Center Z axis vs Z axis on left/right pillars of Y Gantry?

Hey there,

As I'm considering building my own "little" CNC router (500mmX500mm) - I'm looking at MOST CNC routers and they have a very standard format: bed is static, Y gantry moves in the X axis, and Y gantry supports the Z axis. However, 3D printers are built differently where the Y gantry moves in the X axis AND Z axis and the extruder just moves in the Y axis. In the case of CNC routers, vertical motion happens in the blue rectangle as seen in the picture I drew. 3D printers have vertical motion in the red rectangles. I understand why 3D printers would opt for moving the entire gantry up and down, because it only moves up as material is added layer by layer, so there's no risk of bumping into anything, while having a smaller footprint Z axis for a CNC makes sense because you may travel up and down more.

Are there any machines that make use of both red and blue vertical motions? Are there specific names for either the red design or the blue design?

While the machine I'm building will primarily be used as a CNC, I want to have the option to attach an extruder instead of the spindle, or a laser for example - I know it's less than ideal, but I'm just curious about the different motion patterns.

Best,
John

I have only seen one machine set up like that, an old metal planer that had been converted to a CNC mill. In that case it was a fixed gantry with a moving table. The gantry could move up and down manually with a crank for rough height adjustment. The spindle assembly was on a more or less conventional rail assembly for the main Z axis. Also consider that a knee mill has a dual Z axis adjustment, in most cases, the knee moves up & down for rough adjustment and the quill is normally the main Z axis under CNC control. I call the knee motion the ''K'' axis on my DRO.

But what to call your design? Maybe Z_A and Z_B Or maybe Z and ''G'' for gantry?

As far as how to build it and control it, I'm not even going to think about that. :)