Z Probe Height

If I'm using a proximity sensor as my Z-probe and it is mounted above the extruder, does that mean that my Z Probe Height will be a negative number?


  • No, that only means you can probe without using a servo to activate probe.

    Z-Probe height is distance nozzle to bed when probe triggers. That should be before you hit the bed and thus is a positive value.
  • Okay got it.
    Then what is Max_Z_Probe to Bed Dist.?
  • That is the maximum distance of z probe to bed. If you enable z probe and z is higher it will enforce your height to be that + z probe height. I have set it to 10 and start probing at levels of8 or so which is save enough to not hit anything.
  • Hello,

    In my printer, the 2 hotend lift over the probe.

    The z probe height can be negative?

  • Negative values are only possible if extruder presses the bed for probing. In all other cases it must be positive otherwise your nozzle would need to go through bed to trigger nozzle.

    Important is the distance when probe triggers not the physical distance. So if you have a inductive sensor this is above nozzle height but triggers before nozzle hits bed so you still have a positive distance for trigger-nozzle distance.
  • on my machine I have 3 positions

    Position 1: Extruder 1 is 8mm lower than Extruder 2
    Position 2 Extruder 1 is 8mm upper Extruder 2
    Position 3 Extruder 1 and 2 are at the same level, and probe lower the extruders

    distance between probe un position 3 and nozzle in position 1 is around -2mm (need move up the printer)
  • What type of probe ? what is its triggering range
  • Position 3 makes no sense.

    Define extruder 1 active = z = 0 regarding z offsets. Then z probe height is trigger height for extruder 1 active. Set z offset for extruder 2 so that it matches the reference height from extruder 1. Height when inactive is not important.
  • If the Z probe height is the "distance between the nozzle tip and bed
    at the time the z probe switches to high" and I know the Z probe offset (the distance in mm between the Z probe and the Hot End, measured along the Z axis, basically up and down)  couldn't I run A G30 and get the position that the Z probe gets triggered and then subtract the Z probe offset and get the height of the hot end when the Z probe gets triggered?
  • G30 includes the z probe height already in output. But G30 with known height is a way to correct a wrong value. That is exactly how the menu correction in 1.0 works. There you run from known height and firmware computes the corrected value.

  • Okay, how about running G29 for Average height then subtracting Z probe Z offset to get Z probe height?

  • G29 only works for leveled bed or you will have only a average height but not real value.

    Easy solution is run G32, check error correct and G32 again until you are satisfied. That is what you thought about G29 just working as rotation is also considered this way.
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