What brand of ABS do you use?
Can you share all your profile settings please?
The most absurd thing is that since I opened the printer’s packaging, I have done about a dozen prints without any problems. We have verified that the firmware and software cannot be the cause of the issue, leaving only the profile settings or electro/mechanical wear.
So far I only bought bambu filaments and used the standard profile in studio.
Did you check if the friction felt constant moving the head along the rods? My printer is basically brand new and it still felt better after a clean. Wish I had felt how they feel just after a fail in case som thermal expansion has an effect
yes i check the friction may times, but without cleaning the carbon rods i print good with PLA or in ABS with door open, but now i have news…
My test with aux fan at 70% prints fine, as expected i get some warping form the side the air comes.
The cham temp stay for all the print at 49°, this means that is not a mechanical/electronic issue, I always fail my prints before with 43°.
I think the problem is related to the part cooling fan in conclusion, i do another test now and give you a feed.
Ok, I’m starting to go crazy. I set the aux fan back to 0 and enabled the part fan to 100%, as is done for PLA. The print failed again, right before my eyes.
As you can see from the attached images, the nozzle did NOT hit any protrusions on the object. Currently, this makes me think again of a mechanical issue and how the aux fan might be affecting the heating of certain parts like the carbon rods, the belt, or something on the stepper pulleys.
As you can clearly see, just before crashing, the infill layers started to misalign. This further confirms that, at that stage, the problem is generated by mechanical movements and not the other way around.
Now I am at a crossroads: either I start disassembling the entire printer until I find the problem, or I return it to Bambulab under warranty. I hate that flagship products like this have to use users as guinea pigs to solve problems. I spent entire nights fixing issues with my Creality printers, and now they work perfectly. I thought the price paid for an X1-C was mainly to avoid all of this.
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This is inline with what I though might be the case. It could be related to something in the upper part of the printer getting hotter with aux fan off as my measurement suggested, steppers or something mechanical getting sticky from thermal expansion.
I would suggest turning the printer of when the print fails and move the head around and see how it feels. Think I will do a test of just heating the chamber up and test.
Does anyone know if the pulleys on the steppers are only glued btw. Unfortunately the shaft end is coverd in glue, would have liked to marked that with a line to rule out any slipping.
Either press-fit and/or glue, no detectable screws as far as I can see
Test done and 99% sure this is the issue: Heated up the chamber to 59c at the top and then moved the head, it had very high friction at a portion. Have a video, just need to upload it somewhere.
Friction can be felt in the same spot when cold and cleaned with IPA but just slightly and not enough to cause any issue.
Video Link added:
https://youtu.be/HLHDBiI2Bn8
great test! @Mattias_Svensson 
you can upload as a private on youtube and share here the link
Link added to previous post
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Interesting. Mine rods also exhibit this same behavior when the chamber is heated, no matter how much I clean them. How does this explain the print being able to reach a certain amount of layers though? Friction eventually heating the rods up enough to the point where they expand so large that the head can no longer move smoothly without causing the motors to skip? Every time my print fails, it makes an awful noise along with it.
I initally thought the problem could be related to the MC board, so I replace its fan with a much larger one and mounted it directly over the heat sink, but that didnt change anything, so I think you might be onto something here. That, or there could be an issue with the belts / steppers
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mine do the same in the same location, i cant believe that carbon rods are altered at this temps, in my opinion is something on the belt circuit, i’ll disassemble the whole printer, I’m sure once the belt is unhooked all move smooth.
I look forward to hearing what both of you find. This could also explain why one person said they were able to complete a print as long as it was in the corner of the build plate. The central areas is where all the resistance seems to be located
i think resistance is upper right, and the issue comes in my opinion after a certain number of prints, remember that i print fine at least a dozine.
more realistic on what can be altered by temp on the rods path can be the holes of the hot end where the rods flows
When cold there is just a slight friction and the longer the chamber is heated the more friction will be created until there is so much the steppers skips steps or there is belt slip that could explain the horrible sound we have heard.
Carbon has no thermal expansion so I imagine it’s a case of rods out of spec and something around or in the bearings thermally expanding. I have seen a post here showing that they have changed bearings recently from bronze with grafite inserts to standard steel bearings with teflon coating. So that update might be the core issue.
What??? The bearings in the hotend are made in brass?? Really??
This is for sure an issue, how can Bambulab can think that brass dont expand near an hotend that can reach 300° next to a bed over 100°??
I point to change same bearings with graphite or better with hardened steel, have you a link of this?
he is saying the printers used to have brass bearings wtih graphite (and those printers can print enclosed just fine) compared to the new updated bearings being steel with teflon (which we are experiencing the failure with). That does sound like a big change and could explain why the new printers are failing. My machine that is failing was ordered on the last week of march and was delivered the first week of april