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another DRO whine

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  • another DRO whine

    The Z axis DRO readout on my mill goes haywire when I turn the motor on. Works perfect when motor is off. No problems with X and Y axis.
    Any ideas? Thanks guys.

  • #2
    VFD on the spindle? Might be creating enough noise to interfere with the signals from the encoder. Try rerouting the scale cable. You can also get some shielded cable for the motor instead of the generic SJO cables thats probably there now.


    • #3
      Check the routing of the wire from the Z axis pickup. If it is routed near the motor, try rerouting it. Also check that the wire is shielded and that the shield is connected to ground at only 1 end. Connecting the shield at both ends may cause some interesting effects.


      • #4
        On the rear of my Chinese DRO cabinet was a little brass fitting that I ignored. It was a ground connection and one day when I was MIG welding near-by the “noise” fried my DRO circuit. My replacement unit now has that ground securely connected and I’ve had no problems since.

        Check to see if you have an auxiliary ground that needs attention.
        Illigitimi non Carborundum 😎
        9X49 Birmingham Mill, Reid Model 2C Grinder, 13x40 ENCO GH Lathe, 6X18 Craftsman lathe, Sherline CNC mill, Eastwood TIG200 AC/DC and lots of stuff from 30+ years in the trade and 15.5 in refinery unit operations. Now retired. El Paso, TX


        • #5
          +1 for grounding, and make sure your DRO isn't on the same circuit that the VFD's using.
          That includes neutrals and grounds.

          Then check your building ground spikes.

          rusting in Seattle


          • #6
            My DROs are iGaging . I don't have VFD and grounding not a factor. No more than they cost I will just $hitcan the bad one and get another.


            • #7
              The first thing I would suspect is a bad connection somewhere in the wiring to either the motor or the Z axis sensor. The motor's vibration could be causing that connection to make and break.


              You can trouble shoot this by first holding the wire firmly in different positions at each connector (in, out, left, right, up, down, back, forward, etc.) and running the motor. If the problem goes away when you do this, then there is very likely a bad connection inside of or near that connector. Repair or replace the cable.

              AND when installing the new cable, try to include better strain relief for the new one. Electric cables do not like to be constantly bent back and forth. Copper is subject to bending fatigue and will eventually break if constantly bent first one way and then the other.

              And yes, grounds are important. But if it did work for a (long) time that is probably not the issue unless one of them broke via bending fatigue as described above.

              Without going into it in great detail, there are ways to design circuitry so that it is very resistant to outside electrical noise, therefore requiring a good shield and/or ground. And there are other ways, perhaps cheaper, that do not resist that outside noise. This means that good grounds and shielded cable can be an imperative on one system while another one can operate forever without any special precautions.
              Last edited by Paul Alciatore; 03-05-2022, 03:08 PM.
              Paul A.
              SE Texas

              And if you look REAL close at an analog signal,
              You will find that it has discrete steps.


              • #8
                I will check that out Paul. Thanks.


                • #9
                  Proper grounding is ALWAYS an issue. It is important for both safety and operation of equipment. To dismiss it is foolish. Just my $.02.

                  Happily working on my second million Gave up on the first