Z-Axis Considerations in a Dedicated, Large-Volume Paste Extrusion MPCNC

Hello all! I ran out of pocket money for my own MPCNC, but I’ve just been handed a golden ticket by my University Professor to build one as our test rig for “small scale” proof of concept for printing in clay, mud, cement and other paste materials fed via a bowden tube into the nozzle. For reference I’m planning to experiment with huge nozzle diameters between 2.5-10mm at slow printing speeds.

I’ve shown him the MPCNC and have been asked to come up with a bill of materials for a 2’ x 2’ x 2’ build area (hopefully utilizing bundles for sale here on the website). I know that there really isn’t any issue with the X and Y axis, but looking around here on the forums, I’ve realized that the average Z axis is below 1’ due to needs for high rigidity required for CNC use, but if I’m using this only for printing, and only for relatively basic shapes (through a big honking nozzle at that), is this something that would be considered doable just by structural reinforcements and longer conduit?

Alternatively, I do have plans to design a Z axis with ACME rods at all 4 four corners, quite literally lifting and lowering the entire gantry to change layer height, but this would add quite a lot of development time that I hope to avoid. Otherwise, I think option 3 would be me haggling down the build height to 1’

What do y’all think?

High rigidity is more necessary for cutting parts with a router than printing especially at slow speeds. Conduit is super cheap, just make a set of 1ft and a set of 2ft legs. A whole second set is like $2 worth of conduit.

ACME rods in all 4 corners is extremely interesting but may be harder to achieve than you think. Many printers have enough issues with just 2 that are in a line with each other let alone 4 in a square. Additionally you would need to upgrade your stepper driving system for the z axis. The ramps board has dual outputs for the z axis since most printers use 2 steppers on the z. But that is doing the same thing that we do by wiring them in parallel. I would be extremely hesitant to put 4 steppers on 1 driver. Although, the worst case scenario is destroying like $40 worth of electronics and possibly causing a small fire, sounds like fun to me.

If you go the 4 z axis stepper way, you might be able to run wires from where the z stepper driver plugs into the ramps board out to an external stepper driver that is rated for 4 steppers (may require power from a source other than the ramps board).

I like your idea of having multiple leg lengths handy. I’m Totally gonna do that.

In regards to the idea for the 4 corner acme rods, I think I could do it with one Nema 23 (or greater) or two Nema 17 steppers. The design with that would be more or less a carbon copy of the Z-Axis of the Micro 3D. It was my first printer (I have a Kossel Mini now) and for all the other flaws with the design, I found the Z axis quite novel in that four threaded rods in each corner were turned by a single motor, via a closed timing belt. The initial setup and calibration would be aggravating, to say the least, but quite doable. I think the hardest part would be sourcing one large (closed) timing belt, or 4 smaller timing belts. With that design the gantry would no longer be part of the structural support, so an outer skeletal structure is needed, but beyond that it would be a matter of anchoring the threaded rod to the X-Y gantry.

Dear god, the more I talk about it, the more I want to do it… For now I want to try to stick to the existing build as much as possible for the sake of expediency.


Thats a pretty good idea with 1 stepper moving all 4 corners. I would go with a nema 23 for that.