SOLVED Z-axis autohome issue

Discussion in 'Build Help' started by kevclarx, Sep 6, 2016.

  1. kevclarx

    kevclarx Active Member

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    So after fixing my loose wires I again attempted the autohome comissioning procedure however running into an odd issue.

    I set my z-offset to -5mm in controls, lowered my IR sensor and ran auto-home - so far all good. I then adjusted the z-axis so the nozzle barely touches the glass(the other nozzle slightly above but figure will adjust that later).

    I put the 50mm strip of belt underneath the sensor and lowered it so it was pressing on the belt and tightened it up. After that the wiki says to run auto-home again.

    This is where the issue starts, it raises the bed too far and grinds against the nozzle, for some reason the IR sensor is not firing in time. I checked with a level and the bed seems level.

    I've tried this procedure 5 times or so, the only thing I can think of is lowering the IR sensor more than the belt padding will allow. Any ideas?
     
  2. wfredette

    wfredette Well-Known Member

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    I never had good luck with the procedure as described in the online instructions. In fact, I ran into exactly the problem you're describing. My solution was to adjust the IR sensor's position without using the strip of belt material. I found (as you have come to suspect) that I had to lower it a bit in order to stop the glass from grinding into the nozzle on auto-homing.
     
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  3. kevclarx

    kevclarx Active Member

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    Thanks for the quick response, glad I am not alone with this issue. I'll give it a shot with some guesstimating, I really hate to hear the sound of the nozzle pressing up against the glass!
     
  4. wfredette

    wfredette Well-Known Member

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    Me, too. Just make small adjustments to the sensor. I backed off the mounting screws just enough to let them provide a little resistance to my attempts at moving it. That way, it would stay in place while I tested the auto-homing. And, keep one hand on the power switch when you test. :)
     
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  5. markoaurelije

    markoaurelije Active Member

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    The problem that I had was that PCB heatbed was bending in the middle so the glass in the middle didn't sit right on top of the PCB heater. Try to support the PCB heater from underneath so it touches the glass. The IR sensor should trigger sooner.
     
  6. richgain

    richgain Well-Known Member

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  7. Alex9779

    Alex9779 Moderator
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    Just to add my two cents: the IR triggers the upper surface of the build plate. The PCB has nothing to do with the trigger distance...
     
  8. Mark Curry

    Mark Curry Well-Known Member

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    Alex is right, the surface of the glass reflects the IR into the sensor. One thing that I have found is that you need to be very critical of the angle of the sensor to the build plate. Typically at belt height it is ok,if the angle is correct. Try angling it forward and back a little and you will see the trigger light come on at different angles. As the IR PCB is a little off square it means I have to angle the bracket. I am using the V1.1 BTW which has a long bracket that is hard to angle correctly... YMMV..
     
  9. markoaurelije

    markoaurelije Active Member

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    That was my understanding also, but... I had problems with IR triggering too late (nozzles hit the bed before IR triggered) and after I lifted the PCB under the glass with the bed support thingie it got resolved so I figure the PCB has to do something with it. :confused:
     
  10. markoaurelije

    markoaurelije Active Member

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    Oh... that might be the thing that got my problem solved. I did two things in the same time:
    - lifted the PCB heatbed with the bed support
    - adjusted the angle of the IR sensor so it is level with the glass

    So I guess the angle was the culprit ;)
     
  11. Mark Curry

    Mark Curry Well-Known Member

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    It was with mine, shortly before I attempted suicide I figured it out....
     
  12. kevclarx

    kevclarx Active Member

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    Thanks for the feedback on this, it was indeed the angle/position of the IR sensor. As I tightened the sensor to the carriage it would pull away at an angle. Eventually I got it by just applying some pressure, basically if the red light on the sensor is on when you remove the bit of belt, it is good to go. When it was incorrect the light would go off as soon as I removed the belt or tightened it. Simple in retrospect, but maddening at the time.

    Now I am struggling with levelling the bed. This is my off and on diy project every other week or so, it has been a bit maddening :)
     

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