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RE: [VanDeGraaffGenerator] Roller Crown Clarification

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  • Richard Linder
    ... I finally got back to my VDG project. I have my shafts, bearings, Teflon and Nylon (Nylon 6/6 from McMaster-Carr... is that the right stuff ?), My records
    Message 1 of 17 , Mar 1, 2008
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      Don:

       

      -------------------------------------------------------------------------------
      I finally got back to my VDG project. I have my shafts, bearings,
      Teflon and Nylon (Nylon 6/6 from McMaster-Carr. .. is that the "right
      stuff"?),

       

      My records show the nylon to be MDS filled nylon McM #2889K13   I do recall one variety of nylon that did not work. I know I dumped that stuff and probably disposed of the paperwork so I am pretty sure the 2889K13 is OK.

      ------------------------------------------------------------------------------

      and a local old-timer tool and die maker has agreed to make
      my rollers, using the same basic construction as the rollers in your
      machines... that is, with the bearings to the sides of the rollers...
      not in them. He had several ideas about how he would make them:

      ----------------------------------------------------------------------------

      My bearings are not fastened to the rollers. See the pictures.

      -----------------------------------------------------------------------------

       



      1. Start with pieces of material larger than the desired rollers.

       

      2. Drill undersized holes through the centers for the shafts

      3. Press the shafts into the rollers.
      4. Use a collet, rather than a 3-jaw chuck

      5. Turn the blank to a perfect cylinder, a little larger diameter than
      the finished roller will be.

      6. When cutting the crown, set the compound rest on the lathe and cut
      one side. Then, take the roller out of the lathe, and put the other
      end of the shaft in the collet. Use the same compound setting to cut
      the other side of the crown. That way, both crown angles will be
      exactly the same.

      ----------------------------------------------------------------------------

      Re: 1-6  My shafts are a press and any eccentricity was eliminated in the turning process.

      Using a compound rest will result in a conical profile. I think the ideal situation would be to have an arc contour. I made a template that had the contour and actually crowned the rollers with a file and a lot of patience.  


      7. Make the lower roller and drive pulley in one piece. The drive
      pulley will be between the bearings, like the roller. This results in
      a more-compact setup. No need to connect the pulley to the shaft, and
      disassembly for cleaning is simplified without removing the drive pulley.

      ---------------------------------------------------------------------------------------------------------------------

      A good idea if you want to forgo the option of changing pulley diameters. Some folks prefer a variac and universal motor rather than mess with pulley diameters.  That’s what I am using.

      ------------------------------------------------------------------------------------------------------------------


      I still l have a question concerning the proper crown for use
      with the coated Nylon fabric belt material from McMaster-Carr. I read
      all your posts that mention rollers... 45 of them!

      ----------------------------------------------------------------------------------

      Yup 45 posts. I was in roller-crown hell during that time. That’s why, out of frustration I wound up crowning the rollers manually, literally cutting and trying to achieve a crown that was compatible with the belt material (MCM #8810K123). In other words in the case of a “non stretch”  belt the crown is very slight otherwise the belt will not wrap around a more pronounced contour. In the case of stretchy belts the crown is less fussy but stretchy  belts do all kinds of nasty things at high speed.

       

       I did some reverse
      engineering to determine exactly what worked for you. There were three
      specifications you recommended:

      A. Roller crown angle is 1/8" per foot.

      B. 6" wide rollers, 3.065" at center, and 3.020" at ends.

      C. I chose a belt material …..worked well with about a 2-3 degree crown.
      Any more than that prevented the edges of the belt from actually
      touching the roller.

      Let's see...
      Tan 2 Deg = 0.03492, that's 0.41904" of taper per foot, and
      Tan 3 Deg = 0.05241, that's 0.62892" of taper per foot.

      What's the final verdict?

      ---------------------------------------------------------------------------------------

      First of all by comparing my results with yours, it looks like I could have been successful with a more severe crown but…. once I achieved reliable tracking, I quit while I was ahead. Also, I always had the option of shaving a bit more off ..you can’t put the stuff back!   One other thing to keep in mind is the belt material you have might be different   from mine even though it has the same Cat#. The mfg has the prerogative to change the vinyl and nylon characteristics which might influence the tracking characteristics AND the triboelectric characteristics as well!.

       

      I would err on the safe side. A return trip to the machinist to increase the crown is better than having to reduce the crown by reducing the roller diameter and re-crowning.  

      -----------------------------------------------------------------------------------
      One more question... How are triboelectric- series charts developed? Is
      there a way to determine where something that is not on any of the
      charts would fit? Can I do it?

      -----------------------------------------------------------------------------------

      If you picture the triboelectric  list vertically with + on top and – on the bottom: If material “X”  is rubbed with material “Y” and material “Y” assumes a + charge and material “X” assumes a – charge then material “Y” will be above (more +) material “X” on the list. You would need to be able to measure the polarity and quantity of the charge to determine the proper  location  on the tribo list.  Logically, if your rollers were at opposite ends of the list, you would choose a belt material that was mid way. Well, life is not like that. As you know a lot of other considerations enter into the choice of roller and belt materials.

      Dick

    • jacobsmach
      Dick, Thanks for your prompt and informative reply. Things were getting a little slow in the group, and it s good to see some action. ... I ll try rubbing my
      Message 2 of 17 , Mar 1, 2008
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        Dick,

        Thanks for your prompt and informative reply. Things were getting a
        little slow in the group, and it's good to see some action.

        ----------------------------------------------------------------------
        > Don wrote:
        > I finally got back to my VDG project. I have my shafts, bearings,
        > Teflon and Nylon (Nylon 6/6 from McMaster-Carr... is that the "right
        > stuff"?)
        >
        > Dick replied:
        > My records show the nylon to be MDS filled nylon McM #2889K13 I do
        > recall one variety of nylon that did not work. I know I dumped that
        > stuff and probably disposed of the paperwork so I am pretty sure the
        > 2889K13 is OK.
        >
        I'll try rubbing my chunk of Nylon 6/6 with rabbit fur to see if it
        dissipates the charge. I assume that the Nylon that didn't work for
        you was slightly conductive. I sure don't want to have the piece
        remade because I picked the wrong material. I'll let you know how
        things "turned" out.
        >
        ---------------------------------------------------------------------
        > Dick wrote:
        > Using a compound rest will result in a conical profile. I think the
        > ideal situation would be to have an arc contour. I made a template
        > that had the contour and actually crowned the rollers with a file
        > and a lot of patience.
        >
        Actually, I was thinking of a trapezoidal crown with the center a flat
        cylinder. I'll ask the machinist to make an arced crown which, I
        assume, would be circular in profile.
        >
        ---------------------------------------------------------------------
        > Don wrote:
        > 7. Make the lower roller and drive pulley in one piece. The drive
        > pulley will be between the bearings, like the roller. This results
        > in a more-compact setup. No need to connect the pulley to the shaft,
        > and disassembly for cleaning is simplified without removing the
        > drive pulley.
        >
        > Dick replied:
        > A good idea if you want to forgo the option of changing pulley
        > diameters. Some folks prefer a variac and universal motor rather
        > than mess with pulley diameters. That's what I am using.
        >
        That's what I plan also. I got a Variac and 1/2-HP 10,000-RPM AC-AC
        motor on eBay. It's way more than needed to run the VDG. Unlike AC
        motors, which will overheat if very-lightly loaded, DC motors run cool
        under the same condition. I figure a one-to-one pulley ratio will be
        good. I plan to use small 1" drive pulley diameters. Larger pulleys
        would connect the motor to the lower-roller pulley more solidly, but I
        am hoping that the drive belt will slip if anything in the VDG jams...
        sort of a mechanical fuse. I will tension it no more than required to
        run the VDG.
        >
        ---------------------------------------------------------------------
        > Don wrote:
        > I still l have a question concerning the proper crown for use
        > with the coated Nylon fabric belt material from McMaster-Carr. I
        > read all your posts that mention rollers... 45 of them!
        >
        > Dick replied:
        > Yup 45 posts. I was in roller-crown hell during that time. That's
        > why, out of frustration I wound up crowning the rollers manually,
        > literally cutting and trying to achieve a crown that was compatible
        > with the belt material (MCM #8810K123). In other words in the case
        > of a "non stretch" belt the crown is very slight otherwise the
        > belt will not wrap around a more pronounced contour. In the case
        > of stretchy belts the crown is less fussy but stretchy belts do
        > all kinds of nasty things at high speed.
        >
        Roller-crown hell is something I would rather avoid. I intend to
        learn from your experience. It makes sense that the minimum crown that
        gets good tracking is best, as the belt must touch the rollers for the
        VDG to work. Excess roller crown can only be detrimental because it
        would make a non-stretchy belt lift off the rollers at the sides.

        I was thinking of roller diameters and centrifugal force, which a
        smaller roller diameter would reduce. I'll have to do some more
        figuring to see if the increased RPMs for the same belt-surface
        speed would counteract any benefit. Even if the belt will not stretch
        enough to allow the up and down sides of the belt to contact, there
        must be some point at which charges will be exchanged due to skinny
        rollers.

        I also wondered if aerodynamic forces become a factor at high belt
        speeds. If air is drawn in under the belt when it contacts the
        rollers, it might contribute to lifting it off the roller. Eliminating
        the air by operating in a vacuum is no good, as the charge combs work
        by ionizing the air. I wonder if there is a way to block some of the
        air from entering between the belt and rollers without interfering
        with the operation of a VDG. Its something on which I'll work.

        Don Jacobs
      • Richard Linder
        Don: Yes, this group has an immense aggregate of electrical talent and any sign of its demise is troublesome. I hope anyone out there who might not be posting
        Message 3 of 17 , Mar 2, 2008
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          Don:

           

          Yes, this group has an immense aggregate of electrical talent and any sign of its demise is troublesome.  I hope anyone out there who might not be posting questions for whatever reason should overcome their shyness and please jump in. We are here to help, swap ideas and keep the group active.    

           

          We are in the home stretch of the 2007-2008 static electricity show. Every year the Burlington Science Center tours the schools with a show that lasts about an hour. About six years ago I was invited to go to the Boston  Museum of Science and  operate the “original” VDG.  Quite a thrill. That experience motivated me to build the one that I use in the show.

           

          OFF TOPIC:   Your latest reply contains my response to your last e-mail. As you can see, I separated your (edited) text from my response with dashed lines. When you replied to me, did you add your name and my name to the respective paragraphs or do we have a very smart e-mail / forum system that did it automatically  ???

           

          Dick

           


          From: VanDeGraaffGenerator@yahoogroups.com [mailto:VanDeGraaffGenerator@yahoogroups.com] On Behalf Of jacobsmach
          Sent: Saturday, March 01, 2008 7:23 PM
          To: VanDeGraaffGenerator@yahoogroups.com
          Subject: [VanDeGraaffGenerator] Re: Roller Crown Clarification

           

          Dick,

          Thanks for your prompt and informative reply. Things were getting a
          little slow in the group, and it's good to see some action.

          ------------ --------- --------- --------- --------- --------- -

          > Don wrote:
          > I finally got back to my VDG project. I have my shafts, bearings,
          > Teflon and Nylon (Nylon 6/6 from McMaster-Carr. .. is that the
          "right
          > stuff"?)
          >
          > Dick replied:
          > My records show the nylon to be MDS filled nylon McM #2889K13 I do
          > recall one variety of nylon that did not work. I know I dumped that
          > stuff and probably disposed of the paperwork so I am pretty sure the
          > 2889K13 is OK.
          >
          I'll try rubbing my chunk of Nylon 6/6 with rabbit fur to see if it
          dissipates the charge. I assume that the Nylon that didn't work for
          you was slightly conductive. I sure don't want to have the piece
          remade because I picked the wrong material. I'll let you know how
          things "turned" out.
          >
          ------------ --------- --------- --------- --------- --------- -
          > Dick wrote:
          > Using a compound rest will result in a conical profile. I think the
          > ideal situation would be to have an arc contour. I made a template
          > that had the contour and actually crowned the rollers with a file
          > and a lot of patience.
          >
          Actually, I was thinking of a trapezoidal crown with the center a flat
          cylinder. I'll ask the machinist to make an arced crown which, I
          assume, would be circular in profile.
          >
          ------------ --------- --------- --------- --------- --------- -
          > Don wrote:
          > 7. Make the lower roller and drive pulley in one piece. The drive
          > pulley will be between the bearings, like the roller. This results
          > in a more-compact setup. No need to connect the pulley to the shaft,
          > and disassembly for cleaning is simplified without removing the
          > drive pulley.
          >
          > Dick replied:
          > A good idea if you want to forgo the option of changing pulley
          > diameters. Some folks prefer a variac and universal motor rather
          > than mess with pulley diameters. That's what I am using.
          >
          That's what I plan also. I got a Variac and 1/2-HP 10,000-RPM AC-AC
          motor on eBay. It's way more than needed to run the VDG. Unlike AC
          motors, which will overheat if very-lightly loaded, DC motors run cool
          under the same condition. I figure a one-to-one pulley ratio will be
          good. I plan to use small 1" drive pulley diameters. Larger pulleys
          would connect the motor to the lower-roller pulley more solidly, but I
          am hoping that the drive belt will slip if anything in the VDG jams...
          sort of a mechanical fuse. I will tension it no more than required to
          run the VDG.
          >
          ------------ --------- --------- --------- --------- --------- -
          > Don wrote:
          > I still l have a question concerning the proper crown for use
          > with the coated Nylon fabric belt material from McMaster-Carr. I
          > read all your posts that mention rollers... 45 of them!
          >
          > Dick replied:
          > Yup 45 posts. I was in roller-crown hell during that time. That's
          > why, out of frustration I wound up crowning the rollers manually,
          > literally cutting and trying to achieve a crown that was compatible
          > with the belt material (MCM #8810K123). In other words in the case
          > of a "non stretch" belt the crown is very slight otherwise the
          > belt will not wrap around a more pronounced contour. In the case
          > of stretchy belts the crown is less fussy but stretchy belts do
          > all kinds of nasty things at high speed.
          >
          Roller-crown hell is something I would rather avoid. I intend to
          learn from your experience. It makes sense that the minimum crown that
          gets good tracking is best, as the belt must touch the rollers for the
          VDG to work. Excess roller crown can only be detrimental because it
          would make a non-stretchy belt lift off the rollers at the sides.

          I was thinking of roller diameters and centrifugal force, which a
          smaller roller diameter would reduce. I'll have to do some more
          figuring to see if the increased RPMs for the same belt-surface
          speed would counteract any benefit. Even if the belt will not stretch
          enough to allow the up and down sides of the belt to contact, there
          must be some point at which charges will be exchanged due to skinny
          rollers.

          I also wondered if aerodynamic forces become a factor at high belt
          speeds. If air is drawn in under the belt when it contacts the
          rollers, it might contribute to lifting it off the roller. Eliminating
          the air by operating in a vacuum is no good, as the charge combs work
          by ionizing the air. I wonder if there is a way to block some of the
          air from entering between the belt and rollers without interfering
          with the operation of a VDG. Its something on which I'll work.

          Don Jacobs

        • Steve
          ... I m no expert in VDG making, but- I think a smaller roller will -increase- the force separating the belt from the roller. Consider the same belt speed: the
          Message 4 of 17 , Mar 2, 2008
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            --- In VanDeGraaffGenerator@yahoogroups.com, "jacobsmach" <hihoag@...>
            wrote:


            > I was thinking of roller diameters and centrifugal force, which a
            > smaller roller diameter would reduce. I'll have to do some more
            > figuring to see if the increased RPMs for the same belt-surface
            > speed would counteract any benefit. Even if the belt will not stretch
            > enough to allow the up and down sides of the belt to contact, there
            > must be some point at which charges will be exchanged due to skinny
            > rollers.

            I'm no expert in VDG making, but- I think a smaller roller will
            -increase- the force separating the belt from the roller. Consider the
            same belt speed: the smaller roller must turn at much higher RPM. That
            isn't the problem: the belt must change direction much more quickly on
            a small roller than a large for a given belt speed.

            > I also wondered if aerodynamic forces become a factor at high belt
            > speeds. If air is drawn in under the belt when it contacts the
            > rollers, it might contribute to lifting it off the roller. Eliminating
            > the air by operating in a vacuum is no good, as the charge combs work
            > by ionizing the air. I wonder if there is a way to block some of the
            > air from entering between the belt and rollers without interfering
            > with the operation of a VDG. Its something on which I'll work.

            Knurling? I'm thinking chevron V grooves cut so the points contact the
            belt first, so the air has a path to rush out of. Like tire tread
            designed to avoid hyrdoplaning. Square bottomed grooves would be
            better than V bottomed, because it provides a larger path for air
            without sacrificing more contact area.

            Steve Greenfield
          • Steve
            Oh, and if you use smaller rollers, it will be more likely for the belts to contact itself between the top and bottom. Steve Greenfield
            Message 5 of 17 , Mar 2, 2008
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              Oh, and if you use smaller rollers, it will be more likely for the
              belts to contact itself between the top and bottom.

              Steve Greenfield
            • jacobsmach
              Dick, Thanks for your positive sharing attitude. The amount of information available here is shocking . It must have been inspiring to operate the big VDG
              Message 6 of 17 , Mar 2, 2008
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                Dick,

                Thanks for your "positive" sharing attitude. The amount of information
                available here is "shocking". It must have been inspiring to operate
                the big VDG at BMS. The machine shown on the group's home page is the
                one about which you're speaking, right? Apparently, it "sparked" a
                continued interest.

                About my annotated reply... the system is as dumb as ever. I added our
                names at the appropriate places places for the benefit of others.
                Otherwise, there was a "potential" for confusion.

                Don Jacobs

                Richard Linder wrote:
                >
                > Don:
                >
                > Yes, this group has an immense aggregate of electrical talent
                > and any sign of its demise is troublesome. I hope anyone out
                > there who might not be posting questions for whatever reason
                > should overcome their shyness and please jump in. We are here
                > to help, swap ideas and keep the group active.
                >
                > We are in the home stretch of the 2007-2008 static electricity
                > show. Every year the Burlington Science Center tours the schools
                > with a show that lasts about an hour. About six years ago I was
                > invited to go to the Boston Museum of Science and operate the
                > "original" VDG. Quite a thrill. That experience motivated me to
                > build the one that I use in the show.
                >
                > OFF TOPIC: Your latest reply contains my response to your last
                > e-mail. As you can see, I separated your (edited) text from my
                > response with dashed lines. When you replied to me, did you add
                > your name and my name to the respective paragraphs or do we have
                > a very smart e-mail / forum system that did it automatically ???
                >
                > Dick
              • Richard Linder
                In general all parameters in a VDG will have a bearing on others. Belt speed relates to roller diameter which relates to centrifugal force -tracking-belt
                Message 7 of 17 , Mar 2, 2008
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                  In general all parameters in a VDG will have a bearing on others. Belt speed relates to roller diameter which relates to centrifugal force –tracking—belt material—delivery of charge to the hv terminal-- bearing temperature – noise – integrity of belt splice and on and on.

                   

                  I guess you would start the thought process by establishing a desired voltage at the terminal. This would determine the minimum diameter of the sphere, its involute and the minimum/maximum  value of resistance / leakage along the support column. Once this is established the delivery of electrons to the sphere will involve spacing and quantity of spray & collector points,  belt area per unit time passing the spray points, belt width, linear speed, roller diameter, tracking etc. and of course choice of roller and belt materials. Often overlooked is the method of splicing the belt so that at the design speed and curvature of the rollers  the splice doe not fail in two minutes.

                   

                  That’s why most of us start with what looks like a reasonable design and then fine tune the initial model for revision !, 2, 3, etc.  What is cool is if you can build a prototype whose configuration is easily varied. For example a support column whose length can be changed by adding or removing sections. Roller supports that are roomy enough to allow a variety of roller diameters. A Variac controlled universal motor and a variable number and spacing of spray/collector points.

                   

                  There are no pictures of my prototype. The goal of the first prototype was to establish a belt and roller design:-- belt and roller material and dimensions, belt speed and desired charging current. Since there was no high voltage involved, the roller supports, terminal support and other related items were constructed of  medium hard wood.  Given an adequate supply of wood and glue,  everything was thrown away except for the final roller, belt and drive mechanism.  It was at this point the rollers, belt and charging current was established

                   

                  Since there was a mention of roller diameter consider this: at a given belt speed as we reduce the roller diameter the splice will have to endure a more severe flexing as it passes over the roller. Bearing temperature will become an important consideration as will bearing wear and noise. Crowning and tracking may also become touchy due to reduction in allowable tolerances.. Roller balance can also become a problem.  With a larger diameter roller those issues are diminished.

                   

                  When I was building the big one I was inclined to mentally scale things up from the smaller generator. This turned out to be a pretty good assumption. Having said that,  I never planned to achieve 100 uA at 60mph but, when initially testing the VDG I discovered that at 30mph belt speed I had not reach a current plateau so I kept going. To this day I am not sure I have yet reached that limit but, at this point I am not inclined to push the generator much beyond 60 mph and 100 uA  (chicken)!

                   

                  Please excuse the long dissertation. I am re-living the construction of the “big one”.

                   

                  Dick

                    

                   

                   


                  From: VanDeGraaffGenerator@yahoogroups.com [mailto: VanDeGraaffGenerator@yahoogroups.com ] On Behalf Of Steve
                  Sent: Sunday, March 02, 2008 1:17 PM
                  To: VanDeGraaffGenerator@yahoogroups.com
                  Subject: [VanDeGraaffGenerator] Re: Roller Crown Clarification

                   

                  --- In VanDeGraaffGenerato r@yahoogroups. com, "jacobsmach" <hihoag@...>
                  wrote:

                  > I was thinking of roller diameters and centrifugal force, which a
                  > smaller roller diameter would reduce. I'll have to do some more
                  > figuring to see if the increased RPMs for the same belt-surface
                  > speed would counteract any benefit. Even if the belt will not stretch
                  > enough to allow the up and down sides of the belt to contact, there
                  > must be some point at which charges will be exchanged due to skinny
                  > rollers.

                  I'm no expert in VDG making, but- I think a smaller roller will
                  -increase- the force separating the belt from the roller. Consider the
                  same belt speed: the smaller roller must turn at much higher RPM. That
                  isn't the problem: the belt must change direction much more quickly on
                  a small roller than a large for a given belt speed.

                  > I also wondered if aerodynamic forces become a factor at high belt
                  > speeds. If air is drawn in under the belt when it contacts the
                  > rollers, it might contribute to lifting it off the roller. Eliminating
                  > the air by operating in a vacuum is no good, as the charge combs work
                  > by ionizing the air. I wonder if there is a way to block some of the
                  > air from entering between the belt and rollers without interfering
                  > with the operation of a VDG. Its something on which I'll work.

                  Knurling? I'm thinking chevron V grooves cut so the points contact the
                  belt first, so the air has a path to rush out of. Like tire tread
                  designed to avoid hyrdoplaning. Square bottomed grooves would be
                  better than V bottomed, because it provides a larger path for air
                  without sacrificing more contact area.

                  Steve Greenfield

                • Richard Linder
                  Don: Thanks for adding the names. It does clear things up for the initial reader. Yes that VDG is the one that was built by Robert J. Van deGraaff. While at
                  Message 8 of 17 , Mar 2, 2008
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                    Don: Thanks for adding the names. It does clear things up for the initial reader.

                     

                    Yes that VDG is the one that was built by Robert J. Van deGraaff. While at MIT, there was an insulated enclosed bridge between the two spheres.  Many experiments that had to be conducted in a high voltage gradient environment were conducted by scientists in that bridge while the VDG was humming away.

                     

                    They had many instruments up there that required 115 VAC to operate. Surely they could not have a long extension cord running to ground potential!  They had an alternator in the bridge driven via a long belt by an electric motor at ground level.

                     

                    BTW it is legend that RJV had a bad back and used to lay on the floor at MIT and just watch the VDG arc. He claimed the VDG had therapeutic qualities. I think he was getting high on the ozone!  

                     

                    Dick

                     


                    From: VanDeGraaffGenerator@yahoogroups.com [mailto: VanDeGraaffGenerator@yahoogroups.com ] On Behalf Of jacobsmach
                    Sent: Sunday, March 02, 2008 3:24 PM
                    To: VanDeGraaffGenerator@yahoogroups.com
                    Subject: [VanDeGraaffGenerator] Re: Roller Crown Clarification

                     

                    Dick,

                    Thanks for your "positive" sharing attitude. The amount of information
                    available here is "shocking". It must have been inspiring to operate
                    the big VDG at BMS. The machine shown on the group's home page is the
                    one about which you're speaking, right? Apparently, it "sparked" a
                    continued interest.

                    About my annotated reply... the system is as dumb as ever. I added our
                    names at the appropriate places places for the benefit of others.
                    Otherwise, there was a "potential" for confusion.

                    Don Jacobs

                    Richard Linder wrote:

                    >
                    > Don:
                    >
                    > Yes, this group has an immense aggregate of electrical talent
                    > and any sign of its demise is troublesome. I hope anyone out
                    > there who might not be posting questions for whatever reason
                    > should overcome their shyness and please jump in. We are here
                    > to help, swap ideas and keep the group active.
                    >
                    > We are in the home stretch of the 2007-2008 static electricity
                    > show. Every year the Burlington
                    Science Center tours the schools
                    > with a show that lasts about an hour. About six years ago I was
                    > invited to go to the Boston Museum of Science and operate the
                    > "original" VDG. Quite a thrill. That experience motivated me to
                    > build the one that I use in the show.
                    >
                    > OFF TOPIC: Your latest reply contains my response to your last
                    > e-mail. As you can see, I separated your (edited) text from my
                    > response with dashed lines. When you replied to me, did you add
                    > your name and my name to the respective paragraphs or do we have
                    > a very smart e-mail / forum system that did it automatically ???
                    >
                    > Dick

                  • jacobsmach
                    ... Oops, I was thinking of a constant roller RPM, and not belt speed when I suggested a smaller diameter roller. You are quite right about smaller rollers
                    Message 9 of 17 , Mar 2, 2008
                    • 0 Attachment
                      > > Don wrote:
                      > >
                      > > I was thinking of roller diameters and centrifugal force, which a
                      > > smaller roller diameter would reduce. I'll have to do some more
                      > > figuring to see if the increased RPMs for the same belt-surface
                      > > speed would counteract any benefit. Even if the belt will not
                      > > stretch enough to allow the up and down sides of the belt to
                      > > contact, there must be some point at which charges will be
                      > > exchanged due to skinny rollers.
                      >
                      > Steve wrote:
                      > I'm no expert in VDG making, but- I think a smaller roller will
                      > -increase- the force separating the belt from the roller. Consider
                      > the same belt speed: the smaller roller must turn at much higher
                      > RPM. That isn't the problem: the belt must change direction much
                      > more quickly on a small roller than a large for a given belt speed.
                      >
                      Oops, I was thinking of a constant roller RPM, and not belt speed when
                      I suggested a smaller diameter roller. You are quite right about
                      smaller rollers increasing the centrifugal force. Oh well...
                      <
                      ---------------------------------------------------------------------
                      > >
                      > > Don wrote:
                      > > I also wondered if aerodynamic forces become a factor at high belt
                      > > speeds. If air is drawn in under the belt when it contacts the
                      > > rollers, it might contribute to lifting it off the roller.
                      > > Eliminating the air by operating in a vacuum is no good, as the
                      > > charge combs work by ionizing the air. I wonder if there is a way
                      > > to block some of the air from entering between the belt and
                      > > rollers without interfering with the operation of a VDG. Its
                      > > something on which I'll work.
                      >
                      > Steve wrote:
                      >
                      > Knurling? I'm thinking chevron V grooves cut so the points contact
                      > the belt first, so the air has a path to rush out of. Like tire
                      > tread designed to avoid hydroplaning. Square bottomed grooves would
                      > be better than V bottomed, because it provides a larger path for
                      > air without sacrificing more contact area.
                      >
                      I think you're on the right "track" with your tire-tread idea. Chevron
                      cuts would be difficult to machine... especially while maintaining
                      balance. Any air pressure between the belt and the roller should be
                      sufficient to force the air along straight cuts and out where the belt
                      leaves the roller on the other side. Inverted V grooves, with the
                      pointy end of the V on the roller's surface, takes your idea a step
                      further and increases the contact area between the belt and roller.

                      Maybe a series of little holes across the roller's surface, connected
                      to the sides of the roller by holes parallel to the roller's shaft
                      would work. That would increase the contact area even more, but would
                      be nightmare to machine. After making such a roller, dynamic balancing
                      might be required. The place to start experimenting is probably with
                      straight grooves to see if increased belt speed is possible by
                      reducing the trapped air between the belt and roller.

                      Don Jacobs
                    • jacobsmach
                      In an earlier post, I said, I ll try rubbing my chunk of Nylon 6/6 with rabbit fur to see if it it dissipates the charge. This was after Dick Linder said he
                      Message 10 of 17 , Mar 2, 2008
                      • 0 Attachment
                        In an earlier post, I said, "I'll try rubbing my chunk of Nylon 6/6
                        with rabbit fur to see if it it dissipates the charge." This was after
                        Dick Linder said he tried using an unknown kind of Nylon that did not
                        work as a VDG roller. He finally used MDS-filled Nylon, and it works
                        well. Anyhow, I was incorrect in my choice of rabbit fur for rubbing
                        the Nylon. They are both pretty close to each other on the + end of
                        the triboelectric series. I'd be better off using Orlon, Rayon, or
                        Polyester, which are far into the - end of the series. Any difference
                        in the rubbed materials will produce opposite charges on each piece,
                        but the further away they are from each other on the triboelectric
                        series, the better the effect will be.

                        Rabbit fur would be good for testing material for a - roller. It is
                        further up the + end of the scale than cat fur. I rubbed my live cat
                        with my 2" x 5" piece of Teflon, and held it up to my ear. An easily
                        audible snap confirmed that it had collected the cat ions. I
                        understand cat pelts are available, but I don't want it to look like
                        someone's pet! I'm waiting for my rabbit pelt to arrive.

                        When it does, I will make an electrophorus. The original plan was to
                        use a 12" x 12" Teflon plate, but anything thick enough to remain flat
                        when used for the dielectric plate would be too expensive. I plan to
                        use a thin layer of Teflon that has been etched on one side to make it
                        bondable with epoxy (McMaster-Carr has it). Then, I'll stick it to a
                        piece of 12" x 12" PVC plate. The PVC will act as an insulator and
                        keep the thin Teflon flat. I'm looking for a 12" pizza pan with a big
                        rolled edge for the metal plate. The big rolled edge will prevent
                        charge loss through corona discharge. Add an insulating handle for the
                        pizza pan, and it's finished.

                        The electrophorus is simple enough to understand and explain to young
                        kids with no previous electrical knowledge. An inexpensive one could
                        even be a good project to make and keep. Then, the kid could maintain
                        interest, explain it to others, and perhaps be inspired to do some
                        further research. Gee, fun and education combined!

                        Don Jacobs
                      • Richard Linder
                        Not based on experience but a gut feel:- texturing or grooving etc the roller surface may reduce the surface area touching the belt to the point where the
                        Message 11 of 17 , Mar 3, 2008
                        • 0 Attachment

                           

                          Not based on experience but a gut feel:-  texturing  or grooving etc  the roller surface may reduce the surface area touching the belt to the point where the triboelectric action between the roller and belt may be compromised.

                           

                          Just entered my mind…. For the bottom roller to attract electrons from the spray points it must become positively charged. It is important to not have spray points near the edges of the belt. I have left a generous 10%  of “unsprayed” belt on both edges of the belt. This is to insure that you do not spray the exposed roller ends with electrons which would reduce the + charge of the roller and thus diminish electron  transfer to the belt. Of course if the belt were a bit wider than the roller and the belt did not meander left and right, this would not be an issue.

                           

                          Dick


                          From: VanDeGraaffGenerator@yahoogroups.com [mailto: VanDeGraaffGenerator@yahoogroups.com ] On Behalf Of jacobsmach
                          Sent: Sunday, March 02, 2008 4:07 PM
                          To: VanDeGraaffGenerator@yahoogroups.com
                          Subject: [VanDeGraaffGenerator] Re: Roller Crown Clarification

                           

                          > > Don wrote:

                          > >
                          > > I was thinking of roller diameters and centrifugal force, which a
                          > > smaller roller diameter would reduce. I'll have to do some more
                          > > figuring to see if the increased RPMs for the same belt-surface
                          > > speed would counteract any benefit. Even if the belt will not
                          > > stretch enough to allow the up and down sides of the belt to
                          > > contact, there must be some point at which charges will be
                          > > exchanged due to skinny rollers.
                          >
                          > Steve wrote:
                          > I'm no expert in VDG making, but- I think a smaller roller will
                          > -increase- the force separating the belt from the roller. Consider
                          > the same belt speed: the smaller roller must turn at much higher
                          > RPM. That isn't the problem: the belt must change direction much
                          > more quickly on a small roller than a large for a given belt speed.
                          >
                          Oops, I was thinking of a constant roller RPM, and not belt speed when
                          I suggested a smaller diameter roller. You are quite right about
                          smaller rollers increasing the centrifugal force. Oh well...
                          <
                          ------------ --------- --------- --------- --------- --------- -
                          > >
                          > > Don wrote:
                          > > I also wondered if aerodynamic forces become a factor at high belt
                          > > speeds. If air is drawn in under the belt when it contacts the
                          > > rollers, it might contribute to lifting it off the roller.
                          > > Eliminating the air by operating in a vacuum is no good, as the
                          > > charge combs work by ionizing the air. I wonder if there is a way
                          > > to block some of the air from entering between the belt and
                          > > rollers without interfering with the operation of a VDG. Its
                          > > something on which I'll work.
                          >
                          > Steve wrote:
                          >
                          > Knurling? I'm thinking chevron V grooves cut so the points contact
                          > the belt first, so the air has a path to rush out of. Like tire
                          > tread designed to avoid hydroplaning. Square bottomed grooves would
                          > be better than V bottomed, because it provides a larger path for
                          > air without sacrificing more contact area.
                          >
                          I think you're on the right "track" with your tire-tread idea. Chevron
                          cuts would be difficult to machine... especially while maintaining
                          balance. Any air pressure between the belt and the roller should be
                          sufficient to force the air along straight cuts and out where the belt
                          leaves the roller on the other side. Inverted V grooves, with the
                          pointy end of the V on the roller's surface, takes your idea a step
                          further and increases the contact area between the belt and roller.

                          Maybe a series of little holes across the roller's surface, connected
                          to the sides of the roller by holes parallel to the roller's shaft
                          would work. That would increase the contact area even more, but would
                          be nightmare to machine. After making such a roller, dynamic balancing
                          might be required. The place to start experimenting is probably with
                          straight grooves to see if increased belt speed is possible by
                          reducing the trapped air between the belt and roller.

                          Don Jacobs

                        • trevor_mixie
                          Hi! every one. I have just joined your group and am looking forward to building a couple of VDG s and Wimshurst machines. I had biult a couple some years back
                          Message 12 of 17 , Mar 4, 2008
                          • 0 Attachment
                            Hi! every one. I have just joined your group and am looking forward
                            to building a couple of VDG's and Wimshurst machines. I had biult a
                            couple some years back and am now just starting to get back into it.
                            My name ie Trevor and I live in the tropics (Cairns) where VDG have
                            to be built rather well to work. My last effoert produced 18" sparks
                            with 30uA. I also had to use the hair dryer a few times. If any one
                            can giuve me advise on the rollers as I have been reading It would be
                            apprieciated. My top roller is going to be nylon and the bottom PVC
                            Pipe as these seem to readily available now and are at the extremes
                            of each other. I do have problems tryiong to get belts though. The
                            ones I use to have were a webbing used for seats and had a 1mm
                            natural rubber inside. Thanks people hope to hear from you and I
                            hope can contribute as I am going.





                            --- In VanDeGraaffGenerator@yahoogroups.com, "Richard Linder"
                            <linder@...> wrote:
                            >
                            >
                            >
                            > Not based on experience but a gut feel:- texturing or grooving
                            etc the
                            > roller surface may reduce the surface area touching the belt to the
                            point
                            > where the triboelectric action between the roller and belt may be
                            > compromised.
                            >
                            >
                            >
                            > Just entered my mind.. For the bottom roller to attract electrons
                            from the
                            > spray points it must become positively charged. It is important to
                            not have
                            > spray points near the edges of the belt. I have left a generous
                            10% of
                            > "unsprayed" belt on both edges of the belt. This is to insure that
                            you do
                            > not spray the exposed roller ends with electrons which would reduce
                            the +
                            > charge of the roller and thus diminish electron transfer to the
                            belt. Of
                            > course if the belt were a bit wider than the roller and the belt
                            did not
                            > meander left and right, this would not be an issue.
                            >
                            >
                            >
                            > Dick
                            >
                            > _____
                            >
                            > From: VanDeGraaffGenerator@yahoogroups.com
                            > [mailto:VanDeGraaffGenerator@yahoogroups.com] On Behalf Of
                            jacobsmach
                            > Sent: Sunday, March 02, 2008 4:07 PM
                            > To: VanDeGraaffGenerator@yahoogroups.com
                            > Subject: [VanDeGraaffGenerator] Re: Roller Crown Clarification
                            >
                            >
                            >
                            > > > Don wrote:
                            > > >
                            > > > I was thinking of roller diameters and centrifugal force, which
                            a
                            > > > smaller roller diameter would reduce. I'll have to do some more
                            > > > figuring to see if the increased RPMs for the same belt-surface
                            > > > speed would counteract any benefit. Even if the belt will not
                            > > > stretch enough to allow the up and down sides of the belt to
                            > > > contact, there must be some point at which charges will be
                            > > > exchanged due to skinny rollers.
                            > >
                            > > Steve wrote:
                            > > I'm no expert in VDG making, but- I think a smaller roller will
                            > > -increase- the force separating the belt from the roller. Consider
                            > > the same belt speed: the smaller roller must turn at much higher
                            > > RPM. That isn't the problem: the belt must change direction much
                            > > more quickly on a small roller than a large for a given belt
                            speed.
                            > >
                            > Oops, I was thinking of a constant roller RPM, and not belt speed
                            when
                            > I suggested a smaller diameter roller. You are quite right about
                            > smaller rollers increasing the centrifugal force. Oh well...
                            > <
                            > ----------------------------------------------------------
                            > > >
                            > > > Don wrote:
                            > > > I also wondered if aerodynamic forces become a factor at high
                            belt
                            > > > speeds. If air is drawn in under the belt when it contacts the
                            > > > rollers, it might contribute to lifting it off the roller.
                            > > > Eliminating the air by operating in a vacuum is no good, as the
                            > > > charge combs work by ionizing the air. I wonder if there is a
                            way
                            > > > to block some of the air from entering between the belt and
                            > > > rollers without interfering with the operation of a VDG. Its
                            > > > something on which I'll work.
                            > >
                            > > Steve wrote:
                            > >
                            > > Knurling? I'm thinking chevron V grooves cut so the points
                            contact
                            > > the belt first, so the air has a path to rush out of. Like tire
                            > > tread designed to avoid hydroplaning. Square bottomed grooves
                            would
                            > > be better than V bottomed, because it provides a larger path for
                            > > air without sacrificing more contact area.
                            > >
                            > I think you're on the right "track" with your tire-tread idea.
                            Chevron
                            > cuts would be difficult to machine... especially while maintaining
                            > balance. Any air pressure between the belt and the roller should be
                            > sufficient to force the air along straight cuts and out where the
                            belt
                            > leaves the roller on the other side. Inverted V grooves, with the
                            > pointy end of the V on the roller's surface, takes your idea a step
                            > further and increases the contact area between the belt and roller.
                            >
                            > Maybe a series of little holes across the roller's surface,
                            connected
                            > to the sides of the roller by holes parallel to the roller's shaft
                            > would work. That would increase the contact area even more, but
                            would
                            > be nightmare to machine. After making such a roller, dynamic
                            balancing
                            > might be required. The place to start experimenting is probably with
                            > straight grooves to see if increased belt speed is possible by
                            > reducing the trapped air between the belt and roller.
                            >
                            > Don Jacobs
                            >
                          • jacobsmach
                            ... I would be happy with the charging rate currently achieved using untextured rollers. The 100 uA you get with a 6 belt is something of a benchmark among
                            Message 13 of 17 , Mar 4, 2008
                            • 0 Attachment
                              Richard Linder wrote:
                              >
                              > Not based on experience but a gut feel:- texturing or grooving
                              > etc the roller surface may reduce the surface area touching the
                              > belt to the point where the triboelectric action between the
                              > roller and belt may be compromised.
                              >
                              I would be happy with the charging rate "currently" achieved using
                              untextured rollers. The 100 uA you get with a 6" belt is something of
                              a benchmark among home-built machines. I wonder how the big one in
                              Boston stacks up. If there is ever an Olympic competition for
                              maximizing charging amperage per unit of belt width, I may actually
                              try some of the air-pressure-relieving techniques.
                              >
                              > Just entered my mind.. For the bottom roller to attract electrons
                              > from the spray points it must become positively charged. It is
                              > important to not have spray points near the edges of the belt. I
                              > have left a generous 10% of "unsprayed" belt on both edges of the
                              > belt. This is to insure that you do not spray the exposed roller
                              > ends with electrons which would reduce the + charge of the roller
                              > and thus diminish electron transfer to the belt. Of course if
                              > the belt were a bit wider than the roller and the belt did not
                              > meander left and right, this would not be an issue.
                              >
                              So, if belt meandering can be reduced to an acceptable amount, a
                              roller narrower than the belt and a spray array as wide as (or wider
                              than) the belt may allow more belt width to be used, increasing
                              charging current. An interesting concept worth further study.

                              Regarding my earlier post about Nylon 6/6, I was amazed at the number
                              of variations of the material. The name is for the chemical
                              composition of the Nylon 6/6 molecule. After that, the types and
                              amounts of additives are numerous. The same goes for Nylon 6, a
                              slightly different Nylon molecule. MDS-filed Nylon 6 is available with
                              several different proportions of MDS. I presume the MDS-filed Nylon
                              you used for the bottom rollers of your machines is whatever
                              McMaster-Carr stocked when you built them. Anyhow, I read somewhere
                              that Nylon 6/6 can absorb atmospheric moisture up to 1.6% of its
                              weight. Not only can this alter its dimensions but, probably, its
                              electrical conductivity. I'm glad I looked into it before having my
                              rollers machined.

                              I had considered the MDS-filled stuff, but decided against it, not
                              knowing if MDS is conductive. apparently not, judging from your
                              success with the MDS-filled Nylon. MDS (molybdenum disulfide) is a dry
                              lubricant. This brings to mind another question regarding lubricating
                              the needle bearings on your big machine. Do you lubricate them? If so,
                              with what? I had eliminated using oils and greases because of possible
                              conductive contamination of the other parts of the VDG. I am thinking
                              of using MDS.

                              Don Jacobs
                            • Richard Linder
                              _____ ... Don wrote: I would be happy with the charging rate currently achieved using untextured rollers. The 100 uA you get with a 6 belt is something of a
                              Message 14 of 17 , Mar 4, 2008
                              • 0 Attachment

                                 

                                 


                                Dick wrote:

                                >
                                > Not based on experience but a gut feel:- texturing or grooving
                                > etc the roller surface may reduce the surface area touching the
                                > belt to the point where the triboelectric action between the
                                > roller and belt may be compromised.  
                                style='color:navy'>

                                Don wrote:
                                I would be happy with the charging rate "currently" achieved using
                                untextured rollers. The 100 uA you get with a 6" belt is something of
                                a benchmark among home-built machines. I wonder how the big one in
                                Boston stacks up. If there is ever an Olympic competition for
                                maximizing charging amperage per unit of belt width, I may actually
                                try some of the air-pressure- relieving techniques

                                Dick wrote:

                                Pictures of the VDG on the MOS website show two belts. I think this was the early stages of construction at Round Hill because two more sets of holes for additional pillow blocks are clearly visible. When I visited the MOS five years ago I seem to remember four belts about 36” wide. The rollers are steel and are sprayed with rows of old fashioned phonograph needles connected to a HV power supply. I would guess charging current in the vicinity of 1200 uA.  

                                .

                                >
                                > Just entered my mind.. For the bottom roller to attract electrons
                                > from the spray points it must become positively charged. It is
                                > important to not have spray points near the edges of the belt. I
                                > have left a generous 10% of "unsprayed" belt on both edges of
                                the
                                > belt. This is to insure that you do not spray the exposed roller
                                > ends with electrons which would reduce the + charge of the roller
                                > and thus diminish electron transfer to the belt. Of course if
                                > the belt were a bit wider than the roller and the belt did not
                                > meander left and right, this would not be an issue.
                                >

                                Don replied:
                                So, if belt meandering can be reduced to an acceptable amount, a
                                roller narrower than the belt and a spray array as wide as (or wider
                                than) the belt may allow more belt width to be used, increasing
                                charging current. An interesting concept worth further study.

                                Dick replied:

                                Theoretically.

                                Don wrote:
                                Regarding my earlier post about Nylon 6/6, I was amazed at the number
                                of variations of the material. The name is for the chemical
                                composition of the Nylon 6/6 molecule. After that, the types and
                                amounts of additives are numerous. The same goes for Nylon 6, a
                                slightly different Nylon molecule. MDS-filed Nylon 6 is available with
                                several different proportions of MDS. I presume the MDS-filed Nylon
                                you used for the bottom rollers of your machines is whatever
                                McMaster-Carr stocked when you built them. Anyhow, I read somewhere
                                that Nylon 6/6 can absorb atmospheric moisture up to 1.6% of its
                                weight. Not only can this alter its dimensions but, probably, its
                                electrical conductivity. I'm glad I looked into it before having my
                                rollers machined.

                                I had considered the MDS-filled stuff, but decided against it, not
                                knowing if MDS is conductive. apparently not, judging from your
                                success with the MDS-filled Nylon. MDS (molybdenum disulfide) is a dry
                                lubricant. This brings to mind another question regarding lubricating
                                the needle bearings on your big machine. Do you lubricate them? If so,
                                with what? I had eliminated using oils and greases because of possible
                                conductive contamination of the other parts of the VDG. I am thinking
                                of using MDS.

                                Dick replied:

                                I cannot guarantee a particular Nylon from McMaster since the formulation may change thus influencing the electrical properties. Don’t forget, I built this thing 5 years ago. During those years McMaster has changed a lot of catalog numbers. You might note this when you order something and you are often confronted with a substitute “same as”  catalog number. Who knows?

                                The speed and radial loading specifications of my roller bearings were way in excess of what the VDG service presented so I never lubricated the bearings and we’re going on 5 years trouble free. Can’t say the same about “Junior”. I used oilite bearings in that generator and always paid attention to the status of the bearings.  

                                 Dick

                              • jacobsmach
                                ... Do any if the machines still exist. If so, please post some photos. Ideally, they should show construction details. ... Welcome to the group, Trevor. 18
                                Message 15 of 17 , Mar 4, 2008
                                • 0 Attachment
                                  Trevor Mixie wrote:
                                  >
                                  > Hi! every one. I have just joined your group and am looking forward
                                  > to building a couple of VDG's and Wimshurst machines. I had built a
                                  > couple some years back and am now just starting to get back into it.

                                  Do any if the machines still exist. If so, please post some photos.
                                  Ideally, they should show construction details.

                                  > My name is Trevor and I live in the tropics (Cairns) where VDG have
                                  > to be built rather well to work. My last effort produced 18" sparks
                                  > with 30uA. I also had to use the hair dryer a few times.

                                  Welcome to the group, Trevor. 18" sparks is very impressive, as is
                                  30uA. Many of us could benefit by learning more about these machines.

                                  > If any one can give me advise on the rollers as I have been
                                  > reading It would be appreciated. My top roller is going to be
                                  > nylon and the bottom PVC Pipe as these seem to readily available
                                  > now and are at the extremes of each other. I do have problems
                                  > trying to get belts though. The ones I use to have were a webbing
                                  > used for seats and had a 1mm natural rubber inside. Thanks people
                                  > hope to hear from you and I hope can contribute as I am going.

                                  Nylon on the top and PVC on the bottom will make your machine a
                                  positive-charging one. Negative-charging machines seem to work better
                                  for some reason. I suggest using the Nylon on the bottom and the PVC
                                  on the top. The archived posts contain information on several aspects
                                  of VDG building. However, there is not much here on Wimshurst
                                  machines. I suggest reading the older posts. You will find sources for
                                  belt and roller materials, as well as many subjects.

                                  Keep in touch.

                                  Don Jacobs
                                • trevor_mixie
                                  Thanks Don Nice to hear from someone and it appears I sent the same message a few times. Ny apologies for that to everyone. I will do as you suggest as I do
                                  Message 16 of 17 , Mar 5, 2008
                                  • 0 Attachment
                                    Thanks Don

                                    Nice to hear from someone and it appears I sent the same message a
                                    few times. Ny apologies for that to everyone.
                                    I will do as you suggest as I do want negative ions. The reason is it
                                    is good for you and does not produce as much ozone in the air.
                                    Negative ions are godd for asthma sufferers as well. Its the negative
                                    ions in the air priot to a good thunderstorm that makes you feel real
                                    good before it hits of course. I will also send some pics as I am
                                    going ahead with the machine.

                                    Thanks
                                    Trev


                                    --- In VanDeGraaffGenerator@yahoogroups.com, "jacobsmach"
                                    <hihoag@...> wrote:﷯﷯
                                    >﷯﷯
                                    > Trevor Mixie wrote:﷯﷯
                                    > >﷯﷯
                                    > > Hi! every one. I have just joined your group and am looking
                                    forward ﷯﷯
                                    > > to building a couple of VDG's and Wimshurst machines. I had built
                                    a ﷯﷯
                                    > > couple some years back and am now just starting to get back into
                                    it.﷯﷯
                                    > ﷯﷯
                                    > Do any if the machines still exist. If so, please post some photos.﷯﷯
                                    > Ideally, they should show construction details.﷯﷯
                                    >  ﷯﷯
                                    > > My name is Trevor and I live in the tropics (Cairns) where VDG
                                    have ﷯﷯
                                    > > to be built rather well to work. My last effort produced 18"
                                    sparks ﷯﷯
                                    > > with 30uA. I also had to use the hair dryer a few times. ﷯﷯
                                    > ﷯﷯
                                    > Welcome to the group, Trevor. 18" sparks is very impressive, as is﷯﷯
                                    > 30uA. Many of us could benefit by learning more about these
                                    machines.﷯﷯
                                    > ﷯﷯
                                    > > If any one can give me advise on the rollers as I have been ﷯﷯
                                    > > reading It would be appreciated. My top roller is going to be ﷯﷯
                                    > > nylon and the bottom PVC Pipe as these seem to readily available ﷯﷯
                                    > > now and are at the extremes of each other. I do have problems ﷯﷯
                                    > > trying to get belts though. The ones I use to have were a webbing ﷯﷯
                                    > > used for seats and had a 1mm natural rubber inside. Thanks people ﷯﷯
                                    > > hope to hear from you and I hope can contribute as I am going.﷯﷯
                                    > ﷯﷯
                                    > Nylon on the top and PVC on the bottom will make your machine a﷯﷯
                                    > positive-charging one. Negative-charging machines seem to work
                                    better﷯﷯
                                    > for some reason. I suggest using the Nylon on the bottom and the PVC﷯﷯
                                    > on the top. The archived posts contain information on several
                                    aspects﷯﷯
                                    > of VDG building. However, there is not much here on Wimshurst﷯﷯
                                    > machines. I suggest reading the older posts. You will find sources
                                    for﷯﷯
                                    > belt and roller materials, as well as many subjects. ﷯﷯
                                    > ﷯﷯
                                    > Keep in touch.﷯﷯
                                    > ﷯﷯
                                    > Don Jacobs﷯﷯
                                    >﷯﷯
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