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gap between print head and bed after probing

paulndpaulnd
edited October 2016 in General
Hello,

I posted this on github but perhaps it has been missed as I didn't open a new issue, apologies for the double post.

Hello, I'm using the latest dev version but also experience this on a cartesian printer.

My steps are


  • Measure z probe height by measuring the distance between the head just
    touching the bed and the height at which the probe triggers and enter
    into dev configuration web page along with other parameters and settings

  • Clear eeprom by uploading a standard eeprom clear sketch

  • Upload configuration generated by the dev web page

  • Home xyz (Z is max at the top of the printer)

  • G30 S2 and the board is probed

However when I print, the print head is a few millimetres above the
bed and I have to manually adjust the max z height in eeprom until the
head is at the correct distance from the bed

Paul



Comments

  • RepetierRepetier
    Add error to z probe height and G30/G32 should correct the error.
  • shaissshaiss
    edited November 2016
    @Repetier, I'm having a similar issue and process to the original poster.  Can you clarify your response?  Possibly including the variable names we're supposed to change?

    "Probing height is our preferred height for measuring and MUST be positive (otherwise it makes no sense). z probe bed distance is distance to nozzle when it triggers. For inductive sensors always positive. " is that we should be adjusting  Z_PROBE_BED_DISTANCE and not Z_PROBE_HEIGHT.  I think this is where there is some confusion.  In my case, adjusting the zprobe height from 7mm-1mm did nothing to bring the nozzle closer to the bed.  Changing the z_probe_bed_distance from 10mm to 8mm seemed to bring the nozzle close enough to the bed to get resistance on the paper.

    @paulnd.  You don't have to upload a new empty sketch to clear the eeprom.  see https://www.repetier.com/documentation/repetier-firmware/rf-installation/ and search for The EEPROM trap.  I use this as my quasi version control and incrament it by 1 everytime i upload and add a comment on that line with the date and reason I changed it.

    @paulnd, could you also explain this a bit in more detail as I'm strurggling with this part and doing my best to guess and use my calipers when I can, but it's a best guess effort.  I'm curious how you're measuring and what measurements are you using for Z_PROBE_BED_DISTANCE and Z_PROBE_HEIGHT

    paulnd said:
    • Measure z probe height by measuring the distance between the head just touching the bed and the height at which the probe triggers and enter into dev configuration web page 
  • RepetierRepetier
    All I say is for 1.0dev version. Older versions may have small variances.

    Z_PROBE_BED_DISTANCE is starting height for measurements like bed probing. It is not supposed to have any influence on the result.
    Z_PROBE_HEIGHT and Z_PROBE_Z_OFFSET (bed coating in eeprom) are supposed to have an influence on the height for z=0. Assuming you have z max homing (otherwise everything gets complicated) you need to home and run G32 S2 to make changes take effect. This will correct z length, so homing + G0 Z0 has a different result.
  • paulndpaulnd
    could you also explain this a bit in more detail as I'm strurggling with this part and doing my best to guess and use my calipers when I can, but it's a best guess effort. I'm curious how you're measuring and what measurements are you using for Z_PROBE_BED_DISTANCE and Z_PROBE_HEIGHT

    I have an IR probe sensor and lower the print head until the probe triggers, note the position, lower the head further until it is paper thickness off the bed, note the position and the difference between the two is the probe height.

    Whilst adding the "error" to the probe height may work (I haven't been able to test it yet), I feel that this is a work around for a calculation error in the firmware and not a long term solution.
  • shaissshaiss
    @paulnd, I was using a similar guess method to you.  I think it needs to be more clearly defined or detailed in the FW or it's instructions.

    I had homing set to zmax, but for now gone back to manual leveling on my corexy as z is 400mm and it takes forever to home all the way to zmax.
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