Z-Probing Instructions?

I am trying to set up my z-probe in accordance with this:

What is the Znew and Zold in this equation represent they are not mentioned int he instructions:

ZHnew = ZHold + Z0 + Znew - Zold - ref_height


  • I am just having a real hard time trying to get this autlevling feature to work with repetier. I've tried reading many sources, and nothing seems to be straight forward.

    I am totally confused about something, because I have calibrated the printer by taking probe points at the center and in a circle around my 300mm bed, and I am too the point that the probe points are within +/- .06mm. What I don't understand is even though the probe points are matching up, when I manually move the hot end from center to outside of the circle, it noticeable moves upward the farther I go to the outside of the diameter, like a bowl.

    how can this be if the probe using g30 p0 are giving me equal measured distances?
  • With delta printers very much is possible due to nonlinear behaviour. Especially to the outsides all errors get more and more prominent. Make sure distortion correction is disabled when measuring. Also check if z probe has set offset to effector center correctly. For calibration measure as far to the outside as you can. A bowl is normally an error between diagonal and horizontal length. If the ratio is wrong it gets either up or down when you leave the center. But this also happens when you build a height map with host for example. Another thing often happens is that it goes well until you cross the connection between 2 pillars. It's like a swing going up after crossing the line. Reasons are error in geometry deviating from optimal value like angles between pillars not 120° but only 119.7° or diagonals having a difference of 0.2mm in length. Some cause effector to rotate, others only to be not where expected. Therefore you can tweak the geometry in eeprom values to reduce these effects. Not easy but works. And as last resort you can add distortion correction to fix up/down for start height.
  • I will try and mess with that, any answer to the equation? What is Znew and Zold reperesenting?
  • Have adjusted naming in documentation:

    And note the z height as Zold. Next we adjust z until the metal block fits exactly below the nozzle. You will see that when you have a gap you can easily rotate the block. If you are too low, it will give a “clong” sound when you press bed down. This makes it much more exact then the typically used sheet of paper. Once you think you found exact level, send M114 again and note it a Znew.

    So what we now have is starting height as firmware would assume it from first probe Z0 using our initial Z_PROBE_HEIGHT (ZHold). We also know that we needed to go up Znew-Zold to reach ref_height. From this we can compute the exact real value required from Z_PROBE_HEIGHT (ZHnew):

    ZHnew = ZHold + Z0 + Znew - Zold - ref_height

  • Thanks that makes more sense now!

    I am suspicious of a problem with my Z-Prove, it is an inductive proximity sensor, which uses magnetic field. Buildtak Flexplate System which I have uses magnets to hold the bed down. Do you think this will mess up  the probe, and if so if a capacitive proximity sensor would work better
  • I'm no expert with z probe types. Have 2 mechanical probes and one inductive with fixed points.

    It should be simple to test it. Simple go from left to right and measure z starting at a low height. In center the field is stable and quite uniform so results should be similar. At the edges the field will change so if there is a influence you should see different Z values that indicate your bed is bending. If you draw x-z measured on a plot you will get a range that is linear and maybe some deviation at the end. Then you know where you can measure consistent and where results get wrong.
  • Magnets on the bed will deffinitly mess with inductive AND capacitive probes
  • What does ZHold represent in that equation?
  • Zold = ZHold
  • If you have LCD and current dev version there is now a function in setup to measure z probe height. Just put a block under extruder where you know the height, adjust z until in just touches and then set z in that fucntion to current real z. The probe will then trigger and measure the distance and set it for you.
  • Can anybody, please, make a picture of where does the above equation come from? 
  • Thank you. I read that dozens of times. But it does not work out.

    See how I do it and show me, please, where I understood your instructions wrong way.

    Prusa acrylic. No hardware Z-stops, neither min, nor max. Capacitive sensor is connected to Z-min pin with resistor, correctly reports L to M119 when not triggered and H when triggered.

    1/ Z-probe height in EEPROM is 0.6


    2/ QUOTE: “First we go close to the bed at a distance that the z-probe does not trigger and send a G30 P0”

    We start 10 mm above the bed and send G30 P0 and get

    < 23:37:19: Z-probe:9.67 X:100.82 Y:99.80

    We memorize z0=9.67

    3/ Now we heat up the nozzle, clean it and send M114:

    < 23:41:07: X:100.00 Y:100.01 Z:10.000 E:0.0000


    4/ The metal block we have has height of 21.9 mm

    ref_height = 21.9

    QUOTE: “Next we adjust z until the metal block fits exactly below the nozzle.. send M114 again and note it a Znew.”.

    So, we lift the nozzle up until it touches the block. M114

    < 23:47:08: X:100.00 Y:100.01 Z:21.900 E:0.0000


    5/ ZHnew = ZHold + Z0 + Znew - Zold - ref_height

    ZHnew = 0.6 + 9.67 + 21.9 -10 -21.9 = 0.27

    6/ We change in EEPROM Z-probe height from 0.6 to 0.27

    Here, just to know, we move the carriage down until sensor gets triggered. Then we move it lower with 0.1 mm steps. After 7 steps = 0.7 mm we feel the friction of paper sheet between bed and nozzle. This simple paper sheet test tells us that Z-probe height is 0.7 mm. We just note it for later.

    7/ sending G32

    Trying to print: filament is not smeared on the bed but lies on it without adhesion. The nozzle is definitely too high above the bed.

    8/ Changing the Z-probe height in EEPROM back to 0.6 and sending G32 and then printing: nice smear, adhesion and good print.

    I could live with calibration with paper sheet. But I like the Repetier Host and Firmware. And I like to understand it. And I like other people to understand it and work with it. Thank you for explanations on this and other questions as well.
  • The problem is M114 on step 4. If it is 21.9 just as block height that just means it is perfectly leveled. Meaning indicated Z is real Z. But in that case it should also measure 10mm in steps 2 for M114 = 10. And if that would be true you get again 0.6mm as z probe height.

    So why is first or second measurement 0.33mm off? The answer will show the source. Would it make a difference if you heat up from the beginning? Can not really imagine this making 0.33mm difference.

    One other reason could be z steps per mm being wrong. That would also add such an error. But that should be simple to measure measuring at 2 heights knowing what differecne it should have compared to what it has.
  • Thank you very much fuer Erkalaerung, ich gehe jetzt diese 0.33 mm suchen. :-) 
  • So, once we have this number which parameter does it get loaded into? 
  • It is for computing z probe height.
  • I i know that, but which eeprom parameter is it loaded into? You do not specify in your instructions where to put the info ZHnew. Quote:
    "Enter this value in eeprom and your measurements will be as precise as you can get it." 
  • I thought that was clear: "z-probe height" is the name in eeprom.
  • Nope, I reread it numerous and ask others to read it as well. And I work at university lol
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