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Re: Concrete filled extrusions

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  • kd006
    Ken & Leon, Concrete is always used under compression, as has been pointed out threaded rods and plates are used when constructing beams as used in bridges
    Message 1 of 12 , May 5, 2008
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      Ken & Leon,

      Concrete is always used under compression, as has been pointed out
      threaded rods and plates are used when constructing beams as used in
      bridges transferring the bending force to compressive forces on each
      part. The question is I suppose is filling an extrusion with concrete
      meant to increase its flexural strength or mass or both? If it's
      simply a matter of mass then the lead shot would certainly do it,
      although Pb is on the outlawed list these days. I had to go to five
      tire shops to get a bucket of old wheel weights last year to cast a
      counterweight for my trebuchet, at last I found a manager who knew
      what one was and he gave me a 5 gallon pail full. Everyone else told
      me it was toxic waste and they could not let me have it by law! It
      would also end up making the machine weigh more than a full cast iron
      casting which is why I think concrete is being considered as a
      lightweight alternative.

      As for the shrinkage of the concrete, I think that could be
      accommodated by pre-coating the inside of the extrusion with an
      elastomer which would compress when the concrete was cast and rebound
      back to keep things in contact. When I was employed making high
      pressure feed through seals we had a job where the thermal properties
      of the housing and the epoxy filling was causing leaks and we solved
      it by using I think Polysulfone which was pre-filled into grooves in
      the housing, cured and then the epoxy resin was cast around the wire
      bundle. That solved the problem of the difference of coefficient of
      expansion between the metal housing and epoxy as it was cured and
      baked. Those things passed a Halogen leak test at 30,000 PSI after
      that! Well almost all of them, a few blew into the wall when they
      failed but we were doing 100% QC on the parts for a GE nuke plant.

      Kristin

      --- In taigtools@yahoogroups.com, "Leon" <leon355@...> wrote:
      >
      > ----- Original Message -----
      > From: "Ken Cline" <cline@...>
      > To: <taigtools@yahoogroups.com>
      > Sent: Monday, May 05, 2008 4:21 AM
      > Subject: Re: [taigtools] Concrete filled extrusions
      >
      >
      > >
      > > On 4 May 2008, at 7:47 AM, Anthony Costello wrote:
      > >
      > >> the concrete will be brittle.
      > >
      > > Concrete is brittle, so it is often tensioned when used for
      structural
      > > purposes. One way to do this is to leave holes in the concrete
      > > through which threaded rods are run, then attaching plates to the
      ends
      > > and forcing them against the concrete by tightening nuts.
      Thinking
      > > about this approach, I realized you could achieve a similar
      result for
      > > your lathe by just filling the tube with sand (no cement) and
      pressing
      > > it in place with some threaded rods between end caps.
      > >
      > > The modulus of elasticity of concrete is 17-31 GPa, significantly
      less
      > > than that of aluminum (70-79) or steel (190-210), meaning
      concrete is
      > > much more flexible than the metal tube. Because of this, the
      > > concrete's mass should be more significant in preventing
      vibration
      > > than any additional stiffness. I have not done calculations to
      > > confirm this, but if my assumption is correct using plain
      aggregate
      > > (sand) under compression might work just as well.
      >
      > Lead shot should work even better.
      >
      > Leon
      > --
      > Leon Heller
      > Amateur radio call-sign G1HSM
      > Yaesu FT-817ND transceiver
      > Suzuki SV1000S motorcycle
      > leon355@...
      > http://www.geocities.com/leon_heller
      >
    • Daniel Gutzwiller
      Michael Re. ...corrosion potential of the alkaline concrete... I think you may have this backwards...the alkalinity of concrete prevents corrosion of iron.
      Message 2 of 12 , May 5, 2008
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        Michael Re. "...corrosion potential of the alkaline concrete..." I
        think you may have this backwards...the alkalinity of concrete
        prevents corrosion of iron. E.g. re-bar embedded in concrete does not
        corrode in spite of the massive amounts of water in concrete, due to
        the alkalinity.



        --- In taigtools@yahoogroups.com, "Michael Fagan" <woodworker88@...>
        wrote:
        >
        > I'm working on a new project called OpenLathe, which is trying to
        > build a high-precision hobby lathe using an open-source mentality.
        > One idea that we're considering is using steel extrusions filled
        with
        > concrete to help add mass, while allowing the parts to be easily
        > machined and shipped without undue weight. I know that the Taig
        lathe
        > is constructed in this manner, but does anybody know how they
        actually
        > do it? The two main issues I'm interested in learning about are
        > corrosion and shrinkage. The Taig extrusions are aluminum, but I
        > would assume they have some ferrous metal fasteners that would be
        > susceptible to the corrosion potential of the alkaline concrete.
        > Secondly, concrete shrinks as it cures, and it would seem to me that
        > taking a hollow tube and filling it with a material that then
        shrinks
        > would result in something that didn't really help dampen vibrations.
        > I'm curious as to how they get around this problem. If nobody knows
        > the answer, I may just call Taig and ask them.
        >
        > Anybody have any ideas?
        >
        > Michael
        >
        > PS you can check out the OpenLathe project at
        groups.yahoo.com/group/OpenLathe
        >
      • Martin Dobbins
        Since the object of the exercise is to increase mass to increase stability then a good move would be to make the bed of cast iron with a steel top. However, I
        Message 3 of 12 , May 5, 2008
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          Since the object of the exercise is to increase mass to increase stability then a good move would be to make the bed of cast iron with a steel top. However, I believe the objective was to use hollow aluminum extrusions for simplicity, in which case Leon's suggestion makes sense-lead has more mass than concrete or sand with none of the attendant "containment" problems. It would be even simpler to melt the lead and pour it into the extrusion than to have to try to contain the lead shot. However lead is on the blacklist in parts of the world for a very good reason, so if it can be obtained treat it with a lot of care because there is no cure for lead poisoning. Use the same caution when machining and handling 12L14 steel, it machines nicely because it contains a deal of lead.

          Tungsten is more expensive than lead, masses more, and has less healthcare risks, but is to all intents unmachineable in the home shop. Since fishing seems to be moving away from lead weights and the Pinewood Derby suppliers are seeking a way to give kids a safe way to weight their cars, different Tungsten shapes and offcuts are becoming more commonly available:

          http://www.maximum-velocity.com/

          Martin







          Leon wrote:
          ----- Original Message -----
          From: "Ken Cline"


          > I have not done calculations to
          > confirm this, but if my assumption is correct using plain aggregate
          > (sand) under compression might work just as well.

          Lead shot should work even better.

          Leon
          --
          Leon Heller
          Amateur radio call-sign G1HSM
          Yaesu FT-817ND transceiver
          Suzuki SV1000S motorcycle
          leon355@...
          http://www.geocities.com/leon_heller





          ---------------------------------
          Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.

          [Non-text portions of this message have been removed]
        • Michael Fagan
          Right. In our ideal world, the entire bed would be made of iron castings, perhaps with hardened and ground steel ways on top. However, part of the project
          Message 4 of 12 , May 5, 2008
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            Right. In our ideal world, the entire bed would be made of iron
            castings, perhaps with hardened and ground steel ways on top.
            However, part of the project involves using easily available
            components and shipping them around the country, thus one important
            aspect being that the weight should be added as late in the process as
            possible.

            Thanks for all the good ideas. We have been discussing the Epoxy
            Granite and Polymer Concrete products extensively, and I think that
            these could work, as well as standard concretes with minimal water
            added.

            Thanks again
            Michael

            On Mon, May 5, 2008 at 7:33 AM, Martin Dobbins <trainnutz@...> wrote:
            >
            >
            >
            >
            >
            >
            > Since the object of the exercise is to increase mass to increase stability
            > then a good move would be to make the bed of cast iron with a steel top.
            > However, I believe the objective was to use hollow aluminum extrusions for
            > simplicity, in which case Leon's suggestion makes sense-lead has more mass
            > than concrete or sand with none of the attendant "containment" problems. It
            > would be even simpler to melt the lead and pour it into the extrusion than
            > to have to try to contain the lead shot. However lead is on the blacklist in
            > parts of the world for a very good reason, so if it can be obtained treat it
            > with a lot of care because there is no cure for lead poisoning. Use the same
            > caution when machining and handling 12L14 steel, it machines nicely because
            > it contains a deal of lead.
            >
            > Tungsten is more expensive than lead, masses more, and has less healthcare
            > risks, but is to all intents unmachineable in the home shop. Since fishing
            > seems to be moving away from lead weights and the Pinewood Derby suppliers
            > are seeking a way to give kids a safe way to weight their cars, different
            > Tungsten shapes and offcuts are becoming more commonly available:
            >
            > http://www.maximum-velocity.com/
            >
            > Martin
            >
            >
            >
            >
            >
            >
            >
            > Leon wrote:
            > ----- Original Message -----
            > From: "Ken Cline"
            >
            > > I have not done calculations to
            > > confirm this, but if my assumption is correct using plain aggregate
            > > (sand) under compression might work just as well.
            >
            > Lead shot should work even better.
            >
            > Leon
            > --
            > Leon Heller
            > Amateur radio call-sign G1HSM
            > Yaesu FT-817ND transceiver
            > Suzuki SV1000S motorcycle
            > leon355@...
            > http://www.geocities.com/leon_heller
            >
            > ---------------------------------
            > Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it
            > now.
            >
            >
            > [Non-text portions of this message have been removed]
            >
            >
          • S or J
            Hi Michael: Just one further thought on the concrete option. Long ago the tasking was to install one of those umbrella type clotheslines in the backyard. I dug
            Message 5 of 12 , May 7, 2008
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              Hi Michael:

              Just one further thought on the concrete option.

              Long ago the tasking was to install one of those umbrella type
              clotheslines in the backyard. I dug a hole in the ground, waxed
              the base of the aluminium pole, braced it centered in the hole,
              and filled with standard concrete. Months later I pulled out
              the pole and the lower end was mainly missing -- Swiss
              cheese holes everywhere.

              I suspect the reason for massive corrosion was the continuous
              damp condition of the ground and concrete; so this experience
              likely does not apply to a one time moistening of concrete to
              fill an aluminium extrusion. But an experiment first might
              be advisable. Minor one-time corrosion would be acceptable;
              any worse might suggest the need for a simple barrier coat
              inside the extrusion.

              FWIW

              Steve -- in Thunder Bay, Ontario

              Mon May 5, 2008 "Michael Fagan" wrote
              > Right. In our ideal world, the entire bed would be made of iron
              castings, perhaps with hardened and ground steel ways on top.
              However, part of the project involves using easily available
              components and shipping them around the country, thus one important
              aspect being that the weight should be added as late in the process as
              possible.
              Thanks for all the good ideas. We have been discussing the Epoxy
              Granite and Polymer Concrete products extensively, and I think that
              these could work, as well as standard concretes with minimal water
              added. Thanks again Michael <
            • Monte
              ... This wasn t due to the moisture, it was a chemical or galvanic reaction that the aluminum didn t survive. The moisture was part of the reaction, but it
              Message 6 of 12 , May 7, 2008
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                --- In taigtools@yahoogroups.com, "S or J" <jstudio@...> wrote:
                >
                > Hi Michael:
                >
                > Just one further thought on the concrete option.
                >
                > Long ago the tasking was to install one of those umbrella type
                > clotheslines in the backyard. I dug a hole in the ground, waxed
                > the base of the aluminium pole, braced it centered in the hole,
                > and filled with standard concrete. Months later I pulled out
                > the pole and the lower end was mainly missing -- Swiss
                > cheese holes everywhere.
                >
                > I suspect the reason for massive corrosion was the continuous
                > damp condition of the ground and concrete; so this experience
                > likely does not apply to a one time moistening of concrete to
                > fill an aluminium extrusion. But an experiment first might
                > be advisable. Minor one-time corrosion would be acceptable;
                > any worse might suggest the need for a simple barrier coat
                > inside the extrusion.
                >
                > FWIW

                This wasn't due to the moisture, it was a chemical or galvanic
                reaction that the aluminum didn't survive. The moisture was part of
                the reaction, but it wasn't the whole cause.

                I'm not sure what fully cured cement based concrete will do to
                aluminum in the long run if there is no moisture source available and
                the concrete is allowed to "dry". Cement based concrete is alkaline
                on the ph scale, going toward neutral as it ages.

                Monte
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