Heating bed for probing & postition before printing



  • Hi
    I am having some issues with mesh bed probing…
    I have tried to make my homeall.g file to mesh probe the bed before I start a print, and I want the bed to heat up and wait some time before probing but now the probing starts and it doesnt heat up until the probing is finished. How should my code look for that to work? (The mesh leveling is at the end of the file)

    [c]; homeall file for use with dc42 Duet firmware on CoreXY printers
    ; This file assumes the endstop switches are at the low end of each axis.
    ; Reverse the X and Y movement for high-end switches.
    ; Adjust the bed upper and lower limits in config.g (M208 commands) to get the correct homing positions

    G91 ; relative mode
    G1 Z3 F200
    G1 S1 X-360 Y-380 F3000 ; course home X or Y
    G1 S1 X-360 ; course home X
    G1 S1 Y-380 ; course home Y
    G1 X4 Y4 F600 ; move away from the endstops
    G1 S1 X-10 ; fine home X
    G1 S1 Y-10 ; fine home Y

    ; If you are using a microswitch for Z homing, insert similar code for the Z axis here,
    ; but use lower feed rates suitable for your Z axis.

    G90 ; back to absolute mode

    ; The following code assumes you are using a Z probe to do Z homing. Remove it if you are using a microswitch.
    ; Adjust the XY coordinates in the following to place the Z probe over a suitable spot,
    ; preferably near the centre of the bed if your Z probe supports that

    G1 X180 Y190 F5000
    G30
    G1 Z4
    G1 X0 Y0 F5000
    ; This file leaves the head at the zprobe trigger height so that you can slip a piece of paper under it and then do G0 Z0 to check the height.
    ; If you prefer to send the printer to X0Y0Z0, un-comment the following lines
    ;G1 X0 Y0 F5000
    ;G1 Z3

    ;Mesh bed leveling

    M140 S55 ; heating the bed
    M557 X20:380 Y00:300 S70 ; at specified coordinates
    G29 ; probing the bed
    [/c]

    When the probing is done the hot end is at (about) X330 Y340, can I start the printing from there and the printer will start printing where the object was placed in the slicer (S3D)? or will it use some other position (have been to afraid to test…) And is the printer going to use the heightmap or do I have to tell somewhere that it should load the heightmap?
    Any hints would be great!


  • administrators

    As long as the printer has been homed first, the print will start from the position that the slicer determines, regardless of where the head is when you tell it to print.

    To wait for the the heaters to reach the commanded temperatures before continuing, use the M116 command.

    After G29 completes successfully, the height map is used automatically.

    If you want to test things out before starting a real print, you can temporarily reduce the motor currents using the M906 or M913 command, so that less damage will be done if things go wrong.



  • Hi David
    And thanks for reply!
    I did a test and the position was of the wall, it went back to a -position and started printing some strange thing so I was forced to stop it, maybe something wrong in S3D also…
    So, the lines above are good? or do I have to home it again after G29?
    The fact that the heating of the bed now starts after G29 is finished, is it because its not waiting for the heating of the bed?
    How would the code look?
    M140 S55
    M116 P0
    M557 X20:380 Y00:300 ....
    G29
    Is there a way to delay the waiting time so the thick aluminium-plate evens out in temp?


  • administrators

    Yes that code looks good. You can use the G4 command to insert a delay.



  • Ref the thick aluminium plate and thermal inertia. I had the same problem in that the temperature sensor was between the silicone heater and the bottom of the plate so it was controlling the heater based on the temperature of the underside of the plate and not the top. When I started the bed heating, it took a very long time for the heat to get through to the top of the plate - especially as the thermistor kept switching the heater off because the underside/heater junction was up to temperature long before the upper side. My solution was to drill a 3 or 4mm diameter hole in the edge of the plate, as deep as the drill bit would allow (about 50 or 60mm) and as close to the top edges as possible without it breaking through (takes a care and patience to achieve). Then I inserted the temperature sensor in there so the reading is much more representative of the actual upper surface temperature.



  • Ahhh, I think I should have the reprapwiki g-codes printed out and read as bedtime-book, but you are amazing and I can´t thank you enough for all the help you are putting in here!!!
    So it should look like this?:
    M140 S55
    M116 P0
    G4 S120
    M557 X…....
    G29
    Just so I get this right...
    (And probably there is more questions coming..) Have a good saturday evening!



  • @deckingman
    Yeah I know! And thank you, I also did mill a slot (for the cable) and a hole for the thermistor and cemented it down with heat-conducting silicone first before I added the silicone heater. I think it works great and with a 230v silicone heater it heats up fast but it needs some time to get all the way out to the edges.


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