Actual Nozzle Diameter

General discussion of 3D printers

Actual Nozzle Diameter

Postby vgordin » Sun Mar 31, 2013 6:55 pm

Is there a way to experimentally figure out the actual nozzle diameter for an extruder? I've noticed variability among my printers' output (hole sizes) and after isolating the rest of the variables, this seems to be the only thing left to check.

I'm running Printrbot Ubis extruders with a nominal diameter of .5mm.
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Re: Actual Nozzle Diameter

Postby Digitalmagic » Sun Mar 31, 2013 7:26 pm

You can extrude forward manually (not a print job), you get a "spaghetti", measure it with a caliper.
There is always a diameter expansion, by example, a 0.35mm produces a 0.40mm spaghetti.

You will probably get a spaghetti >= 0.55mm, my guess.
Human has 20 nail ... extruders.
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Re: Actual Nozzle Diameter

Postby orcinus » Sun Mar 31, 2013 9:46 pm

That's an extremely inaccurate way to gauge a nozzle.
Not only do you not know how much the free air extrusion swells, but that can also vary with extrusion speed and other parameters.

(try it, extrude very fast, then very slow, then measure the extrusion diameter in a few places down its length)
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Re: Actual Nozzle Diameter

Postby vgordin » Mon Apr 01, 2013 12:24 am

I agree. So is there a better way to take a measurement.
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Re: Actual Nozzle Diameter

Postby BenJackson » Mon Apr 01, 2013 6:05 am

Yes, you need a set of pin gauges.
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Re: Actual Nozzle Diameter

Postby Digitalmagic » Mon Apr 01, 2013 9:01 am

Of course, you can always measure the real nozzle diameter, indeed, but the thing impacting your printing is the extruded filament.
So, in a practical way, this diameter matters.
You can use mini drill bits, too.

BTW, it is interesting to enter the measured "spaghetti" diameter in the slicer filament settings, as we do for the filament diameter (entering 1.72 measured, instead of 1.75 by example). Indeed, the slicer is interested in the real volumes of plastic (input & output diameters) to compute filament advancement more accurately..

Now, if you focus on nozzle geometry, you can always make your own nozzle, like I do.
I wished to have more nozzle choice: 0.317mm 0.30mm, 0.28mm, between 0.35/0.25
This way, you have a total control on nozzle design.
Human has 20 nail ... extruders.
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Re: Actual Nozzle Diameter

Postby brnrd » Mon Apr 01, 2013 1:04 pm

I think that slic3r needs the nozzle diameter to optimize the extruded cross section. Since the layer height is manually set, it uses the nozzle diameter to accurately calculate the optimal extruded filament width so that extruded filament won't sag or break when going across bridges or sparse infills. If the filament stretches too much, it will snap. If it's not stretched enough, it will sag. So, with slicer, I usually tweak the nozzle diameter using a bridge test piece to get good bridges after I calibrate the extruder steps per mm. To calibrate the steps per mm, follow the slic3r calibration wiki.
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Re: Actual Nozzle Diameter

Postby Digitalmagic » Mon Apr 01, 2013 1:24 pm

brnrd wrote:... usually tweak the nozzle diameter using a bridge test piece to get good bridges...

Interesting method.
I presume that your tweaked diameter is always greater than geometrical nozzle diameter? less??!

It is always about calculating the flow of delivered plastic, the bridge being THE very critical construct.
Human has 20 nail ... extruders.
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Re: Actual Nozzle Diameter

Postby brnrd » Mon Apr 01, 2013 2:45 pm

With the 3 j-head mk-v that I'm using, it ends up around 0.34-0.35 mm. But I once tried an Arcol V4 nozzle that gave the best bridges with somewhere around 0.4 mm even though it was supposed to be 0.35 mm also. Afterwards, I verified that the nozzle was indeed larger than 0.35 by using a series of syringe needles as gauge.

A microscope would be a good way to measure the nozzle diameter but I've never gone through this trouble.
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Re: Actual Nozzle Diameter

Postby Digitalmagic » Mon Apr 01, 2013 3:15 pm

So, your experience is like you always touch up the nozzle diameter by a slightly higher value, never lower.
This is related to the increased spaghetti going out of the nozzle.

Actually, the slicer is only managing quantity of plastic, which is bigger than what nozzle section x flow represents.
Like comparing 2 cylinders, a theoretical one (nozzle) and a real one (extruded plastic).
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