Use z probe to update z height at single point

My corexy printer homes to Z Max and mechanically trams the build platform for the 2 ballscrews they move upon.

The platform them moves up and the printer uses a load cell touch sensor to touch with the nozzle on the bed with a G32 command and level.

Is it possible to probe with the z probe at a pre defined spot and temporarily update the Z location this way? I know G32 does this but I need to have the printer clean the hotend before a bed level probe. My hotends are hot swappable and not precisely the same height, thus moving to a set point from z max does not always work for my self cleaning function.

Any advice would be appreciated.


  • You mean something like G32 without having point 2 and 3 or a grid? You would still need to heat up/clean extruder for it to work. G29 would measure Z as average but I do not think it plays well with autoleveling, so I think the answer is no.
  • Hi, yes. Like G32 without having point 2 and 3 or a grid. The nozzle heats up depending on the filament sensed for the cleaning cycle. the head needs to touch a defined area to get a rough Z height. Then it proceeds to the dump/cleaning area and performs the nozzle cleaning. Only then it will perform the G32 for final height. 
  • As you home z max you have already a defined height from last G32 S2 +/- difference between nozzle. Is that more then expected inaccuracy when doing coarse measurement, which would be G32 without saving results? 
  • When ever the printer starts operation it assumes that the z stage has moved without the controller knowing and the position of the left and right ballscrew nut is unknown. When the steppers are powered down the z stage slowly falls to the max of the bed. The stage is heavy and ballscrews have very low friction. Thus, to make sure the z stage is trammed, I have 2 z max endstops to level the bed out at each ballscrew. It is only for that purpose and z max limit that I home to max, not to update z height. 

    Also, i may have swapped out the nozzle thus altering the z heigh of the printer (i have volcano, mk8 and custom style hotends for different nozzle sizes and materials)

    The system works very well, but I want to fully automate the system. Currently I have to manually clean the nozzle before a print to make sure G32 functions properly. 

    Alternatively, is there a way to change the homing direction on the fly, as my z probe is connected to my z min pin.

  • No, homing sequence is compiled in as these are different code parts. So on the fly it is not. Only always z min or always z max.
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