RE:

CORE ONE VFA MAYBE SOLVED?

Here is a summary as of 2nd September 2025  - I will mark it as best answer until we get any significant progress from Prusa or here.

Timeline 2025:
11 Feb - Reported my VFA Issues to Prusa Support
25 Feb - Sent My Core One back
24 Apr - Received Refund
...
19 June - Prusa officially Looking into widespread VFA problems ( https://www.reddit.com/r/prusa3d/comments/1lf9mjv/psa_lets_address_the_vfa/)
1st July - Prusa VFA update 2 - investigating adjusting tensioning ( https://www.reddit.com/r/prusa3d/comments/1lp3eo7/psa_vfa_update_2/)
17 July - New firmware with Phase Stepping - No difference
20 July (?) - New Belt Tensioning App suggests higher tension (95hz vs old 85hz) improvements minimal - VFA still there
1st September - Prusaslicer and tensioner updates to tackle VFA - WAITING FOR TESTING ( https://blog.prusa3d.com/new-in-prusaslicer-consistent-surface-finish-and-nerfing-vfas_120400/)

Forum Investigations:

Things that don't work:
- Changing to toothed idlers has very little effect - It's been done to death and doesn't resolve it ( )
- Phase Stepping Calibration - No change
- Input Shaping Calibration - No change
- Creating belt soft mounts in the kinematics - No change

Things that slightly work:
- Changing to 1.5GT Belts and pulleys - Requires a change on the printer config to scale the model correctly to compensate, reduces VFAs considerably
- Tensioning Very high (~100hz) - Reduces VFAs but they are still there and the tension will slip over time - may damage printer long term
- Printing fast - If you print fast enough the filament will be matte and it will hide the VFA - it will still be there

Things that need testing:

- New PrusaSlicer profiles and tensioning regime - Can someone follow the suggestions on this blogpost, tensioning and prusaslicer  on a Core One and test print a gridfinity box with the "balanced" profile with silk/shiny filament and inspect the result under light? 

Gridfinity print-in-place test model (2x1): https://www.printables.com/model/465050-gridfinity-container-with-lid-print-in-place/files
Here is the original g-code for comparison prints: https://drive.google.com/file/d/1T7X2J3Gm2UYetzKfY6ZBBM5pxz3wiFaG/view?usp=drive_link

Help! I have VFA on my Core One, what do I do?

The best you can do right now is tension your belts high (100hz), print as fast as possible (avoid structural and stealth modes) and use filaments that minimise the effect. Currently Prusa suggest following their new tensioning regime and using the latest and greatest PrusaSlicer profiles (Balanced) - although this has yet to be confirmed by the community.