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On their website they say the following

0.25 mm nozzle: 150 to 60 micron
0.40 mm nozzle: 200 to 20 micron
0.60 mm nozzle: 400 to 20 micron
0.80 mm nozzle: 600 to 20 micron

That confuses me. Why can I go down to 20 micron with the 0.40, 0.60 and 0.80 nozzle but only down to 60 micron with the much smaller 0.25 nozzle? Is that a typo and should say 6 micron?

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  • $\begingroup$ Have you found & fixed the problem? If any of the answers helped you to get an answer to your question or come to your own conclusions then please do vote & accept an answer (using the tick button next to it). This helps us reduce the unanswered questions list & stops the question from being bumped once in a while. If you found another answer (than those already posted), please add that answer (& accept after 48 hours) to share your experience with the community. If you have not been able to address the problem please update your question. $\endgroup$ – 0scar Sep 11 '18 at 21:06
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You need a certain minimum flow rate to achieve consistent extrusion. Flow rate is the product of print speed, extrusion width (proportional to nozzle size) and print speed. If you use a very small nozzle and very low layer height, you'd need a very high printing speed to achieve a reasonable flow rate. Therefore, it's quite possible this is not a mistake and intentional.

Keep in mind that Ultimaker uses 2.85mm filament. With a 0.3mm extrusion width, 0.02mm layer height and 60mm/s print speed, you would need a feedrate of 0.06mm/s into your extruder. The extruder might not be able to develop enough force on the filament at such a low speed (which, owing to the small nozzle size, requires a relatively large amount of force).

The ultimaker can not print 6 micron layers since the smallest increment the Z-axis can move in is 5 microns. 6 microns is not a multiple of that.

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  • $\begingroup$ I would say that extruder force is not an issue. However, accuracy is, since 0.06 mm/s means a very limited number of steps: assuming 3:1 gear ratio and (very approximately) 4 mm hobb bolt radius, we are talking of about 2.5°/s on the stepper motor: 1.5 steps per second. Microstepping brings it to 24 steps/s, but microstepping are not always very accurate and the position of the axis may lag easily several microsteps on an extruder, resulting in inconsistent extrusion. $\endgroup$ – FarO Jan 8 at 16:12
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In addition of Tom van der Zanden's answer, when the filament moves too slowly through the heated part of the printhead it is very likeley to clog.

I have had this multiple times on my UM1+, most of the time resulting from a heated printhead with no extrusion (before or after prints). So you need to be sure to have a minimum of filament extrusion happening, wich is most likeley not the case when having 0.25mm * 20 micron instead of 0.60mm * 20micron, for example.

You could of course make the printhead move faster, resulting in a higher extrusion, but that will lower the print quality again.

But let me tell you this: Always look out for high extrusion, removing clogs is a real pain!

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