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Thread: ? for resident homebuilt CNC gurus

  1. #1
    Join Date
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    Default ? for resident homebuilt CNC gurus

    Finally got my Seig2 (mill that fell off a truck) mini mill together and wired. The problem is that while the steppers turn they don't turn consistantly. Sometimes the steppers will just stutter and sometimes they will do what they are supposed to. just as often if I jog in a specific direction the steppers will do just the opposite.
    Curriculum Vitae.

    Mach 3, Gecko 201s, campbell breakout board. keling 23 steppers. Motors tuned as per Mach 3 manual(however both dir and step pulse freq. are maxed out at 5.)

    Right now I'm thinkin' there may be interference somewhere along the line. But I'd like to hear from a pro.

  2. #2
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    Sounds like a problem with the 5v logic to the drives.
    Not familar with the Campbell board though as I use the CNC4PC boards and these have an outside 5v source.

    Keep power cables to the drives, motor cables and logic cables seperate.
    Check grounds.

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    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  3. #3
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    Shields on data cables , motor cables and power supplies should only be grounded at one end, never both ends. Data grounds run inside the shield. Grounds should be in a star configuration meaning that all parts of the system including the shields should share the same ground point. Neutral on the mains should NOT be connected to ground in any of the boxes.
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  4. #4
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    Data lines that are inputs, limit switches for example generally cause false switch trips in Mach3 if you have noise/grounding problems. (boy did I learn that the hard way).

    In the motor tuning, the times must be at 5us for Gecko 201's or they will appear to run properly but actually miss many steps. You said you are set at that but I figured I would mention it anyways.

    Few things to check/verify:

    With power off, do things turn nice and free by hand?

    Gecko 201 current limiting. What is the current rating for the motors you are using? What value resistor do you have on the Geckos?

    A very very common mistake, that causes symptoms like you have- switched step and dir lines!!! Also check Mach3 setup for proper active low/high settings.

    Double check motor tuning. Can't tell you what steps/per should be set at approx. without knowing if your direct driving the screws or belt ratio and your TPI of the leadscrew. Give us that info and your present settings and we can tell you if your in the ballpark.

    What sort of voltage are you running to the steppers? Is the supply voltage sagging with the motors running?

    If the wiring between the Gecko and the motor is mixed up, the motors will grunt, groan, try to turn but just not go. Same for a disconnected wire. Verify the motor winding to gecko hookup. (power off of course!)

    There is a few things to check for starters.

    (check the step/dir lines are not reversed first and the active high/low, that is a extremely common mistake/problem)

    I did a setup almost exactly like yours recently and am now in the process of doing my bridgeport with Mach, gecko's and steppers which should be done in the next couple days. I have made a lot of mistakes and learned a lot along the way.
    Last edited by Sparky_NY; 02-01-2008 at 09:43 AM.

  5. #5
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    Sounds like you're losing a phase. Check that all the connections between motor & driver are tight (you probably already did this multiple times), but double check that the wires are in the right order.

    The behavior you describe is very common when one motor phase is wrong: with no load it may step correctly, under a load or at a different speed it can stutter, or go backwards.

  6. #6
    Join Date
    Nov 2005
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    LOL

    Everything these guys have suggested gives the symptom you see and I have seen every one of them in my own CNC work:

    - Don't forget to check Mach 3's parameters to make sure they all agree with what you'd like. You can vary whether Mach things signals should be hi or lo to reflect "on" for example.

    - I had 3 steppers, but on 1, I reversed 2 wires in the cable, Step/Dir. I knew I had reversed them and thought I could keep it straight. Worked well first time. Then I took it all apart to make a change and forgot step/dir were reversed when I put it back. Got exactly your symptom and took a bit to remember what I'd done. DOH! Now I put labels on the wires instead of relying on the colors.

    - Noise, yup. I only use shielded wire now, and try to make sure I get the grounds right on everything.

    - I had a "many wired" stepper one time and got one of the coils misconnected. It acted much as you describe.

    The good news is that it doesn't take too long to recheck all the wires and maybe conduct an experiment or two.

    Cheers,

    BW

  7. #7
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    Another thing. It would probably be easiest to just play with one axis at a time. Once you find the issue and get that axis working, all bets are its the same problem with the other axis. Playing with them all at once just makes for confusion.

    (Wiring steppers this afternoon, so I know how easy it is to get confused.)

  8. #8
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    Thank you everyone. This place is the best. The motor cables are shielded but not grounded. I'll give that and the other stuff a try this weekend.

  9. #9
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    An ungrounded shield on a cable carrying strong signals such as motor power will act as a transmitter of noise. Be sure to ground them well at the supply end. If you need to shield a cable or wire set you can buy stainless steel braided shielding from the auto parts performance section. Another source is stainless steel shielded hose in the plumbing department. That makes a good flex cable. Another trick for a shielded flex cable is a screen door spring.
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  10. #10
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    Quote Originally Posted by Rustybolt
    Thank you everyone. This place is the best. The motor cables are shielded but not grounded. I'll give that and the other stuff a try this weekend.
    Remember, only connect the shield at the controller end, the shield at the motor end is trimmed back and unconnected. Tie all the shields at the controller end to the same point, chassis ground, not power supply ground.

    Double check the wiring from controller to motor, a miswired phase is a more likely cause of your issues and your going to be in there anyways.

    Got my bridgeport running 100 ipm reliably last night during my initial tests! Today is setting up the limit switches and coolant/spindle relays and I am done! The only other item is to figure out a chip enclosure around the table to keep the mess in the garage down. 3 sides are straight forward, its the rear side towards the column I have to figure out something that contains the chips but clears the ram and column. Anyone with pictures of something would be a real help!

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