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Re: damaging bearings with current

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  • mattdbartlett
    The current is what is going to do most of the damage (well, the combination is). It seems like a better approach would be to insulate your contact tip from
    Message 1 of 15 , Jun 4, 2012
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      The current is what is going to do most of the damage (well, the combination is). It seems like a better approach would be to insulate your contact tip from the spindle nose, and avoid this alltogether. Is that possible?

      At 20mV you are going to need an amplifier or something to increase the voltage so that you can see the "touchoff" aren't you? Led's are around 1.2-1.7V at about 15-60mA, and piezo buzzers are on the order of 5v (not sure of current).

      In any case, minimizing current through your bearings is good. Seems like you could machine a non-conductive spacer to insulate the conductive tip from the shank, though I am not familiar with your design.

      --- In mill_drill@yahoogroups.com, "Rick Sparber" <rgsparber@...> wrote:
      >
      > I have heard a lot of compelling arguments on why 1.5V at 1 amp through a
      > bearing can start and sustain an arc that could pit the surface. What if I
      > used 20 milli volts at 1 amp?
      >
      >
      >
      > Rick
      >
    • Mark Cason
      ... Maybe something from here will help: http://www.gtsaz.com/service/trouble-shooting.php It s been 20 years, but one of the machines I used to maintain, was
      Message 2 of 15 , Jun 4, 2012
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        On 06/04/2012 08:26 AM, Rick Sparber wrote:
        >
        > I have heard a lot of compelling arguments on why 1.5V at 1 amp
        > through a bearing can start and sustain an arc that could pit the
        > surface. What if I used 20 milli volts at 1 amp?
        >
        > Rick
        >

        Maybe something from here will help:
        http://www.gtsaz.com/service/trouble-shooting.php

        It's been 20 years, but one of the machines I used to maintain, was a
        Kulicke & Soffa (K&S) Dicing Saw. It had a high speed spindle with air
        bearings, that touched off on a touchoff point while the spindle was
        running. The spindle was grounded only during touchoff, so maybe that
        would be something to look at?

        We weren't allowed to disassemble the spindle (K&S service contract),
        so I never figured out how it was grounded. I'm assuming it was done
        through some sort of a slip ring/brush assembly. However it was done,
        it was designed to be operated in a class 100 clean room, which means
        ultra low particulate.

        Dicing saws use a sheet of pure carbon as the blade, to cut silicon
        wafers. The touchoff point, is a sacrificial point, insulated from the
        rest of the machine, that gets cut to determine the diameter of the blade.

        Even if a dedicated touchoff point has to be added to a machine, with
        a known location, it will still work for determining tool length.

        --
        -Mark

        Ne M'oubliez ---Family Motto
        Hope for the best, plan for the worst ---Personal Motto
      • Jerry Durand
        ... I don t know about that saw, but I ve seen high speed shafts grounded with a conductive slippery plastic post lightly touching the center of one end of the
        Message 3 of 15 , Jun 4, 2012
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          On 06/04/2012 06:28 PM, Mark Cason wrote:
          > We weren't allowed to disassemble the spindle (K&S service contract),
          > so I never figured out how it was grounded. I'm assuming it was done
          > through some sort of a slip ring/brush assembly. However it was done,
          > it was designed to be operated in a class 100 clean room, which means
          > ultra low particulate.
          I don't know about that saw, but I've seen high speed shafts grounded
          with a conductive slippery plastic post lightly touching the center of
          one end of the shaft. Very little drag from it yet grounds out built up
          charges.

          --
          Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
          tel: +1 408 356-3886, USA toll free: 1 866 356-3886
          Skype: jerrydurand
        • Mark Cason
          ... I know that the spindle had brushes, as it was essentially a custom hight speed brushed servomotor, so it wouldn t be too much of a stretch to assume that
          Message 4 of 15 , Jun 4, 2012
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            On 06/04/2012 08:41 PM, Jerry Durand wrote:
            >
            > On 06/04/2012 06:28 PM, Mark Cason wrote:
            > > We weren't allowed to disassemble the spindle (K&S service contract),
            > > so I never figured out how it was grounded. I'm assuming it was done
            > > through some sort of a slip ring/brush assembly. However it was done,
            > > it was designed to be operated in a class 100 clean room, which means
            > > ultra low particulate.
            > I don't know about that saw, but I've seen high speed shafts grounded
            > with a conductive slippery plastic post lightly touching the center of
            > one end of the shaft. Very little drag from it yet grounds out built up
            > charges.
            >

            I know that the spindle had brushes, as it was essentially a custom
            hight speed brushed servomotor, so it wouldn't be too much of a stretch
            to assume that it was grounded the same way. However, a post touching a
            slip ring to ground the spindle, might be an alternative... Graphite
            impregnated nylon maybe?

            --
            -Mark

            Ne M'oubliez ---Family Motto
            Hope for the best, plan for the worst ---Personal Motto
          • Rick Sparber
            Matt, I completely agree and wrote this up back on May 28th: http://rick.sparber.org/LTEEF.pdf The problem I found was that people were not interested in this
            Message 5 of 15 , Jun 4, 2012
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              Matt,

              I completely agree and wrote this up back on May 28th:

              http://rick.sparber.org/LTEEF.pdf

              The problem I found was that people were not interested in this solution.

              It takes more than 4 amplifiers to get this circuit to work but I'm using
              LM324 quad op amps which I buy at Circuit Specialists for 25 cents each.
              Even at Radio Shack they are only $2.50. So cost is not an issue.

              I do have another design that uses 1 mA instead of 1 amp. It has so much
              gain that I think I am picking up a local radio station through the leads. I
              can't imagine it working in a regular, electrically noisy machine shop.

              Rick

              -----Original Message-----
              From: mill_drill@yahoogroups.com [mailto:mill_drill@yahoogroups.com] On
              Behalf Of mattdbartlett
              Sent: Monday, June 04, 2012 11:26 AM
              To: mill_drill@yahoogroups.com
              Subject: [mill_drill] Re: damaging bearings with current

              The current is what is going to do most of the damage (well, the combination
              is). It seems like a better approach would be to insulate your contact tip
              from the spindle nose, and avoid this alltogether. Is that possible?

              At 20mV you are going to need an amplifier or something to increase the
              voltage so that you can see the "touchoff" aren't you? Led's are around
              1.2-1.7V at about 15-60mA, and piezo buzzers are on the order of 5v (not
              sure of current).

              In any case, minimizing current through your bearings is good. Seems like
              you could machine a non-conductive spacer to insulate the conductive tip
              from the shank, though I am not familiar with your design.
            • Rick Sparber
              Mark, If people would be willing to put down an insulator as your reference describes, it would be a very simple problem to solve. Rick ... From:
              Message 6 of 15 , Jun 4, 2012
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                Mark,

                If people would be willing to put down an insulator as your reference
                describes, it would be a very simple problem to solve.

                Rick

                -----Original Message-----
                From: mill_drill@yahoogroups.com [mailto:mill_drill@yahoogroups.com] On
                Behalf Of Mark Cason
                Sent: Monday, June 04, 2012 6:28 PM
                To: mill_drill@yahoogroups.com
                Subject: Re: [mill_drill] Re: damaging bearings with current

                On 06/04/2012 08:26 AM, Rick Sparber wrote:
                >
                > I have heard a lot of compelling arguments on why 1.5V at 1 amp
                > through a bearing can start and sustain an arc that could pit the
                > surface. What if I used 20 milli volts at 1 amp?
                >
                > Rick
                >

                Maybe something from here will help:
                http://www.gtsaz.com/service/trouble-shooting.php

                It's been 20 years, but one of the machines I used to maintain, was a
                Kulicke & Soffa (K&S) Dicing Saw. It had a high speed spindle with air
                bearings, that touched off on a touchoff point while the spindle was
                running. The spindle was grounded only during touchoff, so maybe that would
                be something to look at?

                We weren't allowed to disassemble the spindle (K&S service contract), so
                I never figured out how it was grounded. I'm assuming it was done through
                some sort of a slip ring/brush assembly. However it was done, it was
                designed to be operated in a class 100 clean room, which means ultra low
                particulate.

                Dicing saws use a sheet of pure carbon as the blade, to cut silicon
                wafers. The touchoff point, is a sacrificial point, insulated from the rest
                of the machine, that gets cut to determine the diameter of the blade.

                Even if a dedicated touchoff point has to be added to a machine, with a
                known location, it will still work for determining tool length.

                --
                -Mark
              • Mark Cason
                ... I was thinking along the lines of maybe a MDF, or plastic sacrificial base, to set the stock on. But then, I realized that the clamps would have to be
                Message 7 of 15 , Jun 4, 2012
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                  On 06/04/2012 10:35 PM, Rick Sparber wrote:
                  >
                  > Mark,
                  >
                  > If people would be willing to put down an insulator as your reference
                  > describes, it would be a very simple problem to solve.
                  >
                  > Rick
                  >

                  I was thinking along the lines of maybe a MDF, or plastic sacrificial
                  base, to set the stock on. But then, I realized that the clamps would
                  have to be insulated as well. I would have to convert my mill to use a
                  ground insulated tooling plate...

                  --
                  -Mark

                  Ne M'oubliez ---Family Motto
                  Hope for the best, plan for the worst ---Personal Motto
                • Rick Sparber
                  Mark, Yup, Those hold down clamps are what bothered my friend. He still wants to be able to connect up a box and not change his set up. Rick ... From:
                  Message 8 of 15 , Jun 4, 2012
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                    Mark,

                    Yup, Those hold down clamps are what bothered my friend. He still wants to
                    be able to connect up a box and not change his set up.

                    Rick

                    -----Original Message-----
                    From: mill_drill@yahoogroups.com [mailto:mill_drill@yahoogroups.com] On
                    Behalf Of Mark Cason
                    Sent: Monday, June 04, 2012 8:55 PM
                    To: mill_drill@yahoogroups.com
                    Subject: Re: [mill_drill] Re: damaging bearings with current

                    On 06/04/2012 10:35 PM, Rick Sparber wrote:
                    >
                    > Mark,
                    >
                    > If people would be willing to put down an insulator as your reference
                    > describes, it would be a very simple problem to solve.
                    >
                    > Rick
                    >

                    I was thinking along the lines of maybe a MDF, or plastic sacrificial
                    base, to set the stock on. But then, I realized that the clamps would have
                    to be insulated as well. I would have to convert my mill to use a ground
                    insulated tooling plate...

                    --
                    -Mark
                  • Mark Cason
                    ... I can see several options: 1) make a set of insulated touch probes in the diameters that you normally use. THEN, use a magnetic pigtail with a low ohm
                    Message 9 of 15 , Jun 4, 2012
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                      On 06/04/2012 11:00 PM, Rick Sparber wrote:
                      >
                      > Mark,
                      >
                      > Yup, Those hold down clamps are what bothered my friend. He still wants to
                      > be able to connect up a box and not change his set up.
                      >
                      > Rick
                      >

                      I can see several options:

                      1) make a set of insulated touch probes in the diameters that you
                      normally use. THEN, use a magnetic pigtail with a low ohm resistor to
                      ground. $

                      2) use a insulated tooling plate. $$$

                      3) put in ceramic bearings, with a slip ring, and brush, and ground
                      the spindle through a resistor. OMG!$$$$$

                      4) both 2, and 3 OMG!$$$$$$$$


                      Using a high quality resistor to ground guarantees a known value that
                      your box can be calibrated to.

                      --
                      -Mark

                      Ne M'oubliez ---Family Motto
                      Hope for the best, plan for the worst ---Personal Motto
                    • mattdbartlett
                      I checked out the link you posted, it jogged my memory. Funny, I was just watching a video on YouTube where the guy was talking about welding parts mounted in
                      Message 10 of 15 , Jun 4, 2012
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                        I checked out the link you posted, it jogged my memory.

                        Funny, I was just watching a video on YouTube where the guy was talking about welding parts mounted in the lathe/mill, and the importance of current not going through the spindle bearing. People elsewhere in the thread have mentioned slip rings of various forms. That may be a good solution. In any case, limiting current to a few mA, especially if you have already introduced an amplifier should keep the bearings from harm.

                        --- In mill_drill@yahoogroups.com, "Rick Sparber" <rgsparber@...> wrote:
                        >
                        > Matt,
                        >
                        > I completely agree and wrote this up back on May 28th:
                        >
                        > http://rick.sparber.org/LTEEF.pdf
                        >
                        > The problem I found was that people were not interested in this solution.
                        >
                        > It takes more than 4 amplifiers to get this circuit to work but I'm using
                        > LM324 quad op amps which I buy at Circuit Specialists for 25 cents each.
                        > Even at Radio Shack they are only $2.50. So cost is not an issue.
                        >
                        > I do have another design that uses 1 mA instead of 1 amp. It has so much
                        > gain that I think I am picking up a local radio station through the leads. I
                        > can't imagine it working in a regular, electrically noisy machine shop.
                        >
                        > Rick
                        >
                        > -----Original Message-----
                        > From: mill_drill@yahoogroups.com [mailto:mill_drill@yahoogroups.com] On
                        > Behalf Of mattdbartlett
                        > Sent: Monday, June 04, 2012 11:26 AM
                        > To: mill_drill@yahoogroups.com
                        > Subject: [mill_drill] Re: damaging bearings with current
                        >
                        > The current is what is going to do most of the damage (well, the combination
                        > is). It seems like a better approach would be to insulate your contact tip
                        > from the spindle nose, and avoid this alltogether. Is that possible?
                        >
                        > At 20mV you are going to need an amplifier or something to increase the
                        > voltage so that you can see the "touchoff" aren't you? Led's are around
                        > 1.2-1.7V at about 15-60mA, and piezo buzzers are on the order of 5v (not
                        > sure of current).
                        >
                        > In any case, minimizing current through your bearings is good. Seems like
                        > you could machine a non-conductive spacer to insulate the conductive tip
                        > from the shank, though I am not familiar with your design.
                        >
                      • davekelloggs
                        Hi Folks - For EEF, has anyone considered using a high frequency circuit in combination with resistance detection? I m kind of on the edge of my knowledge
                        Message 11 of 15 , Jun 5, 2012
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                          Hi Folks -

                          For EEF, has anyone considered using a high frequency circuit in combination with resistance detection? I'm kind of on the edge of my knowledge here, but if you get up toward 10 - 100 MHz, inductance comes into play, and there may be an avenue to a "simple" solution.

                          Its just a thought for the gurus here.
                          Dave Kellogg
                        • Rick Sparber
                          Matt, I hope you now understand that shorting out the bearing with slip rings just makes it harder to see touch-down. It is essential that I develop a voltage
                          Message 12 of 15 , Jun 6, 2012
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                            Matt,

                            I hope you now understand that shorting out the bearing with slip rings just
                            makes it harder to see touch-down. It is essential that I develop a voltage
                            between cutter and work piece before touch-down. Only then can I detect a
                            drop in voltage which tells me I am at touch-down.

                            Rick

                            -----Original Message-----
                            From: mill_drill@yahoogroups.com [mailto:mill_drill@yahoogroups.com] On
                            Behalf Of mattdbartlett
                            Sent: Monday, June 04, 2012 10:40 PM
                            To: mill_drill@yahoogroups.com
                            Subject: [mill_drill] Re: damaging bearings with current

                            I checked out the link you posted, it jogged my memory.

                            Funny, I was just watching a video on YouTube where the guy was talking
                            about welding parts mounted in the lathe/mill, and the importance of current
                            not going through the spindle bearing. People elsewhere in the thread have
                            mentioned slip rings of various forms. That may be a good solution. In any
                            case, limiting current to a few mA, especially if you have already
                            introduced an amplifier should keep the bearings from harm.
                          • Rick Sparber
                            Dave, It is hard to beat DC for simple. I have another design that uses a 2 KHz square wave but can t get it to work. Lots of complex issues in it. I will
                            Message 13 of 15 , Jun 6, 2012
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                              Dave,

                              It is hard to beat DC for simple. I have another design that uses a 2 KHz
                              square wave but can't get it to work. Lots of complex issues in it. I will
                              probably revisit it later but if I can get it to work, the circuit will
                              probably be at least twice as complex plus very sensitive to noise like from
                              VFDs.

                              Rick

                              -----Original Message-----
                              From: mill_drill@yahoogroups.com [mailto:mill_drill@yahoogroups.com] On
                              Behalf Of davekelloggs
                              Sent: Tuesday, June 05, 2012 7:04 AM
                              To: mill_drill@yahoogroups.com
                              Subject: [mill_drill] Re: damaging bearings with current


                              Hi Folks -

                              For EEF, has anyone considered using a high frequency circuit in combination
                              with resistance detection? I'm kind of on the edge of my knowledge here,
                              but if you get up toward 10 - 100 MHz, inductance comes into play, and there
                              may be an avenue to a "simple" solution.

                              Its just a thought for the gurus here.
                              Dave Kellogg
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