What's better on z-axis? Belts or leadscrews?

Hi guys,

I just saw a 3DP with design using 2 stepper motors and belts to motivate the extruder, which means acting as z-axis.(the machine is called Phoenix) It sounds strange to me though. Feels like it's VERY likely to slip. What do you think?

The phoenix uses a standard direct drive extruder
but it is built in to X-trolley making it harder to put another extruder/hotend on printer.
The Z-axis is run by one stepper motor driving belt system to move both Z-trollies to
move Z-Axis
Well there is the teeth on a timing belt pulley or threads on a leadscrew,
and steps of a stepper motor.
There is 4 feet of belt and the adjustment / attachment to two trolleys,
on belt drive.
Both differently problematic for Z-axis layers.

Seems like the Phoenix printer used belts on all axes --- No leadscrews

IMHO --- there is a great need for helical belts and pulleys to get fine resolution
or positioning feedback. ( optical reading of position of each axis)

Well I thought there were two motor for z-axis.

I think, a belt is not accurate enough to move z-axis.

Edited 2 time(s). Last edit at 01/09/2014 07:26PM by jpan.

Belts and cables work great for Z axis. The Up printer uses belts. Printxel uses belts. Tantillus has cable Z axis version. Ingentis uses belts on Z. All RepRap delta bots use belts or cables on all their axis and they are all vertical like the Z axis. They all have excellent layer alignment and ZERO z wobble. I would never consider building another machine that uses a Lead screw.

Edited 2 time(s). Last edit at 01/09/2014 10:07PM by Sublime.

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I have to say that it IS common to use belts for x-and y-axis, but it's my first time seeing a belt for z-axis. I check and find that the printers you said are using belts for z axis. But resolution is a big problem isn't it? Also when the motor is off, the extruder drops.
similar topicI just found a topic in this forum that says the same thing

Yes it can reduce the possible layer heights that do not have rounding errors. For my cable driven Tantillus I can print at 0.099, 0.149 and 0.258 without any worry of rounding errors. There are many more possible layer heights with only a slight rounding errors. Some machines like Ingentis use a gearing system to give it the same resolution as a metric lead screw.

Yes the axis can drop when the motors power is cut but that is not a bad thing on most of the machines that have cables or belts on Z axis. Most of them have a bed that drops and not the carriage so when it drops after the print it actually helps by getting the printed part away from the hotend. On a Mendel variant I could see a need to keep the axis enabled which is only a small change in the firmware. On most of the Delta bots the axis is so light it usually does not drop even with the power off.

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I see.. In my case( Phoenix ) the carriage does drop but is not a big deal, right?
I searched and found that Tantillus uses a leadscrew for z-axis. Maybe you got an older version? Anyways I guess I'll have to accept the resolution.. Maybe it's not that bad as I thought aha?

hmm no z wobble you say? I might have to look into this for my machine, how many belts would it take hold a large heated bed, 18". I bet i could work out some sort of pulley system to increase the accuracy and distribute the load.

Quote
jpan
I see.. In my case( Phoenix ) the carriage does drop but is not a big deal, right?
I searched and found that Tantillus uses a leadscrew for z-axis. Maybe you got an older version? Anyways I guess I'll have to accept the resolution.. Maybe it's not that bad as I thought aha?

I am actually the creator of Tantillus and yes the instructions do have the lead screw but that is because I released the cable Z as a Beta part and have been too lazy to update the instructions for the cable Z. Also both parts are available in the Repo. Release announcement [forums.reprap.org]

Yes for the phoenix you could disable the feature that turns off the motors if idle as well as be sure not to disable them in the gcode at the end of the print (hopefully they have done those already).

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Quote
aduy
hmm no z wobble you say? I might have to look into this for my machine, how many belts would it take hold a large heated bed, 18". I bet i could work out some sort of pulley system to increase the accuracy and distribute the load.

Have a read through the Tantillus forum I posted above. Also Ingentis is large and has a heavy bed (Ingentis [forums.reprap.org] )

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I think the best way for my printer would be with a few reductions using a length of spectra line with a high load capacity. or another thought, what if you had a single threaded rod that ran the same length as the z axis, however it is not connected directly to the bed, instead the threaded rod has one nut and that nut is attached to the belts or spectra line, which is then routed through pulleys to hold up the z axis. then you get the torque of a threaded rod with zero wobble because the threaded rod is not connected to the z axis directly.

Quote
aduy
I think the best way for my printer would be with a few reductions using a length of spectra line with a high load capacity. or another thought, what if you had a single threaded rod that ran the same length as the z axis, however it is not connected directly to the bed, instead the threaded rod has one nut and that nut is attached to the belts or spectra line, which is then routed through pulleys to hold up the z axis. then you get the torque of a threaded rod with zero wobble because the threaded rod is not connected to the z axis directly.

Check out Sampo, it is a derivative of the early Darwin designed to use a single lead screw in the bottom pulling four cables. Also be aware that cheap threaded rod (and some cheap lead screws) have variation in the threads that can cause a similar effect as the infamous Z wobble but not from the bent screw.

Also be sure to have the cable pre tensioned. That is have the cable pulling up and down so it is at its maximum stretch so the weight of the bed and print do not stretch it and cause the layer height to change while printing.

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cool one of my friends has an extra ball screw so maybe ill give it a go, although with this design i could probably use a thing stainless steel cable instead. I find kinematics fascinating.

My Stratasys printer has two belts that raise and lower the heated bed up to the nozzle.

It's nice and rigid but at the same time if you mess up the first layer height the belts will flex, instead of ripping the extruder nozzle off

the stepper motor holding it up is a beast though... impossible to move when it's powered up!

HI Sublime,
So you are the creator of Tantillus? Why did you close your store?

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jpan
HI Sublime,
So you are the creator of Tantillus? Why did you close your store?

We had a child and I am a stay at home dad now and I just do not have the time to manufacture the parts. I do still make the hard to find parts like the hobbed bolt for people that ask.

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Hum that's a pity.
I'm curious. Are you guys who have your own design all professional? I mean, do you all have engineering background?

Quote
jpan
Hum that's a pity.
I'm curious. Are you guys who have your own design all professional? I mean, do you all have engineering background?

I have a lot of experience but I am not a professional. I have been an apprentice machinist and welder. I used to build custom vehicles and bikes. Basically a jack of all trades with a passion for building and learning.

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Encouraging

im a college student haha, i started 3d printing only a year ago and designed and built my own 3d printer last summer. at some point once i finalize my design i would like to document it and maybe sell kits for it.

Seems like many people do so on Kickstarter.