I notice most reprap models are belt driven, except for the z axis.

3D Printing
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1

I notice most reprap models are belt driven, except for the z axis. Is there a benefit to this?

I caught the bug and I think I am going to attempt to make a printer from scratch, I have already converted my 3020 CNC machine and it seems great after some initial calibration/user errors. The 3020 is leadscrew driven on all axis, and in my mind this would seem to be a better day sign than belt driven. So that leaves me wondering if the repraps are belt driven for cost savings or another reason?

Any other suggestions for building from scratch would be appreciated as well.

2

Acme lead screws are the best. Belts can slip. I would guess you’d need the same tension on the z axis? Anyways go with a screw I think

3

Belts allow for much higher speed. You can’t achieve it with leadscrews and in 3D printers you don’t need the torque that they create.

4

@Miroslav_Mandov after some testing I just cranked up my steppers to 50mm/s and it seems to be doing fine so far. What’s the speed comparison for belt vs lead screw? Like the max of each for a somewhat clean print?

5

50 is a good speed. For bigger things I use 70, but printing clean requires less.
The issue is that the motors will overheat since you need to print several hours in this speed.
If you are making a hybrid machine that needs to do both, then you have no choice except leadscrews.

6

OK u take that back lol, 50 may be a little too fast for some things, but its fine for others

7

dont’ forget the travel speed
150mm/s on most printers and can be up to 300-400mm/s for deltas.

travel speed is very important for the oozing when the hotend travel from one point to another without printing.

8

My printer has a Bowden setup and Jumps Speed is set to 250 mm/s. With much slower jump speed I would have a problem with oozing.

9

High travel speeds are important (and screw-driven axes are often limited by the firmware’s maximum step rate to much slower speeds than those that are possible with belt drives), but acceleration is a bigger concern. Extruder pressure lags, so you want to avoid accelerating and decelerating as much as possible. When you come to a corner, you want to maintain a constant extruder speed even though one of the linear axes is coming to a complete stop and the other is starting from zero. This means infinite acceleration, which obviously isn’t achievable, but the less moving mass you have, the closer you can get. Screws not only have to deal with the mass of the carriage they’re moving around, which is usually more than with belt-driven carriages just because of the hardware involved, but they also have to deal with their own angular momentum.