Printing at .4mm with .4mm nozzle

[Johnmgg 1]

Hi all, I have a quick theory question. I am printing a part that in Cura 5.0 I set to a .8 nozzle size and .4mm layer height. Now here is the thing. I forgot to change out nozzles in my E3D REVO. It had a .4mm nozzle installed. By the time I remembered that I needed to change the nozzle I had printed at least 1 or 2 layers. But these layers look perfect. Nice extrusion everything was great. I just wonder why would this not work. And if it will work why couldn't I tell CURA that I am printing with a 1.0 or 1.2 nozzle and a .8mm layer height. I know for the first layer you can over extrude to achieve a better bed Adhesion. Like .6mm layer height even though you only have a .4mm nozzle. So what if any are the advantages or disadvantages?

[GregValiant 1,408]

A lot goes on in that little space below the nozzle.

If you had set up to print a 0.4 layer height at 0.8 line width then that tells Cura how much filament to push.  The nozzle size doesn't come into that.  I think the nozzle size is used to set up the default line widths (and in 5.0 maybe the minimum line width, etc.) but the volume of any extrusion is calculated from the Line Width x Layer Height x Length of Extrusion.  In that formula there is no mention of nozzle size.

Theoretically you could print that same gcode file with a 0.2 nozzle provided your print speed was slow enough to allow time for the required volume of filament to extrude through a really little hole.  Speed plays a big part.  The faster the material moves through the nozzle the more turbulence is created within the nozzle.  The material next to the walls of the orifice moves slower than the material going down the center.

I ran a test on my printer and using a .4 nozzle at .4 line width and .2 layer height.  The extruder/hot end couldn't keep up at a print speed above 175mm/sec.  With those numbers that comes out to 14mm³/sec.  That is the number that is truly important because above that, my printer can't keep up with the demand for more plastic.  Given that ceiling of 14mm³/sec I could only print your gcode file at 45mm/sec because that's where my extruder/hot end combination can't keep up anymore.  Even at 45mm/sec, my extruder/hot end would be on the ragged edge.

Then there is also the question of the cooling effect of the plastic moving through the hot end.  The higher the volume of flow, the greater the cooling effect, and now you are making temperature adjustments.

So to answer your question "Will it work?" the answer is yes, but with caveats.  "Everything affects Everything".

 

When you said "...you can over extrude to achieve a better bed Adhesion. Like .6mm layer height..." that is in error.  Simply increasing the layer height causes Cura to calculate a higher "volume" for the extrusion, but doesn't effect the flow ratio.  I routinely run "Initial Layer Flow" at 105% because it gives me some leeway for my manual bed leveling.  That builds in a 5% over-extrusion for the initial layer.  Over-extruding has nothing to do with the layer height but rather the ratio of "Volume of filament in" to "Volume of extrusion out".  When that ratio is 1:1 you are at 100% flow.  That is why on many printers calibrating the E-steps is important, and though often over-looked but just as important, is measuring the actual diameter of the filament and entering that into Cura.  Both of those effect the "Volume of filament in".

 

Of course all of that could just be a bunch of BS that I just made up.  It's been known to happen.