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So I’m in the process of building a custom 3d printer and weighing up options I have never seen a belt driven z axis is there a reason for this ?

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soon as you lose power the assembly is going to go crashing in to the bed

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As well, having a belt driven z axis would probably result in much more vibration. I don’t know for sure but I’d also imagine it would greatly decrease the minimum layer height could possibly do due to the loss of accuracy. The z axis just never actually needs to move fast, it’s not necessary. Unlike the other axis, it only moves when a layer is finished. This would mean that your belt would have to be bearing the full weight of the heated bed and print which in the long term may lead to stretching. Consider as well that the other axis never actually are supporting any load, but rather just moving it.

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Interesting points, I’m planning on building a corexy printer so the print head never moves in the z direction just the build platform. So head crashing is a non issue as the resting position of the bed will be fully down, as for vibration that might be an issue, although I’m planning on the bed being supported at all 4 corners and with the belts properly tensioned (possibly a spring loaded auto tensioner of some sort) I think that issue could be overcome. Which leaves minimum layer height I’ve done some calculations, using belts I can go to as little as 0.01 layer height (minimum I use is 0.1 tbh) I totally agree about the speed, but fast homing to the print head would be nice (remember it will be at the toppossibly, greater than 300mm of travel) I’m just weighing up the pros and cons, I did find a couple of belt driven CNC and printers on YouTube, they looked like they worked pretty smoothly.

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A belt driven system is possible but not seen for several reasons.

An acme screw driven stepper motor has a large mechanical advantage over the build plate meaning the torque required is fairly low. The trade off is that more rotations are required to move the same distance, this is advantageous in this case though because it means the resolution is increased. Removing this mechanical advantage by going with a z belt drive reduces both resolution of the movement and increases the required torque from the motors, neither of which are a good thing.

Another issue that is seen in a belt driven set up is a constant torque is needed to hold a belt driven Z in position, the belt driven Z is constantly fighting gravity. Compounding this problem, as more material is placed onto the bed the required torque to keep the bed in position goes up. This torque is not needed on a screw driven z axis since the z axis has sufficient internal friction to keep the bed in place even with the stepper is shut off.

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