What does the nozzle diameter setting actually do?

[PCLoadPLA 0]

I've been wondering this for years now. 

 

When I switch between 0.4 and 0.6 nozzles, I always change the nozzle diameter in Cura. Doing this the first time, was actually not easy to learn how to do...there's no nozzle diameter setting in the normal print settings; the nozzle diameter is actually defined in the printer profile. For some printer profiles, you can choose "alternates" to change between nozzle sizes. For my original printer profiles, there wasn't even a way to change it and I had to figure out how to add "alternates" to my printer config to even enable the 0.6 option. And never is there a way to choose an arbitrary nozzle size like 0.45; usually there are only a couple standard sizes like 0.4 and 0.6, and if you need something weird like 1mm you might not have that option.

 

So I don't know why nozzle size isn't just a print setting right there with the other settings like line width and flow etc. in the first place, but besides that, I don't know what changing the nozzle size in Cura actually does.

 

People have told me they ignore nozzle size completely. They just leave it at 0.4 or whatever, and set line width to whatever is appropriate for their nozzle. For example, when they install a 1mm nozzle, they just set line width to 1.2 and layer height to 0.5 or whatever and leave the nozzle diameter at 0.4 in Cura and ignore it. 

 

So if nozzle diameter doesn't impact anything, why does it exist in Cura? And if it does impact things, what things?  

[Slashee_the_Cow 493]

It affects the values which Cura will warn you about (the input box goes yellow) when they're too high or too low. It affects some values which are automatically calculated by default (though I can't remember which off the top of my head).

 

Fortunately for you there exists exactly what you want: open Marketplace at the top right and find the plugin "Printer Settings":

 

Now in the print settings menu, you can adjust not just nozzle diameter but a whole bunch of other stuff:

(there's more than that, just figured it'd be indicative to show you a section with six different nozzle settings in it)

 

Now you can make your nozzle size as arbitrary as you'd like! (up to three decimal places by the looks of it)

 

 

[PCLoadPLA 0]

This is interesting and I shall check out this plugin. But it doesn't answer the question of what nozzle diameter actually does in the slicer. As far as I can tell, with the same line width and height, the same gcode will be generated even if you change nozzle size.

 

It does make sense that the nozzle size could be used to generate warnings. That seems reasonable enough. But if that's all it does, I think I'm not going to bother changing it. I've been more or less changing it out of superstition. 

Edited April 5 by PCLoadPLA

[Slashee_the_Cow 493]

Well regardless of nozzle, the same layer height x line width x speed is always going to be the same flow rate. There are settings like wipe and retraction prime where you're likely to want different values for different nozzle sizes, but even if your printer definition has variants with different nozzle sizes, I don't think it actually saves the changes per variant, so... ¯\_(ツ)_/¯

The point of a wipe is to cover the Z seam by going over it without extruding, using whatever's left in the nozzle to wipe it closed, and to try and avoid stringing. A bigger nozzle is going to have a larger chamber which might have more left inside it, so you may want to wipe further (or if there's a lot left in there, coast instead of wipe).

And you can prime an extra amount of material after a retraction to make sure there's enough pressure in the nozzle chamber, again that's just extruding a certain amount more and not going to change the gcode. But a bigger nozzle requires more material in it to reach the same pressure.

 

I think if anyone can answer this question it's probably @ahoeben

[ahoeben 2,016]

CuraEngine does not actually use the Nozzle Size setting, but instead it uses the Line Width setting and some other more specific line width settings. In part this is a leftover from a time where most Ultimaker profiles would use a line width that was 7/8th of the nozzle size (so a 0.4 mm nozzle would print with a 0.35 mm line width).

 

The optimal Line Width to print with is affected by the nozzle diameter. But you can print fatter and thinner lines than the nozzle diameter.

 

The line width and the layer height determine how much material needs to be extruded. The material diameter is used to convert that to the amount of E-steps. The flow parameter is just a multiplier to adjust for slight miscalibrations and material slipping.

 

For printers that have a nozzle size dropdown, you are actually not just affecting the nozzle size, but you are loading an entire settings profile that could have many other setting changes (such as printing speed, material temperatures, etc).

 

Edited April 6 by ahoeben