Serious step loss while milling : cannot find the problem


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Thread: Serious step loss while milling : cannot find the problem

  1. #1
    Member johnloque's Avatar
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    Default Serious step loss while milling : cannot find the problem

    Hello there,
    i'm not sure to be at the right place to ask as i don't know where does the problem come from, but i'm using mach3 mill with a cnc router running a XHC controler board.
    Since i started, i get a step loss once every 20 operations more or less.
    At first, the spindle were out of the wood piece keeping on milling with no change in the mach3 coordinates. Could be a few centimeters or 70 centimeters.
    Now, the tool path is good, at the right place, but the coordinates are crazy. I stop (pause) the milling because the noise of the axis is strange.
    This morning i captured the screen, look how the Z is -900 mm and X and Y are not at all like the GCode instructions.

    People say it can't be Mach3, if it was, people would know it, such a big error, and it can't be the XHC controler board because it's reliable.

    So what can it be?

    I did not build the machine myself, i bought it, ready to use, and i've done some work aleady by the way, it can work correctly but in the end, it's not reliable and it's a lot of worry.

    So before i throw it away, maybe i can change the board?

    Any help is welcome...

    Thanks



  2. #2
    Community Moderator Jim Dawson's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    Anything that's on the screen is generated in Mach3. Mach3 is an open loop system and has no idea what the machine or the controller is actually doing. If what you are seeing on the screen does not match the G code, then there is a problem with the setup or maybe the computer.

    If the motors are making strange noises, then you may have a mechanical issue like something binding. This could also be related to a computer or Mach3 issue.

    Jim Dawson
    Sandy, Oregon, USA


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    Member routalot's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    Is the router a known brand machine or a homebrew?It makes finding a solution a lot easier if there are others out there as the problem may not be a unique situation.A home made machine presents another series of problems and I wouldn't have expected something with the huge user base that Mach 3 has to be suffering just because of the software.Electrical noise and insufficient power to the steppers would suggest themselves as likely candidates.What size are the steppers and what mechanism are they driving?Looking a bit further upstream,what amount of power is being delivered to the steppers?A couple of pics might be helpful,as would details of the cutting operation being done-depth of cut,material,feed speed for example.



  4. #4
    Member johnloque's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    The machine is "Blue Elephant" from China. They really don't help, as they don't answer. I have 0 information about the motors. The problem can occur in any type of operation, planing, pocket, scallop, parallel, contour. The pictures are from a contour operation running at 1000 mm/min, 24000 rpm, 0.5 stepover 2mm stepdown, with a 3.17 flat mill. No big effort asked to the motors.



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    Quote Originally Posted by johnloque View Post
    The machine is "Blue Elephant" from China. They really don't help, as they don't answer. I have 0 information about the motors. The problem can occur in any type of operation, planing, pocket, scallop, parallel, contour. The pictures are from a contour operation running at 1000 mm/min, 24000 rpm, 0.5 stepover 2mm stepdown, with a 3.17 flat mill. No big effort asked to the motors.
    USB or ethernet interface on XHC controller?.
    I have seen various paces recommend only using win 7 or earlier with the USB version. If using win10 that could be the culprit.
    Could even be simply USB noise.



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    Member johnloque's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    Quote Originally Posted by dazp1976 View Post
    USB or ethernet interface on XHC controller?.
    I have seen various paces recommend only using win 7 or earlier with the USB version. If using win10 that could be the culprit.
    Could even be simply USB noise.
    It's USB on XHC. And yes, i use win10. The computer is quite old, but supports win10.
    That could be only that? That's a mod i can try. Win7 should be OK?



  7. #7
    Member johnloque's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    Quote Originally Posted by johnloque View Post
    It's USB on XHC. And yes, i use win10. The computer is quite old, but supports win10.
    That could be only that? That's a mod i can try. Win7 should be OK?
    My computer is 64 bits, must i install a 32 bits windows 7 or a 64 bits windows 7?



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    Member Billcase's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    Just a thought assuming you are not running the steppers to fast or ramping up and down to fast, those kind of issues. Even though its a "factory built" machine sometimes the factory screws up, as I found out with an $85K machining center, the factory ran a prox switch with un shielded cable with the 220v lines to the tool changer, and the tool changer couldn't count correctly until I put shielding around the prox cable and problem solved.
    Your machine should have a electrical line filter that goes to the drives. I also put a electrical line filter in front of the computer. Hopefully your break out board is optically isolated, If not, wow, electrical noise highway right into the computer. Make sure you don't have unshielded limit switch wires tied to the wires that go to the stepper motors. Look at all your wiring, remembering that stepper motors and the drives put out bigtime electrical noise and so does a frequency drive for the spindle. Simply running a wire through a Iron machine casting will put electrical noise in that line. Whenever I am on a fix it project and the customer says "I'm getting different fault messages", BINGO, electrical noise. Can electrical noise make you lose positioning? Hell yes it can! I have been retrofitting milling machines for almost 40 years now and I have seen what can happen with electrical noise. I have been a student of electrical noise and will never be the Master because electrical noise can come from anywhere, even if your power cable is looped around a metal truss in the rafters, and I'm still learning! Lunch break is over, I have to get back to work, I'm retrofitting a Hurco, not with steppers!



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    Member awerby's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    It doesn't sound like your typical lost step error, because that doesn't show up on the DRO screens; the numbers look normal, as commanded by G-code, but the location is wrong. In your case, it's wrong on the DRO screen, which sounds more like it's picking up erroneous instructions from somewhere. The usual cause of this is RFI - Radio Frequency Interference. Something could be interfering with the rather weak step/direction signals being sent from the computer, corrupting the stream of information that's reflected in the DRO.

    The first thing I'd try is running the program without activating the spindle. Spindle wires are potent sources of RFI, and if your program works well "in air", then that's a clue. Enclosing the spindle wires in braided shielding that's grounded could fix the problem.

    The next thing to try, if that doesn't seem to be it, would be to check the grounds on your system. The regular electrical ground through the power cord might not be working, or sufficient. Sometimes adding wires from the bare metal components of your system to the nearest plumbing pipe can fix these problems.

    If neither of these seems to work, then you're going to have to figure out what else in your control system might be picking up RFI and messing with your G-code. It could be that the ground wires are connected incorrectly, producing a "ground loop" that acts as an antenna. The proper way to connect the grounds is to bring them all to a central point; this is called "star" grounding. If your grounds are hooked up like a "daisy-chain", that could be your problem. Or the wires going from your computer to the control box could be too long, or too close to something with a lot of current in it. Troubleshooting stuff like this requires looking at every possible vulnerability and dealing with them one by one until you're either successful or you've torn out all your hair and thrown the machine into a lake...

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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    Member johnloque's Avatar
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    Default Re: Serious step loss while milling : cannot find the problem

    Thank you for the replies. One issue is that i can't reproduce the bug when i wan't. If i redo the same tool path after a trouble, it will work most likely. I did it many times. It is often the first tool path of the day thet fails, but not everytimes...It's hard to know...
    So i will install win7 and use a shorter usb wire...

    Other thing : sometimes, the axis stop moving, the screen is frozen, nothing move and then the screen makes a refresh and the milling resumes...Scaring, but no harm.

    Other thing : i've got the fuling inverter, and many times, the spindle does not start correctly. The power is too low and the spindle turns too slow. Never 24000 turns as i ask. And it falls into error ans stops. I thought it was not related but maybe it is...



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Serious step loss while milling : cannot find the problem

Serious step loss while milling : cannot find the problem