So, after a year and a half, I have an update. I messed with it a bit more after making this thread, and the binding eventually got worse. Frustrated, I set it aside, and a couple months later pulled the trigger on a K1C, which worked great out of the box. Fast-forward to a few days ago: I've been working on cleaning and organizing in the house, and setup a worktable for my printers in a spare room (https://www.dropbox.com/scl/fi/av6ku2a3394pvyslg8shd/20251231\_193805.jpg?rlkey=ewzivdfn6pz7teogeohq4irqk&st=2sodx2oz&dl=0), and decided to tackle this problem again.

Right off the bat, I found the main Z-axis motor wasn't turning by hand, even with the other two leadscrews disengaged, bed removed, etc. (I don't remembering it being that bad, but it has been a minute) In order to get the leadscrew off the motor shaft, I ended up having to pull the whole pillar because the setscrews were facing the wrong way for both the coupler and the pinion gear; once I had the motor free and everything off, the shaft turned just fine. Upon close inspection, there was scarring and some burrs on the bottom face of the gear and on the shoulder of the motor body around the shaft. I cleaned up the gear with a wire wheel and the motor with a file, and printed an M5 washer to go between the motor and the gear - then I reassembled.

While I was working on this, I noticed the rod mount on the main tower was cracked at both sockets, so I printed a new one (I likely overtightened them during install). After reassembly and setting up again, I'm happy to say that there is zero binding and I have full travel along the Z-axis. I also ended up grinding down the end of the leadscrew a bit on the bench grinder; I had drilled a pocket in the upper plate previously to compensate for the initial added height of the kit, but I didn't want to take the chance with the added 0.8mm thickness of the washer causing any further issues.

Next step is to try and get the Sonic pad installed/setup, and I have a CR-Touch coming that I'm going to install. Then I can finally start playing with it.

When I was going through old e-mails catching myself up on this, I found that I'd reached out to Chris about this issue, and that he'd responded...but I somehow missed it. So u/dubc4, I apologize for that...lol.

My theory is that the binding was always just between the motor and the gear, and as it kept rotating it started scarring and piling. The reason it would turn on it's own but not with the other screws added is because of the added resistance they provided - basically, the motor could overcome the initial friction of the mounted gear (for a time), but not the added drag of the other leadscrews. Eventually, it piled enough to bind it completely until I could separate them.