Help with strange diagonal banding on Ultibots D300VS+ ?!
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Well, everyone who had money on the extruder as the source of the problem can cash their chips in.
@DigitalVision and @JoergS5 , thanks for pushing me to take a closer look at the extruder, because I was dead convinced it was an issue with the motion system.
I considered that under extrusion might have been the issue, so I just cranked up the extrusion multiplier during one of my test prints, and sure enough, the pattern immediately changed. Interestingly, there was no actual under extrusion as the printed width was exactly what was requested, so I did another test.
In the image linked below are three test prints at different layer heights with otherwise identical slicer settings. On the largest layer height print, the imperfections are so close together they are almost hard to see, but as the layer height gets smaller the "ripples" get farther apart and at a shallower angle. I repeated the test at all kinds of amperage and micro-step combinations and got the same result. For grins, I also tried another extruder stepper and different filaments but got the same result. So, as far as I am concerned, there must be some mechanical issue with the E3D Titan Aero that repeats at a constant volumetric extrusion amount, causing the issues I have been having...
For now, I'm going to take this to the E3D forums for some more focused discussion, but if anyone has any other suggestions, I'm all ears!
Thanks again for the help everyone.
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@wwmotorsports said in Help with strange diagonal banding on Ultibots D300VS+ ?!:
For now, I'm going to take this to the E3D forums for some more focused discussion, but if anyone has any other suggestions, I'm all ears!
Can you please post a link to your E3D forum thread? While I don't think I have anything to contribute in regards to a solution, I'm very interested in the problem and what solutions might be suggested.
Thanks
Gary -
In my experience with the aero there are a few things that may be your issue.
The aero gears need to be perfectly aligned to mesh smoothly. The whole body has to turn slightly to get them just right.
The bearings are fickle. Even though you say it turns smoothly my learned instinct says never to trust them. I'd replace them out of spite.
The large gear may need to be adjusted on the hobbed gear to get the filament path lined up on the teeth.
The idler tensioner tension has a sweet spot of not too tight and not too loose.
Just throwing some ideas out there.
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@garyd9 , sure thing. See the link below:
https://forum.e3d-online.com/threads/titan-aero-repeating-pulse-pattern-on-prints.3138/#post-32237
@Phaedrux , thanks for the tips! I definitely agree that this thing appears to be pretty picky. I have already clocked the body and adjusted the large gear on the hob to get the hob and filament path to align. I have replacement bearings on their way as I type this, so I can eliminate that as the issue soon.
The only other thing that I can think of is where the stepper shaft gets centered into the heat sink. Since there is not a bearing in there and I'm sure that the idler is moving the shaft around a little, I wonder if the shaft is actually making contact with the aluminum housing and causing a repeating stick-slip condition? Hmmm...
If I can't get this resolved shortly, I'm probably going to nuke the Titan Aero and go get an effector from 713 Maker and put an E3D V6 and a Zesty Nimble on it since I had such good luck with that basic setup in the past. I'll report back on whatever I find that actually fixes this!
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@wwmotorsports You have two bearings inside the stepper, so non-centered bearings could be a cause.
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As I read this thread today, I did also a test:
I printed a 50 mm diameter cylinder in vase mode. Identical settings. On the left, 0.13 mm layer height, on the right 0.2. On the right, you see like a twisted symmetrical spiral all around the print (in live- version even more than on the photo) which is absolutely gone on the left... Really strange!
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@JoergS5 : that's definitely a possibility, but I have tried two different brand new E3D steppers (compact and pancake) and had the exact same defect so I doubt that's my issue in this case.
@kuhnikuehnast : what kind of extruder are you running?
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@wwmotorsports said in Help with strange diagonal banding on Ultibots D300VS+ ?!:
@JoergS5 : that's definitely a possibility, but I have tried two different brand new E3D steppers (compact and pancake) and had the exact same defect so I doubt that's my issue in this case.
@kuhnikuehnast : what kind of extruder are you running?
It is a zesty nimble. Really strange! Has anyone an idea how this is possible?
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EDIT: I had the extruder gear ratio in the wrong place in the calculations, please see my comments in the next post
Well, I am not 100% sure, but I think this may all stem from a full step positioning error of the extruder stepper, at least in my case.
I was updating to the 2.02 firmware last night when I noticed that the StealthChop mode was now available, so I thought I would give it a try. First thing, it was really impressive how much quieter the printer was with that chop mode enabled. Second, there was a noticeable difference in the print quality changing the chop mode, which I did not expect. In the picture below, the part on the left was printed with StealthChop and the part on the right was printed with an old firmware version using constant off time chopping. The difference isn't dramatic, but it is noticeable:
I wondered why that might be and I did a little research about that chopping method and saw that they claim it helps minimize zero-crossing positioning error. That got me thinking and I calculated the volumetric flow of the Titan Aero per full step of the extruder and compared that to the length of extrusion required to consume that same volume of filament (accounting for the fact that the edges of the extrusion are actually radiused). Lo and behold, the spacing between the ripples in my prints match the volume of extrusion per full step of the extruder almost exactly for all of the layer heights I have tested. See a screengrab of my calculations below (note: I'm tessting with a 0.6mm nozzle):
I figured this all out pretty late last night, so I haven't had time to experiment more, but my next step is to switch the extruder stepper to the other driver that I am currently not using to see if that helps. However, after a little more math, I'm not wildly optimistic that even the most precise stepper driver would fix this.
I have a 400 step/rev stepper with a 16 tooth pulley on my towers, giving me 12.5 full steps/mm of travel for the motion components, which seems reasonable that the human eye would not likely detect the stepping error at that close proximity.
The extruder, on the other hand, with a 400 step/rev stepper, a 3:1 gear ratio and a 7.3mm hob printing with a 0.6mm nozzle at a 0.2mm layer height has a 2.86 MM/STEP ratio when you compare the volume of extrusion per full step to the motion required to consume that volume. In other words, even with a geared extruder and a 0.9° stepper, the extrusion is 35.75 TIMES less accurate than the motion of the carriage...
It seems to me that the only way to remedy that is to run an extremely high gear ratio on the extruder which would cause significant speed issues, or run a filament diameter smaller than the nozzle diameter to alleviate the natural "inverse gearing" that happens when you squeeze a 1.75mm filament through a 0.4mm hole (inverse volumetric ratio of roughly 19:1 by my math).
Someone, please tell me my math is wrong because otherwise, this is a pretty sad realization...
@dc42 , any thoughts on this?
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I had a ripple similar to yours
It was the flex cable on the extruder.But your extrusion problem looks more cyclic than mine.
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@wwmotorsports Your findings are very interesting and I am curious what the others will say.
Instead of your expected reason I can think of another reason also: the delta segments the movement into small linear movements, and maybe your extruder stepper changes directions between the segments, resulting in backlash - and backlash resulting in underextrusion. I don't know how to test it: maybe it's possible to make a constant extrusion for the whole line and segmented movements for the axes. -
@JoergS5 Thanks, I am interested to see what the community thinks as well. While that may be a great explanation for other controllers, the Duet Wifi hasn't used segment approximation for delta movements since 2015, one of the major reasons that it has taken the delta printer market by storm. There may be some funky back torquing going on for other reasons, but I don' think it is as a result of segmentation.
It also turns out that I was moving too fast when doing those calculations and put the gear ratio of the extruder in the wrong place (how embarrassing), and the volume/step doesn't line up with the ripples at all... Sorry for the red flag folks... See my updated calculations with the gear ratio in the CORRECT place below:
CORRECTED Extrustion Ripple Calculations w/ Extruder mm/Step
The extruder is still roughly 4X less precise than the movement of the print head, but not nearly as bad as I was thinking. I guess I'm back to digging for a mechanical issue and I'll come back if I find any solutions.
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@wwmotorsports I think I have seen the same surface finish as you show in your last picture here: https://photos.google.com/share/AF1QipP0LgD2KayuBlFW1rtLkxyyz1ocY5nyEo4LoMh0iB94N_AW0Mr4rREXntzW---4GA?key=SkZRTkRHdE9Md0ZQWGp4ZVZfbE9veGc3MTlqVWZR
I'll snap some photos later today to compare. I have the same Titan Aero setup as you.
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@kuhnikuehnast said in Help with strange diagonal banding on Ultibots D300VS+ ?!:
@wwmotorsports said in Help with strange diagonal banding on Ultibots D300VS+ ?!:
@JoergS5 : that's definitely a possibility, but I have tried two different brand new E3D steppers (compact and pancake) and had the exact same defect so I doubt that's my issue in this case.
@kuhnikuehnast : what kind of extruder are you running?
It is a zesty nimble. Really strange! Has anyone an idea how this is possible?
Diagonal banding seemed like a common problem with the Nimble back when I was using it. I could never fully get rid of it on mine, and that's why I no longer use it. There was a fairly large thread in the Zesty forums discussing it and people were trying many things to fix it, but I never found a definitive fix. Maybe that's changed since then (mid-late 2017), but with as much time as I spent with it, i'm not confident in it.
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@wwmotorsports, does the period of the banding correspond to one band per revolution of the hobbed shaft in the extruder? If so then I suggest replacing the large gear + hob in the Titan. OTOH if it corresponds to one band per revolution of the motor, try replacing the small gear.
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@dc42 The period of the banding corresponds with 0.17mm of linear filament movement into the extruder, or roughly 0.405mm^3 of volumetric extrusion. As far as I can tell, that coincides with the following movements in the extruder (roughly):
- 9 full steps of the stepper motor/pinion gear
- 8.2° degrees of rotation of the stepper motor
- 2.7° of rotation of the large drive gear
- 1/2 of the pinion gear pitch
The only thing that I can relate any of those numbers to (and this is a stretch, I'll admit) is that there appear to be only 2 teeth meshing between the pinion gear and the drive gear, so it is possible that this phenomenon is related to every time a tooth in the gear drive makes or loses contact with its mating gear. I wonder if switching to a helical cut gear set of the same size would eliminate the issue?
@Phaedrux FYI: I replaced the bearings in the extruder last night with brand new replacements from E3D with no impact to the banding. Nice to have that eliminated as a possible cause though.
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0.2 layer height, 0.68 extrusion width, 2 perimeters, PLA at 195c, 900mm/min jerk, 450mm/min accel, 35mm/s speed.
Was meant as a test print for ringing, but instead I noticed these diagonal bands.
Look similar? They are hard to capture, but you can kind of see them in the reflections.
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@phaedrux YES! That looks identical to the pattern I'm seeing, glad I'm not the only one.
Out of curiosity, can you tell me the length of one of the straight walls and count the number of bands you see where they interesect the top edge? I'll throw your numbers in to my calculator and see if we are getting the same volume of extrusion/band.
If it turns out that the volume/band is the same on your CoreXY as on my Delta, then we may really be on to something.
I ran a print last night that really shows this issue as clear as day. Normally, I would immediately say it is an under extrusion issue, but my single and double wall test prints come out at the exact right wall thickness, so I don't think that's the. See the link below to see what I'm talking about.
Anyone else have further thoughts?
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@wwmotorsports Is that photo of the top edge of the perimeters? Mine definitely do not look like that.
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Hello all,
Sorry for the long silence here, but I thought I would share my findings and final satisfaction with this printer in case anyone runs into the same problem.
I wound up building a new effector to use a standard E3D V6 hot end and built a 9:1 belt reduction drive bowden extruder since I was so certain the extruder was the source of the issue, but low and behold, the exact same surface ripple persisted...
At this point, I was at the end of my rope and almost gave up but just started really trying to shake stuff around. It wasn't until then that I noticed that the carriages on the printer were flexible enough that I could pretty easily get one of the three wheels to come off of the aluminum extrusion if I pushed in the correct directions. So, I ordered some 12mm knockoff MGN12H rails and carriages and the delta carriages from RobotDigg. With a little bit of cursing and filing, everything fits up pretty great and the first test print shows that the artifact is GONE!!
So, I put the E3D Titan Aero back on and the result repeated, NO MORE SURFACE RIPPLES! After all of that, it was just an issue with the carriages being a little too flexible and creating what must have been some kind of stick/slip where the wheels are supposed to roll up the towers...
In the links below, you'll see a picture of the installed rails and the before and after test print comparison. The black print is with the new rails and the blue print is with the old carriages. The horizontal sections you see are my experimenting with different speeds and extrusion rates.
With that change, this is now hands down the best "consumer" grade printer I have ever been around and would gladly recommend it to anyone that can get their hands on one.
Any way, happy New Year and happy printing!
