RE: VFA Artifacts on X+Y Straight Edges
Hello, this is a repost from the XL forum, as there isn't much activity there, and my idea also applies to the Core one.
I had the following theory, but I haven't had time to test it yet: The VFAs are strongly pronounced on some printers, while other printers produce a near perfect surface finish. Looking at the motion equations X = 1/2 (A + B) and Y = 1/2 (A - B) and assuming that the toolhead only moves in X direction, both motors must turn at the same rotational speed.
What if, on some printers, the two belts are aligned in such a way, that the gripping of the belt by the two motor pulleys is synchronized, while on other printers the gripping of the two pulleys is offset by half a tooth, so that the gripping effects cancel each other out. The solution would be to loosen one belt and offset it by about half a tooth.
The manufacturing tolerances of the pulleys are also important. Perhaps changing the pulleys around altered the phaseshift between the two motor pulleys.I don't know how these are manufactured, or whether the alignment between the groove and the belt teeth varies.
Please let me know whether my theory could be correct or is complete nonsense?
RE: VFA Artifacts on X+Y Straight Edges
I don't have a before-after; I installed the Gates pullies from the start and just wanted to give people another datapoint. So I was trying to show different orientations/walls. The first picture is between the 45 degree and 60 degree spokes, and the second is between the 60 and 30. I see pretty similar artifacts all the way around though.
I'm by no means an expert at reading this, but it looks like if I keep away from 60mm/s, 90mm/s, and 100m/s perimeters, those seem to be better for me.
RE: VFA Artifacts on X+Y Straight Edges
So who’s gonna be the next volunteer to swap the pulleys? 😂
I think if one more end user swaps them out and it solves the issue, then it’s pretty much conclusive that’s where the issue lies.
My only hesitation is the lucky dip of finding ‘good’ pulleys…that sounds like a potential pita.
I've just ordered 6 Gates pulleys and a couple of Gates toothed and smooth idlers. I imagine I will not receive them for at least a week.
RE: VFA Artifacts on X+Y Straight Edges
Can anyone confirm the gates p/n for replacement idlers and pulleys for the core one?
RE: VFA Artifacts on X+Y Straight Edges
Hello, this is a repost from the XL forum, as there isn't much activity there, and my idea also applies to the Core one.
I had the following theory, but I haven't had time to test it yet: The VFAs are strongly pronounced on some printers, while other printers produce a near perfect surface finish. Looking at the motion equations X = 1/2 (A + B) and Y = 1/2 (A - B) and assuming that the toolhead only moves in X direction, both motors must turn at the same rotational speed.
What if, on some printers, the two belts are aligned in such a way, that the gripping of the belt by the two motor pulleys is synchronized, while on other printers the gripping of the two pulleys is offset by half a tooth, so that the gripping effects cancel each other out. The solution would be to loosen one belt and offset it by about half a tooth.
The manufacturing tolerances of the pulleys are also important. Perhaps changing the pulleys around altered the phaseshift between the two motor pulleys.I don't know how these are manufactured, or whether the alignment between the groove and the belt teeth varies.
Please let me know whether my theory could be correct or is complete nonsense?
I absolutely get your point, but as the printhead moves in a plain 2D plane and not by "pixels" I think it's almost impossible that belt ripples could be as repetitive as we got.
RE: VFA Artifacts on X+Y Straight Edges
Has anyone checked whether it makes a difference which of the grub screws on a pulley is screwed against the flat part of the motor shaft? I can't try this myself at the moment but it should be possible to switch without disassembling anything.
RE: VFA Artifacts on X+Y Straight Edges
Unless I'm misunderstanding that, it won't make any difference. The motors should be off when tensioning, which means that the motors are free to turn. This means they will rotate to wherever they need to be based on the length of the belt. It's not like a timing belt/chain on a car where the #of teeth between pulleys matters.
RE:
Hello, this is a repost from the XL forum, as there isn't much activity there, and my idea also applies to the Core one.
I had the following theory, but I haven't had time to test it yet: The VFAs are strongly pronounced on some printers, while other printers produce a near perfect surface finish. Looking at the motion equations X = 1/2 (A + B) and Y = 1/2 (A - B) and assuming that the toolhead only moves in X direction, both motors must turn at the same rotational speed.
What if, on some printers, the two belts are aligned in such a way, that the gripping of the belt by the two motor pulleys is synchronized, while on other printers the gripping of the two pulleys is offset by half a tooth, so that the gripping effects cancel each other out. The solution would be to loosen one belt and offset it by about half a tooth.
The manufacturing tolerances of the pulleys are also important. Perhaps changing the pulleys around altered the phaseshift between the two motor pulleys.I don't know how these are manufactured, or whether the alignment between the groove and the belt teeth varies.
Please let me know whether my theory could be correct or is complete nonsense?
Are you suggesting that it might have something to do with the relative orientation between the pulley teeth and the motor steps between the two motors? For example, if you could simply rotate the location of the milled "flat" on one of the motor shafts by a specific amount, or shift the set screw on the pulley in relation to the milled teeth.
To test this, someone with a "good" and "bad" pulley on hand would need to carefully measure the orientation between the milled teeth and the set (grub) screw to see if there is somehow a difference.
If I'm conceptualizing correctly, in order to make a scaled correction, you'd need to make sure the milling of the "flat"on the shaft is tightly standardized in its orientation to the internals/steps of the motor...AND if the combinations need to be offset between motors, you'd need two unique pulley parts and keep them separated in the assembly line to make sure one of each ended up on each machine.
I may be misunderstanding your theory though. If nothing else it's a fun mental exercise to try and conceptualize. 😅
-J
RE: VFA Artifacts on X+Y Straight Edges
The artifacts are visible on walls 45° to the x and y axis. Only one of the motors rotates during this type of movement so it's unlikely that synchronization between the motors are a cause.
RE: VFA Artifacts on X+Y Straight Edges
I'm even gonna add - X and Y should be your smoothest walls even when one or both of the motors are wonky. Especially X.
In my case my X wall was pristine and my Y wall was just very slightly rippled - even with bad pulleys. While my diagonal walls were horrid. Replacing the pulleys smoothed out diagonals and also smoothed out that very tiny ripple on Y.
The artifacts are visible on walls 45° to the x and y axis. Only one of the motors rotates during this type of movement so it's unlikely that synchronization between the motors are a cause.
RE: VFA Artifacts on X+Y Straight Edges
That pretty much disproves my theory.
I meant both motor pulleys beeing synchronised in their phase angle. So if you take one pulley mentally and put it above the other pulley, the teeth on both are aligned. This would result in the synchronised grabbing of the teeth on both belts at the same time. That is the worst case since the grabbing effects add up. The best case would be an offset of one half pitch, so that when the tooth on one belt is starting to get grabbed by the pulley, the tooth on the other belt is already fully grabbed.
However, if the artefacts are visible when only one motor is running, this would rule out this theory.
So it seems, that the main cause is manufacturing tolerances of the pulleys.
RE: VFA Artifacts on X+Y Straight Edges
Please consider my post above. I didn't actually mean that, but that's an interesting theory. I actually dont think, that the motor steps have to do anything with the artifacts. For 0.9 degree steppers the movement of the beld for one step is: 0.9° * pi/180 * 12.22 mm / 2 = 0.096 mm. So the position of the milled flat should make no difference at all. The 2 mm artifacts must be caused by something related to the belt teeth. Did anyone use belts with a different pitch before?
RE: VFA Artifacts on X+Y Straight Edges
Did anyone use belts with a different pitch before?
Qidi Plus 4 uses 1.5GT. A few people in the thread ordered 1.5GT belts and pulleys on Aliexpress, but I don't think anyone received them yet. I've ordered them myself before I managed to fix my printer with just pulleys and a bit more tension (and maybe those toothed idlers helped, I don't know). I won't be putting them in anymore, but I am very curious if this would improve things.
RE: VFA Artifacts on X+Y Straight Edges
Not really sure how to read this, but here we go.
The way I read that: the lower speeds show more pronounced VFAs related to the belts. The higher speeds start showing a lot more layer shifting which I would expect as the harder it has to sling the extruder around, the more likely it is to be slightly off. The diagonal artifacts in the 9th and some higher zones are interesting and look similar to what people have been complaining about in the git bug before prusa stepped in and told people they were bitching about an unreleased feature.
If you think about it for a minute, belt ripples at low/medium speeds makes sense as the teeth riding over a smooth pulley will slightly increase or decrease the tension on the belt as it rolls uphill over a tooth contacting the pulley and then back downhill as the tooth leaves contact with the pulley and thus exhibit the VFAs as the head predictably speeds up/slows down.
It also makes sense that they would be less pronounced at higher speeds because the motor current and belt velocity is much higher at high speeds so it doesn't change speeds as much. You can still see them but they are much less pronounced. This, of course, is fine for just frilly stuff but if you want to print more structurally sound parts, high speed is going to make that worse plus introducing other artifacts as you start approaching the edges of the useful tuning that can be done with relatively low power motors.
RE: VFA Artifacts on X+Y Straight Edges
I did do PS calibration before that print. Although I do need to remove some foam from beneath my paver to compress it a bit more, then do PS and IS again.
RISPONDI: VFA Artifacts on X+Y Straight Edges
Good morning, I have never written on this forum but I have followed the whole discussion on the VFA. I own a MK4S and I too, after ordering the upgrade kit for Core One, decided to cancel the order after reading this discussion and hearing opinions from other sources.
The idea I got is that the problem is not easy to solve, changing belts and pulleys could improve the thing but I don't think it solves the problem seeing the somewhat evasive answers that have been given to some users by the assistance center makes me think that the problem is more rooted perhaps in the design of the gantry which is all metal and therefore causes excessive vibrations (hypothesis made CNC to be verified) or in the software which is clearly dated it only uses a 32 bit card with Marlin and has difficulty managing complicated algorithms (something also reported by Aurora Tech several times). I also noticed that in some short films published by Prusa showing objects printed with the Core One, there are VFA artifacts (and then they say that the machines they have in the factory do not have these problems). I hope Prusa will solve these problems, but I think that if they are so intrinsic we will only see improvements on a probable Core OneS. I like the Prusa ecosystem and I would not want to abandon it, but the quality-price ratio is no longer what it used to be. I hope they correct their aim, then I will be very happy to continue buying their products. While other companies try to do something innovative, see Bambu with the double hot end and active management of the chamber or Qidi that used belts and pulleys with 1.5 mm pitch obtaining good results, Prusa remained behind and when they presented the Core One the thing they advertised the most was the fish that attaches with the magnet and the reversible door (in plastic). Furthermore, the Core One does not have a minimally watertight chamber, the frame is full of holes and drafts without gaskets on the door and panels. I haven't tried it, but I don't think it's ideal for printing materials like ASA, even with the very expensive optional filter installed. I really hope they step up because I really regret having to change printer brands for my next purchase.
RE: VFA Artifacts on X+Y Straight Edges
I also noticed that in some short films published by Prusa showing objects printed with the Core One, there are VFA artifacts (and then they say that the machines they have in the factory do not have these problems).
Not really disagreeing with you, but the statement was that the Core One wouldn't have worse VFAs, compared to the competition. Not, that they wouldn't see any.
the frame is full of holes and drafts without gaskets on the door and panels. I haven't tried it, but I don't think it's ideal for printing materials like ASA, even with the very expensive optional filter installed.
Yeah I'm having my doubts too.. In theory, as long as the airflow is high enough, air will only flow into the chamber, not out of it.
Luckily there are already mods for the corners and the remaining holes should be small enough to keep the negative pressure in the chamber.
RE: VFA Artifacts on X+Y Straight Edges
This whole issue is so weird. I noticed on a handle reprint (added a fitting so I could easily swap tubes from a drier), which is a pyramid-ish shape, that vfa would temain aligned vertically for 5ish layers up the angled side, then shift a bit and again... 5 layers aligned till another shift. If it's belt related, it changes based on the relationship of the two belts to each other not just a belt over idler.
RE: VFA Artifacts on X+Y Straight Edges
This whole issue is so weird. I noticed on a handle reprint (added a fitting so I could easily swap tubes from a drier), which is a pyramid-ish shape, that vfa would temain aligned vertically for 5ish layers up the angled side, then shift a bit and again... 5 layers aligned till another shift. If it's belt related, it changes based on the relationship of the two belts to each other not just a belt over idler.
RE: VFA Artifacts on X+Y Straight Edges
This whole issue is so weird. I noticed on a handle reprint (added a fitting so I could easily swap tubes from a drier), which is a pyramid-ish shape, that vfa would temain aligned vertically for 5ish layers up the angled side, then shift a bit and again... 5 layers aligned till another shift. If it's belt related, it changes based on the relationship of the two belts to each other not just a belt over idler.
Might be speed related. In my vfa towers I found the frequency of the artifacts increased with increasing extruder speed.