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Belt test X tension always same regardless how loose  

Eminent Member
Belt test X tension always same regardless how loose

I noticed something with my i3 MK3S+ belt est X tension.  NO matter how loose the belt is, the belt test always end up somewhere between 261-269.  I could remove all the tension of the belt so it is a flappy soft, and the X belt tension would still return 268.

Is something wrong with the X-stepper motor?  I did have the same MK3 -> MK3S -> MK3S+ for almost 3 years.

Posted : 04/08/2021 6:00 am
Peter M
Noble Member

Did you use the filament that the maker of the stl advised? And I do not know if it is then different.

Maybe search internet how to set the belt, search more then one user and combine this, so you can adjust without the stl.

Posted : 04/08/2021 10:27 am
Reputable Member
Print this


It is a tool for testing belt tension. It must be printed in Prusament PETG to get correct tension

Read the description and look at the video 👍 

The belt tension numbers don't measure belt tension, just checking how hard it is to move the axis.

Hope it helps

Prusa i3 MK3S+ FW 3.11.0 (kit dec -20), PrusaSlicer 2.5.0+win64, Fusion 360, Windows 10

Posted : 04/08/2021 11:15 am
Active Member
Same here

This was my experience as well despite many support articles out there seeming to say that all you had to do was go off the numbers. I used the aforementioned tool and it worked well. 

A tip for the tool and the x axis that may or may not work for you. Set the tension with the adjustment screw until it’s at the “min”, and then tighten the stepper motor itself which should bring it halfway between min and max. 

Posted : 04/08/2021 7:16 pm
Illustrious Member

The belt tension figure is a measure of the resistance felt by the stepper when moving the axis. On a correctly set up machine this does equate, roughly, to belt tension.

But other things can affect mechanical resistance.

First, with the power off, move the axis by hand; is is smooth? Does the resistance stay the same over the whole range?

Clean and lubricate the smooth rods, check they are not damaged/scratched. Check the idler pulley is not clogged, out of line, or damaged (loosen the belt and try turning it with your fingertip, is it smooth?)

With the belt loose try turning the stepper motor by hand; is is smooth?

Retighten the belt until it just begins to make a low musical note when plucked...

If the printer works, make your next print this:

It MUST be printed in Prusament PETG or the spring tension will be wrong.

Let us know how you get on.


Posted : 04/08/2021 11:12 pm