I don't see any "accepted" gear ratios for a stud-less direct-diagonal gear combination on sariel's excellent gear coupler

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but by shifting 12t gears such that they mesh off-center, it seems to work (i.e. spin correctly)

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Any potential issues with this? will they wear down faster? will they not deliver as much torque as normal? is it less efficient than other combinations for those positions?

1 Answer 1


In your setup, the space between both axles is about 11.31mm (1 stud brick = 8mm).

On the central part of the gear (the band where teeth protude), the pitch diameter is 11.9mm (outer diameter of 13.8mm, root diameter of 10mm). Hence the gears would not mesh if mounted in the same plane (because 11.9 > 11.31).

However, if you consider the beveled part of the gear to be like a smaller spur gear, its outer diameter is about 12mm (possibly smaller) and the root diameter is at most 8mm (more likely 7.9mm). The gears mesh because (12+10)/2 < 11.31 and (13.8+8)/2 < 11.31.

You can check the measures with a caliper.

What might be a problem is that in this setup, gears will be forced to rotate at the same speed while having different pitch diameters depending on the part of the gear, so the gears are likely to wear down faster. Now, the bevel gears are made of a softer plastic which whistands deformations better than other gears so it might just do.

  • even with a digital caliper, I am not having much luck measuring sub-millimeters due to the roundness of the surfaces Sep 10, 2015 at 20:05

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