I cut a shoulder into the lead screw at both ends of the Z axis on my machine. Secure mounting of the pillow bearing blocks serves to form a "Clamped" lead screw. The only "Play" left is in the recirculating ball bearing nut assembly of the Z itself. I did have to experiment with different "Shims" in mounting of the pillow block bearings until I achieved movement without any binding. Also, I used the set screw hole of the coupler as the guide for where to drill an indendation into the lead screw into which the set screw is locked. Never had any slippage since! Engravings in particular require precise repeatable movements to within .001" I realize this post is almost a year old, but perhaps anyone else who may be building their own machine, may benefit from this comment. Have a blessed new year!