4 ms·

I read somewhere that the tolerance on the lego pieces has to be very small so that all the pieces fit well enough (not too loose, not to tight).

rkangel 4y ago
Lego bricks are made to 1um tolerance (1 thousandth of a millimeter). The reason they have to be is to make sure that larger models fit together properly. The "not too loose, not too tight" thing is part of it, but isn't actually the key reason which is "accumulation of tolerance". Imagine two rows of 100 bricks. The difference in length between the two rows is 100 times that 1um tolerance. If the tolerance was less good, things wouldn't fit together well. Lego model design guidelines actually have a maximum size of a "fully" connected block of bricks because eventually even this precise manufacturing can't cope. Really big models have purposefully designed decoupling between sections.
- 988747 4y ago
  > The difference in length between the two rows is 100 times that 1um tolerance. Doesn't tolerance work both ways? One brick is 1um longer than it should, another one is 1um shorter - in the row of 100 bricks those differences will mostly cancel each other out, won't they?
  - MagnumOpus 4y ago
    Not necessarily -- for instance, it could be that the mould for 1x1 bricks is too short and the mould for the 2x1 bricks is too long. Now if someone builds pillars from 1x1 and 2x1s respectively, the differences accumulate.
    - rkangel 4y ago
      See my sibling comment about tolerance analysis. Also, it's not just about variance between different bricks (1x1 vs 2x1) it's about variance between different parts out of the same tool (the correct term for a mould is a "tool"), and variance between different tools producing the same brick. Some really subtle effects affect the size of parts if you care down to the level of 1um - all sorts of temperature variation, pressure, humidity, colour mix etc.. Lego's skill is the ability to control or compensate for all of these confounding factors and get consistent results, regardless of age of mould tool, manufacturer of machine, ambient conditions etc.
  - rkangel 4y ago
    There are a number of different approaches to tolerance analysis. I kept it to simple arithmetic analysis for the explanation, but yes there are other approaches too: https://en.wikipedia.org/wiki/Tolerance_analysis https://en.wikipedia.org/wiki/Tolerance_analysis

rkangel 4y ago

Lego bricks are made to 1um tolerance (1 thousandth of a millimeter). The reason they have to be is to make sure that larger models fit together properly. The "not too loose, not too tight" thing is part of it, but isn't actually the key reason which is "accumulation of tolerance". Imagine two rows of 100 bricks. The difference in length between the two rows is 100 times that 1um tolerance. If the tolerance was less good, things wouldn't fit together well. Lego model design guidelines actually have a maximum size of a "fully" connected block of bricks because eventually even this precise manufacturing can't cope. Really big models have purposefully designed decoupling between sections.

988747 4y ago
> The difference in length between the two rows is 100 times that 1um tolerance. Doesn't tolerance work both ways? One brick is 1um longer than it should, another one is 1um shorter - in the row of 100 bricks those differences will mostly cancel each other out, won't they?
- MagnumOpus 4y ago
  Not necessarily -- for instance, it could be that the mould for 1x1 bricks is too short and the mould for the 2x1 bricks is too long. Now if someone builds pillars from 1x1 and 2x1s respectively, the differences accumulate.
  - rkangel 4y ago
    See my sibling comment about tolerance analysis. Also, it's not just about variance between different bricks (1x1 vs 2x1) it's about variance between different parts out of the same tool (the correct term for a mould is a "tool"), and variance between different tools producing the same brick. Some really subtle effects affect the size of parts if you care down to the level of 1um - all sorts of temperature variation, pressure, humidity, colour mix etc.. Lego's skill is the ability to control or compensate for all of these confounding factors and get consistent results, regardless of age of mould tool, manufacturer of machine, ambient conditions etc.
- rkangel 4y ago
  There are a number of different approaches to tolerance analysis. I kept it to simple arithmetic analysis for the explanation, but yes there are other approaches too: https://en.wikipedia.org/wiki/Tolerance_analysis https://en.wikipedia.org/wiki/Tolerance_analysis