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devilhunter
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Motor with integrated leadscrew question

Tue Feb 20, 2018 8:41 pm

I don't quite know what to get for the cartesian printer i'm building (Prusa i3 Haribo 320)

It's either a motor with a integrated leadscrew need about 420mm, found one here

or a normal Nema 17 with a coupler and a leadscrew.

What gives a better print quality?


Prusa said this at the MK2 announcement:
Integrated leadscrew Z axis

You can see a lot of clones using trapezoidal threads for Z axis but they always have one big problem. Cheap, springy, spongy coupler which introduces wobble into the print. From my experience M5 threaded rod with flexible tube coupling works better. But there is one way to improve – ditch the coupling. We ended up having our custom motors manufactured with integrated trapezoidal lead screws. This means no coupling, no wobble and awesome layer alignment!

This way Z axis got also way faster and more wear resistant which leads to possibility of using Z Lift where the nozzle lifts up on travel moves and prevents scarring (leaving unpleasant mark on already finished layer, by dragging the nozzle on top of it). The i3 MK2 is an ideal platform for this as the extruder is quite small and won’t wobble compared to boxed printers which would have to quickly lower and raise a heavy print bed in Z axis to achieve something similar but not quite as the object moves the whole time as well causing further issues.
What no Z-Hop possible without a integrated leadscrew?

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devilhunter
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Re: Motor with integrated leadscrew question

Tue Feb 20, 2018 10:12 pm

Ah, i see.
The flex couplers will introduce some tiny misalignments every time the Z axis hops from one place to another. This will result in worse outer layers.

What about the stiff couplers like this?
https://www.amazon.com/RepRap-Champion- ... 01MFBPV9N/

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devilhunter
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Re: Motor with integrated leadscrew question

Tue Feb 20, 2018 10:34 pm

For documentation's sake, i'll include what i find on the net.

From Thingiverse:

If you are using a printer where the shaft is secured and fixed to a member of the printer, then you need to use flexible.

On my Anet A8,I printed rigid couplers and used them on the Z axis because of special case. THESE NOTES ARE ONLY APPLICABLE to Prusa type Z axis. I dowloaded the model from thingaverse. The flexible couplers on Prusa type printer Z axis are like printing through springs. They can raise or lower the layer heights during printing, especially if the extruder is hitting something that is slightly raised on the print, which happens once in a while (like support or raft material). I noticed that switching to solid increased the layer height consistency of my prints. The printer also has enough flexibility in the X axis support rods to deal with any bumps in the road with a rigid coupler. If you switch to rigid, just make sure the rods are aligned and do a full travel check before printing. I loosened the motor fasteners a bit during the full range check and tightened the fasteners once i realized the travel was OK. You will be glad that you switched.
It seems stiff couplers also have this problem, but to a much lesser extent.

So i guess integrated leadscrews it is then...

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joan.t
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Re: Motor with integrated leadscrew question

Wed Feb 21, 2018 12:47 am

the Mk1 prusa i3 original, used 5mm studding, and pvc tube for the connector... (not even a proper flex coupling... no screws to keep parts aligned, just tension from the enforced expansion of the pvc tube to fit the motor shaft and studding!)

so integrated leadscrew motor, is a massive improvement

having said that, the Mk1 printer was still a functional proposition.

if you end up withe separate parts, you can butt the leadscrew against the motor shaft inside the flex coupling and reduce the effect of any z hop...


regards Joan
I try to make suggestions that I believe to be well founded and safe,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions,
what you do, is YOUR responsibility.

eric.k4
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Re: Motor with integrated leadscrew question

Wed Feb 21, 2018 10:34 pm

On another machine i have a rod wobble in 10mm circles.... just one side. i didn't fix it because the thing prints top notch.... it has zero z-banding... actually its better than my MK2s... which could be something else like the extruder but it's pretty spot on. it has flexible couplers. if anything i would fix it because it's annoying doing large z travels, lol.

I also had threaded rod Z axis once with plastic tubes as couplers. zero banding there too. when i changed the lead screw i saw no difference in quality. but they looked cooler so i left them.

i run 2mm pitch rods now, no worry about them going out of position when the motors are off and any Z/microstepping error is spread across more steps per mm. plus you could do like 0.01 micron height or something but not really a big deal.

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