Height Map Z Values



  • Hi,

    The values for Z that can be displayed at each point on a height map: what are they referenced to?

    I keep getting messages about too much offset even though all points have close to the same Z value.

    I don't know what to do to fix this.

    Thanks.

    Frederick


  • administrators

    They are referenced to where the printer thought Z=0 was prior to running G29 to probe the mesh. That will normally be the Z=0 position set by Z homing.

    To avoid getting an offset, it's best to home Z by doing a single G30 probe at the centre of the bed; or if the printer is a delta, do one cycle of auto calibration between homing and running G29 S1.



  • @dc42 said in Height Map Z Values:

    They are referenced to where the printer thought Z=0 was prior to running G29 to probe the mesh. That will normally be the Z=0 position set by Z homing.

    To avoid getting an offset, it's best to home Z by doing a single G30 probe at the centre of the bed; or if the printer is a delta, do one cycle of auto calibration between homing and running G29 S1.

    I am using G30 to probe the center of the bed as part of the macro that probes the grid using G29.

    Below is the essence of what I am doing:

    M307 H7 A-1 C-1 D-1
    M558 P9 H5 F300 T12000 A5 S0.01 R0.2
    G31 X0 Y24.5 Z1.400 P25
    M280 P7 S160
    G29 S2
    M290 R0 S0
    G90
    G1 Z5 F240
    G1 X0 Y-20 F6000
    G30
    G1 Z5 F240
    M208 Y-115:100
    M557 X-140:140 Y-90:90 P2:2
    G29
    G29 S3 P"heightmap_FAST.csv"
    M208 X-150:150 Y-100:100
    G29 S2
    M290 R0 S0
    G1 Z5 240
    G1 X0 Y0 F6000

    There are some commands that may not be needed but I don't think they cause any problems.

    Is there anyway to post formatted gcode so tabs (or spaces) are preserved?

    Thanks.

    Frederick



  • Well after thinking about it for awhile I realized that I could do a nine point grid which will reveal what the Z value for the center of the bed was.

    It appears that I have some sort of mechanical problem.

    MF1 9 point height map.png

    The structural member that the X axis linear guides are mounted on is a 40 x 20 extrusion. Given the hot end assembly doesn't weigh all that much I would be surprised if it was a sagging issue but maybe that is the case.

    Checking with a precision straight edge doesn't reveal anything.

    More thinking to be done.

    Thanks.

    Frederick


  • administrators

    @fcwilt said in Height Map Z Values:

    Given the hot end assembly doesn't weigh all that much I would be surprised if it was a sagging issue but maybe that is the case.

    If the X axis was sagging then you would get an apparent rise in the centre of the height map, not a dip.



  • @dc42 said in Height Map Z Values:

    @fcwilt said in Height Map Z Values:

    Given the hot end assembly doesn't weigh all that much I would be surprised if it was a sagging issue but maybe that is the case.

    If the X axis was sagging then you would get an apparent rise in the centre of the height map, not a dip.

    Right, of course, typing before thinking.

    Thanks.

    Frederick


  • Moderator

    @fcwilt said in Height Map Z Values:

    Is there anyway to post formatted gcode so tabs (or spaces) are preserved?

    Yes, use the ``` characters to denote a code block, and another set at the end to close it.



  • @Phaedrux said in Height Map Z Values:

    Yes, use the ``` characters to denote a code block, and another set at the end to close it.

    Thanks much.

    Frederick


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