screwless fixing of z axis. reduce z wooble.
remove screw on top left of your oneup. install part-three first then part-one, then reattach the removed screw again and as last one part-two.
see animated gif ;-)
after printing the parts i had to clean the edges with a knife and used a drilling machine with 8mm an 10mm for enlarging the holes. --> needs a further optimizing of the 3d model.