The Z axis stage is basically identical to the Y axis stage for ease of assembly and in order to simplify part production. The only real difference between the two is that the Z axis stage has ten counter bored holes towards the end of the plate which are used for attaching various tool heads.
The Z axis stage uses four linear ball bearing blocks, two per each rail, as opposed to the X and Y stages which each use two. This was implemented in order to give the Z stage a larger degree of rigidity when subject to transverse loads. In the above image, the through holes on the Z beam are clearance for the screws that fasten into the linear bearing blocks. Speed is not an issue for the Z axis because it moves very small distances (~.425 mm) only intermittently (once per 3D printed layer). So, this stage uses 3/8″-12 (1 start) ACME threaded lead screws. This gives the Z axis a high resolution for traversing to each incremental layer while a part is being printed. Layer height is crucial when 3D printing high quality parts.
Here the Z beam, with the newly attached Z axis stage, is mounted onto the Z axis support structure. Once again, the Z beam is positioned with laser cut jigs so that when the plastic extruder is attached, its nozzle will be perfectly centered over the build base.
The larger your build volume gets, the more attractive it becomes to use a moving toolhead design instead of moving table. Don’t get me wrong, I really like the ambition and ruggedness of this design, you’re definitely pushing it with this design…
That is not necessarily true, you have to keep in mind that I also designed this machine to be capable of doing some light milling, in which case a stationary spindle/Z Axis would be best.