## Re: [SCA-Archery] poundage question

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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
Message 1 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/
• 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 2 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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• 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 3 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
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]
>
>
>
>
>
>
>
> ________________________________________________________________
> The best thing to hit the Internet in years - Juno SpeedBand!
> Surf the Web up to FIVE TIMES FASTER!
>
>
> ---8<---------------------------------------------
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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
Message 4 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
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]
>
>
>
>
>
>
>
> ________________________________________________________________
> The best thing to hit the Internet in years - Juno SpeedBand!
> Surf the Web up to FIVE TIMES FASTER!
>
>
> ---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]
>
>
>
>
>

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• 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 5 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

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/
• ... Exactly ___________________________________________________________________________ THL Siegfried Sebastian Faust
Message 6 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/
• ... No carolus, it does make a difference, the shorter string causes a higher angle of deflection to get to 28 Siegfried
Message 7 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/
• 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 8 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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• What numbers have you recorded? Carolus On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust ...
Message 9 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
>
> 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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• 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 10 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
>
> 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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• 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 11 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
> >
> > 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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>

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• ... 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 12 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/
• ... 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 13 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/
• 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 14 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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• ... 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 15 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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