Not printing at correct height from the Heatbed



  • Hi Guys,
    The Custom printer I built has No probe ( check previous posts ), everything is working, and i am trying to do some test prints and cannot get it going correctly, i will explain..
    When i calculated the limits for my z axis travel, i used the nozzle tip and a gauge of
    .15 mm thick to level the heatbed at 4 positions Since I have 4 screws . When I calibrated the Z, and remember my end switch is at bottom Like the ultimaker 2 , i raised the bed through Web interface until nozzle tip touched bed with Gauge thickness 0.15 mm sandwiched in between.
    I noted the value and used it for z limits in config, home z and home all .
    I use Cura and First layer height is 0.3mm , send the GCode to duet , but I have to use baby steps adjustments To start Extruding !!! It’s a pain ...
    Isn’t there a way just to send the GCode and it will print correctly at the correct height for the first layer???
    What am I missing here ? Am I doing something wrong ?? Any suggestions would be appreciated
    I read about z offset and calibration, but i have no probe.



  • This is the inherent problem with homing to Z max. You're setting the Z0 position based on something that is as far as possible from the actual nozzle tip.

    All is not lost though.

    You say you don't have a probe, but reprapfirmware has a clever way of letting you probe the bed even without any probing hardware. If you set the probe type to P0 it will allow you to use all of the probe based functionality like G30, G29, etc. And any time the probe hardware would be called into play, you are given a popup window with jog buttons that let you manually move the nozzle to touch the bed surface.

    So you may want to look into using that. At least to define the Z0 position.

    There are other ways to use a Z max endstop that make measuring the distance between the Z0 position and the Z max endstop trigger a little easier. For instance, I use a macro to automatically set the Z axis travel limit based on the distance of travel from Z0 to the trigger point. The firmware will automatically save the value to config-override.g and load it at boot time. This uses the G1 H3 function. https://duet3d.dozuki.com/Wiki/Gcode#Section_G0_G1_Move

    The macro looks something like this:

    G90 ; absolute positioning
    G1 X150 Y150 ; move nozzle to center of bed assuming X and Y are homed
    M558 P0 ; enables manual probing
    G31 X0 Y0 Z0.15 ; sets the offsets of the probe to be at the nozzle, plus 0.15mm for your gauge
    M561 ; clear any bed compensation
    G30 ; probe the bed to get Z0
    ; you will manually jog the nozzle to touch the bed using your gauge and when you hit OK the height will be set to 0.15 mm
    G1 Z400 H3 ; move the Z axis until the endstop is triggered and then set the M208 Z axis maxima to the height at trigger
    M500 ; save the M208 height to config-override.g. Make sure you have M501 at the end of config.g to load the saved value at power on.
    

    You can post your current config.g and homing files so we can see what's going on. Perhaps you have an offset adding in somewhere.


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