> we have implemented a tip clearance of only 0.5mm (120mm models) or 0.7mm (140mm models) in order to minimise leak flows through the gap between impeller and frame.

> Achieving such small tip clearances is essentially at the absolute limit of what injection moulding can consistently reproduce

For folks thinking about Lego tolerances [1] that are an order of magnitude tighter at 10 microns or 0.01 mm, it turns out that the largest Lego moving parts are a turntable at 50mm or so, and rotate at an rpm an order of magnitude slower (100 or so rpm vs 1200 rpm), so these tight clearances (not tolerances [2]) are quite tricky to achieve, and more importantly, maintain over the life of the product, apparently.

[1] https://en.wikipedia.org/wiki/Lego?#Design

[2] changed 'tolerances' to 'clearances' per note below

0.5mm is the clearance, not the tolerance. Tolerance must be significantly smaller than clearance.