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  1. #1

    Custom CNC Z-Axis travel woes

    Built a CNC machine 1000mm x 800mm running MKS DLC and Gerber. (Hope this is enough info)

    Using Candle I jog all axis just fine, except y-axis runs backwards but I'll reverse motor wires to correct.
    The z-axis can be jogged in all increments, i.e. .1, 1, 5, etc. just fine.

    I have Vcarve Pro and am trying to run a very simple program, that runs fine on my MySweety desktop machine but when I try to run with vcarve post processor settings set for large machine the z-axis drops way more each iteration than what it's supposed too.
    The post processor settings I have are for gerber(mm).tap and I change extension to .nc and run in Candle.

    I am very new to CNC.

    Thanks for any help.

  2. #2
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    Re: Custom CNC Z-Axis travel woes

    Are you running servo motors or steppers? With steppers, you can change the direction in software; I don't think swapping wires helps.
    The incremental drop of the Z axis sounds like lost steps on the upstroke. You might try reducing the acceleration of that axis by half or so to see if that helps. There also could be mechanical problems like a loose coupler or lack of lubrication that cause that. Or it might be that your spindle assembly is too heavy, and a gas spring to counteract that might be required.
    Andrew Werby
    Website

  3. #3

    Re: Custom CNC Z-Axis travel woes

    Andrew,

    Running Steppers, it's funny I have a MKS DLC32 and it runs correctly, I also have a MKS DLC and the y-axis runs in reverse. Both running GRBL! Not sure whats going on there but that's a minor problem.

    The problem with losing the USB connection when I start the motor. I bought some new wire and am going to rewire the spindle. Right now I don't have the ground wired up and thinking this might be part of the problem. The case is tied to pin 4 so it will have a solid earth ground.
    If that doesn't cure the problem then I'm really at a lose.

  4. #4
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    Re: Custom CNC Z-Axis travel woes

    Just because one machine works doesn't mean another will too - even if they're identical. USB signals aren't very robust; the least little thing can upset them. Grounding can definitely help, but if the issue persists, you might try shielding the spindle leads, which are a notorious source of RFI. A braided wire tube over all of them, attached to ground on the controller end, is generally recommended. Some shielding on the logic-level leads won't hurt either.
    Andrew Werby
    Website

  5. #5
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    Re: Custom CNC Z-Axis travel woes

    Quote Originally Posted by awerby View Post
    Just because one machine works doesn't mean another will too - even if they're identical. USB signals aren't very robust; the least little thing can upset them. Grounding can definitely help, but if the issue persists, you might try shielding the spindle leads, which are a notorious source of RFI. A braided wire tube over all of them, attached to ground on the controller end, is generally recommended. Some shielding on the logic-level leads won't hurt either.
    You can't use a Braided wire tube over the outside of the wires like this, it can be very dangerous if to do this.

    A shield is never attached to anywhere a Ground wire is attached, they must be attached direct to a Ground Plane

    Shields are also connected Direct 360° clamped at Both Ends to be affective.

    Cable Shields terminated at one end provide only electrostatic protection against low-frequency, capacitive coupled interference and emission

    I would suggest you do some study (education) on this subject before posting incorrect information
    Mactec54

  6. #6

    Re: Custom CNC Z-Axis travel woes

    Thanks y'all

    I bought some Double shielded 16/4 spindle cable kit off ebay. Got this after doing much research and learning the hard way by trying to go cheap. Arg

  7. #7
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    Re: Custom CNC Z-Axis travel woes

    Quote Originally Posted by mikeh32259 View Post
    Andrew,

    Running Steppers, it's funny I have a MKS DLC32 and it runs correctly, I also have a MKS DLC and the y-axis runs in reverse. Both running GRBL! Not sure whats going on there but that's a minor problem.

    The problem with losing the USB connection when I start the motor. I bought some new wire and am going to rewire the spindle. Right now I don't have the ground wired up and thinking this might be part of the problem. The case is tied to pin 4 so it will have a solid earth ground.
    If that doesn't cure the problem then I'm really at a lose.
    You can usually reverse the direction in the control software Active High active low, losing the USB connection when you start the motors is a noise or Grounding problem

    What is the spindle you are using; a shielded cable is required for this if you are using a VFD Drive.
    Mactec54

  8. #8

    Re: Custom CNC Z-Axis travel woes

    Mactec54,

    I have a Huanyang VFD and a 2.2K 220V water cooled spindle from Vevor

  9. #9
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    Re: Custom CNC Z-Axis travel woes

    Quote Originally Posted by mactec54 View Post
    You can't use a Braided wire tube over the outside of the wires like this, it can be very dangerous if to do this.

    What danger is involved? I've done it this way and it worked fine, with no problems. If you have a spindle with its own unshielded wires attached, how else are you going to provide shielding?

    A shield is never attached to anywhere a Ground wire is attached, they must be attached direct to a Ground Plane

    I didn't say to attach it to another ground wire, but all the advice I've ever read says to use "star" grounding to avoid creating ground loops.

    Shields are also connected Direct 360° clamped at Both Ends to be affective.

    What do you mean by "Direct 360° ? Are you saying to clamp all the way around the shield, or something else?

    Cable Shields terminated at one end provide only electrostatic protection against low-frequency, capacitive coupled interference and emission

    That was the sort of problem the OP seemed to be having. What additional benefits accrue by grounding both ends of the shield?

    I would suggest you do some study (education) on this subject before posting incorrect information
    Sometimes the only way we can get our misconceptions corrected is by posting the things we think we know. What sources would you recommend I read on the subject of cable shielding and grounding?
    Andrew Werby
    Website

  10. #10
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    Re: Custom CNC Z-Axis travel woes

    Quote Originally Posted by mikeh32259 View Post
    Mactec54,

    I have a Huanyang VFD and a 2.2K 220V water cooled spindle from Vevor
    Check that the spindle 4th Pin is Grounded, most are not, with a meter set to continuity check the pin 4 to the spindle body if it is not connected, then you will have to remove the top of the spindle and correct it like this snip
    Mactec54

  11. #11

    Re: Custom CNC Z-Axis travel woes

    The case is grounded to pin 4, check3ed that last night.

  12. #12
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    Re: Custom CNC Z-Axis travel woes

    Quote Originally Posted by mikeh32259 View Post
    The case is grounded to pin 4, check3ed that last night.
    If everything has been terminated correctly Shields wiring then you should be good to go, you may need an EMI power Filter for the VFD Drive and any Power supplies you have

    The main EMI Filter has to be mounted close as possible to the VFD Drive input power the same for the Power supplies, this is the type I recommend, but they are hard to get / find right now

    TDK Lambda RSEN-2030L the complete part number is important others can be used look for 2 stage
    Mactec54

  13. #13

    Re: Custom CNC Z-Axis travel woes

    Cable made the difference, running like a pro now.

    Only one problem it will run when I output gcode in mm from vcarve pro but not in inches.
    Vcarve Pro is outputting the correct gcode but something in GRBL or (Candle/UGS) that isn't set right. But that is a minor problem.

    Thanks everyone for your help!

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