ABS Under/Over Extrusion Issues with Ultimaker 2+ Ext.

[ianrossg 1]

Having an issue on a Ultimaker 2+ Ext running ABS. The photographed print may amplify the issue due to the scale of the object requiring it to be printed on a 45° angle. I am seeing under-extrusion on the left inner side (very extreme on the convex curve) and over extrusion on the right inner side. On the back side (relative to the Cura screenshot) all but the most recent print (can be identified as it's taller and shinier) (new material manufacturer) have a very course texture, although nothing necessarily visible besides some little nub lines that can be easily scraped off (as if there were a Z seam which there isn't).

 

I've attempted adjusting flow and print speed rates, fan speeds, retraction length and speed, printhead temp and even a new material manufacturer. Throughout my testing I've cleaned all the components, gave the nozzle a acetone bath, and polished the printhead brass to reduce and potential for material sticking.

 

I have a suspicion it's related to the Cura 5+ slicing methods exaggerating materials related setting, but haven't tested out slicing in 4.* yet. The issues seem fairly repeatable when running the same print and in prints that are positioned with straight lines moving primarily on the X or Y axis the issues can still be identified on the curves.

 

Any advice would be greatly appreciated as I've run through over 1kg of material on this and have made no significant progress to date besides changing material manufacturers which unfortunately isn't a great solution.

 

 

 

SL+30deg.R1.4.3mf

[gr5 2,228]

This is just basic underextrusion.  I don't think it has anything to do with where it happens - those are more subtle reasons related to changes in speed, retractions, etc.  Ignore all that for now.  The basic problem is underextrusion pure and simple.

 

1) Were you printing ABS with no troubles for a while and then after something like 50 or 200 hours of printing it slowly got worse?  If so it's probably related to the teflon part.  If it has always been a problem then let's ignore this for now.

 

2) What is your nozzle temp?  And what is your printing speed?  You probably want around 240C to 245C.  If you go too hot it can quickly turn into a gum like substance after a few minutes.  If you go too cold it's too thick (viscous) and you get underextrusion.  There is no magic temperature as you are always too viscous or too dangerously hot but I like around 240-245.  0.2mm layer and 40mm/sec is a good starting volume/sec for a 0.4mm nozzle.

 

3) ABS is a very difficult material and I recommend you pick something else.  It's going to be a weaker material for the most case until you become an expert (so the first 100 prints or so are likely to be weaker than PLA).  You can ask me about how to make ABS parts stronger but really - it's best not to use ABS.  If you want higher temp materials maybe you should go for something easier and stronger like Nylon or PETG.  If you want something strong, well you probably picked the wrong material as best case you might be able to match the strength of petg or pla and never as tough as nylon.  Did you pick ABS for strength?  For temperature resistance?  Oh and ABS smells awful.

 

After you answer these 5 questions I'll help you diagnose the problem some more.  I have a list of about 30 causes for underextrusion.

 

[ianrossg 1]

I've been printing solely in ABS for the past 6+ years on this machine and never had an issue with under-extrusion, if anything the opposite for a while until I turned the down flow rate from the default 107% for ABS to 100%. My parts require ABS or ASA for high-heat applications. Back when I started working with the ABS ASA wasn't readily available or popular yet and PETG has remained off my radar until recently as well. Unfortunately ABS sucks to print, but I've learned to simply grit my teeth, embrace the smell, and yell at anyone who leaves a building door open which might upset the print chamber temperature.

 

I originally didn't want to get into specific temps in the original post because I've changed materials, but I was printing at 260°C (the upper limit for the printhead) with the previous material and that worked great for years. This new material (Kodak) I've dropped way down to 240°C and am seeing similar flow characteristics (slightly more warping at the same 105°C bed-temp, but that's another issue). The outer wall is set to print at 75.0 mm/s on a 0.8mm nozzle.

 

I went ahead and pulled the printhead apart, cleaned the hot end very thoroughly, but found the isolator (original) to have some slight charring on the end. Despite this not being the recommended fix, I used a hole deburring tool and cleaned up the edge to remove any charred burrs and took some measurements to ensure I was within spec (measured 3.05mm ±0.05mm ID on both ends).

 

Since going through the entirety of the printhead (less intimidating than I thought) I'm seeing identical prints (turned the flow up to 102% not that that's enough to see anything).

 

 

[gr5 2,228]

When you said 6+ years ABS and recently printing at 260C I was like "change the teflon part".  But you got it working for now.  Still you should order 1 or 2.  They will go out of stock some day as UM doesn't officially support UM2 series printers anymore so I assume (I could be wrong!!) that they will run out at some point.

 

I see that fbrc8 still has them: https://fbrc8.com/collections/ultimaker-2/products/tfm-isolator-coupler-um2-um2-go-ext-plus

 

Anyway the problem isn't usually so much the "char" as that the teflon gets much softer and more flexible at that end such that when it is compressed inside the print head, this teflon part squeezes the filament.  Quite hard.  You can remove only the nozzle and with the print head cold you can pass filament through the print head and feel the resistance.

 

Deburring or really making the hole slightly larger (just 0.1mm is often enough) can make a huge difference.  If you widen the teflon too much the filament can expand in that space and get stuck when it goes solid again.  If it's working I'd just order 2 spares and not worry about it until you start getting underextrusion again.

[ianrossg 1]

Yeah, I've already got them on order now that I've been reading the horror stories people have gone through with them and how simple a fix it is to swap out.

To clarify, the issue is still occurring, and in running some older parts I'm seeing that the issue isn't occurring on them. So my guess is something within my print profiles has become problematic with the Cura 5.* slicer. I'm going to try running a print with the Cura defaults and see if by chance that will provide some clues.

[gr5 2,228]

Before you take the head apart again, do a cold pull to clean out the heater block.  then remove the nozzle and let things cool down below 50C and take the bowden off the head and slide some filament though.  See how much pressure there is squeezing the filament.  If it's less than 1/2 pound friction then the teflon part is probably fine (or maybe leave the bowden on - sometimes the bowden can push pretty hard down on the teflon if you loosen the 4 screws, get the bowden on their tight and then tighten the 4 screws to get the bowden even tighter).

 

 

[ianrossg 1]

So nothing's changed besides adjusting the feeder slightly tighter after realizing there was a good chance the under-extrusion was partially caused by a feeder that was easily put into a slip state (I put my finger up to the feeder input, pressed against the material to get a feel for the feed rate and retraction rate and felt slippage from the extra resistance). After running a print I'm unfortunately back to determining what's going on within my Cura configuration profiles. because I'm still seeing the same issue.

 

2 hours ago, gr5 said:

Before you take the head apart again, do a cold pull to clean out the heater block.

ha, yeah so that was yesterdays fiasco. Haven't been able to master the atomic pull as I usually just get what I assume to be a good pull and instead I come to find the material breaking at the entrance to the heater block. So anyway, I ended up pulling everything apart, heating the block up, and cleaning it out the old fashion way, 150psi air through it for the bulk material, and I finished up with a makeshift pipe cleaner/solder wicker (14Ga wire stripped and twisted). I am now fairly certain feed resistance isn't the issue.

 

I'm still seeing under-extrusion on the left inner walls while the inner right walls have some slight over-extrusion, or at least on the flat surface, the curved surface is perfect.

 

What I'm wondering is if this may have something to do with acceleration or retraction settings. The layers start with the infill on the left side, then there is a retraction and combing travel across the skin where the under and over-extrusion occurs. Once the infill finishes there is a similar travel back to the left center support where the skin starts its extrusion (or lack of).

Come to think of it, the infill might be a dead giveaway. My issue is that I've got some ooze issues with the 0.8mm nozzle, so I've got (whats in my mind is) a high retraction of 6.25mm. I guess I could get frisky with the print temp and drop it down, but I feel like that'll lead to other issues.

Edited October 27, 2022 by ianrossg
embedded photo issue

[gr5 2,228]

For UM2 the defaults in 4.X were:

1) accel and jerk control OFF

2) all printing speeds the same (almost all) so top/bottom/infill/wall speeds must all be the same!  If there are speed changes you get under and over extrusion.

 

Regarding retraction distance - that isn't set in cura but is in the preferences on the UM2.  Too much retraction allows air in through the base of the nozzle.  You want just barely enough retraction to releive pressure without actually pulling up out of the print head.  If you look at the top of the curve of the bowden you should see the filament start out touching the top inner surface of the bowden and then when retraction is complete the filament is resting on the bottom inner surface. This is all at the top of the arc of the bowden.

 

If you look at the filament where it is just entering the print head it should not move at all there.

 

Typicall 6.5mm is typical for UM2.  More for extended. 4.5mm for um2go.

 

 

REGARDING FEEDER

 

It should push with about 5 to 10 pounds of force.  use the MOVE command to put the filament about half way down the bowden (or at least well up away from the print head).  Then move the filament slowly with one hand on the controller and the other hand fighting the feeder by pulling down HARD.  One thing you can do is hold a 5 pound weight in your hand and squeeze it against the filament so that the filament is carrying all the weight and your hand is just holding the 2 things together.

 

slipping at 5 pounds is not fantastic but typical for a UM2.  A UM2+ feeder should be able to do 10 to 12 pounds typically.  4 pounds or less is just not good - something probably wrong.

 

This test helps you differentiate issues with feeder versus the hot end.  Knowing that it definitely *is* or *isn't* the hot end only takes a few minutes and tells you a lot.

 

 

[gr5 2,228]

low acceleration could indeed explain why you have low accel in one half and high accel in the other half.  Default accel is I believe 5000 mm/sec/sec (5 meters/s/s).  for it to accel so slow that one half is over extruded - well that would be very slow.  

 

More typically you would get underextrusion in the middle of the travel and over extrusion at both ends where it is travelling slower.  For 5m/s/s acceleration you are up to full speed within 4mm (even if printing speed is 200mm/sec).  So I kind of doubt accel is the issue.  Speed changes from infill to wall and vice versa - yes that could be the issue.

 

I still strongly suspect you have overall underextrusion but that it is showing up in places where you have slight changes in extrusion rates.  But I could certainly be wrong!

[gr5 2,228]

Okay so they added speed changes?  I hate this B.S.  There should be no speed changes for a UM2.  I checked cura 4.12 and it also has these speed changes in the profiles.  I'm pretty sure Cura didn't used to do this.  Also I see accel and jerk control defaults on.  This is B.S.  The UM2 doesn't need speed changes nor accel control.  I have 3 very active um2 printers and I have all these set to the same speed (circled).

 

These speed changes can definitely cause what you are seeing however I still think this is in combination with some overall underextrusion.

 

When you have a very high resistance somewhere in the print head (like the nozzle is no longer 0.4mm for example or the teflon is getting too old e.g. over 1000 hours printing) then the speed changes are more serious because the changes in pressure in the nozzle are more extreme and so the resulting extrusion amounts change more than typical.

 

Also check that your front fan is working.  If that fails then you get, well, underextrusion issues.  Especially after 10 minutes of printing.