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How to calibrate Z-Axis?

Discussion in 'Control Software' started by jeffmorris, May 9, 2019.

  1. jeffmorris

    jeffmorris Veteran
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    I have CNC XPro V3 board, DQ542MA Stepper Motor Drivers, and CNC router with ball screws. I use OpenBuilds Control software. How do I calibrate Z-Axis? I already calibrated X and Y axis. I found out that I have to use 316.032 steps/mm for X and Y axis. It is impossible to use a ruler.
     
  2. Alex Chambers

    Alex Chambers Master, Openbuilds Team
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    If you have calipers that will measure depth then machine a pocket in suitable material (not wood - acrylic or aluminium for best accuracy) and measure the actual depth compared to the programmed depth. You need a fairly accurate measuring tool like calipers because you will only want to machine (say) 10mm or so.
    Alex.
     
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  3. jeffmorris

    jeffmorris Veteran
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    I have digital calipers but I don't have acrylic or aluminum. I think I saw a video on calibrating Z-Axis using calipers but I don't remember which one.
     
  4. Alex Chambers

    Alex Chambers Master, Openbuilds Team
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  5. David the swarfer

    David the swarfer OpenBuilds Team
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    ah! calipers!
    with those you can measure 2 things, 1 thing about .5" thick and another of 1 to 2" thick (depends on your Z travel). Ball races would be good. bigger difference is better.

    Then use the technique at 03:14 in this video to jog to the height of the small one and set zero there.

    Then set the height with the larger item (by jogging carefully as before).

    Now the GUI shows the 'commanded distance' and the 'actual distance' is the difference between the measured sizes of the objects you are using.

    Then you can use the wizard to calibrate, or just use the formula from
    C-Beam™ Machine - Plate Maker
     
  6. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    V1.0.166 or older of OpenBuilds CONTROL -> Connect to Machine -> Grbl Settings Tab -> Scroll down to $100-102 -> Click the "Fine Tune" button
    v1.0.167 or newer of OpenBuilds CONTROL (Coming out soon) -> Wizards and Tools -> Calibrate [x,y or z from menu]

    wizardcalib.PNG
     
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  7. jeffmorris

    jeffmorris Veteran
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    After trying to calibrate Z-Axis a few times, I jogged the Z-Axis so that it touches a piece of wood using a piece of paper as feeler gauge. I made a mark on the Z-Axis carriage. I used "Fine Tune" tool to move Z-Axis up 50mm. I made another mark on the carriage. I made marks on piece of paper. I measured the distance between marks using ruler. I entered the distance into tool. I found out that the steps/mm was 366.6667 so I changed it to 632.064. I cut out flowers from piece of wood and it worked.
     
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  8. jeffmorris

    jeffmorris Veteran
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    I think that the feed speed is too fast. How can I reduce the feed speed? I have VCarve software.
     
  9. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    In VCarve you need to edit the Tool, and change the parameters:

    EDIT FEED.PNG
     
  10. John Fisk

    John Fisk New
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    I have been successful at calibrating my 3 axes using the calibration program using OpenBuild Control macro and Black Box.

    My question is about precision. I am using a digital caliper in contact with a router bit. I zero out the caliper and run the Control macro. If i then repeat the process several times, while attempting to control all variables, I get a variation in the values. This does not surprise me, but what is an expected variation using the Control macro that I can expect and call this precision number good? I know that my application will drive the "goodness" of the precision. I am just wondering what the community is seeing and accepting as "good"?

    If i need to tighten up the precision of my machine where should I attack? I have lead screws on all axes.

    Thanks Ya'll,
    Texasinmi
     
  11. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Check the following:
    - Couplers between motors and leadscrews are tight
    - Wheels properly adjusted
    - Anti Backlash Nuts properly adjusted
    - Frame square, level, and built as-perfect-as-possible (Its only as good as the guy who puts it together)
    - Motor current properly adjusted

    How much of a deviation are you seeing, some pics of the testing etc may help

     
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  12. John Fisk

    John Fisk New
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    Here are my results for ten runs using the X axis macro. I added a pic of my setup:
    Result of 100mm input Calculated $100 Value
    Start 319.736
    99.87 320.152
    100.18 319.577
    99.74 320.410
    100.24 319.643
    99.73 320.508
    100.02 320.444
    100.11 320.092
    100.14 319.644
    99.59 320.096
    100.25 320.160
     

    Attached Files:

  13. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    What is X Axis Macro?
    OpenBuilds CONTROL comes empty with no macros included, so no context to this?
     
  14. John Fisk

    John Fisk New
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    My Control software (v 1.0.172) that works with a Black Box has a section where several macros reside. One will allow you calibrate the X axis, as well as Y and Z. It will ask you to input the zero location, next it will drive the X axis 100mm, you then input how far the machine actually moves then the macro will calculate the grbl value $100 for you and enter it into the Control for use on the next run. It is pretty slick.

    The values I sent represent the actual distance driven in mm and the $100 value from that distance.

    John Fisk
     
  15. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    This is MACROS:
    macros.PNG

    What you are referring to is under Tools and Wizards... Ie its a Calibration Wizard :)
     
  16. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    OK so that explains better what you did.

    So each time you redo the test you should be getting a little closer to true (provided you can help by hitting the reset button on the controller between runs)

    As its ballscrews though, I would rely on math, not on trial-and-error calibration. If you trust the screws you have... That way if you still have deviation at least you know its mechanical, not the steps value
     
  17. John Fisk

    John Fisk New
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    My bad, it is under Wizards and Tools.

    What is the math you refer to having to do with ballscrews?

    John
     
  18. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Example:
    Say you have the following hardware:
    - 4mm pitch screw (Advances the carriage 4mm for one revolution of the screw)
    - 200 steps per rotation motor (1.8deg per step, 200 steps per rotation (1.8*200=360))
    - Stepper driver set to 1/16th microstep

    Then calculate:
    200 steps per rotation * 16 microsteps = 3200 steps per rotation.
    One rotation moves the carriage 4mm (4mm pitch leadscrew)
    So to get 1mm of movement (steps per mm) we do 3200 / 4 = 800 steps per mm

    If its a metric screw, likely will be a round number
    Note I dont have the specifications of your screws or motors, or what microstepping your drivers are set to. So substitute accordingly.
    Metric screws should end up with a nice round number
    Looking at your trial results, I'd guess 320 to be the actual number...
     
  19. David the swarfer

    David the swarfer OpenBuilds Team
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    Unless they are precision ground screws they are never exact (most are made by a rolling process), you do need to do calibration for all screws. (but do start with the calculated number)

    Also, the process you use for the calibration makes a difference.
    I found that returning to 0 before changing the $10x values worked best. Maybe a reset is even better.
     
  20. David the swarfer

    David the swarfer OpenBuilds Team
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    those values are hovering around 320 with a slight upward trend. I think you are seeing measurement error more than thread pitch error (-:
    upload_2019-6-6_9-57-13.png
     
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  21. John Fisk

    John Fisk New
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    Thanks for the feedback.

    The question I really have is "If you saw number like this out of your machine, would you be happy with them and leave things alone saying to yourself ""Wow, those are some tight statistics."" or would you work to make things tighter saying to yourself ""Wow, those statistics really suck""?"

    I really don't know where I am at on the bad to good scale of things.

    John
     
  22. David the swarfer

    David the swarfer OpenBuilds Team
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    I would cut stuff and see if there is a size issue on assembly.
    Can we detect when a bit of wood is 0.1mm oversize? I just don't know, yet...
     
  23. John Fisk

    John Fisk New
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    Great suggestion

    Thanks

    John
     

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