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Brakes on each axis on my mill

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  • Brakes on each axis on my mill

    My small universal mill has powerfeeds on each axis. Also a brake on each axis. The brake is nothing more than a circular electromagnet clutch. When 24v is supplied to the brake it releases. 24v holds the brake off. I only say this because with the machine unplugged the brakes are on. I will try to retain the brakes on my intended conversion to CNC.

    This mill has really big brushed DC servo motors on each axis. Each motor is about 40cm long. I have been thinking about converting this mill to CNC for a long time. It has ballscrews on all three axis and glass scales. It is a knee mill with a quill. The quill is not powered. I will use a powered knee for the Z movement for the CNC. The mill is 40 years old but in great shape. I bought it from the original owner who bought it new. Very low hours. I am thinking about replacing the motors with NEMA 42 closed loop steppers connected to a Centroid Acorn. The NEMA 42's will bolt right up to the same mounting holes for the original motors. I won't automate the spindle speeds as that is all mechanical dials changing gears. So no VFD for the spindle. I was going to go for the Centroid DCAllin1 control and keep the brushed DC servos but by the time I added encoders to the motors and went through all that it would be easier to use the closed loop steppers and have a more modern system. I will order one of the nema 42 closed loop steppers and the Acorn and connect it to the Z axis(knee) and test it to see if it has enough power. It has a 3 to1 reduction on the knee. The X and Y are direct drive to the double nut ground ballscrews.
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    This is a picture I grabbed off the manufacturers site.
    Click image for larger version

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    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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    • #3
      That's a pretty beefy looking mill, BF! It's cool that it has vert. and horizontal spindles and a swivel table. That one should do any kind of milling you could ever need. Well worth a CNC upgrade.
      Kansas City area

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      • #4
        Nah, its too old for CNC and the electronics are not compatible as it uses reverse polarity 380v 3-phase system.
        send me the address, I’ll send trailer to pick it up. Saves you the visit to scrap yard.
        Location: Helsinki, Finland, Europe

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        • #5
          Originally posted by MattiJ View Post
          Nah, its too old for CNC and the electronics are not compatible as it uses reverse polarity 380v 3-phase system.
          send me the address, I’ll send trailer to pick it up. Saves you the visit to scrap yard.
          Nice Try!
          Location: The Black Forest in Germany

          How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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          • #6
            Depending on the required speeds, you might want to go the servo route instead of steppers. Better wait for someone like Macona to chime in.

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            • #7
              This old tony converted a similar machine (a Maho).

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              • #8
                why do you want to use steppers vs. servos? (not criticizing, just curious) Jim

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                • #9
                  Originally posted by jmm03 View Post
                  why do you want to use steppers vs. servos? (not criticizing, just curious) Jim
                  Mainly because of the availability of the Nema 42 closed loop steppers vs. Delta servos coming from China. And the price is about half for the steppers. Whereas I am a tight SOB I like the sound of less expensive. But I will probably go with the Deltas.
                  Location: The Black Forest in Germany

                  How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                  • #10
                    Steppers are usually used in an open loop configuration. How does a closed loop stepper work?
                    Paul A.
                    SE Texas

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

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                    • #11
                      Originally posted by Paul Alciatore View Post
                      Steppers are usually used in an open loop configuration. How does a closed loop stepper work?
                      Not anymore Paul. In a closed loop stepper there is an encoder on the stepper motor that feeds back to the driver. The loop is closed between the driver and the motor only. There is no encoder feedback to the controller. If the motor cannot keep up with the movement that is commanded the drive will fault. Unlike open stepper setups where the machine keeps going but with inaccurate parts.
                      Location: The Black Forest in Germany

                      How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                      • #12
                        Originally posted by Black Forest View Post

                        Not anymore Paul. In a closed loop stepper there is an encoder on the stepper motor that feeds back to the driver. The loop is closed between the driver and the motor only. There is no encoder feedback to the controller. If the motor cannot keep up with the movement that is commanded the drive will fault. Unlike open stepper setups where the machine keeps going but with inaccurate parts.
                        That's one level of closing the loop.

                        There is another that reads the movement from a DRO, and those verify the actual table move. So even screw wear does not affect them.

                        That's a pretty high end approach, and I'd think that the verification of the stepper having "taken all the steps" would be good enough for most anyone. Any errors would have to be in the pulley or screw system, and those are likely to be quite small unless there is an actual mechanical problem.

                        I don't know what happens to recover from a fault such as you describe. It sure seems there would be a premium on having a stepper system that has enough power to handle all the moves while cutting.

                        Ideally any such errors would be from something like the cutter not turning, etc, and not from the stepper just stalling in a cut.
                        CNC machines only go through the motions

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                        • #13
                          You can get Clearpath servos that are in NEMA form, pretty good price for what you get. https://teknic.com/products/clearpat...-servo-motors/

                          Otherwise you can eliminate the brakes on X and Y, they are not needed, I have never seen brakes on X and Y on a vertical mill, the only axis that needs one is usually the Z axis.

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                          • #14
                            All the steppers I've ever heard running had that zinging robot sound every time they moved. That would make me crazy(er). Have they made the new ones quieter? Servos are normally very quiet.
                            Kansas City area

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                            • #15
                              Originally posted by macona View Post
                              You can get Clearpath servos that are in NEMA form, pretty good price for what you get. https://teknic.com/products/clearpat...-servo-motors/

                              Otherwise you can eliminate the brakes on X and Y, they are not needed, I have never seen brakes on X and Y on a vertical mill, the only axis that needs one is usually the Z axis.
                              I wanted to use Clearpaths but they don't make a size 42. They skipped that size because they didn't have much call for them. Mine has brakes on all three axis.
                              Location: The Black Forest in Germany

                              How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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