The endstop switches used in the K8200 are sometimes triggered during a print when the frame is vibrating too much.
This happens mostly during zig-zag-filling of small perimeters and when using hexagonal infill with higher speeds.
It has the nasty side effect of misaligning all layers printed after the endstop is triggered, often ruining the print.
Basically, the X- and Y-motors are executing a movement command and are interrupted by the endstop triggering, cutting off the power supply to the motor since the printer thinks the end of the print bed is reached. So the remaining movement is not executed, but discarded, leaving the print head in a position a distance away from where it should be.
Sometimes this is only a small offset, but it can reach several millimeters or even centimeters when you're unlucky enough.
One cause is that the endstop switch is actually triggered by the actuator (the small metal tongue) which hits the switch with enough speed to 'click' it.
Another cause is that the connectors from the endstop switches to the controller board are sometimes loosing contact due to the vibrations. This happens when you unplug them too often and they start to wear out.
This problem is indicated by the appearance of log messages looking like this:
16:33:45.089 : echo:endstops hit: Y:0.17
16:48:45.045 : echo:endstops hit: X:0.04
Note: only messages generated during a print are a problem, obviously not the ones while homing the axes.
I heard there exists a patched firmware that ignores endstops during a print, but I don't like this idea. The endstops are there to prevent physical damage to the printer, so circumventing them is IMHO not so clever.
My solution for this problem is twofold:
1) Stop the endstops from firing due to vibrations. (see the pictures)
-You need two strips of soft, elastic material (like protective envelopes or a thin sponge), about 4cm x 1cm (2.5 inches x 0.4 inches).
-Fold a strip twice lengthwise so you get a thicker package about 1 cm square.
(you could also use a thicker elastic material and use it unfolded, of course)
-Punch a hole in the center through all 4 layers, diameter about 4 mm.
-Slide the package over the micro switch actuator (metal tongue), be careful that you do not slide it down in the wrong orientation, this could prematurely trigger or even block the switch.
-Do this for the X- and Y-endstop switches. The Z-endstop is not affected by this problem.
-After installing, check the functionality of the endstops. Do not use big movements towards the endstops before you made sure everything works as expected.
2) Ensure the connectors are not loosing contact to the controller board. You could carefully bend the connector pins to ensure better contact and tie the cables together to stop the vibrations from reaching the connectors. (see last two pictures)