Help with strange diagonal banding on Ultibots D300VS+ ?!
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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!
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Can you please post details on your conversion? What length rails did you purchase and how did you mount them? Did you get the robotdigg "set" (GCr15 MGN12-1H-400 or MGN12-1H-450 Linear Rail and Carriage for Kossel)?
Which parts did you use to interface between the linear rail carriage the the balls?
What did you have to file? Which curse words did you use? (;))
Thanks
Gary -
@garyd9 Sure! The final result is admittedly more "cobbled" than I usually prefer as a result of the RobotDigg carriages having a 40mm distance between the flats compared to the 35mm on the printed effector of the D300VS+, but here goes any way:
- Purchase 3x 700mm MGN12H rails and carriages from Iverntech on Amazon.
- I started with the ones from RobotDigg, but they were really terrible quality, so I wound up using the rails from Iverntec.
- I found that carefully pulling the carriages off of the rails, cleaning with isopropyl alcohol and re-lubricating with Slick 50 Supercharged One Lube is really worth the effort because they move completely smoothly now
- Purchase a set of RobotDigg carriages MGN12H-OP-BLACK
- Carefully chase the threaded holes with an M3 tap as deep as you can go because the anodize inside the threaded holes really gums the threads up
- Again carefully, file off 0.5mm from the faces that each ball stud will mount to for a total distance of 39mm between the faces (this will make more sense later)
- Thread the ball studs in as deep as they will go on each carriage by hand and note that one side has a shallower hole than the other. Remove that ball stud and shorten those threads by that amount and re-install the ball studs on to the carriages so that they are fully seated.
- Get ahold of some NO snap acting microswitches with a lever arm and replace the ones that came with the printer because without the lever the switch will not activate on the top of the MGN12H carriages (the screws for the wipers are taller than the switch plunger)
- While you are doing this, re-route the wires for the switches to the sides of the towers because you will be using the inner-most face of the towers to mount the rails.
- Go ahead and slide the switch mounts up as high as they will go and tighten the mount back down there
- Get some M3 x 8 screws and some 2020 T-slot "hammer-head" M3 nuts and install the rails on to each tower, facing inward.
- I did this by putting bolts in the holes of the rail at even spacings (I think I started one hole from each end and left 4 holes between bolts on my rails) and loosely starting the nuts on the threads.
- When you put the rail against the tower and start to tighten the bolts, the nuts should center the rail on the tower nicely.
- Place the top of the rails just beneath the lever arm of the end stop switch so that when the carriage comes to the end of the rail, it will hit the endstop switch before balls start to fall out of the carriages.
- Assemble the RobotDigg carriages to the linear rail carriages with the tensioning screws pointed down, install the belts and tension them
- If you watch the video on their website, they show wrapping the belt around the tensioning blocks and pressing them into the carriage. Save yourself the headache, it doesn't fit like that. Just run the belt down one side and get some slightly larger washers to pinch the belt in place when you tighten the tensioning blocks in place.
- Purchase some 1m thick shim washers from McMaster (PN 98055A099) and place two between each ball stud and the effector. Now both the carriages and the effector have 39mm between the ball studs.
- I originally planned to shim the effector to the full 40mm of the carriages, but I couldn't get the nuts for the ball studs in the effector to catch. With the 39mm spacing, the nuts just catch on the ball studs in the effector and you can tighten them to the point that they start to compress the plastic in the effector.
- After all of this work you'll frustratingly notice that the springs between the carbon rods don't fit over the carriages anymore. For a moment I thought that was game over myself, but then I just decided to try getting some zip ties and strapping the springs slightly down the rods, away from the carriage so that there would be clearance. To my surprise, this actually works very well.
- The zip ties do walk around on the rods a little, so I may add a little epoxy to hold them in place at some point. For now, however, periodically moving the zip ties back to where they should be seems to be working ok.
Now, after ALL of that work, you should have a rock solid, smooth moving delta carriage system that will eliminate what appears to have been the source of all of my problems. Run the auto delta calibraion a few times, upload the values to your config file and smile at how nice your prints come out all of the sudden!
Happy printing!
- Purchase 3x 700mm MGN12H rails and carriages from Iverntech on Amazon.
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@wwmotorsports said in Help with strange diagonal banding on Ultibots D300VS+ ?!:
Iverntech
Thank you! I've bookmarked this post and hope to come back to it soon. Swapping the wheels for rails is something I'd like to eventually do to my D300VS+, but I was never really sure how to go about it. Your very helpful guide has given me ... A Clue.
Take care
Gary
