I just purchased my first Bambu X1C last week and find myself impressed overall but quite disappointed with the VFAs. Obviously not a new issue to 3D printing, I have had VFAs on every printer to some extend with the exception of my ender 3. My sidewinder is actually the worst which is not a core XY, and my best (least VFAs is the Voron 2.4 I built). On my voron I had decent VFAs at first but 80% of the issues went away when I swapped out the XY motors to another brand (Stepperonline, still 1.8 deg). Another 10% lost by reducing belt tension. Has anyone swapped out the motors on the Bambu??
Not that I have heard of but they are not the problem. Motor ripple occurs at low speeds (below 80mm/s) typically, while the 2mm belt VFA happens above 110mm/s and peaks 130-140mm/s for most people. It is shifted from belt tension but does not go away no matter what tension the belt has. You can distinguish between the belt VFA and motor VFA by the size and consistency of the ripples. The 2mm VFA is very coarse and a consistent size while the motor VFA is subtle and smaller.
You can feel the belt ripple if you make sure power is cut to the motor and very slowly move the toolhead left and right. You can feel it cogging forward and backward as the teeth pop over the smooth idler pulleys.
Throw some electrical tape on the pulleys to see if it helps your printer. It will probably make a bump where the tape overlaps itself. 1-3 layers may improve it. If the electrical tape works, then removing it to put on a non-adhesive tape like teflon can help and is less likely to produce an overlap bump if you wrap it carefully.
I’m still hoping to find a permanent solution other than pulley wrapping or replacement.
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Well below 80 is pretty much where I would want to fix the issue. The motors and reducing belt tension have always been the biggest factor for me improving the quality but I have not messed with this Bambu yet. With the Bambu the worst part for me are the VFAs in the curves which seem to be terrible at any speed.
Here is a video showing my Voron vs X1C VFA test. I wonder if that ARC fitting setting is making it worst somehow
Voron (Left), Bambu (Right)
Came here because I thought the V1.5 Firmware Update for the P1 series introduced VFAs on X-axis. Seems I had the problem all along.
Some very knowledgeable people here, thanks for sharing! 
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That is an issue if using STLs or other lossy formats without a good value set for the curve fitting. If you’re using a step file this issue goes away almost entirely.
Looking at your test models I see a really strong VFA peak on the Bambu print but I can’t tell what speed that might be or even the spacing on it. I stopped using this model because it was not as demonstrative as a simple cube with rounded corners.
HI!
I’d like to share my unsuccessful tests to get rid of these VFAs on X axis.
I’ve changed the GT2 belt for a higher quality one (Gates Power Grip GT), it was a rather easy change, no need to remove sides panels at all.
I’ve tried a few different belt tension with this new belt, and didn’t obtain anything better than with the original old belt (~1600h prints).
So I think the original belt itself isn’t the root cause of the issue.
Following that, I’ve added motor dampers on X and Y motors, sadly without any improvement at all on the print quality.
Of course the calibrations have been redone on each and every change before the VFA test print in Orca.
I’ve tested with the tape around the pulley, it effectively reduce a bit the VFA, but on the other hand the print quality was worse than without, so I removed it.
I agree with other comments here that the non toothed pulley on toothed side of the belt isn’t the greatest idea Bambu had.
Strange choice, probably they is some logical reasons as the cost is the same.
I found these pulley who look like to have the same dimensions as the original one : https://fr.aliexpress.com/item/33023133633.html
I’ve ordered a few and also ordered a new full X axis on Bambu store (100€…).
Once I’ve received all the goods I’ll find a way to remove the original pulley and replace them with the toothed version.
Hope that with proper toothed pulley I’ll see an improvement.
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Sadly it seems it’s not possible to remove the pulleys without damages, someone here post some pictures and found a way to remove them with minor damage (post 168) : Banding / Ringing type artifacts? - #174 by Sticks
Will be easy to design and print a part to maintain the thread in place.
No that is not whats happening here. The VFA model is high enough resolution not to show visible lines in the curves and you can see my Voron did not have these defects in the curves. Here is another example, these were both printed at with the standard Bambu .20 profile, all speeds and accelerations were transferred to my voron profile. The second photo actually looks like it could be poor input shaping
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The Voron seems to have the same belts path but with toothed pulley :https://youtu.be/Zne2IdvE-A8?si=1_5CjekMn3S5mCdH
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If only we could ask someone at Bambu Lab to customize the X-Axis Rods Assembly to test this out the toothed-pulley. 
It does and I used a toothed idler for my build but many also use a bearing double stack instead which is smooth. I don’t think using toothed idlers is going to fix anything with the Bambu, there are always people chasing VFAs on their Voron as well and from what I have read the toothed idler is never a cure. Just one of those issues with so many variables.
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It may be poor input shaping, but it is 100% the result of a model being low-poly.
The model in question definitely has visible polygons in the curves. Bambu may handle them poorly, but it is the result of a low-poly STL and the issue does not appear in step files.
I have not verified because I just switched to using step files, but I believe the bumps are more the result of poor pressure advance than they are poor input shaping.
Replacing the X axis is not something I wanted to undertake given the price and effort involved since it really requires altering the hardware heavily. Unfortunate to hear that the proper belt did not solve the problem. I will be trying that myself next week - I went with the high-temp Gates belt.
I’ll tell you if it’s worth the effort and price in a few weeks.
I checked my Gates GT2 belts, they are rated up to 85°C, far high enough for the Bambu.
there is also polyurethane GT2 belts with steel core, does anyone know and test them ?
There were white poly belts I was really interested in getting from them, but as far as I can find, nobody is stocking them except through custom requests. I was specifically interested in the lining surfaces to ideally have less friction than the typical GT2 belts.
I’ve ordered these one : https://fr.aliexpress.com/item/32957737789.html
Those are steel core, the min radius is very large, there’s a reason no manufacturer uses those for printers.
https://reprap.org/wiki/Choosing_Belts_and_Pulleys
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They’re also polyurethane, which is the last thing you want for trying to get rid of VFA’s, poly belts resonate more than neoprene or EPDM ones
Hey this explanation is indeed plausible. When teeths meets the idler pulley it brings a bit more tension on the belt and when a teeth moves past the pulley it releases a bit of tension, making the toolhead vibrate. This would explain why with speed the distance is increasing and when reaching high speed the inertia of the belt is enough to compensate the tension that it creates.
It would also explain why at 45 or 135 degrees (when only one or the other motor is in action) it is far less noticeable, because there is only one belt contributing to this phenomenon.
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Think you’re right, I won’t install them.