Z axis end stop switch

Z axis end stop switch
	Chapter 6. K8200 or Reprap 3drag

A reliable and precise z axis end stop switch is very important since it determines the quality of the first layer.

Note

When printing with layer thicknesses of 0.2mm or even 0.1mm then it is obvious that the precision of the z-axis switch must be significantly better than this. One turn of the M3 adjustment screw gives 0.5mm. 0.05mm are 36° rotation of the screw.

Also the bed might be not 100% horizontal (when having a glass plate it can at least be assumed that it is flat. With a PCB this is not the case). It is therefore a common habit the print the first layer thicker to equalize those tolerances.

The original Z axis stop switch assembly works but it is far away to be adjustment friendly.

Therefore it is worth to modify it to:

No need to go with a screwdriver between switch and adjustment screw to adjust.
No counter nut to fasten it and having therefore a potential to turn the adjustment screw again.
Adjust y-axis of the adjustment screw to touch the switch lever in the center
Having a simple way to electrically check that the switch has been activated. A simple plug that allows to connect a ohm meter is a way. Using the 3rd pin on the connector and adding a LED would be an other option. However an LED light up the controller board must be prepared to deliver a voltage. The controller is prepared for that but unfortunately it is not clear how to do it.

Figure 6.3. z axis switch improvement

Having an improved Z axis stop switch the adjustment gets easy:

Put the adjustment screw in the upper most position so it does not engage
By hand turn the cleaned extruder down to the bed and use a feeler gauge to have it 0.1 mm above the bed
Make sure that the switch can be electrically observed. Either disconnect it from the controller board and add an Ohm meter or other means as when having added an LED.
Engage the switch by hand to be sure it works.
Turn the adjustment screw down until you hear a click and you see that it has electrically switched.
Lock the adjustment screw
Move the Z axis up and then use the controller board to go the auto home
Make that the motors are not powered (e.g. a simple reset to the controller board) then move the bet by hand to the center and check with the feeler gauge that the distance is again 0.1mm. If not loop this instruction list until it is so.

The ultimate test is start printing and at the first layer interrupt it (as pressing reset) then check the distance with a feeler gauge and compare with what the printer thinks.