thoughts on Z-axis calibration / programming

Discussion in 'Guides, Mods, and Upgrades' started by R Design, Aug 15, 2016.

  1. R Design

    R Design Well-Known Member

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    I was recently looking at the setup routines for the BCN3d sigma. Remember that printer is running marlin 1.1 like us, perhaps a bit more customised.

    There are a number of clever-looking things going on in this video:



    Quite easy to miss at the very beginning that:

    a) it uses a simple microswitch endstop next to each nozzle. That endstop never has to be lowered because it only probes the bed in positions where the nozzle is off the edge fo the glass. Since each nozzle manages to probe 3 positions like that, each time that is enough to define a plane.

    b) the odd thing about this printer is that the two nozzles are on separate heads. Each extruder probes 3 points and two of those points are in common: the ones at the front of the bed. That enables the computer to determine any differences in height that might exist between the nozzles.

    c) notice that having a perfectly rigid steel bed, and a very stiff linear rail system, I don't think there's any need for meshing.

    Is there anything we can learn from? Or be inspired by?
     
  2. Old_Tafr

    Old_Tafr Well-Known Member

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    Interesting to see how other companies approach things... Please take my points as positive and made out of interest, not knocking what looks interesting.

    But (Doh...) Don't understand your point "a" at all :-(

    Do appreciate the checking two points and using them as a ref and three points to define a plane (IF the bed is flat)

    "c" rigidity isn't the question although it helps, it's how flat the bed is. It is somewhat easier to make a steel bed flat by scraping it, using (ironically) a (thick) flat glass plate as a reference. Mesh levelling on the BB allows for a surface that isn't quite flat (whatever that means :) )
     
    #2 Old_Tafr, Aug 15, 2016
    Last edited: Aug 16, 2016
  3. TimV

    TimV Well-Known Member

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    Yes,,. This is absolutely what we need. Easy leveling and alignment.
    And the dual head movong seperately genius.
    And the microswitch level sensing just great.

    Overall very impressive, all on my BB as a 1.2 version
    Would pump the BB to a pro level (semi-pro so far)
     
  4. fpex

    fpex Well-Known Member

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    Except that this printer is not as good as it looks. Nice idea, but I saw it in actions and prints were disappointing. So far the best printer is the Felix Pro1 that I am also an happy owner of.
     
  5. TimV

    TimV Well-Known Member

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    BB is the best, period
     
  6. fpex

    fpex Well-Known Member

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    Good for you then Tim. Still when a printer has perfect dual printing, bed cab ration with sensors integrated in the heads independent from the bed temperature, it prints faster then the BB ... it takes higher marks for me :)

    The BB is nice and moddable, but the bed is a $%#^%$*#^ nightmare. Plus I find repeater better smoothie better than duet firmware better than rumba firmware. What i like in the BB is the titan, which I will install on my purse mike once I get it (and after some playing time)
     
  7. Stian Indal Haugseth

    Stian Indal Haugseth Well-Known Member

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    You meant to say you find "Repetier" better than Smoothie? And so on?
     
  8. fpex

    fpex Well-Known Member

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    Yes, indeed.
     
  9. R Design

    R Design Well-Known Member

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    There's another interesting Z-axis related detail on this printer.

    The bed is supported on 3 points and not 4.

    Firstly the glass bed contains 3 ball shaped magnets (at two adjacent corners and in the middle of the opposite side). These sit in three metal cups in the plane of the PCB heater below. Nice. Makes for a very proprietary arrangement, true. But I just looked up the price on their webstore and the glass with embedded magnets sells for 14.52 euros (tax included).

    Secondly - and this is a point one can appreciate from the video above - the PCB layer of the bed is also supported at just 3 points (from the steel frame below). Two at the front edge of the bed - each of which has an easy adjustment knob - and one in the mid point of the back edge. At the back, instead of a knob there is a combination bolt and spring assembly which allows the bed to move freely and yet remain tight in accordance with the adjustments made at the front. (btw. the three points of the glass bed above are orientated "the other way around" with the two adjacent magnets lying at the back of the bed).

    The more I look at this arrangement the more I really like.

    And, of course, it is one of the enabling features fo the fantastic calibration routine in the video which not only levels the bed but ensures coordinated Z behaviour of the two separate printheads.

    Btw. the build area of this printer is quite comparable to the BB. The one thing that they have got very WRONG is that the PCB heater STOPS a long way from the edge of the glass. Nuts.
     
  10. fpex

    fpex Well-Known Member

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    What really is really helping me is to put springs at the four corners so that I can easily fine tune the bed.
    I find they mesh levelling is great that it makes error that a better tuned bed can solve. Also springs allows the head to push the bed down a little bit. Something that will avoid issues when the sensor or something else messes up the first layer.
     

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