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Can't reduce 8Hz difference between belts  

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jw12866
(@jw12866)
Member
Can't reduce 8Hz difference between belts

Top belt is always 8Hz or so higher than the lower one, adjusting either of the belt tensioning screws seems to affect both belts--and then after some iterations I then check the CoreXY balance (for no/minimal play against the gantry) and adjust to fix and the 8Hz difference is back.

Did I most likely mess up on the belt installs behind the nextruder, i.e. one belt has more teeth through the fixture than the other?

Why don't the belt tensioning screws affect mainly one belt separate from the other?

Posted : 28/07/2025 11:16 pm
Raaz
 Raaz
(@raaz-2)
Reputable Member
RE: Can't reduce 8Hz difference between belts

Why don't the belt tensioning screws affect mainly one belt separate from the other?

Because a CoreXY system is a bit "special".

You probably need to bend the angle brackets. Right now, the belts are correcting that. The goal is to have exactly the same belt tension and a flush/synced gantry. 

Just search for a "how to". Multiple threads, videos etc. available. 

Good luck and report back, when done! 🙂 

Posted : 29/07/2025 1:25 pm
zapta
(@zapta)
Estimable Member
RE: Can't reduce 8Hz difference between belts

Try the 'Y and X axes test' instruction here https://help.prusa3d.com/article/selftest-failed-core-one_837189)?_gl=1*1n2wlv9*_gcl_au*MTkxMzE4NTA0MS4xNzUzNDA3NDA1*_ga*MTYyMzM4NTEwMS4xNzQ1NjI4NTc1*_ga_3HK7B7RT5V*czE3NTM3MjExOTEkbzEyNiRnMSR0MTc1MzcyNTU1MyRqMTUkbDAkaDA.

Make sure to have the belts very loose before you apply force so you don't break the tensioner.

 

Posted : 29/07/2025 8:47 pm
jw12866
(@jw12866)
Member
Topic starter answered:
RE: Can't reduce 8Hz difference between belts

Hi all - thanks for the replies. So I did just finish up on the build (leaving belts at 89Hz and 81Hz) to see if it'd fail the calibration, which it didn't actually. And have printed keychain, benchy, the articulated snake and a couple other things. Practically all turned out as good as I could have hoped. 

I need to go back and fix these belts though--as I saw in one of the posts about fixing tensioning that pulleys could be wrong way up and I don't remember thinking about orientation with those. But seems like this is a tiny tweak and not a major malfunction.

I found this video, which I think is what @Raaz meant by bending the angle brackets? Makes sense that the belts are correcting for that being out of alignment. I will try that first.

I assume also I am not damaging anything by running the printer with the current belt tensioning... (89 + 81)

Posted : 29/07/2025 10:42 pm
Per S.
(@per-s)
Member
RE: Can't reduce 8Hz difference between belts

According to Prua documentation, there is supposed to be a 6Hz difference between upper and lower belt.

Upper belt: 98Hz

Lower belt: 92Hz.

 

https://help.prusa3d.com/article/adjusting-belt-tension-core-one_845048

Posted : 30/07/2025 6:29 am
1 people liked
Raaz
 Raaz
(@raaz-2)
Reputable Member
RE: Can't reduce 8Hz difference between belts

Oops, yeah with the new method, it's supposed to be 98/92 and not 85/85 anymore. Also it's upper/lower belt now, instead of left/right. 

So my post needs correction: the goal is to have exactly these 6 Hz difference and bending the gantry brackets is still the way to go, just not with the goal to have exactly identical Hz, sorry. 

Posted : 30/07/2025 10:05 am
jw12866
(@jw12866)
Member
Topic starter answered:
RE: Can't reduce 8Hz difference between belts

Ah, I got myself confused here - I read the comment from Jan Kratochvíl on this page: https://help.prusa3d.com/guide/9-calibration-first-run_835546, and mistakenly read it as needed to be the app-based frequencies, not what was on the linked page here: https://help.prusa3d.com/article/adjusting-belt-tension-core-one_845048.

So it sounds like I'm not far off, will try a bend tweak on the gantry and see if can get 98/92 spot on. Right now it's still printing pretty sweetly!

Posted : 30/07/2025 1:07 pm
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