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UMO+: Stringy right and back sides of print, but good front and left. Top not so hot. Why?

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I wonder what can cause problems that are really centered on the back side and right on my new UMO+. It has taken me some work to get this successful (?) print. Standard 0.4 mm nozzle. Material: UM silver PLA. I have varied the nozzle temp from 205 C to 210 C. This print is at 205 C. I tried and failed with layer height 0.1 mm, and this print is at 0.15 mm. I have varied the print speed to go from 1.25 mm^3/s up to this print at 6 mm^3/s. The faster works better. It completed the print, hooray!

I presume that I did something funny in the assembly. Any ideas?

 

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I may be dumb but your print speeds mean nothing to me. If you are printing quite slow or no faster than medium then your extruder temp.  for .15 is probably too hot which will cause stringing.

Did you have your fans on? If not that will probably increase the problem.

I print .300 at 30 or 40 mm/s at 200

Edited by Guest

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I may be dumb but your print speeds mean nothing to me. If you are printing quite slow or no faster than medium then your extruder temp.  for .15 is probably too hot which will cause stringing.

Did you have your fans on? If not that will probably increase the problem.

I print .300 at 30 or 40 mm/s at 200

 

Thanks, Yellowshark. My print "speeds" are nozzle diam x layer height x print speed. I figured on varying print speed and nozzle temp in a 2x2 matrix today. Put my Design of Experiments training to use!

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A thought on the right side being stringier - the fan is on the left side. Maybe that's the cause of the right/left difference.

Results of my speed/temp variation test:

Run 1: High speed and high temp. In Cura 15.04.6, I set nozzle temp to 205 and print speed to 125. While printing, I looked in the Tune menu on the UMO+ and saw the speed was only 100. That was the same as the video above, so I stopped the print. The number of globs was only one. The stringiness would be a 1 on a scale of 1 to 5 with 5 being perfect.

Run 2: High speed and low temp. In Cura, nozzle set to 195, print speed still 125. While printing, the Tune menu showed print speed 100. Results: Looked much better, maybe a stringiness of 4. Had 6 globs of filament. I was able to open the hinge. Strings on the inside would be stringiness of 3.

Run 3: Low speed and high temp. In Cura, nozzle set to 205, print speed to 75. While printing, the Tune showed print speed 100 still. So I turned it down to 76 at 5.85 mm height, after 5 globs of filament. It dropped 4 more globs before suddenly STOPPING at 51%, or after 30 minutes of printing! Some filament dripped down the outside of the nozzle while I waited for it to start up again, a minute or so, and then I stopped the print and put it in cool down.

I will try to do run 4, and I will post pictures, but I am really flummoxed here. Cura speed is irrelevant, and it stopped printing with no error message. Whaaat?

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OK that will teach me to watch videos before commenting!!

When you say your print speed is 125, do you mean 125mm/s, if so that is awfully fast. Certainly outside of my experience envelope.

Your video suggest the two prints were done with different filament, another variable which does not help.

Are you sure ALL of your settings, including retraction settings were the SAME on both machines?

The point that the fan is on one side may exacerbate the stringing but it does not cause stringing.

What are your retraction settings and travel speed?

What is that silver/grey filament, e.g. Colorfabb shining silver?

Err I am not sure what you mean by "Cura speed is irrelevant", speed is always relevant. Speed along with layer height determines your extruder temp. If the temp is too hot for the combination of layer height and print speed then that will lead to stringing, irrespective of where the fan is.

I would say that the fact that the print stopped halfway through is an entirely different problem to the stringing. To my mind that would be a software/firmware/machine glitch. Did you notice if your buffer had gone to 0? Even if you had a feed problem I think you would see under extrusion first before the print stopped. Actually that is wrong, even with a feed problem I have never experienced feed causing a printer to stop, it just carries on.

May I suggest you slow this down for the moment and print one at .15/30mm/s/195c. and we go from there. I have no idea what the right temp should be at such a high speed of 125mm/s. I would like to see those retraction and travel speed settings too.

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OK that will teach me to watch videos before commenting!!

When you say your print speed is 125, do you mean 125mm/s, if so that is awfully fast. Certainly outside of my experience envelope. Yes, I mean 125mm/s. From posts here, I see that the volume/sec should be around 5 mm^3/s, so I am varying around there.

Your video suggest the two prints were done with different filament, another variable which does not help. The gold box was done at a makerspace on their UMO+, at whatever settings they had, so I can't answer questions about their filament or settings. I just know that the model is okay.

Are you sure ALL of your settings, including retraction settings were the SAME on both machines?

The point that the fan is on one side may exacerbate the stringing  but it does not cause stringing. True, which is why I'm fooling with all the settings! LOL

What are your retraction settings and travel speed? I'm using retraction speed 35.0 mm/s and 5.5 mm [/b]

What is that silver/grey filament, e.g. Colorfabb shining silver? It came in the box with the Ulitmaker. Normal PLA, anyway.

Err I am not sure what you mean by "Cura speed is irrelevant", speed is always relevant. Speed along with layer height determines your extruder temp. If the temp is too hot for the combination of layer height and print speed then that will lead to stringing, irrespective of where the fan is. I mean that setting my print speed in Cura does not change the print speed in the Tune menu while it's printing. Grrr.

I would say that the fact that the print stopped halfway through is an entirely different problem to the stringing. To my mind that would be a software/firmware/machine glitch. Did you notice if your buffer had gone to 0? Even if you had a feed problem I think you would see under extrusion first before the print stopped. Actually that is wrong, even with a feed problem I have never experienced feed causing a printer to stop, it just carries on. True

May I suggest you slow this down for the moment and print one at .15/30mm/s/195c. and we go from there. I have no idea what the right temp should be at such a high speed of 125mm/s. I would like to see those retraction and travel speed settings too. Okay, I will motivate myself to turn that stupid printer back on! When I printed at 30 mm/s, I was using a layer height of 0.1 mm and nozzle of 0.4 mm, so laying down 1.2 mm^3/s. Bad blobbing. I will try your settings.

 

Maybe the blobbing is a leak around the nozzle. I have previously taken it off and reinstalled it. Maybe another time, following the video I found in the Art of Printing section of the community? But first, your settings, Yellowshark. Probably the blobs, strings and stopping are 3 unrelated issues. I was expecting the printer to be much easier to use!

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Hi PIlla, many thanks for your answers. I am in a bit of a rush but a couple of points.

"From posts here, I see that the volume/sec should be around 5 mm^3/s, so I am varying around there." I do not know what context that post was made in, but either you have misunderstood it or the post is wrong - there is no target volume/sec. in terms of how you print a model.

Let us say you are printing at .300 and 50mm/s satisfactorily. If you were to reduce the layer height to .100, i.e. 1/3 of the volume, you would not increase the speed to 150mm/s, quite the opposite. Really you would only reduce the layer height to increase the quality. Speed too affects the quality, generally speaking (with some exception) slower is better. Now you might want to retain the print speed to try and reduce the increased print time caused by the thinner layer setting, but normally you would reduce the print speed too, in this case say to 30mm/s or 20 mm/s. Bottom line is if you are after higher quality and reduce the layer thickness, it makes no sense to increase the print speed.

None of this should cause blobbing normally. Now your piece looks pretty small and that CAN cause issues here. For the moment I would scale it so it is at least 20mm*20mm*20mm or close. Let's get clarity on whether you have a printer problem first and then we can scale back and address issues.

If you want to print this at .100, fine but I would reduce the temp to 190c for that.

Oh and you want you fans on at 100 %, let's say on from layer 3 and 100% by layer 6.

Personally for the moment I would reduce the retraction to 4.5mm for PLA.

Good luck!

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Note that on the ulticontroller, it shows a feed rate of 100% such that if you change that to 50% it will print at half the speed set in cura. For example if you set the print speed in cura to 40mm/sec and after the print started you changed the feed rate to 200% it would print at 80mm/sec.

Varying the temp from 205 to 210 isn't going to show much. I've printed PLA at 180C and at 240C on the same UMO. PLA is forgiving in that it has a wider range of printing temps than most. The accuracy of the thermocouple can be off by 20C between machines. Anyway when experimenting with temps, change it *while* you are printing. That way you get results faster. Be very careful on the low end as if the temp drops too far the printer will keep going but the extruder will stop turning. I think the cutoff is 170C and if you set to 180C it can overshoot so set to 185C first, then when it dips below 185C and pauses you can go down to 180C. Also be careful on the hot end. 240C can wear out your teflon faster (say 200 hours of printing versus 1000 hours printing? really not sure as it seems to last much longer on UMO than UM2).

Your first though on the fan is spot on.

Stringing is critical on filament color and manufacturer (color more than manufacturer for some crazy reason) and so you might get different results. Most of your strings are really tiny and should be easy to remove I would hope. Maybe using a candle?

Anyway now to the most important part - I suspect your bowden tube is a bit loose. Not critical but...

Reduce pressure on the bowden by turning the extruder gear backwards a few cm. Then gently (1/4 kg force should be enough) push the bowden up and down at the head and at the feeder. It should not slide up and down. If it does remove the clip, push *down* on the white "bowden holder", pull up the bowden a bit then push the bowden further down in. Then lift hard on the "bowden holder" and pull up and down on the bowden a bit to make sure that worked. It helps to loosen the 4 thumb screws a few turns, do this procedure and then tighten the 4 thumb screws such that the bowden isn't forcing downwards too hard but is still not moving.

Alternatively, for every mm the bowden moves up and down, add that to the default retraction of 4.5mm. So if it moves up and down 1mm then set retraction to 5.5mm.

Also in the advanced cura settings you may notice that retraction is disabled if the distance to "hop" is too small. Maybe set that to zero for this print. Also retraction is disabled if it just did a retraction (minimum extrusion before next retraction). You might set that to zero also although for super heavy retraction prints this can eventually cause the filament to grind down and the print to fail but UMO is pretty good about doing 10 or 20 retractions on every spot of filament.

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I have to say thank you, Yellowshark. You have been very helpful. Here's an update while I'm still working on it. My model is a 30 mm cube, overall, with 15 mm cubes hinged together. http://www.thingiverse.com/download:1468108 When I started printing my model at 30 mm/s (as I set in Cura 15.04.6), the Tune menu still said 100 mm/s. So I dialed it down to 30 and the printhead just crawls along - apparently when I thought I was running at 30 mm/s earlier, I wasn't! I watched the fan speed, too. It started at 50% at layer 2 or 3, then went to 100% soon after that. I got underextrusion on the first couple layers. So I stopped.

* I upgraded the Marlin firmware again. It says MarlinUltimaker-UMOP-250000.hex. I also tightened the nozzle again, but this time while it was hot. I tightened the feeder assembly as well. (Have to use my new wrench, you know!) I removed the filament and put it back into the Bowden tube.

Fresh clean start. Going for 30 mm/s, 0.15 mm layer height, 195 C nozzle. Fingers crossed!

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First, I would heed what @gr5 is telling you.

I also wouldn't mess with the feedrate on the Ulticontroller.  Leave it at 100%

I'd also suggest that 30 mm/s is pretty slow, maybe try 40 mm/s.

You're dealing more with finding the right temp for what you are printing.  I just unboxed my Ultimaker 2 last week, it's a refurbished model and I printed a part at 210C and got some of the very same strings you got.  Ultimaker has some tips on that here

In my case, I was printing too fast and too hot and also got the minor strings you got.  They easily cleaned up with a razor blade

As gr5 indicated, you just haven't hit the sweet spot for your print speed and temp.  That takes some trial and error. My UMO's sweet spot is 40 mm/sec and 210 for my Colorfabb PLA, for example

I hope this helps!

Edited by Guest

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Success! Thanks Gr5 and LePaul, and of course, Yellowshark. This print had absolutely NO blobs. After about 45 minutes, I stopped waiting to flick away blobs, and cooked dinner. Strings were few and minor. So here's my interpretation: The nozzle needed to be tightened while it was hot in order to seal it. With no leaking plastic, there were no blobs, and the strings seem to have been related. The Bowden tube was not loose, Gr5. But letting me know that the "100" print speed in Tune meant 100% was a key bit of new knowledge! Now I will optimize my settings. [print=5039][/print]

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