Hello everyone.

I designed and built a Corexy printer and its nearly complete. I have it all belted up and noticed some belt movement that has the belt teeth rubbing the pulley guides when I move the gantry or extruder carriage assembly by hand. I spent a lot of time to make sure that the belt system was aligned/ leveled so this is a bit disturbing to me.

I uploaded a video of what's happening. It appears that it's happening only with the rear pulleys. The belts for each side move away from each other when I move the gantry in one direction and then move towards each other when i move the gantry in the other direction. The same thing happens when I move the extruder carriage. It basically happens when the belts are moved. I dont understand this.

[youtu.be]

I see two possibilities- if the pulleys' axle is not vertical the belt teeth will hit the pulley teeth at an angle. Do the parts of the mechanism flex under belt tension? Or maybe this pulley is vertically offset from the pulley it connects to via the belt. That would cause the belt to ride the flanges and have the angled tooth strike.

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

I dont think the pulley axles are not verticaly true. If anything maybe the pulleys at the end of the gantry have an offset. I'll check it again but I'm nearly certain all the pulleys are leveled. I have missed things before, maybe there's something else I'm missing.

So I have a theory. I'll post pics later when I get home fron work. The z axis of the machine has a lead screw in each corner. I think that maybe each corner might be slightly offset from each other. I have to make sure the z axis is tuned.

Fixed the noise by tapering the pulleys. Works amazing well.

[youtu.be]

What does "tapering" the pulleys mean?

The zippy noise comes from belt teeth hitting pulleys. If you twist the belt so the smooth back sides of the belts touche the pulleys, most of the noise will go away- the remainder will be from the drive pulleys.

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

Glad to hear your problem is fixed. But the way your pulleys are stacked it is impossible that the beltpath are perpendicular.

I'll second what gforce1 said. Your belt paths are not straight. You'll have varying tension through the travel.