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Turning motor shaft

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  • Turning motor shaft

    I have a surplus stepper motor who's shaft I need to turn. The shaft is 1/2" and I need it to be 3/8". How do you do this without damaging the motor.

    I was thinking of using the milling machine with the motor clamped down and using the boring head with the cutting edge facing in, but how you hold the shaft so that it doesn't spin?

    The other idea was to actually run the motor while it's held in the lathe chuck and use Dremel with a grinding stone mounted in the toolpost to grind it down.

    Your ideas would certainly make my weekend productive. Thanks.

    Albert

  • #2
    I like the Dremel tool idea, except if yours is anything like mine the bearings aren't up to producing a smooth finish. The result may be good enough for what you're doing, though. Perhaps it would be a good idea to try it on a piece of scrap first.
    ----------
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    • #3
      How about combining the 2 ideas you've already had?? If you've got a vertical mill and a rotary table with 3 jaw mount, put the motor in the vertical chuck, get the motor stepping and introduce an endmill to shave off the excess? Make sure the endmill runs contra rotation that way you should get a better finish (due to the stop/start mode inherrent in a stepper sequencing). I would be worried about grinding 1/16th off of a shaft in a lathe ~ 0.005 maybe but by the time you get to 0.050 you'll need to dress the stone again. Think of all the crud getting on the shearways!

      Thinking as I type this - finish grind the last 0.005 in the lathe if you don't get a good finish on the mill. BOL - let's know how you fare.

      RR

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      • #4
        Albert: Take motor apart , take off bearings,set up dummy shaft (1/2) to set steady rest to then, use 3-jaw or 4-jaw as needed for how close you want run out..... turn shaft.......

        you could leave bearings on shaft & drive with dog....,strap dog so it will not chatter...(set chuck & steady to bearing dia.) Larry


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        • #5
          Larry,

          If it was any other kind of motor, I would take it apart, however, stepper motors lose their performance once they have been disassembled. I think this is owing to the permanent magnets which lose their strength when it's not always closely coupled.

          Albert

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          • #6
            Why don't you just hold on to the motor in the lathe chuck, and use a "dog" to clamp on the shaft?? You might need to make your own dog..

            brent

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            • #7
              I have also found that stepping motors are never quite the same after they have been disassembled.
              I would make a collar / shield that fit VERY tight to the stepping motors shaft (and extended past the outside of the motors body) so no particles go down into the bearings. Then clamp the motor to the vertical milling machine table, with the shaft facing upwards. Hook up the stepping motor controller and counter rotate the motor against a grinding stone rotating in the vertical mill spindle. Go in a few thousandths and gradually move the spindle up and down till no more sparks. Repeat loop until done.
              Do you have a source for hefty stepping motors that is reasonably priced?

              [This message has been edited by Zoltan Sisko (edited 06-14-2002).]

              [This message has been edited by Zoltan Sisko (edited 06-14-2002).]

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              • #8
                I don't know why stepper motors don't work as well after they're disassembled, but I doubt it's the magnets. You can always make a slug(I guess) to stick in the motor while the arm/rotor? is out. Should keep the mags happy. Brent has a good idea if you don't want to take it apart tho. The lathe is the way to go I think; that's what they're made for.

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                • #9
                  Zoltan!!! My late father's name, also my brother's. You aren't by any chance of Hungarian descent? Don't run across to many Zoltans

                  ------------------
                  gvasale
                  gvasale

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                  • #10
                    It's the magnets....they need a "keeper" to hold the most remanent field. The "keeper" provides a path for the magnetic flux.

                    When there is no path, the flux density is reduced and some of the magnetic "domains" are allowed to flip to a random state, when they used to all be alined from the "charging" field. This results in the effect of those "domains" being lost, i.e. less field strength.

                    When you disassemble, you lose the "keeper" effect of the motor structure, and some field strength is lost.

                    A lot of steppers have a thru shaft that is exposed at both ends. Can you cobble up a steady rest with thin jaws and drive from the backside shaft in a chuck etc?
                    I say chuck because most do not have centers in them.

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                    • #11
                      Do you have the space for a reducer? That would be the best way to do it. Of if you are going to use flex couplers to allow slight misalignment thay can be purchased with different size input and ouput shaft sizes.

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