I have been chasing a recent problem with printing large models. In particular a large flat 2 color print 200x200x10 mm. I have printed this model over 12 times in the past without a mechanical problem. Lately when the layer gets above 55% [>5 mm] what was a near perfect layer [a few strings] becomes a field of Pine Trees and Valleys. This is my 3rd attempt and the same result.
Please note the previous layer is normal. [the one just below the damaged areas.]
I have printed this model several times in both PLA and PETG. But for the last 3 weeks or so I have not been able to complete a print. It requires about 7 hours to print on the X1C in PETG. While watching the printing at the 55% level it seemed to go well. Then as a I turned and walked away I heard a load grinding noise and felt the table that the printer is on shake. Unsure of the cause I looked for an outside cause and then the grinding sound reoccured and the table shook significantly enough to shake an empty box off the table. When I looked inside the near perfect print appeared as shown above.
Before you all start with “Wet Filament”, “Clean Plate”, and Maintenance issues, let me point out the filaments were all recently re-dried for 24 hours prior to use, the plates washed with only one small successful printing of a model 100x100x5 mm high, and just completed cleaning and oiling [Screws,Rods, lidar lenses, etc.] and calibrating. I also cannot do a time laps because it is not allowed under the LAN mode.
The only time I’ve had problems with large pieces was caused by warping. Are you using glue or a PEI plate? You can also try using a higher bed temperature and keep it there (not just the first layer). Also, are you leveling the bed with each print?
What infill pattern are you using? I’ve read many times that grid (due to the overlapping filament passes) can be high enough to snag the nozzle end.
This occurs with any size print where the height is more than 10 mm high, just before the Top most layer which is ironed. and mostly in the middle to front side of the plate. The print is not warped and is PETG filament.
But it is a grid which is the default pattern to a 100% Sparse infill.
It is on a PEI [look at image 770]and the X1 levels before every print…
" I’ve read many times that grid (due to the overlapping filament passes) "
Yes, but this is the default pattern for 100% infill and the strikes only occur at the top most levels. [ironing] I have observed the lower layers to be put down perfectly without a strike.
I have recently seen this nozzle strike occur with support structures causing them to break at various heights. You can hear the strike from [open door] across the room [10-15 feet.]
I found an interesting a secondary problem that maybe a contributing cause in my case. The Silicon boot on the nozzle is torn. [maybe from the repeated strikes.] That has led to a build up of filament under the boot, [especially with multi color prints and a thousand nozzle wipes], that eventually extrudes out near the tear thus allowing a secondary surface to grab the fresh laid filament. Eventually this does grow into a ball that destroys the print and wipes off the entire top surface.
Found the source of the problem, and it is the build plate. As I mentioned before only the top most layers >7mm of a 200x200 mm flat build seems to be effected. It did not matter what filament or slowing and heating of the plate. I even switched to a brand new Engineering plate to see if there was something I was missing with the PEI textured plate that I had been using. Again in the final minutes of the 6 hour print I noticed a movement at the edge of the plate. It was lifting off of the heat plate causing the print head to crash into the build. Thinking my old eyes were failing me I grabbed my iPhone and saw this…
Which resulted in this…
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Thank you for coming back and posting what you found. That’s definitely a problem. I wonder if there’s a home remedy though. 
Found a contributory factor. Lidar interference. Over exposure of light on the build plate. I use an old drafting table with the obligatory overhead adjustable light [florescent]. I use the light to enlighten the interior of the X1 so I can see the details of the printing process. Apparently that level of light compromises the reflectivity of the filament especially the black PETG [which has a series of issues lately!]
This was discovered after I purchased a new X1 C this month and tried to print the same models that all failed on the older X1 C [2022.] The New printer with the upgrade [1.7.02] has a new lidar or software that does a couple of things the older X1 C doesn’t. First, a more complete scan of the surface of the build plate before each print. Second, a more robust error checking capability. As I am writing this I have also found that a new update for the X1 C is available. Let me hope that these updates and improvements will lead to more joy in 3D printing.
I have bright LED strips at the top of my printer, and it has no effect on the Lidar. The Lidar unit creates its own shadow, so the reading process doesn’t seem to be affected. The auto calibration, even on the PEI plate now, seems to work fine. I just printed some Vari-Shore TPU the other day and even it worked on auto calibration. I got a Shore-A 59.5 out of it. I’ll accept that. 
This is the inside of my X1C. This isn’t the brightest setting either.
Thank you for sharing. How should we solve this?
There is a physics lesson here about light and it’s sources. The short answer is source and frequency. My 50 year old florescent light has a yellow cast to it and resonates on what ever frequency the gas is stimulated. Modern LED’s are typically whiter and resonate at a typically higher frequency. All frequencies have harmonic frequencies that can and do interfere with others. Since this is a reflective light that the lidar senses, the quality of the light and the reflective surface can and does in my case interfere as indicated by the system reported error. It is also important to note that the other colors of filament [all PETG] White, Red, and Blue do not seemed to be affected by my light. Thus there must be something inherent with the Black PETG that is contributing to the failures.
Recently, this month, I purchased another X1C and put on a fresh spool of Black PETG. With my old light off I am still getting poor quality prints.
You will note that only the Black has the tortured surface. Perhaps this is one of the reasons that this color of PETG is no longer being continued by Bambu?
My solution: 1. turn off the Old Light when printing. and 2. Find another source for black PETG. I will follow up.
