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It seems to me that the size of hole in the nozzle shouldn't matter in and of itself. If you program in the layer height and line width, then the same amount of plastic has to be extruded, no matter what size the hole is in the nozzle.

Of course I understand that, mechanically, the best results are got with the line width slightly larger than the nozzle size. We couldn't print a 0.3 mm line with a 0.6 mm nozzle, and trying to print a 1 mm line with a 0.4 mm nozzle probably wouldn't work well either. But in terms of what the actual G-code needs to do, the nozzle size doesn't seem to matter. After all, printers feed filament based on length/volume, so the size of the nozzle shouldn't impact the amount of plastic extruded.

What prompted this question: I want to switch from a 0.4 mm nozzle to a 0.8 mm nozzle, but I cannot find out how to change the nozzle size in Cura. There are many bug reports about the nozzle size setting disappearing or not displaying in Cura, and I think that's my problem. However, in the troubleshooting threads, many people claim that you can just change the line width and ignore the nozzle size completely and the result will be the same. In other words, if I want to switch from 0.4 nozzle and 0.48 line width, to 0.8 nozzle and 1 mm line width, I can just keep my slicer set to 0.4 nozzle size, but increase the line width to 1 mm, and if I physically install a 0.8 mm nozzle, it will do exactly the same thing. There are even Cura developers saying the nozzle size setting will be removed in a future version completely.

This may depend on the way individual slicers work. Has anyone tried switching between say 0.4 and 0.6 nozzle settings, while leaving the line width the same (say 0.8 mm line width for both), and see any differences in the G-code? I can't test this myself, because I can't change the nozzle size right now...

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Technically, you don't need the nozzle diameter. All you need is line width, layer height and filament diameter. After all, all the settings are just used to create a displacement of the filament feedstock (volumetric displacement).

But slicers do use the diameter to set initial values for some parameters, e.g. the wall width.

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I never thought about that!

I do know from experience that Cura uses nozzle sizes to sanity check your settings, warning you if you do something unreasonable. That is reason enough to include the feature for me. However, I did wonder what, if any, differenced this actually makes, so I tested it and here's my results:

I went through and tested it on the 3DVerkstan Face Mask. I compiled the same model in the same place in Cura, the only differences between the two being that I changed the nozzle size from 0.4 mm to 0.8 mm. I then ran the VS Code Diff Checker on the files as well as loaded the exported gcode back into Cura to compare and got some interesting results.

  1. The estimated times and filament usages are very slightly different: 2689 seconds for 0.8 and 2698 seconds for 0.4, 6.18899 m for 0.8 and 6.18883 m for 0.4. This means something different is happening somewhere, but it's very similar to within a rounding error.
  2. The brim is exactly the same for both. No differences whatsoever in the G-code.
  3. When the model starts printing, everything in the gcode becomes different. This seems to be down to a few reasons: (note these photos were taken by exporting gcode then re-opening that gcode into Cura)
    • Differing layer start positions 0.8 mm File0.4 mm File
    • Possibly a difference in line overlaps? On the 0.8 mm file, cura shows a larger gap between the brim and the part, and more overlap between the outer wall and inner walls when compared to the 0.4 mm file. Line Overlaps Compared

That's all the differences I can observe in this model. Every layer is different in the gocde, but it seems to be down to the two differences noted above. IMO, that's all inconsequential and you should be fine to change all the settings to how they should be for a larger nozzle and be just fine. Other than the warnings, nozzle sizes may be a holdover from a past version when they were more useful, or simply may have just seemed like a reasonable feature to put in at the time and no one really thought about it.


As far as changing nozzle size goes, I go to Preferences > Configure Cura > Printers > Machine Settings > Extruder 1 > Nozzle Size. If that option is not there, consider creating a new machine of a different type that's similar to what you have. I have an Anet-A8 but use the Prusa i3 printer type in Cura since that's most similar to what I have.

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  • $\begingroup$ I have tried to find the setting in Preferences > Configure Cura > Printers > Machine Settings > Extruder 1 > Nozzle Size, but on my version of Cura there is no option for nozzle size. Other screenshots online show versions both with and without nozzle size setting, and I'm still not sure why. $\endgroup$ – BetterSense May 5 at 1:32
  • $\begingroup$ Good answer. Have you checked "thin walls"? maybe the slicer kills walls much thinner than the nozzle, independently from the set line width. Could you test this too? $\endgroup$ – FarO May 5 at 12:47
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CNC kitchen tested various extrusion widths with various nozzles and in fact there's no difference, only the line width matters. https://www.cnckitchen.com/blog/big-nozzles-how-do-they-make-your-3d-prints-stronger

Of course it's up to you to avoid too thick layers with small nozzles.

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I’m using sli3r. It use nozzle size for some auto value like auto extrusion width which calculate by 105% of nozzle diameter and prevent some error like setting layer height greater than nozzle diameter.

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