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Can anyone explain/diagnose this loud cracking/clicking sound?

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Ok, I would really appreciate it if anyone could explain this loud, sharp cracking/clicking/popping sound happening in my UM when the hot end moves over certain positions. It definitely seems to be coming from the left rear of the machine, at the top where the belts and horizontal rods meet. For the life of me, I cannot figure it out! Here is video of the problem:

Clicking Video (for some reason I could not view it through the forums, so I have also posted a link here: https://www.dropbox.com/s/h2sikp22abveol7/Clicking%20Video.mp4 )


Originally, I was having the the rod banging sound described here (http://umforum.ultimaker.com/index.php?/topic/330-lubrication/?hl=lube&do=findComment&comment=15910

), where the the horizontal rods needed lubrication, and certain moves would bang the end of the rod against the frame of the Ultimaker. A little sewing machine oil fixed that right up. But I have no idea what could be causing this very sharp (louder) banging noise! It sounds like something is popping in and then out, like the sounds compliment one another.

I am worried that something is wearing improperly, or otherwise abrading. I have really no clue here, and it has caused me to drastically limit the use of my machine. I've attempted to tighten any loose bolts, but nothing seems loose, and nothing changes the sound. Any tips would be much appreciated!


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You don't really show the short belt in that corner much. Is it running smoothly - not getting twisted, or catching on the frame? Take a look at the outside of the motor pulley where it sticks through the frame. Any sign of anything odd happening there? can you feel any clicking on the motor or the pulley, or otherwise narrow it down.

You might try loosening the short belts, and see if that changes anything. Perhaps there bearings in the motor or pulley are wearing? Also, try printing a large square, so the movements are more uniform, and see if you can tie the problem down to the head being in specific positions. With it moving erratically as shown in the video, it's hard to tell if its position specific.


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I'm not sure what this is but people have described a similar sound caused when the belt rides up onto the pulley edge and then snaps back into the grooves. I'm 90% sure that's not happening with the 2 long belts in that corner so that would leave the short belt.

One fixes this by making the 2 pulleys lined up and perpendicular to the stepper axis.

Or it could be something totally different. ARe you sure it's not the exturder? Remove the extruder from the back of the UM while printing - if nothing else this will make everything quieter so you can hear the noise better.


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Okkkk, the sound I was experiencing was, as suggested above by several people, a result of the shot belts riding up onto the pulley edge, before snapping back into the grooves. I could never confirm this visually, but the belt was clearly far closer to the edge of the stepper grooves than it should've been.

I tried to "realign" the belts by working them over to the center of the rod surface, but they kept being "pulled" towards the pulley edge again, causing the sound to resume.

The ultimate solution was to try loosening the short belts. I loosened the screws on the motor, moved it up maybe 1-2 mm, and re-tightened the screws, and voila, no sound, and no change to precision of printing (that I can tell). I think there was just too much tension in the short belts, and possibly slightly mis-aligned belts (though right now they still look as though they are moved a little off to one side, but there is no change in print quality or sound).

Thanks for all the suggestions.


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Took me some time to tackle this one too!

MostlyAtomicBob's comment about the short belts got me into the right direction.

I upgraded my belts to 200-2gt with new pulley's.

Now it seems that the plastic spacers are to short.

They are now almost 11mm long, but need at least 12 or even better 13mm.

Going for some new spacers when the shops are open!

They are available in different lengths, increasing by 1mm.



Edit: I bought some M3 25mm bolts and a 15mm spacer.

No more annoying sounds or jerky movements...sliding is very smooth now :wink:


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I had this problem pop as well. It went away when I switched to gt2 belts.

My theory is that the original belts had gotten slightly stretched out, so they weren't in perfect alignment with the grooves. I think it is part of the problem of having a belt/sprocket with a square tooth profile. Never figured out why it always happened at the exact same position along the belt.

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