#3DPrinter Problems, #BambuLab
The print head of my #X1Carbon has recently started banging hard against the back wall (or rather, against the folded metal sheet at the back wall) 
.
Cleaning the carbon axles and recalibrating the printer didn't help in the search for the cause, nor did the internet.
Until the epiphany came 
I recently carried out a skew correction and, as recommended by Bambu Lab, inserted the measured values into the machine's G-code:
M1005 X150.05 Y149.65 ; Skew correction
M500 ; save the values permanently
The solution to the puzzle:
The X value is greater than the Y value for the entered skew correction., i.e. Y movements are corrected upwards - ergo the distance that the print head travels from the front left corner (reference) to the position near the filament cleaner (very close to the rear wall) increases -> leads to impacts against the wall / bended metal sheet because the print head wants to travel further than it can.
Changing the G-Code to
M1005 X150 Y150
M500
and the "head bang" problem was gone. 
No problem if the Y-value for skew correction is bigger than the X-value, but do not do a skew correction if X > Y !!!
Maybe it will help someone.
