Only one belt vibrating (twice in a row) during manual belt tuning
I'm sure I did something wrong. but when trying to use the manual belt tuning test only one belt vibrates during both upper and lower testing. It'll be one or the other, I haven't yet figured out the reason for why upper or lower is the one reacting. I have done a lot of testing while tightening and loosening the tensioners and even had them pop out once, which was fun to fix. I did tighten the belts a fair amount early in the build, so I wonder if I did myself a disservice with that. Before I start disassembling, any ideas? It's a kit.
RE: Only one belt vibrating (twice in a row) during manual belt tuning
Be sure to always tension the belts evenly. Start with completely relaxed belts, loosening the tensioners as much as you can. In that state check that the X gantry is straight, i.e. touches the front left and right end stops at the same time -- if it is not, bend the gantry L brackets to get there. Then gradually tighten the belts, always turning both tensioners by the same amount.
Once the belts are tight enough to produce audible tones when plucked (above 60 Hz), you can switch to the stroboscope-based Manual Belt Tuning wizard in firmware 6.4.0. You should find visible resonances for both belts, although they will not be at the exact same frequency, because the free belt length along the gantry is a bit different.
Detailed and illustrated version of the above procedure:
https://help.prusa3d.com/article/adjusting-belt-tension-core-one-l-core-one_845048
RE: Only one belt vibrating (twice in a row) during manual belt tuning
Thank you. When the tensioners are completely loose should they stick out and interfere with the gantry alignment test?
RE: Only one belt vibrating (twice in a row) during manual belt tuning
You could relax the belts and check whether the gantry is aligned without belt tension. If the metal is bent but perpendicular under tension (forced by the belts) there is be imbalanced force between the belt that shows in resonant frequencies being off. As Jürgen stated above, in a normal setup the different "tuning" comes simply from the different length of the visible belt segments but the force is exactly the same.
RE: Only one belt vibrating (twice in a row) during manual belt tuning
Thank you. When the tensioners are completely loose should they stick out and interfere with the gantry alignment test?
If I recall correctly, they should not collide even in the fully loose position. The movable idler wheel may stick out of the stationary tensioner block a bit, but there is a matching recess in the idler block on the gantry.