Nozzle diameter vs extrusion

I just installed a new 0.4mm nozzle in my Cocoon Create Touch. Extruded 100mm of PLA from a fair height and measured its diameter as 0.47mm.
Does anyone KNOW the relationship between the nominal nozzle size and the diameter of the extruded plastic? It may be too simple to imagine that they are one and the same.
Has anyone else done this? What was the result?

Maybe this can reply to your question:

Thanks. I had seen this, but it doesn’t address my question. I am wondering whether my (new, name brand, nominal 0.4mm) nozzle is out of spec, as the bare filament it extrudes (well clear of the buildplate) is 0.47mm diameter (PLA, 190 deg C).

Hi @roman ! If I understood your situation in the right way, you are extruding the filament and measuring the diameter of the plastic wire which is leaving the hot end with no contact with the heated bed. You are supposing that the filament should leave the nozzle with the same dimension as your nozzle, right?
If you are measuring the free plastic output with 0.47mm you are supposing that your nozzle has 0.47mm instead of the nominal 0.4mm, correct?
Well, that is not true. My background as a mechanical engineer shows that achieving the desired final dimension in an extrusion process is not easy as it looks. Try the following experiment: change the extrusion speed and measure the filament again. Or change the temperature. You will notice that the diameter will change, no matter your nozzle is exactly the same.
If you would like to understand such complexity in more details, take a look at this site:
https://asmedigitalcollection.asme.org/manufacturingscience/article/140/8/081001/377614/Control-of-Final-Part-Dimensions-in-Polymer
I hope my answer helps you!

Hi, MauroGil! Thanks for the response. You have understood my question exactly. As I said in my OP, it is too simplistic to imagine they are one and the same. I shall have a read of your article, of course, but I was hoping someone might have made some measurements and be able to give me an indication whether 0.47mm out of a nominal 0.4 nozzle, (PLA, 190degC, extrusion rate uncertain, unfortunately, but I imagine this will affect the result too) is wildly unreasonable or not.

Don’t worry about the real output diameter. Go to calibration processes and adjust the parameters to reach the expected dimensions. 3D printing is a trial and error process since there are many variables involved in the activity.

Yes…I too have a professional engineering background, and my training suggests that I eliminate as many variables as possible before I start fiddling with the rest . A problem with 15 variables is always easier to tune than one with 25:-)
In this case, I just want to be satisfied that my nozzle is not out of spec. I may remove it and gauge it tomorrow, just for fun!

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Roman, I’m also an engineer with many years of experience in AM. If your still wanting to measure your nozzle to check to see if it per spec you should be using gauge wires of known diameters to check which ones pass through the orifice or not. In this case, your orifice is likely in spec if it’s new. If it was worn from years of use, it may in fact be a bit larger.
I agree with @MauroGil that the calibration process is fairly robust…this is one parameter that can locked in with a nominal parameter and then use Extrusion Multipliers to tune your end result.

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Thanks, Chad. I guess there’s a lot of trial, and even more error, in this process. Find a combo that works, and don’t worry too much about why….

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