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Re: [SCA-Archery] poundage question

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  • Carl West
    ... Same amount of available energy? maybe. Different draw weight? maybe. Different geometry? certainly. Someone with a bow-scale, a measuring tape, graph
    Message 1 of 24 , Apr 1, 2004
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      atruemark@... wrote:
      >
      > In a message dated 4/1/04 1:46:03 PM Pacific Standard Time,
      > crossbow@... writes:
      > > If you shorten your string to have a higher brace height, the limbs are
      > > more flexed because of the shorter string, when you pull it to the same
      > > point, the limbs will be even more flexed that they would have been with
      > > the longer string, and therefore the poundage will have increased.



      > Think of it this way. Imagine your bow as being perfectly straight from
      > riser to limb tip. Now brace it to 6". It will have stored "X" amount of energy
      > in the limbs. Draw it back to your anchor point and it will have "X" amount
      > of more stored energy in the limb. Now twist the string up a bit and increase
      > the brace height to 7". Have you "increased the poundage?" No. All you've
      > done is increase the stored energy in the limb for that increased brace height.
      > If you draw back to your regular anchor, you are still storing the same
      > amount of energy as you would have with a 6" brace height.


      Same amount of available energy? maybe.
      Different draw weight? maybe.
      Different geometry? certainly.

      Someone with a bow-scale, a measuring tape, graph paper, a bow and a little time want to make a chart or two?

      This guy addresses some of the issues, but doesn't speak to the question of draw-weight v. brace-height:
      http://homepage.ntlworld.com/joetapley/bh.htm
      nor does he give any citations of of authorities or research.
      There's no proof that he didn't develop this through rectal extraction.

      He certainly has a lot of stuff on archery on his site. Trim the URL to see. Not all of what he says makes sense to me, but, it's late.

      -- Fritz


      If you try to 'reply' to me without fixing the dot, your reply
      will go into a 'special' mailbox reserved for spam. See below.


      --
      Carl West carlDOTwest@... http://carl.west.home.comcast.net

      >>>>>>>> change the 'DOT' to '.' to email me <<<<<<<<<<<<

      "Clutter"? This is an object-rich environment.
    • atruemark@aol.com
      I agree with Carl that my earlier explanation was simplistic. It s also true, in the same way that saying a chunk of lead is solid, which it is in a real
      Message 2 of 24 , Apr 1, 2004
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        I agree with Carl that my earlier explanation was simplistic. It's also
        true, in the same way that saying a chunk of lead is solid, which it is in a real
        world kind of way. On an atomic level, however, it isn't - in fact, it's full
        of space and in no way a solid. So to with brace height vs poundage. My
        earlier explanation is true, in a general, real world sense. Technically,
        however, all sorts of factors come into play - bow profile, materials, even the mass
        of the string. This is from Archery; The Technical Side, of the Legends of
        the Longbow series compiled by Glenn St. Charles, in an article written in
        March 1931 by C.N. Hickman.

        "This means that a bow braced high does not require much more strength to
        hold, when fully drawn, than if it were braced low....and for all practical
        bracing heights, the force-draw curves merge into one common curve near the end
        of a full draw." (page 19, paragraph 5). Further, "The drawing force for a
        full draw is almost independent of the bracing height of the bow string."
        (page 21, first point under Summary) and "The arrow velocity increases with
        increase in bracing height up to a certain point (if starting with zero brace
        height), after which it slowly decreases with additional increases in bracing
        height." (page 21, point 5 under Summary).

        So, without taking into account a variety of factors, it is safe to say that
        the major impact that lowering or raising brace height has on performance is
        not poundage related, but more in how long the string stays in contact with the
        arrow, thus transfering stored energy into the arrow.

        Regards,

        Andras Truemark


        [Non-text portions of this message have been removed]
      • Carolus Eulenhorst
        I don t find this at all. Testing three crossbows and four recurves (three working recurves and one semi-working recurve), I find the poundage the same at the
        Message 3 of 24 , Apr 1, 2004
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          I don't find this at all. Testing three crossbows and four recurves
          (three working recurves and one semi-working recurve), I find the
          poundage the same at the same draw length regardless of where I have the
          brace height..The bow is flexed the same amount at the same draw length
          though it is, indeed, flexed more at rest with a higher brace height. In
          forty years of shooting I have never found changing the brace height to
          change the total draw weight.

          The effect you see is not the result of poundage change but rather
          distance change. For example, a crossbow braced at 4 inches and drawn 10
          inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
          pull. If the brace height is raised to 4.4 inches it reduces the draw
          length to 9.6 inches. When multiplied against the same 62.5 pound pull
          the result is 600 inch pounds. This is what has led to many
          misunderstandings about the power of crossbows on the combat field. Some
          would say that a 62.5 pound crossbow in too powerful but they are
          ignoring the fact that the power curve is reduced and thus the work done
          on the bolt is decreased resulting in less impact.

          If you do actually see the poundage change I would like more information
          on the poundages at each brace height, draw lengths, and construction of
          the bows.
          Carolus
          On Thu, 01 Apr 2004 16:39:14 -0500 Siegfried Sebastian Faust
          <crossbow@...> writes:
          > At 01:49 PM 4/1/2004, Carolus Eulenhorst wrote:
          > >No. The poundage is determined by the length of the draw, not the
          > brace
          > >height.
          >
          > While you are right that the length of the draw changes the poundage
          >
          > Carolus ... the brace height will ALSO do that.
          >
          > If you shorten your string to have a higher brace height, the limbs
          > are
          > more flexed because of the shorter string, when you pull it to the
          > same
          > point, the limbs will be even more flexed that they would have been
          > with
          > the longer string, and therefore the poundage will have increased.
          >
          > However, with the longer brace height, you will have a shorter power
          >
          > stroke, therefore robbing energy.
          >
          > I, and others, use this effect all the time on combat crossbows to
          > 'tune'
          > them to be around the 600 in-lb mark ... loosen the string to drop
          > poundage
          > but increase power stroke, shorten the string to up poundage and
          > lose power
          > stroke.
          >
          > It isn't a linear curve, and therefore you can often adjust (for
          > combat
          > archery) an 'illegal' 625 in-lb crossbow to be a legal 600 in-lb
          > crossbow
          > through these adjustments.
          >
          > Siegfried

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        • Siegfried Sebastian Faust
          Ok Carolus, I see a slight error here, and I want to try to explain this, if the explantion doesn t work, I ll draw a graphic ... just let me know. I find the
          Message 4 of 24 , Apr 2, 2004
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            Ok Carolus, I see a slight error here, and I want to try to explain this,
            if the explantion doesn't work, I'll draw a graphic ... just let me know.

            I find the
            >poundage the same at the same draw length regardless of where I have the
            >brace height..The bow is flexed the same amount at the same draw length
            >though it is, indeed, flexed more at rest with a higher brace height.
            [snip]
            >The effect you see is not the result of poundage change but rather
            >distance change. For example, a crossbow braced at 4 inches and drawn 10
            >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
            >pull. If the brace height is raised to 4.4 inches it reduces the draw
            >length to 9.6 inches. When multiplied against the same 62.5 pound pull
            >the result is 600 inch pounds.
            [snip]
            >If you do actually see the poundage change I would like more information
            >on the poundages at each brace height, draw lengths, and construction of
            >the bows.

            Ok Carolus, simple physics ... and I'm going to use crossbows as an
            example, just because I find it a better mental model.

            Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
            string. That gives you some amount of brace height.

            Ok, now imagine the crossbow drawn back and cocked. Assume now, that
            there is a 1" wide nut/shelf/etc it is in.

            If you measure the length now, of the string on either side of the nut to
            the tip. You will find it is 12.5" ... half the width of the string, after
            the 1" of nut is taken into consideration. So the angle the prod is being
            held at, is to allow for a 12.5" length of string on either side of it to
            exist. Measure the poundage here.

            Ok, now, take the string off and twist it tighter until it is only 25" long.

            Ok, now put it back on the crossbow, and you will have a higher brace
            height. Agreed?

            So now, pull back/cock the crossbow. Do the same measurements. Now, there
            is only 12" on either side of string. By simple physics, the prod has been
            pulled back farther. There is no other way around it. Now, unless this
            prod 'somehow' has magical properties that give it a smooth unchanging
            poundage (I know of none), the fact that it is being stressed farther,
            means it took more force to get it there, and therefore, if you put a
            bowscale on it now, the poundage will be higher.

            Now, as stated, the power stroke is now shorter, as the string stops
            sooner, and this counteracts 'somewhat' the difference. However, each bow
            is different, and some stringheight/poundage is the optimum for that
            bow/prod, others are less efficient, therefore, depending upon the bow, you
            can adjust it's poundage, and it's power, by playing with that, because in
            my experience, it isn't a smooth curve.

            Siegfried
            (Who will also sit down and do lots of string pulling on one of his
            crossbows for ya if he has to *grin*)



            ___________________________________________________________________________
            THL Siegfried Sebastian Faust http://crossbows.biz/
            Barony of Highland Foorde Baronial Web Minister & Archery Marshal
            Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
            http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
          • eulenhorst@juno.com
            No. The pre-stress is higher but the total stress is identical. A spring tensioned to the same point will only show a certain poundage regardless of the
            Message 5 of 24 , Apr 2, 2004
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              No. The pre-stress is higher but the total stress is identical. A spring tensioned to the same point will only show a certain poundage regardless of the prestress. The archery mechanics site posted earlier has a good discussion of spring loading and prestress under plunger buttons. My results are empirical based on actual tests with a bow scale, not theoretical.

              In Service to the dream
              Carolus von Eulenhorst
              eulenhorst@...
              BTW, that mechanics site has some references on the home page and seems well grounded.
              CvE

              -- Siegfried Sebastian Faust <crossbow@...> wrote:
              Ok Carolus, I see a slight error here, and I want to try to explain this,
              if the explantion doesn't work, I'll draw a graphic ... just let me know.

              I find the
              >poundage the same at the same draw length regardless of where I have the
              >brace height..The bow is flexed the same amount at the same draw length
              >though it is, indeed, flexed more at rest with a higher brace height.
              [snip]
              >The effect you see is not the result of poundage change but rather
              >distance change. For example, a crossbow braced at 4 inches and drawn 10
              >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
              >pull. If the brace height is raised to 4.4 inches it reduces the draw
              >length to 9.6 inches. When multiplied against the same 62.5 pound pull
              >the result is 600 inch pounds.
              [snip]
              >If you do actually see the poundage change I would like more information
              >on the poundages at each brace height, draw lengths, and construction of
              >the bows.

              Ok Carolus, simple physics ... and I'm going to use crossbows as an
              example, just because I find it a better mental model.

              Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
              string. That gives you some amount of brace height.

              Ok, now imagine the crossbow drawn back and cocked. Assume now, that
              there is a 1" wide nut/shelf/etc it is in.

              If you measure the length now, of the string on either side of the nut to
              the tip. You will find it is 12.5" ... half the width of the string, after
              the 1" of nut is taken into consideration. So the angle the prod is being
              held at, is to allow for a 12.5" length of string on either side of it to
              exist. Measure the poundage here.

              Ok, now, take the string off and twist it tighter until it is only 25" long.

              Ok, now put it back on the crossbow, and you will have a higher brace
              height. Agreed?

              So now, pull back/cock the crossbow. Do the same measurements. Now, there
              is only 12" on either side of string. By simple physics, the prod has been
              pulled back farther. There is no other way around it. Now, unless this
              prod 'somehow' has magical properties that give it a smooth unchanging
              poundage (I know of none), the fact that it is being stressed farther,
              means it took more force to get it there, and therefore, if you put a
              bowscale on it now, the poundage will be higher.

              Now, as stated, the power stroke is now shorter, as the string stops
              sooner, and this counteracts 'somewhat' the difference. However, each bow
              is different, and some stringheight/poundage is the optimum for that
              bow/prod, others are less efficient, therefore, depending upon the bow, you
              can adjust it's poundage, and it's power, by playing with that, because in
              my experience, it isn't a smooth curve.

              Siegfried
              (Who will also sit down and do lots of string pulling on one of his
              crossbows for ya if he has to *grin*)



              ___________________________________________________________________________
              THL Siegfried Sebastian Faust http://crossbows.biz/
              Barony of Highland Foorde Baronial Web Minister & Archery Marshal
              Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
              http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/



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            • Scott Jaqua
              Actually Carolus, as a logic thought problem, I come up with more total stress too. Lower brace height equals a shorter string. A sorter string at the same
              Message 6 of 24 , Apr 2, 2004
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                Actually Carolus, as a logic thought problem, I come up with more total
                stress too. Lower brace height equals a shorter string. A sorter string at
                the same draw length means the tip of the limb had to flex further. And thus
                more total stress. But I can't tell you if this is one of the cases where
                the real world observations don't match theory.

                Njall
                (jr rocket scientist, for a real rocket scientist, talk to my dad)

                Scott B. Jaqua
                ----------------------------------------------------------------------------
                -----------------------------
                The most import right of all, is that of free speech. Without that, all your
                other rights will soon be taken away. So, I may disagree with what you say,
                but I will defend until death, your right to say it!
                ----- Original Message -----
                From: <eulenhorst@...>
                To: <SCA-Archery@yahoogroups.com>
                Sent: Friday, April 02, 2004 2:16 PM
                Subject: Re: [SCA-Archery] poundage question


                >
                > No. The pre-stress is higher but the total stress is identical. A spring
                tensioned to the same point will only show a certain poundage regardless of
                the prestress. The archery mechanics site posted earlier has a good
                discussion of spring loading and prestress under plunger buttons. My
                results are empirical based on actual tests with a bow scale, not
                theoretical.
                >
                > In Service to the dream
                > Carolus von Eulenhorst
                > eulenhorst@...
                > BTW, that mechanics site has some references on the home page and seems
                well grounded.
                > CvE
                >
                > -- Siegfried Sebastian Faust <crossbow@...> wrote:
                > Ok Carolus, I see a slight error here, and I want to try to explain this,
                > if the explantion doesn't work, I'll draw a graphic ... just let me know.
                >
                > I find the
                > >poundage the same at the same draw length regardless of where I have the
                > >brace height..The bow is flexed the same amount at the same draw length
                > >though it is, indeed, flexed more at rest with a higher brace height.
                > [snip]
                > >The effect you see is not the result of poundage change but rather
                > >distance change. For example, a crossbow braced at 4 inches and drawn 10
                > >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
                > >pull. If the brace height is raised to 4.4 inches it reduces the draw
                > >length to 9.6 inches. When multiplied against the same 62.5 pound pull
                > >the result is 600 inch pounds.
                > [snip]
                > >If you do actually see the poundage change I would like more information
                > >on the poundages at each brace height, draw lengths, and construction of
                > >the bows.
                >
                > Ok Carolus, simple physics ... and I'm going to use crossbows as an
                > example, just because I find it a better mental model.
                >
                > Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
                > string. That gives you some amount of brace height.
                >
                > Ok, now imagine the crossbow drawn back and cocked. Assume now, that
                > there is a 1" wide nut/shelf/etc it is in.
                >
                > If you measure the length now, of the string on either side of the nut to
                > the tip. You will find it is 12.5" ... half the width of the string,
                after
                > the 1" of nut is taken into consideration. So the angle the prod is being
                > held at, is to allow for a 12.5" length of string on either side of it to
                > exist. Measure the poundage here.
                >
                > Ok, now, take the string off and twist it tighter until it is only 25"
                long.
                >
                > Ok, now put it back on the crossbow, and you will have a higher brace
                > height. Agreed?
                >
                > So now, pull back/cock the crossbow. Do the same measurements. Now,
                there
                > is only 12" on either side of string. By simple physics, the prod has
                been
                > pulled back farther. There is no other way around it. Now, unless this
                > prod 'somehow' has magical properties that give it a smooth unchanging
                > poundage (I know of none), the fact that it is being stressed farther,
                > means it took more force to get it there, and therefore, if you put a
                > bowscale on it now, the poundage will be higher.
                >
                > Now, as stated, the power stroke is now shorter, as the string stops
                > sooner, and this counteracts 'somewhat' the difference. However, each
                bow
                > is different, and some stringheight/poundage is the optimum for that
                > bow/prod, others are less efficient, therefore, depending upon the bow,
                you
                > can adjust it's poundage, and it's power, by playing with that, because in
                > my experience, it isn't a smooth curve.
                >
                > Siegfried
                > (Who will also sit down and do lots of string pulling on one of his
                > crossbows for ya if he has to *grin*)
                >
                >
                >
                >
                ___________________________________________________________________________
                > THL Siegfried Sebastian Faust
                http://crossbows.biz/
                > Barony of Highland Foorde Baronial Web Minister & Archery
                Marshal
                > Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target
                Archery
                > http://highland-foorde.atlantia.sca.org/
                http://archery.atlantia.sca.org/
                >
                >
                >
                > ---8<---------------------------------------------
                > Brought to you YahooGroups Ad Free in 2003 by Medieval Mart
                > Get Medieval at Mad Macsen's http://www.medievalmart.com/
                >
                > [Email to SCA-Archery-unsubscribe@yahoogroups.com to leave this list]
                >
                > Yahoo! Groups Links
                >
                >
                >
                >
                >
                >
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              • eulenhorst@juno.com
                This only works if the draw distance remains constant thus resulting in more draw with the higher brace height. If the bow is drawn to 28 , for example, it
                Message 7 of 24 , Apr 2, 2004
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                  This only works if the draw distance remains constant thus resulting in more draw with the higher brace height. If the bow is drawn to 28", for example, it doesn't matter if it started with a brace of 7" or 8". The draw length in the first case is 21" and in the second 20". If, however we use a draw distance of 20" we get a draw length of 27" with a 7" brace and 28" with an 8" brace. In this case the draw weight does change.


                  In Service to the dream
                  Carolus von Eulenhorst
                  eulenhorst@...

                  -- "Scott Jaqua" <jaqua@...> wrote:
                  Actually Carolus, as a logic thought problem, I come up with more total
                  stress too. Lower brace height equals a shorter string. A sorter string at
                  the same draw length means the tip of the limb had to flex further. And thus
                  more total stress. But I can't tell you if this is one of the cases where
                  the real world observations don't match theory.

                  Njall
                  (jr rocket scientist, for a real rocket scientist, talk to my dad)

                  Scott B. Jaqua
                  ----------------------------------------------------------------------------
                  -----------------------------
                  The most import right of all, is that of free speech. Without that, all your
                  other rights will soon be taken away. So, I may disagree with what you say,
                  but I will defend until death, your right to say it!
                  ----- Original Message -----
                  From: <eulenhorst@...>
                  To: <SCA-Archery@yahoogroups.com>
                  Sent: Friday, April 02, 2004 2:16 PM
                  Subject: Re: [SCA-Archery] poundage question


                  >
                  > No. The pre-stress is higher but the total stress is identical. A spring
                  tensioned to the same point will only show a certain poundage regardless of
                  the prestress. The archery mechanics site posted earlier has a good
                  discussion of spring loading and prestress under plunger buttons. My
                  results are empirical based on actual tests with a bow scale, not
                  theoretical.
                  >
                  > In Service to the dream
                  > Carolus von Eulenhorst
                  > eulenhorst@...
                  > BTW, that mechanics site has some references on the home page and seems
                  well grounded.
                  > CvE
                  >
                  > -- Siegfried Sebastian Faust <crossbow@...> wrote:
                  > Ok Carolus, I see a slight error here, and I want to try to explain this,
                  > if the explantion doesn't work, I'll draw a graphic ... just let me know.
                  >
                  > I find the
                  > >poundage the same at the same draw length regardless of where I have the
                  > >brace height..The bow is flexed the same amount at the same draw length
                  > >though it is, indeed, flexed more at rest with a higher brace height.
                  > [snip]
                  > >The effect you see is not the result of poundage change but rather
                  > >distance change. For example, a crossbow braced at 4 inches and drawn 10
                  > >inches with a draw weight of 62.5 pounds will yield 625 inch pounds of
                  > >pull. If the brace height is raised to 4.4 inches it reduces the draw
                  > >length to 9.6 inches. When multiplied against the same 62.5 pound pull
                  > >the result is 600 inch pounds.
                  > [snip]
                  > >If you do actually see the poundage change I would like more information
                  > >on the poundages at each brace height, draw lengths, and construction of
                  > >the bows.
                  >
                  > Ok Carolus, simple physics ... and I'm going to use crossbows as an
                  > example, just because I find it a better mental model.
                  >
                  > Ok, Let's say you have a 28" wide crossbow prod, and a 26" long
                  > string. That gives you some amount of brace height.
                  >
                  > Ok, now imagine the crossbow drawn back and cocked. Assume now, that
                  > there is a 1" wide nut/shelf/etc it is in.
                  >
                  > If you measure the length now, of the string on either side of the nut to
                  > the tip. You will find it is 12.5" ... half the width of the string,
                  after
                  > the 1" of nut is taken into consideration. So the angle the prod is being
                  > held at, is to allow for a 12.5" length of string on either side of it to
                  > exist. Measure the poundage here.
                  >
                  > Ok, now, take the string off and twist it tighter until it is only 25"
                  long.
                  >
                  > Ok, now put it back on the crossbow, and you will have a higher brace
                  > height. Agreed?
                  >
                  > So now, pull back/cock the crossbow. Do the same measurements. Now,
                  there
                  > is only 12" on either side of string. By simple physics, the prod has
                  been
                  > pulled back farther. There is no other way around it. Now, unless this
                  > prod 'somehow' has magical properties that give it a smooth unchanging
                  > poundage (I know of none), the fact that it is being stressed farther,
                  > means it took more force to get it there, and therefore, if you put a
                  > bowscale on it now, the poundage will be higher.
                  >
                  > Now, as stated, the power stroke is now shorter, as the string stops
                  > sooner, and this counteracts 'somewhat' the difference. However, each
                  bow
                  > is different, and some stringheight/poundage is the optimum for that
                  > bow/prod, others are less efficient, therefore, depending upon the bow,
                  you
                  > can adjust it's poundage, and it's power, by playing with that, because in
                  > my experience, it isn't a smooth curve.
                  >
                  > Siegfried
                  > (Who will also sit down and do lots of string pulling on one of his
                  > crossbows for ya if he has to *grin*)
                  >
                  >
                  >
                  >
                  ___________________________________________________________________________
                  > THL Siegfried Sebastian Faust
                  http://crossbows.biz/
                  > Barony of Highland Foorde Baronial Web Minister & Archery
                  Marshal
                  > Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target
                  Archery
                  > http://highland-foorde.atlantia.sca.org/
                  http://archery.atlantia.sca.org/
                  >
                  >
                  >
                  > ---8<---------------------------------------------
                  > Brought to you YahooGroups Ad Free in 2003 by Medieval Mart
                  > Get Medieval at Mad Macsen's http://www.medievalmart.com/
                  >
                  > [Email to SCA-Archery-unsubscribe@yahoogroups.com to leave this list]
                  >
                  > Yahoo! Groups Links
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                • Siegfried Sebastian Faust
                  Hey Carolus ... Sorry for the delay in my reply, been sick. ... The point is, that if you take a bow/prod ... and put a shorter string on it, then pull it back
                  Message 8 of 24 , Apr 8, 2004
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                    Hey Carolus ... Sorry for the delay in my reply, been sick.

                    Anyway ... I think you are missing something:

                    >No. The pre-stress is higher but the total stress is identical. A spring
                    >tensioned to the same point will only show a certain poundage regardless
                    >of the prestress. The archery mechanics site posted earlier has a good
                    >discussion of spring loading and prestress under plunger buttons.

                    The point is, that if you take a bow/prod ... and put a shorter string on
                    it, then pull it back to the same draw length (not power stroke, but draw
                    length) ...

                    Then because of the shorter string, the 'spring' is NOT tensioned to the
                    same point. To get the shorter string to come back to the same spot, it
                    has to pull the 'spring' farther into deflection. Thereby, stressing the
                    material more, thereby, raising the 'poundage' (While very possibly not
                    raising the power because of the shorter power stroke).

                    Again, clear your mind for a second and imagine a crossbow prod with a 3"
                    brace height, and a 28" string on it. Draw it back to a pin, and you will
                    measure 14" of string on either side of the pin. Now take it off and put
                    a 26" string on it. You have your higher brace height.

                    Now, put it back on the same 'jig', and pull it back to the same pin. The
                    prod is now deflected MORE than it was before, because there is only 13" of
                    string on either side of the pin, forcing the prod to bend more to allow
                    for this.

                    Again, if you need it, I'll draw a picture or take a few photos of this in
                    action.

                    > My results are empirical based on actual tests with a bow scale, not
                    > theoretical.

                    As are mine. I can easily put a shorter string on the same prod and have
                    my bowscale read a higher poundage at the same draw.

                    Siegfried



                    ___________________________________________________________________________
                    THL Siegfried Sebastian Faust http://crossbows.biz/
                    Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                    Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                    http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                  • Siegfried Sebastian Faust
                    ... Exactly ___________________________________________________________________________ THL Siegfried Sebastian Faust
                    Message 9 of 24 , Apr 8, 2004
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                      At 06:45 PM 4/2/2004, Scott Jaqua wrote:
                      >Actually Carolus, as a logic thought problem, I come up with more total
                      >stress too. Lower brace height equals a shorter string. A sorter string at
                      >the same draw length means the tip of the limb had to flex further. And thus
                      >more total stress.

                      Exactly


                      ___________________________________________________________________________
                      THL Siegfried Sebastian Faust http://crossbows.biz/
                      Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                      Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                      http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                    • Siegfried Sebastian Faust
                      ... No carolus, it does make a difference, the shorter string causes a higher angle of deflection to get to 28 Siegfried
                      Message 10 of 24 , Apr 8, 2004
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                        >This only works if the draw distance remains constant thus resulting in
                        >more draw with the higher brace height. If the bow is drawn to 28", for
                        >example, it doesn't matter if it started with a brace of 7" or 8". The
                        >draw length in the first case is 21" and in the second 20". If, however
                        >we use a draw distance of 20" we get a draw length of 27" with a 7" brace
                        >and 28" with an 8" brace. In this case the draw weight does change.

                        No carolus, it does make a difference, the shorter string causes a higher
                        angle of deflection to get to 28"

                        Siegfried



                        ___________________________________________________________________________
                        THL Siegfried Sebastian Faust http://crossbows.biz/
                        Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                        Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                        http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                      • Carolus Eulenhorst
                        Angles might be slightly different. but poundages have measured the same. There may be some small difference but not enough to read on a scale with 1 pound
                        Message 11 of 24 , Apr 9, 2004
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                          Angles might be slightly different. but poundages have measured the same.
                          There may be some small difference but not enough to read on a scale
                          with 1 pound resolution. I would still like to see someone else do some
                          empirical tests on this. Thinking on it while writing this, I might be
                          able to see some difference on a longbow (all my work was on recurves)
                          were the rotation of the tips was not a factor.
                          Carolus

                          On Thu, 08 Apr 2004 23:25:14 -0400 Siegfried Sebastian Faust
                          <crossbow@...> writes:
                          >
                          > >This only works if the draw distance remains constant thus
                          > resulting in
                          > >more draw with the higher brace height. If the bow is drawn to
                          > 28", for
                          > >example, it doesn't matter if it started with a brace of 7" or 8".
                          > The
                          > >draw length in the first case is 21" and in the second 20". If,
                          > however
                          > >we use a draw distance of 20" we get a draw length of 27" with a 7"
                          > brace
                          > >and 28" with an 8" brace. In this case the draw weight does
                          > change.
                          >
                          > No carolus, it does make a difference, the shorter string causes a
                          > higher
                          > angle of deflection to get to 28"
                          >
                          > Siegfried

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                        • Carolus Eulenhorst
                          What numbers have you recorded? Carolus On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust ...
                          Message 12 of 24 , Apr 9, 2004
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                            What numbers have you recorded?
                            Carolus

                            On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust
                            <crossbow@...> writes:
                            > Hey Carolus ... Sorry for the delay in my reply, been sick.
                            >
                            > Anyway ... I think you are missing something:
                            >
                            > >No. The pre-stress is higher but the total stress is identical. A
                            > spring
                            > >tensioned to the same point will only show a certain poundage
                            > regardless
                            > >of the prestress. The archery mechanics site posted earlier has a
                            > good
                            > >discussion of spring loading and prestress under plunger buttons.
                            >
                            > The point is, that if you take a bow/prod ... and put a shorter
                            > string on
                            > it, then pull it back to the same draw length (not power stroke, but
                            > draw
                            > length) ...
                            >
                            > Then because of the shorter string, the 'spring' is NOT tensioned to
                            > the
                            > same point. To get the shorter string to come back to the same
                            > spot, it
                            > has to pull the 'spring' farther into deflection. Thereby,
                            > stressing the
                            > material more, thereby, raising the 'poundage' (While very possibly
                            > not
                            > raising the power because of the shorter power stroke).
                            >
                            > Again, clear your mind for a second and imagine a crossbow prod with
                            > a 3"
                            > brace height, and a 28" string on it. Draw it back to a pin, and
                            > you will
                            > measure 14" of string on either side of the pin. Now take it off
                            > and put
                            > a 26" string on it. You have your higher brace height.
                            >
                            > Now, put it back on the same 'jig', and pull it back to the same
                            > pin. The
                            > prod is now deflected MORE than it was before, because there is only
                            > 13" of
                            > string on either side of the pin, forcing the prod to bend more to
                            > allow
                            > for this.
                            >
                            > Again, if you need it, I'll draw a picture or take a few photos of
                            > this in
                            > action.
                            >
                            > > My results are empirical based on actual tests with a bow scale,
                            > not
                            > > theoretical.
                            >
                            > As are mine. I can easily put a shorter string on the same prod and
                            > have
                            > my bowscale read a higher poundage at the same draw.
                            >
                            > Siegfried

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                          • Carolus Eulenhorst
                            I just ran this through the calculator with an assumption of 3 being normal brace height and 10 of draw. This changes the angel of deflection by 12 degrees
                            Message 13 of 24 , Apr 9, 2004
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                              I just ran this through the calculator with an assumption of 3" being
                              normal brace height and 10" of draw. This changes the angel of
                              deflection by 12 degrees or about 15.5% while shortening the power stroke
                              30% and raising the brace 100% to 6 inches (not taking any rotation of
                              the tips through prod recurve into account. Realizing that the flexion
                              of a spring in not a linear curve and the fact that I would be highly
                              suspect of a bow over braced by this amount, yes, in this case you might
                              see such a change in poundage. However, in practice I don't find it so.
                              Of course, I have only been working with brace height changes in the +-
                              1" range, not the 3" in this case. Extremes do make a difference as
                              shown in some of the "scientific" studies used to prove political points.

                              Carolus

                              On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust
                              <crossbow@...> writes:
                              > Hey Carolus ... Sorry for the delay in my reply, been sick.
                              >
                              > Anyway ... I think you are missing something:
                              >
                              > >No. The pre-stress is higher but the total stress is identical. A
                              > spring
                              > >tensioned to the same point will only show a certain poundage
                              > regardless
                              > >of the prestress. The archery mechanics site posted earlier has a
                              > good
                              > >discussion of spring loading and prestress under plunger buttons.
                              >
                              > The point is, that if you take a bow/prod ... and put a shorter
                              > string on
                              > it, then pull it back to the same draw length (not power stroke, but
                              > draw
                              > length) ...
                              >
                              > Then because of the shorter string, the 'spring' is NOT tensioned to
                              > the
                              > same point. To get the shorter string to come back to the same
                              > spot, it
                              > has to pull the 'spring' farther into deflection. Thereby,
                              > stressing the
                              > material more, thereby, raising the 'poundage' (While very possibly
                              > not
                              > raising the power because of the shorter power stroke).
                              >
                              > Again, clear your mind for a second and imagine a crossbow prod with
                              > a 3"
                              > brace height, and a 28" string on it. Draw it back to a pin, and
                              > you will
                              > measure 14" of string on either side of the pin. Now take it off
                              > and put
                              > a 26" string on it. You have your higher brace height.
                              >
                              > Now, put it back on the same 'jig', and pull it back to the same
                              > pin. The
                              > prod is now deflected MORE than it was before, because there is only
                              > 13" of
                              > string on either side of the pin, forcing the prod to bend more to
                              > allow
                              > for this.
                              >
                              > Again, if you need it, I'll draw a picture or take a few photos of
                              > this in
                              > action.
                              >
                              > > My results are empirical based on actual tests with a bow scale,
                              > not
                              > > theoretical.
                              >
                              > As are mine. I can easily put a shorter string on the same prod and
                              > have
                              > my bowscale read a higher poundage at the same draw.
                              >
                              > Siegfried

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                            • Bruce R. Gordon
                              Greetings I approach this discussion with a certain amount of trepidation, since I am definitely not well-versed in the physics of archery or math analysis,
                              Message 14 of 24 , Apr 9, 2004
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                                Greetings
                                I approach this discussion with a certain amount of trepidation,
                                since I am definitely not well-versed in the physics of archery or math
                                analysis, but...
                                On a standard bow, say, a #35 recurve, it is often said; 35 pounds
                                AT 28 INCHES (emphasis mine). I have always taken this to mean that if
                                I underdraw the bow, I get less than 35 lbs, and if I overdraw it more
                                than 28 in., I get a higher poundage. Is this the case, and does it
                                therefore have relevence to the discussion at hand? Or am I missing
                                some factor here that would make this not to the point?

                                Nigel FitzMaurice

                                > I just ran this through the calculator with an assumption of 3" being
                                > normal brace height and 10" of draw. This changes the angel of
                                > deflection by 12 degrees or about 15.5% while shortening the power
                                stroke
                                > 30% and raising the brace 100% to 6 inches (not taking any rotation of
                                > the tips through prod recurve into account. Realizing that the
                                flexion
                                > of a spring in not a linear curve and the fact that I would be highly
                                > suspect of a bow over braced by this amount, yes, in this case you
                                might
                                > see such a change in poundage. However, in practice I don't find it
                                so.
                                > Of course, I have only been working with brace height changes in the
                                +-
                                > 1" range, not the 3" in this case. Extremes do make a difference as
                                > shown in some of the "scientific" studies used to prove political
                                points.
                                >
                                > Carolus
                                >
                                > On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust
                                > <crossbow@...> writes:
                                > > Hey Carolus ... Sorry for the delay in my reply, been sick.
                                > >
                                > > Anyway ... I think you are missing something:
                                > >
                                > > >No. The pre-stress is higher but the total stress is identical.
                                A
                                > > spring
                                > > >tensioned to the same point will only show a certain poundage
                                > > regardless
                                > > >of the prestress. The archery mechanics site posted earlier has a
                                > > good
                                > > >discussion of spring loading and prestress under plunger buttons.
                                > >
                                > > The point is, that if you take a bow/prod ... and put a shorter
                                > > string on
                                > > it, then pull it back to the same draw length (not power stroke,
                                but
                                > > draw
                                > > length) ...
                                > >
                                > > Then because of the shorter string, the 'spring' is NOT tensioned
                                to
                                > > the
                                > > same point. To get the shorter string to come back to the same
                                > > spot, it
                                > > has to pull the 'spring' farther into deflection. Thereby,
                                > > stressing the
                                > > material more, thereby, raising the 'poundage' (While very
                                possibly
                                > > not
                                > > raising the power because of the shorter power stroke).
                                > >
                                > > Again, clear your mind for a second and imagine a crossbow prod
                                with
                                > > a 3"
                                > > brace height, and a 28" string on it. Draw it back to a pin, and
                                > > you will
                                > > measure 14" of string on either side of the pin. Now take it off
                                > > and put
                                > > a 26" string on it. You have your higher brace height.
                                > >
                                > > Now, put it back on the same 'jig', and pull it back to the same
                                > > pin. The
                                > > prod is now deflected MORE than it was before, because there is
                                only
                                > > 13" of
                                > > string on either side of the pin, forcing the prod to bend more to
                                > > allow
                                > > for this.
                                > >
                                > > Again, if you need it, I'll draw a picture or take a few photos of
                                > > this in
                                > > action.
                                > >
                                > > > My results are empirical based on actual tests with a bow
                                scale,
                                > > not
                                > > > theoretical.
                                > >
                                > > As are mine. I can easily put a shorter string on the same prod
                                and
                                > > have
                                > > my bowscale read a higher poundage at the same draw.
                                > >
                                > > Siegfried
                                >
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                              • Siegfried Sebastian Faust
                                ... Tonight, and/or this weekend, I will take a few of my crossbows and do the measurements on them and post it here ... Siegfried
                                Message 15 of 24 , Apr 9, 2004
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                                  >What numbers have you recorded?

                                  Tonight, and/or this weekend, I will take a few of my crossbows and do the
                                  measurements on them and post it here ...

                                  Siegfried



                                  ___________________________________________________________________________
                                  THL Siegfried Sebastian Faust http://crossbows.biz/
                                  Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                                  Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                                  http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                                • Siegfried Sebastian Faust
                                  ... Ok, at least we are riding the same thought train now :) Now that we agree that it can change the poundage ... I agree that all springs are not linear
                                  Message 16 of 24 , Apr 9, 2004
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                                    >I just ran this through the calculator with an assumption of 3" being
                                    >normal brace height and 10" of draw. This changes the angel of
                                    >deflection by 12 degrees or about 15.5% while shortening the power stroke
                                    >30% and raising the brace 100% to 6 inches (not taking any rotation of
                                    >the tips through prod recurve into account. Realizing that the flexion
                                    >of a spring in not a linear curve and the fact that I would be highly
                                    >suspect of a bow over braced by this amount, yes, in this case you might
                                    >see such a change in poundage. However, in practice I don't find it so.
                                    >Of course, I have only been working with brace height changes in the +-
                                    >1" range, not the 3" in this case. Extremes do make a difference as
                                    >shown in some of the "scientific" studies used to prove political points.

                                    Ok, at least we are riding the same thought train now :)

                                    Now that we agree that it 'can' change the poundage ... I agree that all
                                    springs are not linear curves (not even close), and that the difference may
                                    in fact, depending on the prod be unmeasureable, or visible.

                                    In my experience, on at least some of my crossbows, it has been
                                    measureable, as I have measured differences.

                                    Again, this weekend I will grab a couple of crossbows and play.

                                    Siegfried


                                    ___________________________________________________________________________
                                    THL Siegfried Sebastian Faust http://crossbows.biz/
                                    Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                                    Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                                    http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
                                  • Carolus Eulenhorst
                                    Semantics here. might not can depending on construction and design. I haven t seen it on recurve designs, it is not reported by any manufacturer (their
                                    Message 17 of 24 , Apr 9, 2004
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                                      Semantics here. "might" not "can" depending on construction and
                                      design. I haven't seen it on recurve designs, it is not reported by any
                                      manufacturer (their documentation always gives a range of brace heights
                                      with no reference to poundage change) and only appears relevant when
                                      taken outside the safe range of variation of a bow. Many changes can
                                      happen when design specs are exceeded. Please be sure to give all
                                      relevant measurements with your stats. My tests were with a crossbow
                                      using a Iolo prod, braced from 3-5" pulled to a nut 14" from the prod.
                                      Measured a constant 86 pounds.
                                      Carolus


                                      On Fri, 09 Apr 2004 09:39:54 -0400 Siegfried Sebastian Faust
                                      <crossbow@...> writes:
                                      >
                                      > >I just ran this through the calculator with an assumption of 3"
                                      > being
                                      > >normal brace height and 10" of draw. This changes the angel of
                                      > >deflection by 12 degrees or about 15.5% while shortening the power
                                      > stroke
                                      > >30% and raising the brace 100% to 6 inches (not taking any rotation
                                      > of
                                      > >the tips through prod recurve into account. Realizing that the
                                      > flexion
                                      > >of a spring in not a linear curve and the fact that I would be
                                      > highly
                                      > >suspect of a bow over braced by this amount, yes, in this case you
                                      > might
                                      > >see such a change in poundage. However, in practice I don't find
                                      > it so.
                                      > >Of course, I have only been working with brace height changes in
                                      > the +-
                                      > >1" range, not the 3" in this case. Extremes do make a difference
                                      > as
                                      > >shown in some of the "scientific" studies used to prove political
                                      > points.
                                      >
                                      > Ok, at least we are riding the same thought train now :)
                                      >
                                      > Now that we agree that it 'can' change the poundage ... I agree that
                                      > all
                                      > springs are not linear curves (not even close), and that the
                                      > difference may
                                      > in fact, depending on the prod be unmeasureable, or visible.
                                      >
                                      > In my experience, on at least some of my crossbows, it has been
                                      > measureable, as I have measured differences.
                                      >
                                      > Again, this weekend I will grab a couple of crossbows and play.
                                      >
                                      > Siegfried

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                                    • Siegfried Sebastian Faust
                                      ... But of course :) And I will be doing it with a Gladius prod, one of my own custom Power-Tuff Fiberglass ones, and maybe something else. I swear I have
                                      Message 18 of 24 , Apr 9, 2004
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                                        >Please be sure to give all
                                        >relevant measurements with your stats. My tests were with a crossbow
                                        >using a Iolo prod, braced from 3-5" pulled to a nut 14" from the prod.
                                        >Measured a constant 86 pounds.
                                        >Carolus

                                        But of course :)

                                        And I will be doing it with a Gladius prod, one of my own custom Power-Tuff
                                        Fiberglass ones, and maybe something else.

                                        I 'swear' I have seen the differences with these :)

                                        Siegfried



                                        ___________________________________________________________________________
                                        THL Siegfried Sebastian Faust http://crossbows.biz/
                                        Barony of Highland Foorde Baronial Web Minister & Archery Marshal
                                        Kingdom of Atlantia Deputy Kingdom Earl Marshal for Target Archery
                                        http://highland-foorde.atlantia.sca.org/ http://archery.atlantia.sca.org/
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