Tension pulley broken
Tensioner wearing off after short period of time.
https://help.prusa3d.com/guide/5-corexy-assembly_835522#845225
Both pulleys broke the same way, however it needs noting that I was able to fix it by replacing the faulty elements (which was quicker than sending printer back and forth to Prusa service center). I do not know if it was caused by a a piece of dirt or something but it locked the screw in place and thus made nut chew through the printed element. Perhaps it needs more solid fill around where the nut is being inserted, i dont know. Just posting for awareness...
BTW Getting the pulley out with locked screw is not easy, if you try tilting it to hard against the belt tensioner it will crack.
RE: Tension pulley broken
What about some pictures of the failed part?
RE: Tension pulley broken
Hard to imagine how this happened. Pictures of the faulty part?
How did you replace them and with what?
RE: Tension pulley broken
Unfortunately i did not make pictures other than ones i posted to the support way back when the printer was still assembled and wasnt working:
https://www.icloud.com/photos/#/icloudlinks/0bd0oncyV2uk1c61D0rBeqVEw/0/
It was in fact one of the support engineers who suggested nut may be spinning inside the printed part hence i was not able to modify the belt tension level
I replaced it with these and it is now working like a charm:
https://www.prusa3d.com/pl/produkt/belt-tensioner-pulley/
RE: Tension pulley broken
Mine broke this way too (on my kit) ordered two replacements and am trying to think of ways to make it more robust
RE: Tension pulley broken
Hi there...
...mine broke the same way too... I reused the broken Belt-tensioner-pulley and i melted a thread insert in the tensioner pulley...
Now its fixed and is working perfectly...
RE: Tension pulley broken
mine broke when squaring the gantry up. The part could probably be printed stronger. To avoid this, just make sure that you loosen the belts completely to square the gantry up or the belts will pull as your are squaring it up, breaking the pully holder in half. Belts do not need to be tight to square the gantry up.
RE: Tension pulley broken
Fun fact: I'm going to have to replace it again — and of course, it's the left pulley again. The nut started spinning inside the plastic mount… unbelievable. I'm still having fun with the printer nonetheless, but some components could really use a bit more strength.
RE: Tension pulley broken
How did you properly center the threaded insert? I was thinking of using some JB weld or similar to try to bind the square nut to the tensioner
RE: Tension pulley broken
What procedure are you using to square up the gantry? I chose hard mode for my first real printer (build)
RE: Tension pulley broken
Good to know.
I start assembling this weekend. Maybe it`s a good idea to "grease" the printed parts with some graphite and lubricate the bolt and nut with some grease too?
RE: Tension pulley broken
I called support and they recommended the following:
loosen both belts completely, as if you were to replace the pulley.
At this point, I put a 1x1 square piece of wood on the side that touches the frame first, then, I pull with my hand on the side that is away from the frame to get it square. Remove the piece of wood, and confirm that it is square by sliding the gantry to the front. If it is not square I just repeat the process. Once it is square, I retune the belts using the app.
RE: Tension pulley broken
I finished my core. I found that a few of the square nut are not ok. The screw jammed. So check before installing.
i also put graphite powder on both parts and put some grease on the screw.
Belttensioning is very easy this way and if loosening the stew 1/4 turn the frequency goes down immediately.
RE:
Mine also broke when I was loosening the tension... and what made this even more annoying was it happened when I was building the printer from the kit that took 10 weeks to be dispatched. I hadn't even turned the printer on!
TL;DR
I have fixed the broken ones and potentially "improved" them.
Why They Broke
To work out what was going on I cut the bolt head off with a dremel and then cut the thin wall away to expose the nut. I found that both nuts had both cross threaded within a few mm of the bolt ends.
This made sense as to why they broke whilst loosening as there is a lot more flex when loose, and the pully wheel housing gets twisted by the belt. Keep in mind that they had been fine up until I loosened them
The Fix
To fix, I simply used two 10mm long brass inserts that I pressed into place with a hot soldering iron. These partially span the gap where the square nut was (so the thread starts at the same point), but they also give a longer thread (10mm) and hopefully prevent any future cross threading. They do poke slightly through to the curved surface near the belt/wheel, but do clear it by a around 5mm.
I already had the inserts and spare bolts, but the fix took around 30 mins and I was taking my time.
EDIT: Sounds similar to what @goebel-jens has done.
Unfortunately, I didn't take any photos as I wasn't really sure if I had got the inserts straight enough for it to work, but they are working perfectly. If anyone is interested I will add photos when I do some maintenance.