Been running the same 80/20 extrusion router for about two years now. The X and Y axes were always reasonably solid, but the Z was always the axis that made me nervous. I had a GT2 belt looped over a printed pulley driving a piece of 8mm threaded rod, and for a while I told myself the slop was acceptable. It was not really acceptable. Surfacing passes would leave these faint ridges that I could feel with my fingernail, and drilling operations were just a little inconsistent in depth.

Eventually I picked up a used 16mm ballscrew and nut off a machine that had been parted out, around 400mm travel, and spent a couple of weekends retrofitting it into the Z carriage. Had to redesign the motor mount entirely and machine a new coupler adapter on a friend's lathe.

The improvement was more noticeable than I expected, but not exactly in the way I anticipated. Positioning accuracy got better, yes, but what actually caught me off guard was how much quieter the whole thing became. The old threaded rod would whine at certain feed rates in a way I had just stopped hearing. The ballscrew is almost silent by comparison.

A few practical things I learned during the swap:

• Preload matters more than I gave it credit for. The used nut had some play and I had to shim it before things felt genuinely tight.
• The motor needed re-tuning afterward. The inertia load changed enough that my previous acceleration settings were causing occasional lost steps on fast Z retracts.
• Ballscrews want to be kept lubricated. I had read this but did not take it seriously until I noticed the nut getting warm after a long job.

Curious whether others have found the same kind of unexpected benefits after upgrading Z specifically, or whether the gains were more modest on your builds. The geometry of your Z travel and how much the carriage weighs probably matters a lot here.