RE: VFA Artifacts on X+Y Straight Edges
I just made a interesting observation.
Both of these plates are printed on the same print job, at exactly the same speed (45mm/s) and both are on the X axis. The bottom part was printed at the exact middle of the build plate, the top part was printed around 20mm in front of the other part (near the door).
For some reason there are VFA's on the middle of the build plate but none 20mm in front. This is very strange.
RE: VFA Artifacts on X+Y Straight Edges
Check the belt paths at different XY positions — the issue might be caused by the belts grinding against the idlers; or belt tooth imperfections (swap the belts if it could be done in core one). It could also be due to tension changes, which can affect stepper motors differently (though I’m not very deep into electronics). I did similar experiments with my XL, but didn’t notice any change in surface quality.
I just made a interesting observation.
Both of these plates are printed on the same print job, at exactly the same speed (45mm/s) and both are on the X axis. The bottom part was printed at the exact middle of the build plate, the top part was printed around 20mm in front of the other part (near the door).
For some reason there are VFA's on the middle of the build plate but none 20mm in front. This is very strange.
RE: VFA Artifacts on X+Y Straight Edges
Check the belt paths at different XY positions — the issue might be caused by the belts grinding against the idlers;
That's what I was also wondering about when I saw @boris-3's results. The vertical position of the belts seems rather ill-defined by design: There is really nothing besides the flanges of the idlers to keep them at their target height (or rather, in the tolerance range allowed for by the idlers being slightly wider than the belt).
Apparently it is considered OK for the smooth side of the belt to brush against the flanges -- otherwise, how would the belt ever stay at a "good" height? But maybe it's not ok for the toothed side to touch the flanges -- but how do we avoid that? Maybe if we had sightly wider (taller) idlers in those two positions where the toothed side of the belt goes over the idler -- then the neighboring idlers would force the belt into a more narrowly defined position, and its teeth could never touch the flanges on those wider idlers?
Ah, well -- maybe the fundamental problem is that those belts are used well outside their precision specs in 3D printers? These are timing belts after all, and I assume they are specified to provide timing accuracy to within a certain, reasonable fraction of their tooth pitch. Anything beyond 1/10 of the 2 mm tooth pitch would surprise me as a spec; but in VFAs we notice much smaller deviations.
RE: VFA Artifacts on X+Y Straight Edges
That could also be related to the belts tension/harmonics, because they are at their most even length in the middle with respect to the front and back of the machine. Aka the gantry is in the middle of the machine and the belt length from the gantry to the front and back of the machine is equal.
I would be curious to hear Prusa 's official word on this. Anyone have any ideas on how to get a response, aka they acknowledge the issue and are working on it, or they aren't.
RE: VFA Artifacts on X+Y Straight Edges
Are you sure they are not aligned? Light/reflects and deepness of the artifacts may make them appear slightly offset but I think they are aligned (in mine they are, even if on the picture it doesn't seem).
RE: VFA Artifacts on X+Y Straight Edges
I would say there is a phase shift, yes. In the center of the attached picture the shift is between 110mm/s and 120mm/s on PETG with a wall orientation of 90°.
I can see and feel that when scratching over the surface.
RE: VFA Artifacts on X+Y Straight Edges
I have just accepted a refund from prusa after getting my Core One pre-assembled on release day.
Support tested it with the new firmware and it's the same. They gave me the option to take it back or accept a refund.
Feel a bit let down by prusa, it was my third Prusa after a MK4 and MK4S and it feels like I've paid to be a alpha tester of a new model. Support are sure it will be resolved but I don't expect it from a new purchase and don't really fancy taking the gamble with my £1k+ printer
RE: VFA Artifacts on X+Y Straight Edges
I have just accepted a refund from prusa after getting my Core One pre-assembled on release day.
Support tested it with the new firmware and it's the same. They gave me the option to take it back or accept a refund.
Feel a bit let down by prusa, it was my third Prusa after a MK4 and MK4S and it feels like I've paid to be a alpha tester of a new model. Support are sure it will be resolved but I don't expect it from a new purchase and don't really fancy taking the gamble with my £1k+ printer
Sorry to read that you have given up on the Core One, but I can understand.
Did the support team expect that the new firmware would improve things? After the software developers had to pull the phase stepping calibration from the 6.3.1. release at the last minute, I don't see how that firmware could have impacted VFA performance?
Fingers crossed that the developers will get the calibration to work in 6.3.2, and soon -- and that it will bring a significant improvement on this front. Maybe you will reorder a Core One later this year, once all the dust has settled? Rev.2 with a built-in accelerometer, since Prusa will finally have seen the light and realized that it is needed. 😛
RE: VFA Artifacts on X+Y Straight Edges
I am currently printing storage boxes with my MK4S although the CORE One is available, only because it's PETG and the surface finish on large flat walls is way better on the MK4S than on the CORE One.
My only hope is that a good phase stepping implementation could reduce this effect to at least the XL level. This is the last thing I am waiting before to release my review write-up, I don't count on an official statement. My review unit suffered of almost all the issues we find on the forum, gantry squareness, nozzle cleaning, bad vibrations, loose screws, vertical artifacts. I could solve most of them, but the so-called VFA are the worst, to the point I don't want to upgrade my MK4S yet.
RE: VFA Artifacts on X+Y Straight Edges
Maybe I'll get a Core One later with a revised model parts when they have ironed out the bugs - or sell my morals for the H2D. Hard to know what is the best printer for £1000 right now.
It's taken 61 days from my printer getting delivered and almost as long (50 days) with it being returned to Prusa. I can't wait any more without a printer
RE: VFA Artifacts on X+Y Straight Edges
Maybe I'll get a Core One later with a revised model parts when they have ironed out the bugs - or sell my morals for the H2D. Hard to know what is the best printer for £1000 right now.
It's taken 61 days from my printer getting delivered and almost as long (50 days) with it being returned to Prusa. I can't wait any more without a printer
The H2D has impressed me with the print quality that I've seen so far, but other than that the printer just doesn't fit me. The 2 heads is novel, but already having a 5 head XL it doesn't add anything for me. I just want a single head. Plus some of the other stuff it has is cool, but honestly see no purpose for me and it is just more to go wrong. I also can't get past the locked in eco system. Running a business with proprietary designs I just don't feel comfortable having to put my designs in a place where I can't control it. I realize it has an offline mode, but it's with reduced functionality.
I also like the setup with the special sheet that you install and the machine automatically calibrates itself for the best accuracy. Not sure it's really needed as plastic shrinkage is a way bigger issue with the accuracy of a 3d printed part, but it's neat nonetheless.
Based on that the Core One is just a better fit for what I do, or actually the MK4 is as well. The MK4's I have are my best printers. The draw of the core one for me is the higher chamber temps to help with ASA mainly and the reduced space required vs. an MK4 & enclosure.
RE: VFA Artifacts on X+Y Straight Edges
Maybe I'll get a Core One later with a revised model parts when they have ironed out the bugs - or sell my morals for the H2D. Hard to know what is the best printer for £1000 right now.
It's taken 61 days from my printer getting delivered and almost as long (50 days) with it being returned to Prusa. I can't wait any more without a printer
Ahah I’m on a same boat, I ask for a refund after sending my CORE One to repair.
I have an X1C in the meantime to I can keep printing.
I was thinking about H2D, but if I do buy one it will replace my X1C, and I’m 90% sure that I will buy a CORE One again when phase stepping will be implemented.
RE: VFA Artifacts on X+Y Straight Edges
Still trying to understand the root cause of the VFAs (or belt ripple)...
Contact of the toothed side of the belt with the idler flanges seems like a plausible suspect. Watching the two idlers which contact the toothed belt (left and right of the X rail) on my Core One, I do see the belt moving up and down slightly as the print head moves about. But I don't see how I could avoid that:
- The various idler flanges, and the clamping of the belt ends at the Nextruder, are the only points where the belt height is defined.
- Clamping at the Nextruder seems to be at the correct height. When I move the extruder all the way to one side, the belts are nicely centered on the idlers on that side.
- Height definition via the idlers always leaves a tolerance, since the flanges are a bit further apart than the belt width. So they don't force the belt to be exactly centered. It can still wander up and down a bit, and can still touch the idlers.
So is there anything I can do to enforce better belt centering and avoid its slight wandering up & down? The idlers at the belt tensioners are the next neighbors of the two X-rail idlers which see the toothed belt side. But I can neither height-adjust those idlers, nor tumble their axles (in the hope of nudging the belt in the right direction).
Any other ideas what to do -- to verify or falsify the "teeth touching flanges" hypothesis, or improve the belt alignment?
One thing I was considering was switching to flange-less idlers (with a correspondingly wider running surface) for those two idlers which touch the toothed side. Hopefully the belt would not go totally off the rail, and its teeth could no longer touch any flanges. What do you think -- worth a try if I can find such idlers?
RE: VFA Artifacts on X+Y Straight Edges
I guess it's just the belts. They don't bend uniformly because teeth creates alternations between more and less rigid parts of the belt. Maybe helical or double helical tooth belts would eliminate this issue?
RE: VFA Artifacts on X+Y Straight Edges
I guess it's just the belts. They don't bend uniformly because teeth creates alternations between more and less rigid parts of the belt. Maybe helical or double helical tooth belts would eliminate this issue?
Yes, that's another possibility. I have always felt that in 3D printers, the timing belts are probably used well outside of their spec regarding the evenness of movement.
But still, there seems to be significant variation between individual printers. @nxt3d has just reported that he did not see any VFAs or belt ripple in his newly built Core One yet. So what's the difference? What can I change to make my printer one the of VFA-free (or low-VFA) ones too? 🙄
RE: VFA Artifacts on X+Y Straight Edges
As I mentioned up thread it can't be the idlers with the teeth facing the idler because that would be inconsistent with the frequency change when moving diagonally. As I've thought about it over the last couple of weeks I've been leaning more toward what @biomech said. I was thinking the variation between printers may be due to how in phase all the contributions from each idler are. Could there be enough variation (~1mm) in idler to idler spacing that this would be significant?
RE: VFA Artifacts on X+Y Straight Edges
As I mentioned up thread it can't be the idlers with the teeth facing the idler because that would be inconsistent with the frequency change when moving diagonally. As I've thought about it over the last couple of weeks I've been leaning more toward what @biomech said. I was thinking the variation between printers may be due to how in phase all the contributions from each idler are. Could there be enough variation (~1mm) in idler to idler spacing that this would be significant?
Variations in the belt tensioners' setting are the only source of instrument-specific ~ 1mm deviations I can think of.
And of course as the X gantry moves, the positions of the four idlers on that unit will move vs. the stationary idlers -- changing the phase relationship all the time during the print. So I am not sure that could cause a "global" difference in belt ripple performance?
RE: VFA Artifacts on X+Y Straight Edges
Variations in the belt tensioners' setting are the only source of instrument-specific ~ 1mm deviations I can think of.
And of course as the X gantry moves, the positions of the four idlers on that unit will move vs. the stationary idlers -- changing the phase relationship all the time during the print. So I am not sure that could cause a "global" difference in belt ripple performance?
Thanks. I appreciate your insight as you apparently put in a lot of thought while you were assembling your unit and I bought an assembled unit. I don't know the correct terms for the assemblies, but can you imagine much variation between printers in the distance between the two stepper motor assemblies that contain the three idlers?
Focusing on just a single belt, there are six idlers. I agree, the phase relationship between the two idlers on the gantry will change with respect to the rest of the idlers when the gantry moves in the y direction as well as the velocity of the belt on those idlers changes with respect to the rest depending on the direction of movement. The phase relationship between the tension idler and the other three remaining idlers will change printer to printer depending on how much slack you left in the belt prior to tensioning. I would imagine the phase relationship between the two idlers in the motor assembly are pretty reproducible given the short distances involved. That leaves the distance between the two motor assemblies that defines the phase relationship between the two idlers in one motor assembly and the single idler in the other motor assembly.
RE: VFA Artifacts on X+Y Straight Edges
[...] can you imagine much variation between printers in the distance between the two stepper motor assemblies that contain the three idlers?
I would not expect more than a few 1/10 mm of variation. The holes and threads in the sheet metal parts are placed quite precisely, and that certainly includes the CoreXY frame. And the corresponding holes in mounting blocks etc. have very little play. (Prusa rely on them to ensure that the two Y rods are parallel -- according to the kit instructions, you are supposed to just screw the mounting blocks onto the frame and be done with it, no alignment step is considered necessary.)
Heck, there must be a way to track the source of that ripple down... One would expect that Prusa has done this analysis in-house, starting with the XL. Did they not identify the root cause? Did they, but consider it a trade secret? Or did they, but don't want to talk about it since they can't fundamentally avoid the effect?
RE: VFA Artifacts on X+Y Straight Edges
[...] can you imagine much variation between printers in the distance between the two stepper motor assemblies that contain the three idlers?
I would not expect more than a few 1/10 mm of variation. The holes and threads in the sheet metal parts are placed quite precisely, and that certainly includes the CoreXY frame. And the corresponding holes in mounting blocks etc. have very little play. (Prusa rely on them to ensure that the two Y rods are parallel -- according to the kit instructions, you are supposed to just screw the mounting blocks onto the frame and be done with it, no alignment step is considered necessary.)
Heck, there must be a way to track the source of that ripple down... One would expect that Prusa has done this analysis in-house, starting with the XL. Did they not identify the root cause? Did they, but consider it a trade secret? Or did they, but don't want to talk about it since they can't fundamentally avoid the effect?
Thanks. I guess I may be barking up the wrong tree then. I agree we (and Prusa) should be able to identify the cause and maybe even a solution. I think that bothers me more than the VFAs do.
I was thinking of hooking up my own accelerometer to the print head and log the data to see if I can see anything at the frequency of the VFAs. I'm not sure what I would do with that data, but if I can detect something then at least I can quantify it better than just observing the relative visibility of the VFAs.