Clicking noise from timing pully

[coldkryten]

I recently had to adjust and re-tension a timing belt in a robotic arm. Everything was fine for the first several hours of use, but the belt then started making a noticeable clicking noise. I've re-checked the tension and it is OK. The noise appears to be synchronized with the teeth on the belt, and originates from the region where the belt loses contact with one of the pulleys (reverse the rotation and the noise comes from the opposite side of the pulley.) Turning the system by hand seems smooth and free.

My guess would be a little bit of grease on the belt, I'm wondering if there is any experience or opinion that might point to something more serious.

Cheers,
Mike

 

[SincoTC]

You didn't mention the speed of the belt, its size and length, endless or jointed belt, this might help.

Is it the original belt or have you replaced it? if so is it the wrong profile profile and sticking in the pulley tooth grooves. I would expect this to make a buzz rather than a click as the belt is "peeled" off the pulley. Examine belt and pulley for damaged teeth around click area (and noisy pulley's side cheeks if fitted as they may be distorted and pinching belt across width)

Have you observed the Motor Driven pulley when the clicking occurs? Use a marker pen and put a "timing" mark on the pulley and belt, then run it back and forth around where it clicks and see if the belt's skipping over the pulley teeth.

Hope this helps

 

[coldkryten]

I don't have it in front of me right now, but the belt is about 10mm wide, roughly 350mm long, and runs over two ~50mm dia. pulleys.

The belt is original as is the pulley the noise seems to be coming from. The changes were the result of replacing the second pulley, and it appears identical to the original.

The noise is more like the buzz you describe, it isn't tied to a specific location on the belt but rather each time a tooth leaves the pulley. I here distinct clicks because this runs at very low speed. Because both the belt and suspect pulley are original I don't see how the profile could be an issue, but otherwise I think that would be a reasonable description of the noise.

Cheers,
Mike

 

[BobM3]

Maybe the belt tension change is causing the noise. Old pulley and old belt might have had teeth that matched exactly. New tension on the old belt might be stretching the belt so that the tooth width is a bit wider or narrower than the old pulley gap width.

 

[BobM3]

Could one of the shafts tilted a bit during the retensioning such that the two pulley shafts are not parallel?

 

[SincoTC]

Mike,

If the original pulley is making the noise running with the original belt, but the new pulley is quiet, then that suggests to me the possibly that the belt tooth number is an exact multiple of the pulley, so groups of teeth always mesh together, so that over time they will have "bedded in" and any tooth irregularities will will have become imprinted on the components. If you removed and refitted the belt and lost the original relative positions then it may well be noisy. The new pulley has no such wear variations and so is quieter.

Do a quick tooth count of belt and pulley to see if this is the case. If it is, then you will have to move the belt a tooth at a time to find its quiet position (you won't have to traverse the whole belt as the belt tooth number divided by the ratio will give the "repeating" range. You could examine it closely with an eye-glass to see if you can identify the matching teeth. Alternatively, fit a new belt, ideally one with a non-multiple number of teeth (if the centre-distance is adjustable) so that any further tooth wear will be evenly distributed.

Good luck

 

[coldkryten]

The tooth ratio is 55/109 so that should be fine, likewise the shafts are well aligned. I just cleaned the belt and pulleys, and the noise is present with a wide range of tensions, all they way down to just enough to keep the belt from slipping.

Perhaps it is related to change in the belt due to the new pulley. Could the worn belt teeth have been compressed a little by the unworn teeth in the new pulley, and now fit too loose in the old one, similar to BobM3's suggestion?

I'll try running it for a while and keep an eye on it. Anything I should watch for that might spell trouble?

Thanks for all your help,
Mike