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Re: [SCA-Archery] poundage question

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  • 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 1 of 24 , Apr 1, 2004
      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 2 of 24 , Apr 2, 2004
        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 3 of 24 , Apr 2, 2004
          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 4 of 24 , Apr 2, 2004
            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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            > Surf the Web up to FIVE TIMES FASTER!
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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 5 of 24 , Apr 2, 2004
              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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              > Surf the Web up to FIVE TIMES FASTER!
              > Only $14.95/ month - visit www.juno.com to sign up today!
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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 6 of 24 , Apr 8, 2004
                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 7 of 24 , Apr 8, 2004
                  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 8 of 24 , Apr 8, 2004
                    >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 9 of 24 , Apr 9, 2004
                      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 10 of 24 , Apr 9, 2004
                        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 11 of 24 , Apr 9, 2004
                          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 12 of 24 , Apr 9, 2004
                            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 13 of 24 , Apr 9, 2004
                              >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 14 of 24 , Apr 9, 2004
                                >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 15 of 24 , Apr 9, 2004
                                  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 16 of 24 , Apr 9, 2004
                                    >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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