How I fixed my underextrusion--hopefully this helps others!

[qwerty42 1]

I recently got an Ultimaker 2 at my work and immediately found it had under extrusion issues. After looking online it was clear that many users have had similar problems.

Here's what I was experiencing:

underextrusion issues and failed prints, especially on bigger parts

poor printing performance at what I would consider moderate speeds

frequent clicking sounds from the extruder stepper motor from being overloaded

My printer seems to be working well now, so here are the steps I took to fix it.

(1) FACTORY RESET:  I don't know why this made a difference, but it did. Maybe it had something to do with the new firmware it loaded when I first booted Cura. Anyway, all I did was perform a factory reset and things immediately got better, but still not good enough. The print I used as a test piece for the underextrusion issues came from user illuminarti here:

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Here is the before/after from the factory reset, printed at 210C:

(2) BACK OFF THE PRESSURE ON THE EXTRUDER DRIVE: I also have a Makerbot Replicator 2, and from extensive experience with that I know that having the filament pinched too tightly in the extruder can create so much friction that it makes it harder for the extruder to feed the filament. My Ultimaker had very visible teeth marks in the filament with the factory extruder adjustment.

For those who aren't familiar, the extruder drive on the Ultimaker 2 has an internal spring which applies a certain amount of force to the filament, pinching it against the drive gear. There is also an adjustment screw which can add additional preload to the spring to increase this pinching force. If you turn the adjustment screw fully clockwise (GENTLY!--just turn it until it's lightly seated), there is no extra preload on the spring. If you back it out from there about 5 full turns, you'll start to feel it taking more torque to turn the screw. That's the point at which it's starting to add preload to the spring.

n my case, the preload seemed like too much. I turned the screw fully clockwise until it lightly seated to make sure all extra preload was removed from the spring. After this the extruder motor started doing the clicking/drop-back thing a bit less. I also removed all but one of the black plastic clips that holds the wire harness to the bowden tube, figuring that the least friction would result in the tube if it wasn't being pulled off to one direction by supporting the wire harness.

Here's the before/after from adjusting the extruder motor tension. From left to right, the prints were done at 210C, 220C, and 230C:

(3) THIS IS THE BIG ONE--REPLACE THAT CRUMMY TUBE. Maybe this isn't true for everyone, but from all I've read it sounds like friction issues plague this printer. A lot of people are convinced it's from a weak extruder stepper, but I think that's a symptom more than a cause. The real culprit is the ridiculous amount of friction between the filament and the craptastic tubing that comes on the Ultimaker.

Out of curiosity, I pulled the tubing off, and tried shoving a piece of tooth-marked filament through it. Then I tried bending the tubing at a similar radius to what happens to it during a print. I found that it took a very unreasonable amount of force to shove the filament back and forth through the tube. Also, I had previously noticed that many of my extrusion failures on prints tended to begin at a place in the print where the bowden tube is bent at a fairly tight radius.

I happened to have some nice, high quality PTFE tubing on-hand with the same outer diameter, and tried forcing the filament through it. MUCH SMOOTHER, and much less friction and stiction. So, I replaced the original Bowden tube with the PTFE tubing.

THIS MADE A HUGE DIFFERENCE IN PRINT PERFORMANCE! After this change, it was clear that the printer was no longer fighting nearly as much just to get the filament to the extruder. Many people have gone to great lengths to try to reduce force on the extruder, like adding bearings to the filament spool, pre-unwinding filament and straightening it, and so on. These are really all band-aids to fixing the very significant friction of the filament going through the tubing.

Here are the results with the new Teflon/PTFE Bowden tube, at 210C on the left and 225C on the right. The right print is absolutely flawless:

Also, here is a picture of the new tubing and the location of the wire harness clip. I am still only using one of these clips because I think it’s better to let the tubing shift to wherever the filament forces it to keep friction at a minimum:

And here’s the robot test print to show how it’s looking now! I’m quite happy with this, and it definitely looks better than the first time I tried to print the robot.

EDIT 4.24.2015:  The original replacement tubing I used had a larger inner diameter than the OEM Ultimaker tubing. I have since switched to one that matches the original tubing dimensions, but is still made of PTFE, and I am getting the same great print performance from it. I can still feel a big difference in both sliding and static friction between the two. The link for the new PTFE tubing is here:  http://www.mcmaster.com/#5033k31/=ww8h9h

I highly recommend trying this, because I think the tubing that comes with the printer is far from optimal.

Hope this helps some of you!

Edited April 24, 2015 by SandervG

[gixxer 1]

I see that the ID of the new tubing you have fitted is 4.7mm compared to the 3.2mm (I think) standard Ultimaker tube. The larger ID Would provide less friction than the original as the point of contact would be less. However the reason for the original being just slightly larder than the filament size is to constrict movement of the during retractions.

Have you noticed any degradation in the quality of prints after changing the tube?

I does also beg the question as to whether the original tube maintains its ID thorough its length. I wonder what the tolerance on the Id of the original tube is?

This could go some way to explaining why some people have issues with under extrusion while others do not. I haven't had any real issues other than using the UM supplied blue filament myself.

Perhaps others with under extrusion problems could test this theory???

[gixxer 1]

An easy test would be to drop a 3.1mm drill bit down the tube. If it passes straight through there should not be a problem with the original tubing.

[qwerty42 1]

I see that the ID of the new tubing you have fitted is 4.7mm compared to the 3.2mm (I think) standard Ultimaker tube. The larger ID Would provide less friction than the original as the point of contact would be less. However the reason for the original being just slightly larder than the filament size is to constrict movement of the during retractions.

Have you noticed any degradation in the quality of prints after changing the tube?

I does also beg the question as to whether the original tube maintains its ID thorough its length. I wonder what the tolerance on the Id of the original tube is?

This could go some way to explaining why some people have issues with under extrusion while others do not. I haven't had any real issues other than using the UM supplied blue filament myself.

Perhaps others with under extrusion problems could test this theory???

Hey gixxer (600, 750, or 1000? ,

You're right, the tube I replaced the factory part with was indeed larger in diameter. I didn't notice any significant issues with this. It did cause some backlash in the retraction, but it didn't seem to have a big impact on print quality, especially when I changed the retraction distance to 5.5mm instead of the factory default of 4.5mm.

Regardless, I figured it was better to remove the backlash, so I am now using a PTFE tube with very similar dimensions to the factory tubing. I edited my original post and added a link to the new stuff above.

With the new tubing, I am still getting the same print performance. It blasts through the extrusion test without any flaws. I will check the factory tube and see if the diameter is consistent down its length (I'm pretty sure it is). The biggest difference between these two tubes is that even though they're both technically "Teflon", they are not the same fluoropolymer. I think the factory-supplied tube is PFA, and the one I replaced it with is PTFE, which actually has a lower coefficient of friction.

When I run a piece of filament through the factory tube by hand, it feels okay until I bend the tube 180 degrees and try pushing it through again. The frictional increase from this is very significant, and the "stiction" (static friction) is also very noticeable.

With the PTFE tube, using the same test and bending the tube as it would be when printing, you can feel a very noticeable difference in reduced dynamic and static friction. The printer seems to agree with this because it's been working great with the PTFE tube, and the extruder motor skipping has stopped completely.

Josh

[gixxer 1]

Could you check the ID of the original tube for restrictions? This could go a long way to clearing up some under extrusion issues for others.

[gixxer 1]

It's a 750