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Surface Grinders: To buy or not to buy?

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  • #31
    Originally posted by Mcgyver View Post
    He's didn't suggest running a single phase motor on a 3P VFD, he suggested running a 3P motor from a VFD with 1P into the VFD
    Yup, and there just is no 1-phase motor as it wouldn't turn. The "1-phase" motors are usually just 3-phase motors with a running cap connected parallel with one of the coils to create the necessary phase shift to get rotation. So it is easy to just rip the cap off and connect a 3-phase feed to it and tada, 3-phase motor
    Amount of experience is in direct proportion to the value of broken equipment.

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    • #32
      Originally posted by dian View Post
      if its manual you will get to hate it pretty soon. its not easy to check the spindle. a bad grind can be caused by an inappropiate wheel for the test piece, wrong feeds or an inappropriate dress for example, which in turn can be caused by a diamond in bad shape. also the oil can be wrong on flat ways or the ways ruined with balls. if it has a belt that can cause problems also. the "five point method" is useless as has been pointed out.

      jaakko, i believe that will not work, imagine two indicators touching the periphery of a wheel.
      Ditto on the manual, if you can get power feed, go for it.

      You didn't specify where this "five point" (I never said to use points, I said use blocks) has been pointed out to be useless and how.

      Also, the two indicator test will work as this is the real world where the table and bed casting ways will NOT wear to a perfect radius match, especially at the ends of the travel where it's not used very much. Most used grinders I've seen show a considerable flatness & thickness deviation in grinding those 5 test blocks just near the outside edges of the working envelope, while the middle one shows as fat.
      Amount of experience is in direct proportion to the value of broken equipment.

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      • #33
        Originally posted by Axkiker View Post
        Here is a link to several single to three phase converters well over 1 hp.

        https://cdn.automationdirect.com/sta...s/gs2drive.pdf
        Thank you for the correction, I wonder why I've never saw them before? I even (apparently poorly) looked before I went with an American Rotary RPC for my DoAll grinder. Slow starts to start the spindle would be nice over just pulsing the on/off switch a few times.

        Sent from my XT1053 using Tapatalk

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        • #34
          jaakko, as you said yourself, you need to check the flatness of the work. the five blocks method has to be questioned for the same reason as the two indicator setup. rocking chair effect. before grinding the blocks youd have to grind the chuck anyways, which is not easy.

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          • #35
            Jaako-
            Single phase induction motors are 2 phase.
            They use a capacitor to offset the phase 90deg.
            They are not 3 phase.
            In other news,
            a real good reason for a VFD on a grinder
            is to be able to change the wheel speed
            to change it's hard-soft characteristics
            with respect to how it is presented to the
            work.

            --Doozer
            DZER

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            • #36
              Originally posted by Doozer View Post
              Single phase induction motors are 2 phase.
              They use a capacitor to offset the phase 90deg.
              They are not 3 phase.
              Over the pond has to have some weird motors or different terminology that I'm not aware of, as here you take a 3-phase motor, wire a cap across a winding, config the windings as delta and inject neutral and live (1-phase) over one other winding. Tada, 1-phase motor.


              3-phase wouldn't have that cap, just all three phases connected to the windings in Y or delta config.
              Amount of experience is in direct proportion to the value of broken equipment.

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              • #37
                Originally posted by dian View Post
                jaakko, as you said yourself, you need to check the flatness of the work. the five blocks method has to be questioned for the same reason as the two indicator setup. rocking chair effect. before grinding the blocks youd have to grind the chuck anyways, which is not easy.
                Yes, flatness has to be checked, that's what I said originally. If you can't check the flatness of your five blocks, how measuring anything bigger would achieve anything different? And there is no need to grind the chuck for the test, if you are checking flatness of the grind. Of course it helps if you want to grind the blocks from both sides to have them parallel and that way measure them more "easily", though that is supplying a point of error as you are actually measuring parallelism and not flatness.

                As this question arose of the rocking chair effect and theory vs real world, I might go and check the grinders at work later today and see if I can get some measurements. All I know is that they will show differing measurements with two indicators, as both of them grind differently at the ends of the travel than in the middle (about 0.02 mm difference with large plate). So this already confirms that it hasn't worn to be an equal huge radius that the two indicators wouldn't show.
                Amount of experience is in direct proportion to the value of broken equipment.

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                • #38
                  not sure what you are saying. flatness of the blocks? you check their height, right? or are you somehow going to put the granite on the grinder and blue them up? if the grinder is perfect and the chuck is not, then the blocks will not be equal.

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                  • #39
                    Single phase is different than two phase, look at sine wave charts. A two phase motor, common during the early 20th century and actually found on a few Bridgeport's from the factory cannot be run on single phase power.

                    Sent from my XT1053 using Tapatalk

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                    • #40
                      Originally posted by dian View Post
                      not sure what you are saying. flatness of the blocks? you check their height, right? or are you somehow going to put the granite on the grinder and blue them up? if the grinder is perfect and the chuck is not, then the blocks will not be equal.
                      No, check the flatness of what you grind. The height of the blocks doesn't matter if you are only interested in measuring flatness of one surface. Basic measuring job on a surface plate.
                      Amount of experience is in direct proportion to the value of broken equipment.

                      Comment


                      • #41
                        Originally posted by Doozer View Post
                        Jaako-
                        Single phase induction motors are 2 phase.
                        They use a capacitor to offset the phase 90deg.
                        They are not 3 phase.
                        In other news,
                        a real good reason for a VFD on a grinder
                        is to be able to change the wheel speed
                        to change it's hard-soft characteristics
                        with respect to how it is presented to the
                        work.

                        --Doozer
                        Can you explain that hard/soft you speak of by varying the speed? I have a boyar schultz 6x12 with a vfd. I have it set for about 10 seconds acceleration and the same on decel. Being a novice at grinding, I wondered if there might be a use/reason to slow the wheel down for any reason. I don't have a clue.

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                        • #42
                          a fast wheel acts harder and vice versa.

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                          • #43
                            Next best thing to having a surface grinder is to have a friend that has one. You could be that friend.

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