Motors Rattling with new belts

Hey there, I have a coreXY machine on basis of the flsun cube with modified coreXY parts from jand1122 (see pics ).

The printer worked okay but I had to install new belt-clamps to get just a little more tension on the belts.
But now after I installed the new belts the y-motor seems to loose steps near the homing point. In the middle of the bed it works fine...
This utters in rattling motors which causes heavy vibration in the machine.
So directly after homing the printhead should move to X30 Y30 but it is vibrating and moves only to like X30 Y4 or so.
(See this video: [drive.google.com] the z axis still has A4988 drivers so this is the loud sharp tone noise at the end)

I tried snapping back on the old A4988 workin horses for the X and Y axis (instead of the MKS LV8729 I am using) but this makes it even worse:
No matter what direction I want to move the printhead only does a little jerk and the motors do not turn but make a sharp tone.

Could someone tell me how this could happen when the only thing I did to kinematics was slightly increasing the belt tension and using a new belt?
How can I make my machine work properly again?

Thanks in advance

Edited 3 time(s). Last edit at 05/31/2018 08:35AM by Schild0r.

Maybe you over tightened the belts? Or the new belt clamps are causing some slight misalignment (the effect of this would be worse at the ends of your travel which is what you're seeing).

The simple answer to your question is to go back to what worked.

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Trakyan
Maybe you over tightened the belts? Or the new belt clamps are causing some slight misalignment (the effect of this would be worse at the ends of your travel which is what you're seeing).

The simple answer to your question is to go back to what worked.

Pretty sure they are not misalining cause I designed them not to (same outer measurements)
"to go back what worked" is a little bit exaggerated because tightening the belts was not by chance but because of poor quality.
I tinkered a little bit (decreased speed and acceleration) and it seems like the rattling now is more or less randomly occuring (but only at x-positions around X0)

It is just strange that this only seems to happen in y-direction although (due to CoreXY) both motors are turning for either x- or y-movement (just in another rotation-direction) or is there something I miss?

Edited 1 time(s). Last edit at 05/31/2018 06:44PM by Schild0r.

The new belt is the same as before? IIRC there are MXT belts, which have a pitch of 2.03mm vs. GT2 belts with 2mm pitch.

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o_lampe
The new belt is the same as before? IIRC there are MXT belts, which have a pitch of 2.03mm vs. GT2 belts with 2mm pitch.

At least I bought them as GT2 belts on Amazon... hope they are not mislabeled

Did you change anything that could have shifted your rails? Moved/reassembled/tweaked the frame, rail mounts etc. You could have out of parallel rails causing problems with binding. The y axis would be more prone to this I reckon and that matches up with what you're seeing.

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Trakyan
Did you change anything that could have shifted your rails? Moved/reassembled/tweaked the frame, rail mounts etc. You could have out of parallel rails causing problems with binding. The y axis would be more prone to this I reckon and that matches up with what you're seeing.

Only thing I did was install the cable chain and use new cables without dismantling anything that could have an impact on kinematics