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Dob plywood choices

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  • firedancerpig
    I ve been tinkering with the idea of building a 10 inch truss tube dob, and i ve been looking into available plywood. I have a few questions that some of you
    Message 1 of 9 , Mar 30, 2003
      I've been tinkering with the idea of building a 10 inch truss tube
      dob, and i've been looking into available plywood. I have a few
      questions that some of you fellas might be able to answer. First,
      what kind of hardwood ply would be best to use? I think 5/8" would
      work well, but i dont know if i should use oak, birch, or perhaps
      something else. second, is hardwood plywood simply pine with a
      hardwood veneer, or solid hardwood? if not, will the pine core affect
      teh strenth of the project? Thanks for your help :)clear skies
      (without snow)
      Nathan
    • Bob Bunge
      Nathan, Opinions will vary as to what wood to use, but here s mine: For a 10-inch truss, try to find a good 1/2-inch AC exterior grade pine/fir ply. This is
      Message 2 of 9 , Mar 30, 2003
        Nathan,

        Opinions will vary as to what wood to use, but here's mine:

        For a 10-inch truss, try to find a good 1/2-inch "AC" exterior grade
        pine/fir ply. This is considered a softwood ply. At local hardwood
        stores, you will find "hardwood" plys that normally have softwood cores.
        That outer veneer is for looks.

        Remember the thicker the piece, the heavier the scope will be. I've
        built a couple of 10/12-inch class dobs have always been happy with
        1/2-inch. I've pushed the envelope with my most recent scope - a
        12-inch and used almost all 1/4-inch ply. See
        http://www.ladyandtramp.com/ellie/ for details and photos.

        Many will recommend using true hardwood plys - usually you will see
        references to Baltic Birch. This usually comes in 5x5 foot sheets and
        is found at specially wood working stores. It's usually used for
        furniture. BB won't have voids and will be very pretty and only a bit
        heavier then fir/pine.

        But the fir/pine is just as strong, if not stronger and is much cheaper.
        It will have some voids depending on the quality that you find.

        The number of layers - plys - does _not_ affect the strength of the
        wood, only the total thickness.

        Bob Bunge

        firedancerpig wrote:
        > I've been tinkering with the idea of building a 10 inch truss tube
        > dob, and i've been looking into available plywood. I have a few
        > questions that some of you fellas might be able to answer. First,
        > what kind of hardwood ply would be best to use? I think 5/8" would
        > work well, but i dont know if i should use oak, birch, or perhaps
        > something else. second, is hardwood plywood simply pine with a
        > hardwood veneer, or solid hardwood? if not, will the pine core affect
        > teh strenth of the project? Thanks for your help :)clear skies
        > (without snow)
        > Nathan
        >
        >
        >
        >
        > To unsubscribe from this group, send an email to:
        > delmarvastargazers-unsubscribe@egroups.com
        >
        >
        >
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        >
        >
      • Joe Morris
        Nathan -- ... David Kriege (Obsession Telescope) and Richard Berry s book THE DOBSONIAN TELESCOPE recommends (for an 8 inch dob) 1/2 HVHC plywood for the
        Message 3 of 9 , Mar 30, 2003
          Nathan --
          >>
          >> I've been tinkering with the idea of building a 10 inch truss tube
          >> dob, and i've been looking into available plywood. I have a few
          >> questions that some of you fellas might be able to answer. First,
          >> what kind of hardwood ply would be best to use? I think 5/8" would
          >> work well, but i dont know if i should use oak, birch, or perhaps
          >> something else. second, is hardwood plywood simply pine with a
          >> hardwood veneer, or solid hardwood? if not, will the pine core affect
          >> teh strenth of the project?

          David Kriege (Obsession Telescope) and Richard Berry's book THE DOBSONIAN
          TELESCOPE recommends (for an 8 inch dob) 1/2" HVHC plywood for the morror
          cell, cradle, and rocker. They recommend 3/4" SVSC plywood for the side
          bearings and ground board. HVHC (hardwood veneer hardwood core) probably
          won't be found at a local lumberyard, Lowe's or Home Depot. Call around to
          specialty lumber stores and ask for Baltic Birch or ApplePly brands. SVSC
          (softwood veneer softwood core) will be in most lumbar yards. The better
          quality ones are made from fir
        • firedancerpig
          Thanks guys :) Bob- I ve seen your website before....i really like the pringles concept. Is adjusting the secondary mirror difficult with that setup? It
          Message 4 of 9 , Mar 30, 2003
            Thanks guys :) Bob- I've seen your website before....i really like
            the "pringles" concept. Is adjusting the secondary mirror difficult
            with that setup? It doesnt seem like twisting the metal vanes would
            be very accurate....



            --- In delmarvastargazers@yahoogroups.com, "firedancerpig"
            <firedancerpig@h...> wrote:
            > I've been tinkering with the idea of building a 10 inch truss tube
            > dob, and i've been looking into available plywood. I have a few
            > questions that some of you fellas might be able to answer. First,
            > what kind of hardwood ply would be best to use? I think 5/8" would
            > work well, but i dont know if i should use oak, birch, or perhaps
            > something else. second, is hardwood plywood simply pine with a
            > hardwood veneer, or solid hardwood? if not, will the pine core
            affect
            > teh strenth of the project? Thanks for your help :)clear skies
            > (without snow)
            > Nathan
          • Bob Bunge
            I ve never had a problem with it, but then I don t put a laser on it or get hypercritial about the collimation. Since I normally use it at 17x and sometimes
            Message 5 of 9 , Mar 30, 2003
              I've never had a problem with it, but then I don't put a laser on it or
              get hypercritial about the collimation. Since I normally use it at 17x
              and sometimes 25x, it's very much a wide field, low power scope.

              I normally do an eyeball collimation, followed by a star test. From
              that point, the images seem to do it justice for the way that I use it.

              Bob

              firedancerpig wrote:
              > Thanks guys :) Bob- I've seen your website before....i really like
              > the "pringles" concept. Is adjusting the secondary mirror difficult
              > with that setup? It doesnt seem like twisting the metal vanes would
              > be very accurate....
              >
              >
              >
              > --- In delmarvastargazers@yahoogroups.com, "firedancerpig"
              > <firedancerpig@h...> wrote:
              >
              >>I've been tinkering with the idea of building a 10 inch truss tube
              >>dob, and i've been looking into available plywood. I have a few
              >>questions that some of you fellas might be able to answer. First,
              >>what kind of hardwood ply would be best to use? I think 5/8" would
              >>work well, but i dont know if i should use oak, birch, or perhaps
              >>something else. second, is hardwood plywood simply pine with a
              >>hardwood veneer, or solid hardwood? if not, will the pine core
              >
              > affect
              >
              >>teh strenth of the project? Thanks for your help :)clear skies
              >>(without snow)
              >>Nathan
              >
              >
              >
              >
              > To unsubscribe from this group, send an email to:
              > delmarvastargazers-unsubscribe@egroups.com
              >
              >
              >
              > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
              >
              >
            • Art Bianconi
              I am relatively new to this ATM business and, while I lack the experience that many demonstrate on issues related to optics and finding m33 et al, I am an
              Message 6 of 9 , Mar 30, 2003
                I am relatively new to this ATM business and, while I lack the experience that
                many demonstrate on issues related to optics and finding m33 et al, I am an
                engineer and have used most all but the most exotic materials in many designs,
                including my own.

                Wood is a far more precise material than many give it credit for and it can
                maintain a fair degree of dimensional stability, provided that it's stored properly
                before use and sealed well against changes in it's internal moisture content.

                Aircraft and Marine grade plywoods are available in a very broad range of
                thickeness and wood types. It's hard to immagine a grade of aircraft grade
                wood that isn't suitable for telescopes. It's a great material to work with, can be
                finished to a warm, wondeful texture and appearance and although it's heavier
                than I wish to experience, it is strong.

                There are any number of commercial suppliers for aircraft grade plywood and
                the best book for making that choice is availalbe for free from Aircraft Spruce
                and Specialty Corp.

                http://www.aircraft-spruce-com

                You can call them at 800-443-1448

                or you can write to them at

                info@...

                Their prices are NOT the best but the catalog is free and you might save some
                money by shopping around once you have found what you are looking for.

                Good Luck

                Art Bianconi

                3/30/2003 6:22:18 PM, "firedancerpig" <firedancerpig@...> wrote:

                >Thanks guys :) Bob- I've seen your website before....i really like
                >the "pringles" concept. Is adjusting the secondary mirror difficult
                >with that setup? It doesnt seem like twisting the metal vanes would
                >be very accurate....
                >
                >
                >
                >--- In delmarvastargazers@yahoogroups.com, "firedancerpig"
                ><firedancerpig@h...> wrote:
                >> I've been tinkering with the idea of building a 10 inch truss tube
                >> dob, and i've been looking into available plywood. I have a few
                >> questions that some of you fellas might be able to answer. First,
                >> what kind of hardwood ply would be best to use? I think 5/8" would
                >> work well, but i dont know if i should use oak, birch, or perhaps
                >> something else. second, is hardwood plywood simply pine with a
                >> hardwood veneer, or solid hardwood? if not, will the pine core
                >affect
                >> teh strenth of the project? Thanks for your help :)clear skies
                >> (without snow)
                >> Nathan
              • Art Bianconi
                In one of the responses you got to this inquiry, somone alleged that the number of plies and their thickness has no effect on the strength of a wood part. I am
                Message 7 of 9 , Mar 30, 2003
                  In one of the responses you got to this inquiry, somone alleged that the number
                  of plies and their thickness has no effect on the strength of a wood part.

                  I am not sure who told them that but it's incorrect. Loads travel in many
                  directions. What can be an area under tension in one spot can be a load under
                  compression in another. Furthermore, their can be loads in shear and torsional
                  loads. One just doesn't hang a bunch of wood together with nails and glue. One
                  must have an appreciation of how loads are distributed throughout the structure.
                  75% of succesful design is knowing your materials and how to apply them.

                  Furthermore, as the moisture content in wood changes, it will tend to warp.
                  Aside from the optical consequences induced by the distorted geometry there
                  are the internal stresses that can accumulate from the bending loads which can,
                  eventually cause failure of one or more components.

                  Plywood was invented because it gives the manufacturer the ability to orient
                  each ply in a direction that will counter the warping effect of it's neighbor. At the
                  same time, it permits the loads to be distributed more evenly and in a manner
                  that keeps them below the point of failure. Contrary to what you were told,
                  plywood is one the best natural examples I know of where the result is indeed
                  greater than the sum of it's individual parts.

                  Sitka Spruce is bar far on of the strongest of natural composites for a given
                  weight (Yes composites!) Aside from it's organic origins and it's weight, it has
                  few faults. To do better, you'll have to leave this domain and venture into the
                  more modern but messy world of fiberglass, carbon fiber and resin systems.

                  I urge you to get the that Aircraft Spruce And Specialty catalog I mentioned in
                  my previous post.

                  Art Bianconi


                  >I've been tinkering with the idea of building a 10 inch truss tube
                  >dob, and i've been looking into available plywood. I have a few
                  >questions that some of you fellas might be able to answer. First,
                  >what kind of hardwood ply would be best to use? I think 5/8" would
                  >work well, but i dont know if i should use oak, birch, or perhaps
                  >something else. second, is hardwood plywood simply pine with a
                  >hardwood veneer, or solid hardwood? if not, will the pine core affect
                  >teh strenth of the project? Thanks for your help :)clear skies
                  >(without snow)
                  >Nathan
                  >
                • Bob Bunge
                  Hi Art, Thanks for the information. I m the one who made the comment regarding the number of plys. My source is the current bible for truss telescope
                  Message 8 of 9 , Mar 31, 2003
                    Hi Art,

                    Thanks for the information. I'm the one who made the comment regarding
                    the number of plys. My source is the current "bible" for truss
                    telescope making, "The Dobsonian Telescope: A Practical Manual for
                    Building Large Aperture Telescopes by David Kriege and Richard Berry."

                    They have a detailed appendix on the selection of plywoods for
                    telescopes and go into some detail of the different types of woods
                    available. On pg 369, they say "The number of layers in a panel of a
                    given thickness does not appreciably affect the stiffness of the panel".
                    I'm sure their carefully worded statement is much more correct then my
                    quick comment :-)

                    I suspect their statement is based on how mid to large truss dobs are
                    constructed and designed.

                    Cheers,

                    Bob


                    Art Bianconi wrote:
                    > In one of the responses you got to this inquiry, somone alleged that the number
                    > of plies and their thickness has no effect on the strength of a wood part.
                    >
                    > I am not sure who told them that but it's incorrect. Loads travel in many
                    > directions. What can be an area under tension in one spot can be a load under
                    > compression in another. Furthermore, their can be loads in shear and torsional
                    > loads. One just doesn't hang a bunch of wood together with nails and glue. One
                    > must have an appreciation of how loads are distributed throughout the structure.
                    > 75% of succesful design is knowing your materials and how to apply them.
                    >
                    > Furthermore, as the moisture content in wood changes, it will tend to warp.
                    > Aside from the optical consequences induced by the distorted geometry there
                    > are the internal stresses that can accumulate from the bending loads which can,
                    > eventually cause failure of one or more components.
                    >
                    > Plywood was invented because it gives the manufacturer the ability to orient
                    > each ply in a direction that will counter the warping effect of it's neighbor. At the
                    > same time, it permits the loads to be distributed more evenly and in a manner
                    > that keeps them below the point of failure. Contrary to what you were told,
                    > plywood is one the best natural examples I know of where the result is indeed
                    > greater than the sum of it's individual parts.
                    >
                    > Sitka Spruce is bar far on of the strongest of natural composites for a given
                    > weight (Yes composites!) Aside from it's organic origins and it's weight, it has
                    > few faults. To do better, you'll have to leave this domain and venture into the
                    > more modern but messy world of fiberglass, carbon fiber and resin systems.
                    >
                    > I urge you to get the that Aircraft Spruce And Specialty catalog I mentioned in
                    > my previous post.
                    >
                    > Art Bianconi
                    >
                    >
                    >
                    >>I've been tinkering with the idea of building a 10 inch truss tube
                    >>dob, and i've been looking into available plywood. I have a few
                    >>questions that some of you fellas might be able to answer. First,
                    >>what kind of hardwood ply would be best to use? I think 5/8" would
                    >>work well, but i dont know if i should use oak, birch, or perhaps
                    >>something else. second, is hardwood plywood simply pine with a
                    >>hardwood veneer, or solid hardwood? if not, will the pine core affect
                    >>teh strenth of the project? Thanks for your help :)clear skies
                    >>(without snow)
                    >>Nathan
                    >>
                    >
                    >
                    >
                    >
                    >
                    >
                    >
                    > To unsubscribe from this group, send an email to:
                    > delmarvastargazers-unsubscribe@egroups.com
                    >
                    >
                    >
                    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                    >
                    >
                  • Keith C. Lohmeyer
                    Hi Nathan, The type of plywood (oak, birch, pine) for a 10 scope is more a question of looks than a question of strength or durability. The thickness used
                    Message 9 of 9 , Mar 31, 2003
                      Hi Nathan,
                      The type of plywood (oak, birch, pine) for a 10" scope is more a question of
                      looks than a question of strength or durability. The thickness used really
                      depends on the scope design... a scope with a taller rockerbox will need
                      more bracing or thicker plywood than a low profile design.

                      A 10" dob is usually considered a little small to be made as a truss scope
                      unless there is a special reason for doing so such as a travel scope or
                      transportation restraints. Truss scopes take time to setup and take down
                      where with a traditional 10" dob you can be observing at a minutes notice
                      and can be put up just as quick. This usually means it will get more use.

                      Whatever you decide to do please feel free to keep asking questions. There
                      is a lot of ATM experience on this list. Have fun but beware telescope
                      making can be addictive.

                      Keith

                      ----- Original Message -----
                      From: "firedancerpig" <firedancerpig@...>
                      To: <delmarvastargazers@yahoogroups.com>
                      Sent: Sunday, March 30, 2003 5:11 PM
                      Subject: [delmarvastargazers] Dob plywood choices


                      > I've been tinkering with the idea of building a 10 inch truss tube
                      > dob, and i've been looking into available plywood. I have a few
                      > questions that some of you fellas might be able to answer. First,
                      > what kind of hardwood ply would be best to use? I think 5/8" would
                      > work well, but i dont know if i should use oak, birch, or perhaps
                      > something else. second, is hardwood plywood simply pine with a
                      > hardwood veneer, or solid hardwood? if not, will the pine core affect
                      > teh strenth of the project? Thanks for your help :)clear skies
                      > (without snow)
                      > Nathan
                      >
                      >
                      >
                      >
                      > To unsubscribe from this group, send an email to:
                      > delmarvastargazers-unsubscribe@egroups.com
                      >
                      >
                      >
                      > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                      >
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