@diogenes @nicholasfarr14254 thank you very much. Sometimes knowing something is possible is all that’s required to get it done. I removed the clip with scalpels and an inverted broken key extractor lockpick.

Strangely however, the coupling remains retained. It slides a small amount, and seems to come against a shoulder, presumably the groove on the leadscrew for the retaining clip ring. I’m wondering if there is a nack, actual method, or I should attempt to force it – perhaps there is a small burr I can shear – but that would be surprising considering someone put it on there in the first place.

My removal method for prosterity’s sake:

Scalpel A to lift the end away from the shaft and create a gap through which scalpel B could slide, between the shaft and the clip. Then keeping B in place, removing A and sliding an inverted key extractor pick with as much angle as possible through the dog crenelation under the ring. Remove B. Pulling the ring away as far as possible, reaching and driving the leadscrew as described by nicholas above.

Something ia certainty amiss. I’ve given it (relatively) considerable force. A bearing puller was my thought as well, I might fab something up.

It’s worth noting that perhaps 90% of my rubbing issues actually stem from the clip its self rubbing on the coupling. With the clip removed, the coupling spins freely as the carriage is turned. I filed and slightly loosened the clip with some improvement, but it’s still not satisfactory.

I appreciate that it sounds strange but I believe I have eliminated everything else. With the gears removed and only only the leadscrew thrust bearing, two lock nuts, coupling and clip installed, when rotating the handle the carriage couldn’t be smoother in both directions. With even light finger pressure, just enough to hold the coupling from rotating, the jank begins, and through my finger I can feel the intermittent little scratching and grabbing.

Repeating the same test with the clip removed, the jank is nowhere to be found. I can flick the coupling and watch it spin very freely many rotations. It stops dead when clipped. It could be a burr or something on the inner face of the coupling, or burrs on the leadscrew groove similar to what is likely holding on the coupling, but it’s clip related either way.

Worth noting I think this machine has probably only seen an hour of use if even. No wear anywhere, the original brazed tools the previous first and only owner bought with it are still wax sealed bar one, which shows little use.

If there is a break in period that usually wears these kinds of things in, it hasn’t happened yet.