VFA Artifacts on X+Y Straight Edges
Hi guys just got my new assembled Core One,
I had a Prusa MK4S (as a kit) and it was a great printer, all prints came off great with that one.
E1njoying the Core One but currently am getting very visible VFAs on all long X+Y prints.
I did a long print last night in Stealth mode on Structural profile and all the prints had VFAs across basically all axis except Z. There were four instances of the box printed in various orientations on the bed and it VFAd on all sides. I looked at some of the smaller test prints I did when I first got it plugged in and actually noticed they have the same issues (but they have much smaller side faces)
I checked the slicer to see if this was just infill showing through, but the walls are 4 layers solid thick with no infill. So it's not infill.
I'm using Prusament Galaxy Silver PLA and default print settings in Prusa slicers. The printer is on a heavy tile with a damping thin pad foam pad underneath.
To me it seems like input shaping isn't tuned right to the printer setup. Belts seem taught to the touch but hard to tell if it's correct. Overall I see tonnes of ringing which I wouldn't expect and didn't get with the MK4S.
Can anyone help me out here?
RE: VFA Artifacts on X+Y Straight Edges
There is a discussion in a parallel thread which may be related: https://forum.prusa3d.com/forum/prusa-core-one-hardware-firmware-and-software-help/bad-vibrations/
Vibrations are reported at certain travel speeds, which may result in very audible noise and/or print artefacts. There is some speculation that it may be the same issue which originally plagued the Prusa XL and was resolved by implementing "phase stepping" in firmware. (With accelerometer-based individual calibration for each motor.) More details in that thread.
RE: VFA Artifacts on X+Y Straight Edges
I am following that thread. The noise is fine and it's pretty quiet in Stealth mode. There's some louder noises during very fast moves when not in stealth mode.
I just printed a simple box shape again in Structural and Stealth mode. The VFAs were less pronounced but still there - the printer was printing extremely slowly (presumably because of the 1 wall thickness + structural + stealth mode) so I would barely have expected any artifacts at this speed.
RE: VFA Artifacts on X+Y Straight Edges
I touched the belts again, they felt a little bit on the loose side to me so I have increased belt tension by two turns on both sides by adjusting the two bolts on the front of the printer with the door open. On my simple (and very slow) 1 wall print it seems to have helped the problem slightly although I can still see VFAs on the print - same distance apart.
The handbook doesn't specify how to adjust tension nor how to tell if it's correct. I centred the gantry and one belt sounded definitely lower in pitch than the other. Maybe something to tweak later.
I'm going to try printing the original print and see how that turns out now.
RE:
Tensioning the belts has helped a reduce VFAs a bit - however they are still visible clearly on every flat surface on actual prints.
Again this is on Structural and Stealth mode. Tensioning the belts has actually made it audibly resonate a bit more now than previously.
I don't remember my MK4S ever having prints that looked like this
RE: VFA Artifacts on X+Y Straight Edges
To me it seems like input shaping isn't tuned right to the printer setup. Belts seem taught to the touch but hard to tell if it's correct. Overall I see tonnes of ringing which I wouldn't expect and didn't get with the MK4S.
Since the ringing occurs during straight travel at (roughly) constant speed, I don't think it has to do with the input shaping. Imperfections in the drive train (motor windings, belt pulleys, idler bearings...) are more likely candidates, I think. With the longer belts in the CoreXY mechanism, these imperfections may be more prone to excite resonant vibrations than in bed-slinger printers.
I understand that Prusa's "phase stepping" is meant to counteract this via appropriate corrections. Let's see whether they roll this out as a firmware update soon. Apparently it's already in the firmware, just not tunable to actually provide printer-specific corrections.
RE: VFA Artifacts on X+Y Straight Edges
I had a look at the config in the firmware and can see that it does indeed have phase stepping enabled but the toggle and menu is not enabled. Pointless for me anyway as I do not have a prusa accelerometer kit (I've just bought a £1000 printer!)
I see some people online claim toothed idlers reduce VFAs, at the moment these are pretty unacceptable.
I'm going to run a few more test prints.
RE:
I have viewed a few threads where people replaced the smooth idlers with toothed idlers and the results seem mixed to me.
On the one thread the user seemed to be able to completely remove those artifacts with toothed idlers, while on the other thread it didn't really look much improved imo. So I'm not sure that's a home run.
The belt configuration is quite different on the MK4, but it has smooth idlers and my machines have no VFA's, while my XL does. I was able to improve them on the XL with tightening the belts as you have, and they are at I point that they don't bother me. Mostly only visible on black PETG.
That being said I had submitted a GitHub request, but there has been zero action on it.
RE: VFA Artifacts on X+Y Straight Edges
Define VFA, please. 🤓
RE: VFA Artifacts on X+Y Straight Edges
Define VFA, please. 🤓
VFA is short for Vertical Fine Artifacts
RE: VFA Artifacts on X+Y Straight Edges
Posted by: @largriff
Define VFA, please. 🤓
VFA is short for Vertical Fine Artifacts
A ripple which recurs at the same position in every layer, hence forming vertical stripes. And I believe the VFA term is used specifically for ripple on straight surfaces, i.e. in regions where no significant acceleration happens. (In contrast to overshoots after a corner or strong bend in the object.)
RE:
In the latest test I've turned off stealth mode and am running a speed profile, the VFAs are masked a bit by the Matte effect from the heating being uneven but they are still there if you hold them under a light.
Waiting for Prusa to give a proper belt calibration and tuning guide for this
RE:
The Prusa App has just been updated and can tune the Core One belts now. It provides instructions where to move the extruder and states a target frequency of 85 Hz.
RE: VFA Artifacts on X+Y Straight Edges
Ah that's great. I'll give that a go
RE: VFA Artifacts on X+Y Straight Edges
OK belt tension will NOT solve this issue. I've tensioned the belts and managed to get them both close to 85Hz (84/85) I've done many prints now with various settings but the VFAs are still visible, also noticeable to the touch.
For reference I'm running Stealth Mode and Structural profile for most. I did one Speed print in non-stealth mode and the part just came out half Matte, which just hides the VFAs in the Matt texture.
The filament is Prusament Oh My Silverness
It's pretty ridiculous to be getting this kind of finish off a new 3D printer on every single vertical flat surface.
RE: VFA Artifacts on X+Y Straight Edges
I've attached the gcode from Prusa slicer - just make sure your printer is in Stealth Mode and see if you can reproduce with a shiny filament
RE: VFA Artifacts on X+Y Straight Edges
Speculating here, but I wonder if one of the two x/y motors might have a bent shaft. There *could* be a problem with any one of the other 6 rollers per belt, but most of them appear to be supported at both ends of their shafts whereas the motor pulleys are only supported at one end, making them more likely to have a little “runout”. Just a thought.
RE: VFA Artifacts on X+Y Straight Edges
If that were the case, it should not show when the part is printed at a 45° rotation on Z. Maybe worth giving a shot during your tests.
Speculating here, but I wonder if one of the two x/y motors might have a bent shaft. There *could* be a problem with any one of the other 6 rollers per belt, but most of them appear to be supported at both ends of their shafts whereas the motor pulleys are only supported at one end, making them more likely to have a little “runout”. Just a thought.
RE:
Yes, it will show even at 45°, because one belt would be speeding up and slowing down with every revolution of the bent shaft while the other belt speed is constant. CoreXY only moves at exactly 45° when both belts move the same (or exact opposite) speeds.
RE:
Oops, I confused myself (again!) and stand corrected! I misspoke (again).
CoreXY only moves at exactly 45° when ONLY ONE BELT moves while the other belt is stationary. So @el_hopaness is right. A vertical surface printed at 45° would use only one belt, so VFAs should be reduced, especially in the direction that uses the non-bent pulley.
Sorry for the brain-fart!
Yes, it will show even at 45°, because one belt would be speeding up and slowing down with every revolution of the bent shaft while the other belt speed is constant. CoreXY only moves at exactly 45° when both belts move the same (or exact opposite) speeds.