Goal is to remove the compressibility of the Z couplers between the steppers and Z lead screws by making the Z lead screw and stepper shaft into a very flexible ball joint. I used a metal lathe to make parts, but I am thinking a plastic version should be possible (have some ideas if anyone is interested). Way this works is to put a 3.16mm ball bearing (sitting on stepper shaft in pic) between the stepper shaft and Z linear screw and use the Z coupler provided by Robo 3D as a compressive spring to keep everything in contact with the Ball. Takes advantage of the hole in the end of the stepper. To do this, the aluminum spring Z coupler was put in a a 3 Jaw, and the 8mm side bored to a diameter of 0.371" and depth of 0.32". The split in the Z coupler spanned one of the jaws so the coupler did not compress as the 3 Jaw was tightened in place for the boring operation. Next, a 3/8 hex head shoulder bolt was drilled for a 5/16 tap drill and cut off to 0.3" length while being held in a collet. After the cut off, the bolt section was held in the same collet and tapped with a 5/16-18 (Robo lead screw dia/pitch) using the tail stock to hold the tap true. The threaded rod end cone divot where the ball sits was created in the lathe with a 1/16" ball end mill as a starter drill and then using a TIN coated drill bit. Either my threaded rod was hardened or I had an exceptionally dull center drill, so carbide ball end mill. Not sure what the final drill face angle was, but I used one that looked steeper than my normal drills (Harbor Freight special; could also grind a drill face to get a steeper cone angle; not sure it is necessary) Assembly: the 3/8 bolt gets inserted flush into the aluminum coupler. Grease ball and place on end of stepper. Attach coupler over stepper shaft. Place two nuts on threaded rod then insert into threaded 3/8 bolt head. Continue screwing in until ball is engaged and coupler starts to expand. I think I did 1-2 turns more. Tighten first nut against 3/8 bolt head. 2nd nut goes in X/Z carriage like before. Do for each side.