4th axis scale factor (steps per degree)

Thanks Nick. I might start with a similar 4th Axis. I'm also looking for a used microarc.

It is normal, that a HD doesnt have the exact 50 to 1 ratio. This is just a "rounded" number.

It depends on the "gears" and normally a 100 to 1 for example is 101 to 1. This is because the drive axis rotates in the opposite direction of the driven axis. So the difference is always +1

Best regards
Julian