Spent all weekend assembling this Core One. It probably took 14 hours in total. 12 hours to build and 2 hours to troubleshoot issues. Broke some parts made some mistakes but I finished the build.
this post was submitted on 11 Nov 2025
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I broke one of the tension adjustment pulley thing. I loosened the belts to calibrate the y axis. When I was tightening the tension belt I absentmindedly tightened the bolt all the way and then some which broke something. Not sure what but turning that bolt now no longer moves the tension belt pulley. I can see the screw spinning so it's not a stripped screw.
I'm going to look into what actually broke in a few days. Kind of exhausted from assembling the thing. As a result of this the top belt is a bit tight (its like 105HZ) but the prints come out ok-ish so I'm not in a rush to fix it.
Obviously, your next print is a replacement tension adjustment pulley thing, as is tradition.
I have some PETG filament on the way which is another reason why I haven't looked at the issue yet. All I have is PLA at the moment.
I don't know how critical this part is but if it sees any kind of load, re-pint in abs/ASA or better. Petg and PLA creep under consent load.
And look into brick layers for extra durability.
It's pretty critical. It holds one of the pulleys that the belt is attached to. The belt moves the print head in the x/y axis. I actually did print the part in PETG. Hopefully it just works and I won't have to touch it for a year :D
You will definitely want to reprint it in something else while the printer is working. Otherwise you're going to see dimensional accuracy issues crop up over time that require you to keep adjusting the belts.
I can't really print it in a better material until I get ventilation figured out which might not be until spring of next year. I did order some parts from Prusa in case the part I printed fails so worst case I have to swap it out but so far it works very well :D
Gotta give it to them for making the machine so repairable. Even if the design here is a bit questionable.
On the chance that it helps you at all, I broke the same part.
For some reason Prusa loves using those slim squarenuts that tend to bind up due to how few threads they have. Chances are the nut in the pully bound up and stripped out the plastic so now it's just spinning with the bolt.
There's a few community made models on printables that replace the nut with threaded inserts. The part should be printed in pc-cf however, and that's frequently out of stock it seems.
Ah I see. I'm guessing I need a hardened nozzle since it's CF. :/
A hardened nozzle for sure.
You got this repair, you built this thing remember? You are the master of your printer.
I think I'm just going to buy the part from Prusa.
Actually ended up printing the part with PETG. It worked and the issue is fixed (for now). Removing the broken part was a huge pain. I ended up using a drill and just drilling around where the nut is until I could fit tweezers onto the nut then I used the tweezers to keep the nut from moving and a screwdriver to loosen the nut until the part came out. All-in-all it was pretty time consuming and annoying. Hope I won't have to do that again for a while.