Wobbly GT2 Belt on X axis

Hi,

This is an old problem of mine. The GT2 belt on X axis tends to wobble, which is especially visible when the X axis reverses its direction. Please see the attached video:

[www.youtube.com]

On the video, you can see that the belt wobbles on the idler side, but it is quite normal on the motor side. The diameter of the pulleys are equal on both side (around 12.1 mm if I remember correctly). They are aligned and there doesn't seem to be any incllination on both side.

The only way I can fix it is if I use a larger idler (around 16 mm diameter) on the right side. But in that case the diameters don't match on both sides and this results in a loss of parallelity for the belts.

I cannot pin down the exact source of the problem, nor I know if I should be worried about it. If I move the carriage manually, I can feel a loss of tension while reversing directions, however when the motors run and if I hold the carriage lightly I don't feel any effect on the carriage.

I can try a taller idler gear (one that is made for 9 mm belts), I don't know if that would help.

I am open to suggestions.

Thanks

Tighten it up.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Would the tightness explain the asimmetry? It is only happening in one side (at least visibly). I know that the required tightness level is quite high but I've once read that it was tight enough if you can hear a note while plucking the belt (and it is in my case).

Are the pulley axles parallel? They should be parallel to each other and perpendicular to the X axis.

Does the belt lay flat when you take it off the pulleys?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The pulleys are parallel as far as I can tell but I can't say it objectively. They are perpandicular to the X axis.

The belt lays flat mostly but the ends (which are attached to the X carriage) remain bent (probably deformed due to the acute torsion at the junction) but I don't think it will have an influence on overall print quality.

One interesting observation I have made today: I've replaced both the motor pulley and the idler with taller versions (used for 9 mm belts) but still used the 6 mm GT2 belt. The belt on the idler side, which was in the middle of the pulley, climbed upwards when I moved tha carriage and went to the top of the pulley. Could this be happening due to a non-level positioning of the pulleys or is it a side effect of the tightness of the belts?

Edited 1 time(s). Last edit at 03/24/2018 04:07PM by drmaestro.

It could be that the idler pulley is wobbling slightly on the bolt (axle), is the bolt fully threaded ?,ideally it should be partly threaded bolt with a smooth shank(sry, cant remember what they are called)
this would account for the belt twisting as it moves.

Edited 1 time(s). Last edit at 03/24/2018 07:11PM by obewan.

The bolt is fully threaded. I haven’t been able to find one with smooth shank for M5 bolts. Any sources online?

Edit: I have searched Aliexpress. Most of the shoulder bolts (as they are called there) hava a diameter of 6 mm on their smooth surface, which is too big for standard idlers (5 mm bore) and there is no idler with 6 mm bore.

Edited 1 time(s). Last edit at 03/25/2018 06:10AM by drmaestro.