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Workbee / FLexible Coupler / Problem

Discussion in 'CNC Mills/Routers' started by Mace, Jul 26, 2020.

  1. Mace

    Mace New
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    I am at the stage of homing the machine now and it works great except for the Y-Axis.
    You can see in the pictures which I put in this mail that the left side (looking from the front to the machine) has a problem with the flexible coupler when the machine tries to home the y-axis. It doesn't get far enough to reach the limit switch; some centimeters before the machine starts to chatter really loud and the left coupler looks really cramped compared to the right side.
    I have no idea how to fix this issue - maybe you can help me out.

    I tried out different things to solve the problem. I switched the Motors on both sides (including flexible couplers) with the same results. It's always on the left side despite heaving a different coupler or motor. It "works" when I loosen the screws from the Motor - it relaxes the Flexible Coupler so far that I can home the Y-Axis. But now I have a loose nema Motor on the left side.
     

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  2. Alex Chambers

    Alex Chambers Openbuilds team
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    Instructions from Ooznest on this bit of the assembly is to have the leadscrew touching the motor shaft - so the coupler is used as a rigid rather than flexible coupler. Have you squared your machine? Check that the frame is square and (with the motors unplugged from the controller to avoid damaging your stepper drivers) turn the coupler by hand to make sure that the Y gantry plates are the same distance from the end as each other.
    EDIT:- I should also have asked which side you have the Y limit switch on.
     
  3. Mace

    Mace New
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    Thanks for the fast Reply.

    The Limit Switch is on the Left Side (Looking from the Front)

    Here Is what i did/checked regarding this Problem:

    *machine Squareness - check (is on point as far as i can measure)
    *distance from the Gantry Plates - check (also perfect on the millimeter)
    *the Lead Screws are as far in the coupler as i can do it. (i cant see if they are touching but i can imagine they are)
    *changed motors and Flex Couplers - no difference
    *changed Y-End Plaates - still no difference


    its just doing this on the las few centimeters at the back of the y-Axis.


    Slowly i begin to get worried.

    Thanks alot!
     
  4. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Is the leadscrew bent near that end maybe? Hard to see from the pictures but it kind of looks like the shaft side of the coupler is pushed offcenter too.
     
  5. Mace

    Mace New
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    I dont think so - i think if it where bent, the Problem would also be present when the Gantry ist at the front of the machine.
    Or am i wrong?
     
  6. Alex Chambers

    Alex Chambers Openbuilds team
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    Hmmm - @Peter Van Der Walt's comment made me have another look - it certainly looks as though the leadscrew is not in line with the motor shaft. Where did you get the machine from (assembly varies slightly between some suppliers).
    Alex.
     
  7. Mace

    Mace New
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    Thanks you for your help - i really appreciate it.

    Because you both mentioned the Lead Screws i dismantled both of them and gave them a look.
    They look both identical and straight.
    I even switched the Lead Screws on the machine and tried it - but its the same as before.

    I bought the kit directly from Ooznest.
     
  8. Alex Chambers

    Alex Chambers Openbuilds team
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    Well that's good news - if there is anything wrong they'll put it right.
    First take the left motor and endplate off and check the end of the Y C-beam with a square. Check that the aluminium spacers for mounting the motor are all the same length, and that you have used precision shims in all the right places. Have you tensioned the leadscrew yet? Also check that the leadscrew does go all the way into the coupler so that it butts up against the end of the motor shaft. In your pic it must be only part way in. Let us know what you find.
    Alex.
     
  9. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Adding more photos may help, we might spot something
     
  10. Mace

    Mace New
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    UPDATE: i finally figured it out.

    on the left side i placed the wrong aluminium spacers to the backlash nuts.
    They needed the 3mm spacers - like on the right side - this caused the leadscrew to bend slightly.
    I fixed it now and everything seems to work fine now.
     
  11. Alex Chambers

    Alex Chambers Openbuilds team
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    3mm spacers + precision shims? It's important to put the precision shims next to the nut blocks - they are slightly larger diameter than the spacers and sit better on the rim of that recess in the nut blocks.
    Alex.
     
  12. Mace

    Mace New
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    Yes i did everything right now.
    Thank you very much.

    I hope i didnt damage anything on the machine with this fault.
    But i cant imagine that it was too problematic - i didnt run the machine like this and the flexible coupler counterbalanced the force which was caused by the bending of the lead screw.
    I wonder that the nurblocks are still fine since they are made from plastic.
     
    Alex Chambers likes this.
  13. Alex Chambers

    Alex Chambers Openbuilds team
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    Pretty tough plastic. Keep an eye on the flexible coupler(s) that got distorted though, in case they got weakened by the experience. Hope you get that machine running very soon.
    Alex.
     

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