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Re: Restart DYI Mounts

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  • rpasken
    ... It may seem like overkill to use large heavy bearings as your are suggesting, but I agree that this is the best way to get stability and smoothness. I
    Message 1 of 11 , Aug 3, 2007
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      --- In atm_free@yahoogroups.com, Alan Bromborsky <brombo@...> wrote:
      >
      > The DYI discussion is getting to long so I wish to restart it.
      >
      > 1. The easiest mount to obtain precision in is Alt-Azi for telescopes in
      > the >50 lbs range. Commercial ball bearings can be used for the
      > elevation axis (I use 1 inch bore ball bearing rated at over 1 thousand
      > lbs). I am using a high quality lasy susan (18 inch diameter) machined
      > from Al plate and using over one hundread ball bearings
      > (leevalley.com). If this does not work well enough I can use a steel
      > plate with smaller commercial bearing with one larger bearing (1 inch)
      > to take the radial thrust and multiple smaller bearings (0.5 inch)
      > acting as rollers to take the axial thrust (used in the same way the
      > bearing in a Crayford eyepiece are used). The advantage of the Alt-Azi
      > mount is that the thrust on the alt bearing is almost purely radial
      > while the thrust on the Azi bearing is almost purely axial. If you can
      > have good bearings you can have good tracking such as with a Mel Barltes
      > servo system (bbastrodesigns.com).

      It may seem like overkill to use large heavy bearings as your are
      suggesting, but I agree that this is the best way to get stability and
      smoothness. I wonder if using a hardware-store lazy-susan might not
      work just as well to eliminate the machining. You can use a flange
      bearing bolted to aluminum angle to get the basic setup.
      >
      > 2. The only disadvantage of the alt-azi mount is due to field rotation
      > during photographic use. I you wish to do photography you should
      > consider is software field derotation is possible (I think this is what
      > all the largest telescopes now do). Alternately, one could build a
      > hardware field derotator at the foccusser. Think of the Crayford
      > foccusser technology applied to a rotating system.

      The biggest disadvantage to an alt-az mount is not field rotation, but
      that motions of the scope do not correspond directions in the sky.
      When pointed toward the west up/down motion do not correspond the
      north/south NOR east/west. The only time when the motions of the scope
      are close to motions in the sky are for those objects that are within
      a few minutes of the meridian. Field rotation is yet another
      manifestation of this problem.
      >
      > 3. I think those of us with larger newtonian telescope (>=10 inches)
      > would get off much more economically if the together we can solve the
      > problems of using an alt-azi mount for photography.
      >
      > 4. The reasons I excluded equatorial platforms from the solution is that
      > I am looking for the most compact (lightest) solution that does not
      > compromize the dynamic mechanical stability inherent in a good alt-azi
      > design. Also the equatorial plaform would also have the same bearing
      > accuracy problems alluded to in previous discussions of DIY mounts.
      >
      > 5. If you have a large newtonian how frequently do you have to
      > recollimate if you want really good photographic results. Is is cheaper
      > to use expensive materials to build the telescope so the temperature
      > does not affect collimation or should be working on a computerized
      > collimation system so that the cost of the materials for a large
      > reflector does not break the bank. Note that to have an
      > autocollimation system you would need to motorize the secondary (2
      > steppers) and the primary (2 steppers). How many of you (especially
      > those with strut tube newts) check their collimation several times
      > during the evening and night.
      >
    • Alan Bromborsky
      rpasken wrote: -The problem with using a lasy susan for the elevation bearings is that they need to be radial bearings, whereas the lasy susan is an axial
      Message 2 of 11 , Aug 3, 2007
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        rpasken wrote:

        -The problem with using a lasy susan for the elevation bearings is
        that they need
        to be radial bearings, whereas the lasy susan is an axial bearing. The
        elevation bearings
        cost about $20 each new
        -I said the main problem in an alt-azi mount is field rotation
        because I assumed that
        in an alt-azi mount the azi and alt axes would be computer controlled if
        you were going
        to do imaging.


        > --- In atm_free@yahoogroups.com <mailto:atm_free%40yahoogroups.com>,
        > Alan Bromborsky <brombo@...> wrote:
        > >
        > > The DYI discussion is getting to long so I wish to restart it.
        > >
        > > 1. The easiest mount to obtain precision in is Alt-Azi for telescopes in
        > > the >50 lbs range. Commercial ball bearings can be used for the
        > > elevation axis (I use 1 inch bore ball bearing rated at over 1 thousand
        > > lbs). I am using a high quality lasy susan (18 inch diameter) machined
        > > from Al plate and using over one hundread ball bearings
        > > (leevalley.com). If this does not work well enough I can use a steel
        > > plate with smaller commercial bearing with one larger bearing (1 inch)
        > > to take the radial thrust and multiple smaller bearings (0.5 inch)
        > > acting as rollers to take the axial thrust (used in the same way the
        > > bearing in a Crayford eyepiece are used). The advantage of the Alt-Azi
        > > mount is that the thrust on the alt bearing is almost purely radial
        > > while the thrust on the Azi bearing is almost purely axial. If you can
        > > have good bearings you can have good tracking such as with a Mel Barltes
        > > servo system (bbastrodesigns.com).
        >
        > It may seem like overkill to use large heavy bearings as your are
        > suggesting, but I agree that this is the best way to get stability and
        > smoothness. I wonder if using a hardware-store lazy-susan might not
        > work just as well to eliminate the machining. You can use a flange
        > bearing bolted to aluminum angle to get the basic setup.
        > >
        > > 2. The only disadvantage of the alt-azi mount is due to field rotation
        > > during photographic use. I you wish to do photography you should
        > > consider is software field derotation is possible (I think this is what
        > > all the largest telescopes now do). Alternately, one could build a
        > > hardware field derotator at the foccusser. Think of the Crayford
        > > foccusser technology applied to a rotating system.
        >
        > The biggest disadvantage to an alt-az mount is not field rotation, but
        > that motions of the scope do not correspond directions in the sky.
        > When pointed toward the west up/down motion do not correspond the
        > north/south NOR east/west. The only time when the motions of the scope
        > are close to motions in the sky are for those objects that are within
        > a few minutes of the meridian. Field rotation is yet another
        > manifestation of this problem.
        >



        > >
        > > 3. I think those of us with larger newtonian telescope (>=10 inches)
        > > would get off much more economically if the together we can solve the
        > > problems of using an alt-azi mount for photography.
        > >
        > > 4. The reasons I excluded equatorial platforms from the solution is that
        > > I am looking for the most compact (lightest) solution that does not
        > > compromize the dynamic mechanical stability inherent in a good alt-azi
        > > design. Also the equatorial plaform would also have the same bearing
        > > accuracy problems alluded to in previous discussions of DIY mounts.
        > >
        > > 5. If you have a large newtonian how frequently do you have to
        > > recollimate if you want really good photographic results. Is is cheaper
        > > to use expensive materials to build the telescope so the temperature
        > > does not affect collimation or should be working on a computerized
        > > collimation system so that the cost of the materials for a large
        > > reflector does not break the bank. Note that to have an
        > > autocollimation system you would need to motorize the secondary (2
        > > steppers) and the primary (2 steppers). How many of you (especially
        > > those with strut tube newts) check their collimation several times
        > > during the evening and night.
        > >
        >




        >
      • Jacques Savard
        in my case is not restart it realy start for first time I plan to do so a kind of equatorial mount whit a eavy duty bearing from my old lumina car front weel
        Message 3 of 11 , Aug 3, 2007
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          in my case is not restart
          it realy start for first time

          I plan to do so a kind of equatorial mount whit a eavy duty bearing
          from my old lumina car front weel realy very eavy duty and built
          whit 1.5 inch pipe and a kind of T at each end of the arm whit steam
          pipe T this one are bouble stick and i begin to remouve the tread and
          put bearing inside the T


          but your projet ( if I untherstand right) it is to put the main
          bearing on the sol at the vertical and make a lazy suzan and after a
          kind of dobson

          you do not show any picture of sketch
          do you have one

          NB sorry for bad english I have to translated from french and i learn
          my anglish in the book of thechtronic electronic scope

          jack 47'N 71'O

          > rpasken wrote:
          >
          > -The problem with using a lasy susan for the elevation bearings is
          > that they need
          > to be radial bearings, whereas the lasy susan is an axial bearing. The
          > elevation bearings
          > cost about $20 each new
          > -I said the main problem in an alt-azi mount is field rotation
          > because I assumed that
          > in an alt-azi mount the azi and alt axes would be computer controlled if
          > you were going
          > to do imaging.
          >
          >
          > > --- In atm_free@yahoogroups.com <mailto:atm_free%40yahoogroups.com>,
          > > Alan Bromborsky <brombo@> wrote:
          > > >
          > > > The DYI discussion is getting to long so I wish to restart it.
          > > >
          > > > 1. The easiest mount to obtain precision in is Alt-Azi for
          telescopes in
          > > > the >50 lbs range. Commercial ball bearings can be used for the
          > > > elevation axis (I use 1 inch bore ball bearing rated at over 1
          thousand
          > > > lbs). I am using a high quality lasy susan (18 inch diameter)
          machined
          > > > from Al plate and using over one hundread ball bearings
          > > > (leevalley.com). If this does not work well enough I can use a steel
          > > > plate with smaller commercial bearing with one larger bearing (1
          inch)
          > > > to take the radial thrust and multiple smaller bearings (0.5 inch)
          > > > acting as rollers to take the axial thrust (used in the same way the
          > > > bearing in a Crayford eyepiece are used). The advantage of the
          Alt-Azi
          > > > mount is that the thrust on the alt bearing is almost purely radial
          > > > while the thrust on the Azi bearing is almost purely axial. If
          you can
          > > > have good bearings you can have good tracking such as with a Mel
          Barltes
          > > > servo system (bbastrodesigns.com).
          > >
          > > It may seem like overkill to use large heavy bearings as your are
          > > suggesting, but I agree that this is the best way to get stability and
          > > smoothness. I wonder if using a hardware-store lazy-susan might not
          > > work just as well to eliminate the machining. You can use a flange
          > > bearing bolted to aluminum angle to get the basic setup.
          > > >
          > > > 2. The only disadvantage of the alt-azi mount is due to field
          rotation
          > > > during photographic use. I you wish to do photography you should
          > > > consider is software field derotation is possible (I think this
          is what
          > > > all the largest telescopes now do). Alternately, one could build a
          > > > hardware field derotator at the foccusser. Think of the Crayford
          > > > foccusser technology applied to a rotating system.
          > >
          > > The biggest disadvantage to an alt-az mount is not field rotation, but
          > > that motions of the scope do not correspond directions in the sky.
          > > When pointed toward the west up/down motion do not correspond the
          > > north/south NOR east/west. The only time when the motions of the scope
          > > are close to motions in the sky are for those objects that are within
          > > a few minutes of the meridian. Field rotation is yet another
          > > manifestation of this problem.
          > >
          >
          >
          >
          > > >
          > > > 3. I think those of us with larger newtonian telescope (>=10 inches)
          > > > would get off much more economically if the together we can
          solve the
          > > > problems of using an alt-azi mount for photography.
          > > >
          > > > 4. The reasons I excluded equatorial platforms from the solution
          is that
          > > > I am looking for the most compact (lightest) solution that does not
          > > > compromize the dynamic mechanical stability inherent in a good
          alt-azi
          > > > design. Also the equatorial plaform would also have the same bearing
          > > > accuracy problems alluded to in previous discussions of DIY mounts.
          > > >
          > > > 5. If you have a large newtonian how frequently do you have to
          > > > recollimate if you want really good photographic results. Is is
          cheaper
          > > > to use expensive materials to build the telescope so the temperature
          > > > does not affect collimation or should be working on a computerized
          > > > collimation system so that the cost of the materials for a large
          > > > reflector does not break the bank. Note that to have an
          > > > autocollimation system you would need to motorize the secondary (2
          > > > steppers) and the primary (2 steppers). How many of you (especially
          > > > those with strut tube newts) check their collimation several times
          > > > during the evening and night.
          > > >
          > >
          >
          >
          >
          >
          > >
          >
        • Alan Bromborsky
          To see my telescope go to album brombo in atm_free photo s!
          Message 4 of 11 , Aug 4, 2007
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            To see my telescope go to album brombo in atm_free photo's!

            Jacques Savard wrote:

            > in my case is not restart
            > it realy start for first time
            >
            > I plan to do so a kind of equatorial mount whit a eavy duty bearing
            > from my old lumina car front weel realy very eavy duty and built
            > whit 1.5 inch pipe and a kind of T at each end of the arm whit steam
            > pipe T this one are bouble stick and i begin to remouve the tread and
            > put bearing inside the T
            >
            > but your projet ( if I untherstand right) it is to put the main
            > bearing on the sol at the vertical and make a lazy suzan and after a
            > kind of dobson
            >
            > you do not show any picture of sketch
            > do you have one
            >
            > NB sorry for bad english I have to translated from french and i learn
            > my anglish in the book of thechtronic electronic scope
            >
            > jack 47'N 71'O
            >
            > > rpasken wrote:
            > >
            > > -The problem with using a lasy susan for the elevation bearings is
            > > that they need
            > > to be radial bearings, whereas the lasy susan is an axial bearing. The
            > > elevation bearings
            > > cost about $20 each new
            > > -I said the main problem in an alt-azi mount is field rotation
            > > because I assumed that
            > > in an alt-azi mount the azi and alt axes would be computer controlled if
            > > you were going
            > > to do imaging.
            > >
            > >
            > > > --- In atm_free@yahoogroups.com
            > <mailto:atm_free%40yahoogroups.com> <mailto:atm_free%40yahoogroups.com>,
            > > > Alan Bromborsky <brombo@> wrote:
            > > > >
            > > > > The DYI discussion is getting to long so I wish to restart it.
            > > > >
            > > > > 1. The easiest mount to obtain precision in is Alt-Azi for
            > telescopes in
            > > > > the >50 lbs range. Commercial ball bearings can be used for the
            > > > > elevation axis (I use 1 inch bore ball bearing rated at over 1
            > thousand
            > > > > lbs). I am using a high quality lasy susan (18 inch diameter)
            > machined
            > > > > from Al plate and using over one hundread ball bearings
            > > > > (leevalley.com). If this does not work well enough I can use a steel
            > > > > plate with smaller commercial bearing with one larger bearing (1
            > inch)
            > > > > to take the radial thrust and multiple smaller bearings (0.5 inch)
            > > > > acting as rollers to take the axial thrust (used in the same way the
            > > > > bearing in a Crayford eyepiece are used). The advantage of the
            > Alt-Azi
            > > > > mount is that the thrust on the alt bearing is almost purely radial
            > > > > while the thrust on the Azi bearing is almost purely axial. If
            > you can
            > > > > have good bearings you can have good tracking such as with a Mel
            > Barltes
            > > > > servo system (bbastrodesigns.com).
            > > >
            > > > It may seem like overkill to use large heavy bearings as your are
            > > > suggesting, but I agree that this is the best way to get stability and
            > > > smoothness. I wonder if using a hardware-store lazy-susan might not
            > > > work just as well to eliminate the machining. You can use a flange
            > > > bearing bolted to aluminum angle to get the basic setup.
            > > > >
            > > > > 2. The only disadvantage of the alt-azi mount is due to field
            > rotation
            > > > > during photographic use. I you wish to do photography you should
            > > > > consider is software field derotation is possible (I think this
            > is what
            > > > > all the largest telescopes now do). Alternately, one could build a
            > > > > hardware field derotator at the foccusser. Think of the Crayford
            > > > > foccusser technology applied to a rotating system.
            > > >
            > > > The biggest disadvantage to an alt-az mount is not field rotation, but
            > > > that motions of the scope do not correspond directions in the sky.
            > > > When pointed toward the west up/down motion do not correspond the
            > > > north/south NOR east/west. The only time when the motions of the scope
            > > > are close to motions in the sky are for those objects that are within
            > > > a few minutes of the meridian. Field rotation is yet another
            > > > manifestation of this problem.
            > > >
            > >
            > >
            > >
            > > > >
            > > > > 3. I think those of us with larger newtonian telescope (>=10 inches)
            > > > > would get off much more economically if the together we can
            > solve the
            > > > > problems of using an alt-azi mount for photography.
            > > > >
            > > > > 4. The reasons I excluded equatorial platforms from the solution
            > is that
            > > > > I am looking for the most compact (lightest) solution that does not
            > > > > compromize the dynamic mechanical stability inherent in a good
            > alt-azi
            > > > > design. Also the equatorial plaform would also have the same bearing
            > > > > accuracy problems alluded to in previous discussions of DIY mounts.
            > > > >
            > > > > 5. If you have a large newtonian how frequently do you have to
            > > > > recollimate if you want really good photographic results. Is is
            > cheaper
            > > > > to use expensive materials to build the telescope so the temperature
            > > > > does not affect collimation or should be working on a computerized
            > > > > collimation system so that the cost of the materials for a large
            > > > > reflector does not break the bank. Note that to have an
            > > > > autocollimation system you would need to motorize the secondary (2
            > > > > steppers) and the primary (2 steppers). How many of you (especially
            > > > > those with strut tube newts) check their collimation several times
            > > > > during the evening and night.
            > > > >
            > > >
            > >
            > >
            > >
            > >
            > > >
            > >
            >
            >
          • bekirwicz
            Newbie here, Link at end. I thought this mount was worth thinking about. You can scale it up to a 200 inch mirror (smile) if you want. Link from ebay. I have
            Message 5 of 11 , Aug 4, 2007
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              Newbie here,

              Link at end. I thought this mount was worth thinking about. You can
              scale it up to a 200 inch mirror (smile) if you want. Link from ebay.
              I have asked him a couple questions about the mount. You can save all
              the nice clear photos and see what he's done. He has had this listing
              for many months, and recently lowered the price. It was built for his
              latitude north of Miami.

              What I don't like is the focuser is fixed. He said it was a prototype
              for a 24 inch scope he hopes to build. That would have video and
              remote viewing, he doesn't have to be Plastic Man to use it.

              I asked if it was easy to flip the square tube over for alternate
              placement of the eyepiece. Yes, but the finder should be remounted
              elsewhere and the fine declination adjustment would not work on the
              other side.

              Still it's worth considering. I schemed something like this over 30
              years ago. This is the first built one I have encountered. Another
              solution is an Engligh Yoke mount as the Hooker telescope has. Though
              it is simpler you lose access to near the pole. For a planet and
              Lunar-tic like me that is not hard to give up as I would have other
              scopes available.

              http://cgi.ebay.com/Huge-8-Newtonian-Reflector-Telescope-Equatorial-
              Mount_W0QQitemZ280127536861QQihZ018QQcategoryZ28181QQrdZ1QQssPageNameZ
              WD1VQQcmdZViewItem

              Ben Waranowitz
            • rpasken
              ... Sorry I got the impression you were using the lazy susan for the azimuth axis and a radial (possibly a flange bearing) for the altitude axis.
              Message 6 of 11 , Aug 5, 2007
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                --- In atm_free@yahoogroups.com, Alan Bromborsky <brombo@...> wrote:
                >
                > rpasken wrote:
                >
                > -The problem with using a lasy susan for the elevation bearings is
                > that they need
                > to be radial bearings, whereas the lasy susan is an axial bearing. The
                > elevation bearings
                > cost about $20 each new


                Sorry I got the impression you were using the lazy susan for the
                azimuth axis and a radial (possibly a flange bearing) for the altitude
                axis.
              • Alan Bromborsky
                ... I am!!!!
                Message 7 of 11 , Aug 5, 2007
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                  rpasken wrote:

                  > --- In atm_free@yahoogroups.com <mailto:atm_free%40yahoogroups.com>,
                  > Alan Bromborsky <brombo@...> wrote:
                  > >
                  > > rpasken wrote:
                  > >
                  > > -The problem with using a lasy susan for the elevation bearings is
                  > > that they need
                  > > to be radial bearings, whereas the lasy susan is an axial bearing. The
                  > > elevation bearings
                  > > cost about $20 each new
                  >
                  > Sorry I got the impression you were using the lazy susan for the
                  > azimuth axis and a radial (possibly a flange bearing) for the altitude
                  > axis.
                  >
                  >

                  I am!!!!
                • Alan Bromborsky
                  Look at folder brombo in photos. Pictures of both elevation and azimuth bearings. Note that the azimuth bearing moved so easily (the first time I took the
                  Message 8 of 11 , Aug 6, 2007
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                    Look at folder brombo in photos. Pictures of both elevation and azimuth
                    bearings.
                    Note that the azimuth bearing moved so easily (the first time I took the
                    scope to a star party it was windy and it made a good weathervane) that
                    I had to add friction (spring loaded teflon furniture glide). Currently
                    I am adding digital setting circles and stepper motor drives).


                    rpasken wrote:

                    > --- In atm_free@yahoogroups.com <mailto:atm_free%40yahoogroups.com>,
                    > Alan Bromborsky <brombo@...> wrote:
                    > >
                    > > The DYI discussion is getting to long so I wish to restart it.
                    > >
                    > > 1. The easiest mount to obtain precision in is Alt-Azi for telescopes in
                    > > the >50 lbs range. Commercial ball bearings can be used for the
                    > > elevation axis (I use 1 inch bore ball bearing rated at over 1 thousand
                    > > lbs). I am using a high quality lasy susan (18 inch diameter) machined
                    > > from Al plate and using over one hundread ball bearings
                    > > (leevalley.com). If this does not work well enough I can use a steel
                    > > plate with smaller commercial bearing with one larger bearing (1 inch)
                    > > to take the radial thrust and multiple smaller bearings (0.5 inch)
                    > > acting as rollers to take the axial thrust (used in the same way the
                    > > bearing in a Crayford eyepiece are used). The advantage of the Alt-Azi
                    > > mount is that the thrust on the alt bearing is almost purely radial
                    > > while the thrust on the Azi bearing is almost purely axial. If you can
                    > > have good bearings you can have good tracking such as with a Mel Barltes
                    > > servo system (bbastrodesigns.com).
                    >
                    > It may seem like overkill to use large heavy bearings as your are
                    > suggesting, but I agree that this is the best way to get stability and
                    > smoothness. I wonder if using a hardware-store lazy-susan might not
                    > work just as well to eliminate the machining. You can use a flange
                    > bearing bolted to aluminum angle to get the basic setup.
                    > >
                    > > 2. The only disadvantage of the alt-azi mount is due to field rotation
                    > > during photographic use. I you wish to do photography you should
                    > > consider is software field derotation is possible (I think this is what
                    > > all the largest telescopes now do). Alternately, one could build a
                    > > hardware field derotator at the foccusser. Think of the Crayford
                    > > foccusser technology applied to a rotating system.
                    >
                    > The biggest disadvantage to an alt-az mount is not field rotation, but
                    > that motions of the scope do not correspond directions in the sky.
                    > When pointed toward the west up/down motion do not correspond the
                    > north/south NOR east/west. The only time when the motions of the scope
                    > are close to motions in the sky are for those objects that are within
                    > a few minutes of the meridian. Field rotation is yet another
                    > manifestation of this problem.
                    > >
                    > > 3. I think those of us with larger newtonian telescope (>=10 inches)
                    > > would get off much more economically if the together we can solve the
                    > > problems of using an alt-azi mount for photography.
                    > >
                    > > 4. The reasons I excluded equatorial platforms from the solution is that
                    > > I am looking for the most compact (lightest) solution that does not
                    > > compromize the dynamic mechanical stability inherent in a good alt-azi
                    > > design. Also the equatorial plaform would also have the same bearing
                    > > accuracy problems alluded to in previous discussions of DIY mounts.
                    > >
                    > > 5. If you have a large newtonian how frequently do you have to
                    > > recollimate if you want really good photographic results. Is is cheaper
                    > > to use expensive materials to build the telescope so the temperature
                    > > does not affect collimation or should be working on a computerized
                    > > collimation system so that the cost of the materials for a large
                    > > reflector does not break the bank. Note that to have an
                    > > autocollimation system you would need to motorize the secondary (2
                    > > steppers) and the primary (2 steppers). How many of you (especially
                    > > those with strut tube newts) check their collimation several times
                    > > during the evening and night.
                    > >
                    >
                    >
                  • tonyevansau
                    I thought you may like to see a mount made from truck parts so have posted a picture un the photo section in Sitting Hen obsevatory The mount is made from a
                    Message 9 of 11 , Aug 17, 2007
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                      I thought you may like to see a mount made from truck parts so have
                      posted a picture un the photo section in 'Sitting Hen obsevatory'

                      The mount is made from a simi-trailer axle stub cut from a 38,000lb
                      axle (4"/100mm solid) and uses the spider hub and bearings to create
                      a fork eq. mount. The pier is 18"/460mm dia - and starts 1.6M below
                      ground and uses the truck brake drum as a cap.

                      The scope that will be mounted on it is a f4.8 18" Newtonian.

                      Cheers - Tony - Australia.


                      --- In atm_free@yahoogroups.com, "Jacques Savard" <jacquessavard@...>
                      wrote:
                      >
                      > in my case is not restart
                      > it realy start for first time
                      >
                      > I plan to do so a kind of equatorial mount whit a eavy duty bearing
                      > from my old lumina car front weel realy very eavy duty and built
                      > whit 1.5 inch pipe and a kind of T at each end of the arm whit steam
                      > pipe T this one are bouble stick and i begin to remouve the tread
                      and
                      > put bearing inside the T
                      >
                      >
                      > but your projet ( if I untherstand right) it is to put the main
                      > bearing on the sol at the vertical and make a lazy suzan and after a
                      > kind of dobson
                      >
                      > you do not show any picture of sketch
                      > do you have one
                      >
                      > NB sorry for bad english I have to translated from french and i
                      learn
                      > my anglish in the book of thechtronic electronic scope
                      >
                      > jack 47'N 71'O
                      >
                      > > rpasken wrote:
                      > >
                      > > -The problem with using a lasy susan for the elevation
                      bearings is
                      > > that they need
                      > > to be radial bearings, whereas the lasy susan is an axial
                      bearing. The
                      > > elevation bearings
                      > > cost about $20 each new
                      > > -I said the main problem in an alt-azi mount is field rotation
                      > > because I assumed that
                      > > in an alt-azi mount the azi and alt axes would be computer
                      controlled if
                      > > you were going
                      > > to do imaging.
                      > >
                      > >
                      > > > --- In atm_free@yahoogroups.com <mailto:atm_free%
                      40yahoogroups.com>,
                      > > > Alan Bromborsky <brombo@> wrote:
                      > > > >
                      > > > > The DYI discussion is getting to long so I wish to restart it.
                      > > > >
                      > > > > 1. The easiest mount to obtain precision in is Alt-Azi for
                      > telescopes in
                      > > > > the >50 lbs range. Commercial ball bearings can be used for
                      the
                      > > > > elevation axis (I use 1 inch bore ball bearing rated at over 1
                      > thousand
                      > > > > lbs). I am using a high quality lasy susan (18 inch diameter)
                      > machined
                      > > > > from Al plate and using over one hundread ball bearings
                      > > > > (leevalley.com). If this does not work well enough I can use
                      a steel
                      > > > > plate with smaller commercial bearing with one larger bearing
                      (1
                      > inch)
                      > > > > to take the radial thrust and multiple smaller bearings (0.5
                      inch)
                      > > > > acting as rollers to take the axial thrust (used in the same
                      way the
                      > > > > bearing in a Crayford eyepiece are used). The advantage of the
                      > Alt-Azi
                      > > > > mount is that the thrust on the alt bearing is almost purely
                      radial
                      > > > > while the thrust on the Azi bearing is almost purely axial. If
                      > you can
                      > > > > have good bearings you can have good tracking such as with a
                      Mel
                      > Barltes
                      > > > > servo system (bbastrodesigns.com).
                      > > >
                      > > > It may seem like overkill to use large heavy bearings as your
                      are
                      > > > suggesting, but I agree that this is the best way to get
                      stability and
                      > > > smoothness. I wonder if using a hardware-store lazy-susan might
                      not
                      > > > work just as well to eliminate the machining. You can use a
                      flange
                      > > > bearing bolted to aluminum angle to get the basic setup.
                      > > > >
                      > > > > 2. The only disadvantage of the alt-azi mount is due to field
                      > rotation
                      > > > > during photographic use. I you wish to do photography you
                      should
                      > > > > consider is software field derotation is possible (I think
                      this
                      > is what
                      > > > > all the largest telescopes now do). Alternately, one could
                      build a
                      > > > > hardware field derotator at the foccusser. Think of the
                      Crayford
                      > > > > foccusser technology applied to a rotating system.
                      > > >
                      > > > The biggest disadvantage to an alt-az mount is not field
                      rotation, but
                      > > > that motions of the scope do not correspond directions in the
                      sky.
                      > > > When pointed toward the west up/down motion do not correspond
                      the
                      > > > north/south NOR east/west. The only time when the motions of
                      the scope
                      > > > are close to motions in the sky are for those objects that are
                      within
                      > > > a few minutes of the meridian. Field rotation is yet another
                      > > > manifestation of this problem.
                      > > >
                      > >
                      > >
                      > >
                      > > > >
                      > > > > 3. I think those of us with larger newtonian telescope (>=10
                      inches)
                      > > > > would get off much more economically if the together we can
                      > solve the
                      > > > > problems of using an alt-azi mount for photography.
                      > > > >
                      > > > > 4. The reasons I excluded equatorial platforms from the
                      solution
                      > is that
                      > > > > I am looking for the most compact (lightest) solution that
                      does not
                      > > > > compromize the dynamic mechanical stability inherent in a good
                      > alt-azi
                      > > > > design. Also the equatorial plaform would also have the same
                      bearing
                      > > > > accuracy problems alluded to in previous discussions of DIY
                      mounts.
                      > > > >
                      > > > > 5. If you have a large newtonian how frequently do you have to
                      > > > > recollimate if you want really good photographic results. Is
                      is
                      > cheaper
                      > > > > to use expensive materials to build the telescope so the
                      temperature
                      > > > > does not affect collimation or should be working on a
                      computerized
                      > > > > collimation system so that the cost of the materials for a
                      large
                      > > > > reflector does not break the bank. Note that to have an
                      > > > > autocollimation system you would need to motorize the
                      secondary (2
                      > > > > steppers) and the primary (2 steppers). How many of you
                      (especially
                      > > > > those with strut tube newts) check their collimation several
                      times
                      > > > > during the evening and night.
                      > > > >
                      > > >
                      > >
                      > >
                      > >
                      > >
                      > > >
                      > >
                      >
                    • Rom├ín Toledo
                      ... Tony Excellent job, I sure would like to see more photos and details on this fork mount. I have access to those parts once in a while at work that we
                      Message 10 of 11 , Aug 18, 2007
                      • 0 Attachment
                        --- In atm_free@yahoogroups.com, "tonyevansau" <tonyevans2@...> wrote:
                        >
                        > I thought you may like to see a mount made from truck parts so have
                        > posted a picture un the photo section in 'Sitting Hen obsevatory'
                        >
                        > The mount is made from a simi-trailer axle stub cut from a 38,000lb
                        > axle (4"/100mm solid) and uses the spider hub and bearings to create
                        > a fork eq. mount. The pier is 18"/460mm dia - and starts 1.6M below
                        > ground and uses the truck brake drum as a cap.
                        >
                        > The scope that will be mounted on it is a f4.8 18" Newtonian.
                        >
                        > Cheers - Tony - Australia.
                        >

                        Tony Excellent job, I sure would like to see more photos and
                        details on this fork mount. I have access to those parts once in a
                        while at work that we just trow away in the recycle bin, and could put
                        one together down the road.

                        I recently saw another idea using bearing holders and shafts from
                        Graingers or McMaster Carr catalogs that also seemed very nice for a
                        homemade pier and a 12" newt.

                        thanks for sharing hope to see more photos and details if at all
                        possible.

                        Roman
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