Chrisp's problem seems to be a little different than Nicolinux's. If Nicolinux removes any of his teflon he could be left with an ID greater than 3mm (in some regions within the inner wall of the teflon piece), Chrisp changed his reduced inner diameter of 2.5mm to 3mm. A potentially risky proposition for a potential problem?
Edit: shoot I wrote OD where it should read ID woopsy.
In this image I simulate the case where the filament is loaded for the first time. If it is not perfectly straight it could hang on the inner lip in the teflon coupler, right before it enters the nozzle. I think I have seen it when I load filament. Shortly after the filament enters the teflon coupler, I hear a creaking sound and the filament jumps back a bit before it continues. This might be this scenario where it hangs a bit. However this is not the main problem.
I imagine the main problem would be during printing and with retraction enabled. When the filament gets soft it might expand in the cavity at the exit of the teflon coupler. Through retraction this thick section moves up and down (already under pressure) and creates even more friction and resistance.
Does this make sense?
Chrisp's problem seems to be a little different than Nicolinux's. If Nicolinux removes any of his teflon he could be left with an OD larger than 3mm (in some regions within the inner wall of the teflon piece), Chrisp changed his reduced diameter of 2.5mm to 3mm. A potentially risky proposition for a potential problem?
That's exactly what I fear (I am not a native speaker and it gets in the way right now :/ )
It's a ligitiment fear, I don't think I would have even trusted myself to drill a straight hole into the teflon like Chrisp did. Perhaps you should wait until there is official word from UM that there is an extruder issue, or if you haven't tried all the less risky alternatives on this thread one of them might yield a clue as to what is going on; although it looks like you have tried just about everything suggested in this now 17 page thread.
Waiting for Godot
Or maybe you can just get Ultimaker to send you a new teflon piece for a couple of bucks; I can't imagine they are too expensive to manufacture and store.
I think the question is... how well does the hole in the teflon piece line up with the hole in the nozzle/heater piece? Does the 'lip' cover the hole into the heater, or cover the metal of the tube, rather than the hole?
I don't think the plastic is supposed to be soft while it's in the teflon piece, btw - that's the point of the 3rd fan.
@AaronAlai: From my experience the UM folks are very generous. They have already sent me a couple of parts for free while I was tinkering with the UM1. I am thinking more about the downtime right now 
@illuminarti: I think the lip formed because the diameter of the exit hole was smaller than that of the nozzle. When pressure was applied to the teflon coupler, it pushed it against the nozzle and the inner ring got "sucked" into the nozzle a bit. I don't know how the inner cavity came to be. Maybe after the lip was formed, filament had to pass through a narrower hole (nozzle + lip) and the backpressure pushed against the weakened material above the lip, in the inner part of the teflon coupler.
Wild speculations are wild!
I imagine the main problem would be during printing and with retraction enabled. When the filament gets soft it might expand in the cavity at the exit of the teflon coupler.
Ideally you want retraction the exact amount so that the PLA just rests on the bottom of the bowden at the top of the arc. There should be no actual suction down at the nozzle. If there is then:
1) You should reduce retraction.
2) Air will get into the nozzle - that air will make it's way upwards and the hole at the bottom will get covered with PLA. That air pocket will expand and push out some PLA causing nozzle leakage or stringing and later some underextrusion.
Here is my new Spoolholder which feeds the material into the bowden in its natural bending. Enjoy guys ^^
https://www.youmagine.com/designs/ultimaker-2-spool-and-feeder-holder
Note that this can hold 2 extruders up in the air above the spools. The part nearest the camera above connects where the spool holder normally connects.
Note that this can hold 2 extruders up in the air above the spools. The part nearest the camera above connects where the spool holder normally connects.
thx for the clarification ^^
Hi Nico,
What about if you take out the the bowden tube from the feeder mechanism, heat your hot end and manually push the filament through.
You should be able to feel if there is any additional friction when you enter the teflon tube.
It will also give you an impression on how it works by ruling out a suspect of you problem (the feeder).
If your filament passes through without problem I wouldn't mess too much with your teflon tube.
Just likeeee I think Aaron said, you risk filing off too much and that will cause other problems.
Have you tried to run a print with everything put together and some WD40 in your tube?
When you remove your filament after a print, what does the tip of the filament looks like?
Looking forward to hear about your findings,
I haven't put everything together right now. If I do it and filament hangs in the teflon piece then I'd have to take the head apart again. But I can't test it without putting everything together first. Kind of a chicken egg problem.
WD40 arrived today. I will put everything together, do the weight test again and use the spray. Will post my findings.
I have repeated the weight test. My extruder seems to be weaker than others (http://umforum.ultimaker.com/index.php?/topic/4222-pulling-force-of-um-extruder/?p=35326) :(
I noticed Daid posted the "printable" version design of it on youmagine ?
Should be worth a try to print if it's somewhat spring or tension related in your case ?
I wonder if the stepper motor is faulty, maybe the magnets are not as strongly magnetised. I have no idea what the flux density variation between motors is. It could be worth trying another one.
There's some discussion (including from Daid) about how to adjust the current to the extruder here:
http://umforum.ultimaker.com/index.php?/topic/3418-um2-extrusion-rates/
There are some errors in there and back then the Marlin that came with the UM2 blocked these features but supposedly now you can adjust the current. The commands to do it should basically work although I think I got the units wrong so that 2000 is 2 amps maybe instead of what I posted? Anyway someone should mess with it and figure it out. When I tried before it was disabled and I never got back to that subject. Will some day.
I noticed Daid posted the "printable" version design of it on youmagine ?
Should be worth a try to print if it's somewhat spring or tension related in your case ?
Of what? The extruder? Incidentally I have black ABS here so I could print it. But I have never printed with ABS before and I don't want to add another variable to this already complex problem. I will do it however if the UM folks issue an updated version that will get rid of these underextrusion problems for sure.
I wonder if the stepper motor is faulty, maybe the magnets are not as strongly magnetised. I have no idea what the flux density variation between motors is. It could be worth trying another one.
Good idea. Sadly I don't have a spare stepper here.
There's some discussion (including from Daid) about how to adjust the current to the extruder here:
http://umforum.ultimaker.com/index.php?/topic/3418-um2-extrusion-rates/
There are some errors in there and back then the Marlin that came with the UM2 blocked these features but supposedly now you can adjust the current. The commands to do it should basically work although I think I got the units wrong so that 2000 is 2 amps maybe instead of what I posted? Anyway someone should mess with it and figure it out. When I tried before it was disabled and I never got back to that subject. Will some day.
I'll do it if Sander or anybody else from UM says so. I fear that tinkering with this can go very bad and brick the board.
So, I have put everything together. Here are my results:
Before I printed the test object on the far right, I disassembled the extruder (again!) and noticed the filament guide in the encasing was roughed and a bit bent in some places. I filed away a wee tiny bit on these edges. The last test object is a bit better but this could be due to normal variance. The first two tests failed at 5mm^3/s and the later at 6mm^3/s.
I have also noticed that filament tips look weird and mangled now (when I change filament). Don't know why.
I also borrowed a temperature sensor from a friend. The nozzle temp sensor is spot on. The heated bed plate is off by 2-3° but this could be due to the difficult testing (the temperature sensor is tiny and has to make contact with as much of the area as possible).
Now I am done with my todo list. I have still no clue what's wrong here. The level of pain with the UM2 starts to rival my experience with the UM1... (http://umforum.ultimaker.com/index.php?/topic/2716-cannot-lower-bed-to-reach-endstop/).
Of what? The extruder? Incidentally I have black ABS here so I could print it. But I have never printed with ABS before and I don't want to add another variable to this already complex problem. I will do it however if the UM folks issue an updated version that will get rid of these underextrusion problems for sure.
You will want to make that out of PLA so you dont have a chance of a clog when you print with PLA if some bits break out.
Also how was the material fed in in your last test?
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I don't quite understand but if you sharpened your filament to a point before loading would it get by the lip just fine?
I think it's reasonable to always have to sharpen the filament to a point.
Also try sliding PLA through the nylon piece that has been chewed up a bit by the extruder. Will the teeth marks of the extruder get stuck on this lip?
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