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!