Certainly an interesting theory; I'll take a look at the firmware and see if I can see anything that might cause the issue.
Don't suppose you'd care to print those two gcodes again and see if you get the same results?? :smile:
Sure, these are short prints (20min). Will do it when I get back from workout.
I still think you are printing too fast. But also the retraction speed is different in the UM1 I'm sure. What was the retraction speeds for the ulticode method versus the Cura-sets-retraction speed method.
It's possible your retraction speed is too fast although I have been using the max - 35mm/sec on every print.
I still think you are printing too fast. But also the retraction speed is different in the UM1 I'm sure. What was the retraction speeds for the ulticode method versus the Cura-sets-retraction speed method.
It's possible your retraction speed is too fast although I have been using the max - 35mm/sec on every print.
Printing with 0.2 layer height and 40mm/s is too fast? Retraction was set in both cases to 5.5mm and 35mm/s.
Certainly an interesting theory; I'll take a look at the firmware and see if I can see anything that might cause the issue.
Don't suppose you'd care to print those two gcodes again and see if you get the same results?? :smile:
Good catch. Second test run (the objects in the front). Now the regular gcode one also features underextrusion. And I thought I might be onto something...
Printing with 0.2 layer height and 40mm/s is too fast? Retraction was set in both cases to 5.5mm and 35mm/s.
Well - yeah. I prefer .1mm 50mm/sec. You are printing almost double the volume. When it is printing away nice and fast - look at the extruder motor for a full minute or touch it with your finger for a minute and feel if it is slipping back.
I mean you *should* be able to do this if your nozzle is perfectly clean and you are at 230C. But if you are at say 210C then this could be the problem - you could be on the verge of printing too fast. Some people can print much faster.
You will know if you are printing too fast on the UM2 because the extruder slips suddenly many steps and makes a sound. I plan to make a new test showing how fast you can print on the UM2 at various temps.
I plan to make a new test showing how fast you can print on the UM2 at various temps.
gr5.....I'm waiting eagerly for these tests you speak of!
Well - yeah. I prefer .1mm 50mm/sec. You are printing almost double the volume. When it is printing away nice and fast - look at the extruder motor for a full minute or touch it with your finger for a minute and feel if it is slipping back.
I mean you *should* be able to do this if your nozzle is perfectly clean and you are at 230C. But if you are at say 210C then this could be the problem - you could be on the verge of printing too fast. Some people can print much faster.
You will know if you are printing too fast on the UM2 because the extruder slips suddenly many steps and makes a sound. I plan to make a new test showing how fast you can print on the UM2 at various temps.
I didn't hear the extruder skip steps, but I am not 100% sure. I wasn't around all the time. However, I thought UM's are pretty fast. At what speeds do people print stuff when quality doesn't matter all that much? 0.1 layer height takes forever so right now I am printing almost everything at 0.2.
I remember Simon's post (link) where he statest at the end that the limits of a 0.4 nozzle are between 8-10mm³/s. And with these settings I am not asking even half of it. This should really be tested, and I look forward to it. Won't do it myself though due to lack of time.
Yeah, 8-10 seemed to be the limit on the UM1, but no one really knows for sure on the UM2. George did some simple tests that suggested it was a bit lower than for the UM1, and anecdotal evidence seems to support that. I'm also planning some tests to try and reproduce and quantify the issue.
I'm getting the sense that while there is one limit that represents the fastest you can print at, there's maybe another - possibly rather lower limit if you want to retract as part of those prints. Ian recently posted some prints done at high speed and thick layers that came out just fine - but he had retraction off, as his shapes didn't need it.
Yes I have read that post. 0.25 layer height at 90mm/s seems crazy compared to what I have here.
I'll take the head apart soon, hope there is a defect that can finally be fixed. Only then I'll accept the fact that the UM2 is slower with retraction on 
Hey guys. Sander pointed me to this clip https://www.youmagine.com/designs/ultimaker-extruder-mutli-clip
It's a bit long, so I cut down, and am really only using the back half.
It has eliminated play, and you can see in this piece of filament I cut off, it's much better, although, there is still some apparent back pressure bulge. Having said that I've not had the same under extrusion issues yet.
Even eliminating play though via the clip, I still get the feeling there's a slight gap between the end of the bowden tube, and the teflon piece that occurs when you insert the clip.
I'm still tempted to try this bowden clamp.
http://www.thingiverse.com/make:48823
Also, I never print anything with a layer height greater than 0.06 - I'd go lower, but I'm finding, despite the claims the UM2 can print at 0.02 I dont see any visual improvment in the print.
The most important thing for me in a print is surface quality / smoothness, and most of my prints have textural detail.
There's definitely some retraction effect at play - looking at your video's Nicolinux, the problems are happening right after the retraction occurs for the island jump. You can hear the retraction, and see that the filament doesn't flow correctly at first. For some reason the retraction/detraction cycle doesn't pressurize the head as it should. Either it retracts too much, or it doesn't push the filament all the way back, as it should.
It looks exactly like it does when the UM2 extruder clicks back due to printing too fast - but related to retraction somehow. Maybe you don't even get the normal click-back sound - or at least can't really tell - if it happens in the middle of a retraction - since that happens so fast.
I looked at the firmware, and didn't see any obvious problems with the ultigcode implementation of retraction; I didn't chase it all the way through the code, but I don't think there's a firmware component. Given that you had problems with 'traditional' retraction too now, I think I'm going to abandon that avenue of exploration.
That's the exact symptom of the gap between the teflon part, and the end of the bowden tube. Retraction forcing melted material into gap as it pulls back for retraction, then fouling on it as it comes back to continue printing.
There's definitely some retraction effect at play - looking at your video's Nicolinux, the problems are happening right after the retraction occurs for the island jump. You can hear the retraction, and see that the filament doesn't flow correctly at first. For some reason the retraction/detraction cycle doesn't pressurize the head as it should. Either it retracts too much, or it doesn't push the filament all the way back, as it should.
It looks exactly like it does when the UM2 extruder clicks back due to printing too fast - but related to retraction somehow. Maybe you don't even get the normal click-back sound - or at least can't really tell - if it happens in the middle of a retraction - since that happens so fast.
I looked at the firmware, and didn't see any obvious problems with the ultigcode implementation of retraction; I didn't chase it all the way through the code, but I don't think there's a firmware component. Given that you had problems with 'traditional' retraction too now, I think I'm going to abandon that avenue of exploration.
Nicolinux, print any of your models with retraction off as a test, and they'll print with zero underextrusion.
Do a material change first though, pull the head apart and make sure teflon part is clear. You dont need to pull everything apart, just undo the main 4 long screws.
There's definitely some retraction effect at play - looking at your video's Nicolinux, the problems are happening right after the retraction occurs for the island jump. You can hear the retraction, and see that the filament doesn't flow correctly at first. For some reason the retraction/detraction cycle doesn't pressurize the head as it should. Either it retracts too much, or it doesn't push the filament all the way back, as it should.
It looks exactly like it does when the UM2 extruder clicks back due to printing too fast - but related to retraction somehow. Maybe you don't even get the normal click-back sound - or at least can't really tell - if it happens in the middle of a retraction - since that happens so fast.
I looked at the firmware, and didn't see any obvious problems with the ultigcode implementation of retraction; I didn't chase it all the way through the code, but I don't think there's a firmware component. Given that you had problems with 'traditional' retraction too now, I think I'm going to abandon that avenue of exploration.
Ok, thank you for the time you took to look through the code. I believe you that it is related to retraction. While I took the video(s), I didn't hear any clicking. There is sometimes a very quiet, regular ticking. Maybe that's what you ment. Not a full click-back but rather many small jumps. If I hold my finger on the extruder I feel it stuttering very slightly.
Nicolinux, print any of your models with retraction off as a test, and they'll print with zero underextrusion.
Do a material change first though, pull the head apart and make sure teflon part is clear. You dont need to pull everything apart, just undo the main 4 long screws.
Ok, will do.
No, Like I said, maybe the click back sound doesn't happen during the retraction process. I don't know. It just seems that the underextrusion is always happening right after a retraction, not in the middle of a section of printing.
True, I've watched it happen, it doesn't always induce a feeder wheel slip back, it's a quick snag, then back to business with an under extruded layer. Over time though, that snag causes greater under extrusion, and possibly filament grind out.
No, Like I said, maybe the click back sound doesn't happen during the retraction process. I don't know. It just seems that the underextrusion is always happening right after a retraction, not in the middle of a section of printing.
Could the retraction distance be too much or the speed too high?
Ok, I have only read this last page so I am coming in rather blind sighted.. but could it be mechanical?
That it retracts (success), and tries to prime the filament but maybe the teethed gear is just a little bit loose.
And you gear like maybe the tiny setscrew or something else skip. And for the prime only the extruder motor rotates, but freely in the teethed gear. Because of the counter-movement and pressure from the filament the teethed gear/shaft stays at its place. Or at least doesn't prime for a full 100%.
Kinda like comparable with a loose pulley on the Ultimaker Original when you had slanted prints.
How about that?
No, Like I said, maybe the click back sound doesn't happen during the retraction process. I don't know. It just seems that the underextrusion is always happening right after a retraction, not in the middle of a section of printing.
I took a closer look of my last pencil monster print. There is one spoot where underextrusion stop mid-layer. This makes it even more totally random and weird.
Could the retraction distance be too much or the speed too high?
This could be, but given that others have used this setting (5mm at 35mm/s) I believe it to be safe. I could try another test with slower retraction.
Nicolinux, did you ever use any other type of filament than PLA in you UM2?
Also, were you ever able to reproduce the underextrusion in the exact same spots of the print consistently?
We had a lot of sporadic underextrusion after using the beautiful XT. We had run an all-nighter print and filled the fan shroud/hotend with XT because the object loosened from the platform (we didn't use glue that time) and just squirted glue for 10+ hours.
XT is another type of base plastic and to make a "perfect" transition (purge/cleaning) from say ABS to PLA or XT to PLA might be difficult. (I will say that we didn't try to put a lot of time to clean it as we didn't have the time to make a complete disassembly)
After replacing the nozzle to a completely new one it was really smooth again.
That said, we are still getting occasional underextrusion on long prints but that might be also due to friction from the filament guide etc.
Ok, I have only read this last page so I am coming in rather blind sighted.. but could it be mechanical?
That it retracts (success), and tries to prime the filament but maybe the teethed gear is just a little bit loose.
And you gear like maybe the tiny setscrew or something else skip. And for the prime only the extruder motor rotates, but freely in the teethed gear. Because of the counter-movement and pressure from the filament the teethed gear/shaft stays at its place. Or at least doesn't prime for a full 100%.
Kinda like comparable with a loose pulley on the Ultimaker Original when you had slanted prints.
How about that?
Sounds good. Would be an easy fix if one could actually access the teethed gear without taking the extruder apart
But Sander, could you read the entire post? There are hints that the UM2 underperforms at normal speeds when retraction is enabled. gr5 and illuminarti plan to test the speed/temperature/flow limits so new users would have some guidelines when it comes to printing. But I am sure that you guys have already performed tons of tests with the new machine. Would you mind to share some data?
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That's just bizarre, if it wasn't a coincidence of course. Let's hope it wasn't, as that would finally give us something clear to grab onto.
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