths of a meter are known as micron so most people would call this '100 micron' (or '100 micrometers') which is indeed close to 4 thou, as you calculated, and is the level of accuracy of my ~$500 3d printer. 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.
kortex 3y ago
What usually matters more than absolute tolerances is relative tolerance, aka ppm. 100 micron / 4 thou tolerance can be achieved with hand tools and a bit of patience on the benchtop scale, say a 4" part. That's about 1000 ppm, or 0.1%. If I gave you a meter stick, you could probably eyeball marking something +/- 1mm. 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.