Non-circular holes and underextrusion

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Non-circular holes and underextrusion

Postby DurrtySteve » Tue Jun 02, 2020 5:00 pm

Hey there,

My N2 Plus used to make super high quality parts but now it struggles to print circular features/holes and underextrudes.


I'm using a fresh reimport of the eSUN PLA+ open filament program settings with the same material. 0.4 nozzle installed and confirmed in settings. Could the nozzle be worn or something? Or maybe the belts? I'm thinking it might be a hardware issue since parts like these used to print perfectly with the same settings.

Thank you

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Re: Non-circular holes and underextrusion

Postby Jetguy » Wed Jun 03, 2020 1:06 pm

No, it's not belts.
No, unlikely a nozzle.
Yes, probably an extruder or user failing to properly calibrate extrusion volume.
You say this:
I'm using a fresh reimport of the eSUN PLA+ open filament program settings with the same material. 0.4 nozzle installed and confirmed in settings

I read that as a massive failure of logic and reasoning. Yes, a profile is a good baseline, but regardless YOU have to print a test cube, you have to measure filament diameter, you have to put in the correct flowrate for even a different spool of the SAME plastic.

I'm trying to get this collective group up to a baseline of knowledge. Been trying for like 4 years.
If you have a problem, go back to basics.
#1 print the test cube 100% infill test. ... fish#p2620
# Being how shiny that print is, you might be extruding a bit on the hot side of the equation and worse, that could be then causing issues with extruder further into the print failing to extrude the comanded volume of PLA due to heat creep or other issues. In a nutshell, here's what happens. PLA softens at a relatively low temperature well below the melting point. It's important to know this critical temperature. Point being, the extruder feeder has to grip the filament wire and push it into the nozzle with force to create pressure. Because the feeder is at the top and the nozzle is far down below on these printers, there is a long distance of filament being pushed. If that filament is hard and rigid, it pushes easily through the guide tubes inside the extruder head down the path to the nozzle and transmits that pushing force. If however, the block and path and the heatsink of the cold end of the extruder, along with the motor and feeder parts above and that PLA gets even slightly soft, now it's much harder to grip and push. End result is LESS filament than commanded. Let's not instantly jump to the assumption that is the root cause of the problem because I see a potential flaw in the use case where you and many other users have this concept of I just choose a given filament profile and it should be fine with NO OTHER calibration or adjustments, and that's "the problem".

So again, step 1 is ensure your settings and calibration are correct on a test cube. THEN reprint the part. Then if that fails, then go down the rabit hole of what if failures to extrude the commanded volume.

Posts: 3085
Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: Non-circular holes and underextrusion

Postby Jetguy » Wed Jun 03, 2020 7:19 pm

In a nutshell, why I'm saying it's a volume problem.

As simple as I know how to describe it.
Filament represents a cylinder of infinite length to the printer. It has a diameter and we tell the printer commands in gcode which is distances in mm. In other words, a single line of gcode is move the nozzle in XY distance, and at the same time, extrude E length of incoming filament.

So- the big problem- the slicer making that line of gcode from your settings and an STL file. The idea is simple, a line or segment has a height (Layer height), a width (extrusion width) and a length. That forms a volume of space in 3D. Then because you ALSO enter the filament diameter of the filament "wire" into the slicer profile (some people aren't even aware it exists or they had to o should be measuring). the point is, volume in = volume out. You feed an extruder 1.75mm nominal filament diameter and it comes out the diameter of the nozzle. For every 1mm of linear filament pushed in, far more linear length of say 0.40mm hot plastic comes out the nozzle. That's why on a typical line of Gcode, the E value length is going to be he shortest distance almost every time. Again, the point is, the slicer uses filament diameter t figure out for each segment how long E distance should be.

Last- flow rate, the big mystery to far too many folks. It's this simple. Flow rate simply modifies how E length is used. If 100% flow rate, then 100% of the length in the gcode print file is commanded for the extruder motor to move that distance of filament. Greater than 100% is literally the E length times the new percentage. Lower than 100% less than the E value is used.

Last, we are at the big question:
If you properly measured and input the filament diameter into the slicer when slicing the gcode, and you printed a its cube and adjusted the flow rate compensation to fine adjust and actually get the amount of plastic out to fill the 3D space (flow rate makes up for minor errors in how the extruder grips different filament and also mind mistakes or variations from measured filament diameter error).
So again, what I'm saying is, assuming you have a gcode file produced, that matches the actual filament diameter and flow rate was tuned prior to the print, then the print file = the correct volume commanded.

That situation then means mechanically, the printer and specifically the extruder feeder is failing to reliably and accurately extrude the exact distances defined in the gcode print file.

It's one or the other. you failed to tune the settings resulting in an under extruding print file
Your printer is having trouble faithfully executing the commanded print volume.

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