Another broken belt

Broke another belt but i guess its my fault

here is the fraying talking about

here is my pulley alignment

and lastly here is my belt tension. as you can see i can fit a finger under the belt

…good luck. It is frustrating.

Your first pic looks like you are showing a broken belt on the X, then you show the alignment on Y.

That is correct. Also fraying on the y belt

Unfortunately, I’ve never seen a belt fray/break unless the belt is too tight, or the pulleys are not aligned.

Did you check to make sure that the carriages move easily, and you are not making overly-aggressive cuts? Are there any signs of belt teeth being ground off?

Man, that is weird! Mine don’t show any sign at all of that kind of wear.

If im doing or have done something wrong id like to know. Ive tightened the belts as per the instructions and as you see the pulley alignment seems ok. The gantry and x carriage moves easily as far as i can tell. I have nothing to compare it to. Im just concerned the belt is defective

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Looking at your photo (here is my pulley alignment) the belt looks to not be tracking in the center of the smooth idlers and is rubbing on the flanges of the idlers. If the belt rides up on the flange then belt tension goes high and could be one cause of breaking.

Not being there to see the machine in person and relying on photos it is hard to trouble shoot your problem so the above are just some thoughts.

I hope you can work out what the problem is and solve it so you can do the work you bought your machine for.


I think i see what you are talking about. If i remember right those pulleys arent adjustable. Ill have to double check the instructions

You should be able to reset the drive pulley just a mm closer to the stepper motor and the belt should track better on the smooth idlers.


Maybe that’s it.

Do the flat idlers have lead-in’s, or are the “flanges” at 90°?

Just picked up a smooth idler and it has straight sides with the flange corners just chamfered a little. Sharp enough that if the belt were rubbing it could cause the problem.


in the picture of the pulley alignment, it looks like the Left screw is hitting the idler?

Jamie I looked at the assembly drawings and I think it is just the angle of the photo.


yeah just the angle

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If the belt is breaking, that indicates that your tension is way too high. It takes a lot to break those kevlar fibers. When you pluck the belt, it should make a tone like a low bass note, not a guitar string. Hope that helps.

Belts supplied by inventables have fiberglass reinforcement not kevlar.


has nothing to do with this post, but where I can get kevlar reinforced plastic? mesh?..