Bed (z-axis) needs re-level after EVERY print... any fix yet? ... RC6 firmware

Discussion in 'BigBox General Chat' started by Steven, Jul 31, 2016.

  1. Steven

    Steven Well-Known Member

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    This is getting annoying... Even after a 60layer print I need to re-level the bed because when the bed rises after the previous print, it's NOT where the head thinks it is... it about 1-2mm higher... and my nozzle will carve a ditch into the painters tape.

    Even after storing the memory, not shutting down, not rebooting, it is out of calibration when it rises after the print.

    Any fix yet?
     
    Paul Begley likes this.
  2. TimV

    TimV Well-Known Member

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    I fixed my similar issue by 'Restore Failsafe' 1st, reboot, Auto home, level bed.
    It did not only fix this, but also the Move 295 Z axis bump issue I had
     
  3. Steven

    Steven Well-Known Member

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    Not for me. Many others have this issue too. It's a real pain to have to re-level the bed even after killing a print. The upward turn of the Z-Axis is overshooting its mark or turning more revs than the downward motion. Can someone please look at this?
     
  4. Paul Begley

    Paul Begley Well-Known Member

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    I have similar but may be the opposite.
    This has happened a number of times and I was beginning to think I was going mad.
    After spending some time, going through the steps of levelling, positioning the IR sensor and then mesh bed level, on autohoming the head would be a about 0.1mm above the bed (30,30,0) and produce ok results. (Not perfect but I'm still playing).
    Then next day when auto-homing, it would be a few mm above the build plate, and print nothing.

    After going through the above bed levelling steps, things would improve

    Really annoying, should not have to reperform a bed level every day.
     
  5. Stian Indal Haugseth

    Stian Indal Haugseth Well-Known Member

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    Do you actually have to relevel or is it just the distance to bed that is differen?

    I had this on glass bed with glue on. I fixed this by heavy babystepping when doing a rim. Now after I got a red
     
  6. Steven

    Steven Well-Known Member

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    it needs a full re-level. The distance off on the Z- rise to too great.
     
  7. Stian Indal Haugseth

    Stian Indal Haugseth Well-Known Member

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    So you do not really need to re level? If you could adjust z offset enough that would do?

    I'm just trying to figure out if it is a variance in the z probe at homing or the controller forgets the level values?
     
  8. Steven

    Steven Well-Known Member

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    It seem the values stored in memory are ignored or not read.
    Or
    the e-steps for upward screwrod turns are not the same for downward turns.
    Or
    The end-stop value is wrong or miscalculated on the upward screwrod turns when it meets the nozzle.

    Even a small 60 layer print will make the upward turn be off from the original.

    scenario:
    start a small 60 layer print.
    It finishes.
    clear the print bed of the finished item.
    go to reprint the same part...
    After autolevel, the nozzle will dig a ditch into the painters tape (at least 1mm lower than previous Z bed point).
     
  9. Dr Jeep

    Dr Jeep Well-Known Member

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    I'd say test the mechanics before everything else, using 0.1 stepping on z find the switch on point for the led on the IR probe and measure the nozzle gap.

    Now move to z + 300 and back again a few times, is the switching point and the nozzle gap the same ? Or wildly out ?

    One potential cause would be miss stepping due to a tight spot on the z axis as that will move the absolute position of z home
     
  10. Stian Indal Haugseth

    Stian Indal Haugseth Well-Known Member

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    Like @Dr Jeep says. Test for inconsistent IR / Z-probe. There has been some reports about this.

    The IR can be sensitive to light changes and glue residue on the print surface. I had problems with this. Add a bit of silver tape where the IR does it's homing. Or something that should reflect IR light consistently.
     
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  11. Stian Indal Haugseth

    Stian Indal Haugseth Well-Known Member

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    I just swapped aluminium beds where they both are the exact same thickness, same surface finish and cleaned with acetone. Now the IR think it is 1,5mm closer and I'm printing in air. Looking forward to test a inductive z probe .
     
  12. mike01hu

    mike01hu Well-Known Member

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    Did you try the aluminium reflective tape that you suggested?
     
  13. gonzalo

    gonzalo Well-Known Member

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    I moved the IR sensor to the bed with Gregs mod and attached a white paper sticker under the acrylic of the BB frame where the IR looks at to give the IR a nice opaque surface to work against. Re did the calibration with the piece of gt belt to make sure the operating distance of the IR probe is within range and voila! No more issues, I did 8 maybe 10 prints with no visible variation in Z height.
     
  14. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    I've had similar issues with z-axis offset changing. I've taken to running autohome before each print. I was finding that I would sometimes have the nozzle dragging across the glass at start if I didn't or sometimes if the IR reading changed.

    To get around this (to a point) I heat the bed and apply the UHU gluestick before autohoming, this should give consistent conditions but as Stian suggested, lighting conditions probably also change the IR reading. I've also taken to applying glue to the area read during bed levelling, hopefully this keeps the reading fairly consistent. Is there a way to read the values for the bed levelling? I'm just interested to see how level it is.

    It does sound like having the IR sensor read off the frame may allow better consistency by having a better target but how can you level the bed? Is it possible to manually measure the offsets and input them?

    Myself, I've got no problem running a bed level and autohome before each print, it only takes seconds but if the values change then we have an odd problem.

    Cheers

    Jason
     
  15. Stian Indal Haugseth

    Stian Indal Haugseth Well-Known Member

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    Can't find my roll :(
     
  16. mike01hu

    mike01hu Well-Known Member

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    I believe that after the auto home at the start of MBL the IR in not used because the system knows where it is, as all adjustments are via the knob i.e. electronic data for moving. I am sure @Alex9779 will correct me if I am wrong! :D
     
  17. mike01hu

    mike01hu Well-Known Member

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    I have some copper tape, used to deter slugs from eating my plants, that I will try shortly. It didn't work on them :( but it might be OK for this:).
     
  18. gonzalo

    gonzalo Well-Known Member

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    @Jasons_BigBox & mike01hu
    Yes, u use MBL for bed leveling, and correct, MBL process does not use IR, you manually move the bed and use a sheet of paper to set the clearance.
    After this I run a quick print and then:
    I have found myself fine tuning the clearance using a Allen key and flipping the extruder fans enough to access the grubs that hold the extruders to the 3D printed carriage. By turning the grub screws you can do very fine movements to get the bed distance just right.
     
    #18 gonzalo, Aug 4, 2016
    Last edited: Aug 4, 2016
  19. Steven

    Steven Well-Known Member

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    no, I think your missing my issue. Its very repeatable.

    I print ANY object. big print, small print, aborted print does not matter.
    Even say a small print with 60 layers. I did autolevel and level bed routines before print.
    I _should_ be able to re-print the same object or any other object without issues right... no.
    I will ALWAYS get this if I DONT re-level the bed:

    IMG_2747.JPG

    The rise of the bed does not return to the same point it should.
     
  20. Sarah Nicholson

    Sarah Nicholson Well-Known Member

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    What firmware version? What's in your start and end gcode scripts?

    Also I see you're using blue tape (yuck), is it possible the tape is confusing the sensor? After you level the bed, if you do repeated auto home does the bed always stop at the right place? If it does, I suspect the problem may lie in your scripts. Make sure you're not homing individual axes for instance.
     

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