At least I think they should be called jig axles. These pieces of Aluminum rod are used with the coupling rods to ensure the bearings are exactly the right distance apart. Essentially, I will pass these rods through the bearings, fix the coupling rods to the outsides, and then solder the bearing guides to the frame. This allows for a frame that isn’t 100% square and bearings that could be slightly off-centre.
When I made #10, I used commercial tapered jig axles to line up the bearings. They came from one of the UK suppliers, but I really don’t recall which. While they worked, the setup was as wobbly as a jellycopter and I will never know how accurate the bearing guides turned out.
For 622, I wanted an improvement. First of all, there is no need to accommodate different hole sizes in the coupling rods – I know they are 1mm. Secondly, by making the axles extra-long, I can minimize any inaccuracy introduced if the holes in the coupling rods are larger than the pins on the ends of the jig axles.
Pembroke:87 