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I paused my print to change out low filament, and upon resuming the extruder crashed into and dragged across the already printed material. The z axis was way too low. It appeared to be headed to the right spot, but I had to switch it off before it damaged the machine. I have seen other people experiencing this same problem, but nowhere is there an answer. I am hoping I have come to the right place!
There seems to be a rash of this type of problem. This is likely a F/W operation that has not been tuned very well. Have you tried contacting Creality (sorry if this is half the frustration)...
Easy way to test the issue (and document it) is to print a very low print and pause after one layer and see how it normally behaves. Then try 3 layers and see if the resume drops to layer 1 or if it continues where it left off. I am assuming you are using a built-in function to pause the print and not a g-code modification and that you are using sanctioned F/W from Creality.
Well apparently I am not one with magic fingers and light hands. If I move the z axis any while changing the filament it messes up. That makes sense I guess, but "when your extruder is attached to the moving gantry, it's almost guaranteed that touching it will lower it.... unless you have magic hands."
This is one of the reasons when changing form the original, 1.25mm X 8mm all-thread lead screw decided on a T8-2 lead screw.
The lead screws were turning simply because of vibrations, this would have been alright if they turned at the same rate.
But this was not the case they would turn at different rates making the Z-Axis off calibration every time I wanted to Print.
The T8-2 lead screw will not easily move when doing simple filament changes.
To Start I was having problems with the Z-Axis Dual Stepper motors, seemed they needed Z-Axis calibration every print.
The Lead screws on 2nd Printer were T8-8 Trapezoidal lead screws, doing some research discovered that they make several Trapezoidal lead screws. 2mm pitch, 4mm pitch an a 8mm pitch Trapezoidal lead screws. Started with a simple test of gravity shown in the video.
T8-8 Lead-screw Will Drop with Gravity
https://youtu.be/yFHEIdUf2Lw
This was when the decision was made to use the 2 mm pitch lead-screws shown below is a photo. The Lead-screw nuts are turned exactly one revolution.
Attachment 12836
I have not experienced the T8-2 dual stepper lead-screws being out of calibration, or changing positions during filaments changes.
This changed my Z-Axis from 400 steps per unit to 1600 steps per unit in Marlin's Configuration.h
#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 1600, 94.4962144 }
Hey rock, I'm also facing the same problem with my hp printer f4580 while sometimes it works perfectly then when I start printing some long article papers one by one then it starts this unimaginable errors and there's also a line in the side of the paper, I'm also searching out for this.
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