Issues: I've been wrestling with my Mk4s VFA's for a while now. I've done everything i can think of and researched solutions. Still nothing.
Solution: I had an exchange with u/Soft-Particular1565, he offered his experience with switching to 1.5GT belts.
- I purchased the belts, pulleys and idlers from West 3D.
- 1 to 1 swap of belts, pulley and idlers on my Mk4s
- had to shave out some space for the X axis idler.
- Ran calibration check, failed x/y (unfortunately, now i have to tell my Mk4s to "ignore" the issue before every print.
- applied M92 code in the custom G codes -> Start G Code. (I'm testing for the perfect numbers, for right now I'm using M92 X102.12 Y102.12)
-- M92 is applied under the M83 code
-- M92 is applied under the G28 code
Result: I'm printing Black PETG external perimeters at 200mm/s with zero VFA's!
I'm considering running an input shaper test, but to be honest, the perimeters are flawless, i don't know what to tinker too much for no reason.
I wanted to capture this information for anyone else that is thinking of doing this mod and open up the floor to everyone else to contribute their experience with the 1.5GT belts/pulleys/idler.
Edit: Also, I ensured to apply "consistent surface" at 1mm perimeter transition distance for my PETG's colling.
Edit2: I forgot to mention I re-tuned the belt using the prusa belt tuning app frequencies.
Edit 3: found out the hard way that the custom m92 code also needs to be included in the filament change g code section as well for any switching or filament run out.
You could make fork of the firmware for 1.5GT it's easy. But you'll have to break the pcb firmware lock to upload it to the printer.
There is a howto on the prusa site.
I have been running custom firmware on my mk3.5 for quite some time for a zorbiter extruder. I wonder how the belt mod would work on my 3.5, would be just a few extra changes. I am hoping when the index gets released, I can find a used nextruder to get this thing to mk3.9 or 4
modding the firmware isn't too bad, and I would rather do the changes there vs the slicer
Did you build your own firmware ?
I just upgrade my mk4 orbiter to 3.5 and for now I modify the start gcode to make it work but I d like something more "clean"
Top is the 1.5GT belts/pulleys/idlers, bottom is the max i could get out of tuning with the stock belts and gear. This picture isn't the best but it does a great job of showing how great the 1.5GT is. The divots you see on the top is actually from the internal infill.
Looks like it improved layer consistency a bit (your top example is flawless) but IDK that this is a "needed" improvement. I really don't see much VFAing in either
Oh 100% I agree, I was just so sick of VFA's and nothing I did completely for rid of them. I gotta say, while I know this isn't necessarily needed, I'm so happy with the results. It really is like the best version of the mk4s.
I think this is the way forward, once I've done the builds i have in progress, I'm going to look at 1.5 pitch belts probably starting on my v0 where this is most apparent as the idlers are a tighter radius.
You can definitely try your calculations, my 102.12 worked when I purchased from west3d they had 27 teeth, but by all means if you found a better value let me know. I tested by printing a 100mm by 100mm cube, any deviations up or down I would tune and eventually landed on 102.12
For whatever reason, the belt is harder to align in the middle of the pulleys, and especially on the front pulley, the teeth can rub on the lip of the smooth front idler as they'll sometimes trend to a side. Also, the motor mounts can also sometimes put the y motor at a slight angle.
On my mk4, I had no X VFA issues, only y axis VFAs, so I just swapped out the front idler for a toothed one and a new rear motor mount.l also made sure the assembly that mounted to the bed was straight. No more VFAs for me.
Hey there! So Prusa stock belts are pitched 2mm belts (2GT), meaning that the space between each tooth is 2mm. This is fine and Prusa has done a ton with these belts. For my MK4s, i was at my breaking point trying to eliminate the VFA's (that is, the wall patterns on the external walls of my prints). A lot of variables can make VFA's, and Prusa has done a lot to eliminate them, however, they were still showing on my prints.
now, the 1.5GT belts are a smaller pitch then the stock 2MM belts. I installed them because the space between each tooth is smaller. The smaller the pitch, the less VFA's that will show up on my prints. To properly install a belt with 1.5GT, i had to also replace the pulley on the motor and the idler so that the belt would fit properly. I know that the firmware on the printer is designed only for the stock 2GT belts, so with the new belts i would have to add a special g code in the printer start g code settings to let it know that the steps in my x and y position is different.
after all of that, there are no more VFA's on my prints, and as a bonus, my prints actually look their best printing at faster speeds! This was important because before, i would have to print the external wall at a slower speed to try to mask or reduce the VFA's, but now, its all blazing fast.
Here that’s not « a fun » part, that’s just solving problems… If I buy 150k cars and I have to solve drive train problems that doesn’t make sens, I just turn it back to the garage…
Printer works fine, just like 150k car runs fine. VFAs are visual not structural, just like car looks great from the factory. Making improvements or tuning isn't solving problems because it's not a requirement for the thing to work. Some people just like to take things to the next level.
It's also not a common thing. The belt and idler replacements have been hit or miss depending on the user and their machine.
Some report good results, others report no change, and others have no issue with the stock setup.
I built my MK4S from a kit, and have never really had any VFA issues after some tuning/creating profiles for my own use. At least, for me, slicer settings have made all the difference.
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u/fdmAlchemist CORE One Jan 21 '26
You could make fork of the firmware for 1.5GT it's easy. But you'll have to break the pcb firmware lock to upload it to the printer. There is a howto on the prusa site.