## poundage question

Expand Messages
• When one twists the string to increase the brace height does it increase the poundage as well?
Message 1 of 24 , Mar 31, 2004
When one twists the string to increase the brace height does it
increase the poundage as well?
• No. The poundage is determined by the length of the draw, not the brace height. As it changes the resting weight of the bow, it will change the power curve
Message 2 of 24 , Apr 1, 2004
No. The poundage is determined by the length of the draw, not the brace
height. As it changes the resting weight of the bow, it will change the
power curve and therefore affects the flight of the arrow. There are
many changes involved here however, string length, tip placement, tip
angle, travel distance of the arrow under power, etc. All of which
results in fine tuning the arrow's flight but no significant change to
the gross dynamics of the bow.
Carolus
On Wed, 31 Mar 2004 22:33:02 -0000 "Jeff / Luminesce"
<luminesce_duir@...> writes:
> When one twists the string to increase the brace height does it
> increase the poundage as well?

________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
• ... Heya To my understanding it does not in fact increase the effective draw weight at full draw but it does increase the amount of strain the bow must abide
Message 3 of 24 , Apr 1, 2004
On Wed, 31 Mar 2004 22:33:02 -0000, you, with reckless abandon, wrote:

>When one twists the string to increase the brace height does it
>increase the poundage as well?
>

Heya

To my understanding it does not in fact increase the effective draw weight at full draw but it does
increase the amount of strain the bow must abide at brace height and it does shorten the powerstroke
of the bow.

so in effect you loose a little and gain a little which is greater you must test for your self.

Herre Ragi "warm Bear" WulÞarsson of the shire, Isle du Dragon Dormant.
(Sometimes known as RJ Bachner)

Northern shores, East Kingdom SCA.
ragi@...

Come visit the Archery diy Pages @
www.diy.brokenaxe.ca
and the shoppe @
www.shoppe.brokenaxe.ca

House of the broken axe.
www.brokenaxe.ca
• ... 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
Message 4 of 24 , Apr 1, 2004
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

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/
• In a message dated 4/1/04 1:46:03 PM Pacific Standard Time, crossbow@freeshell.org writes: If you shorten your string to have a higher brace height, the limbs
Message 5 of 24 , Apr 1, 2004
In a message dated 4/1/04 1:46:03 PM Pacific Standard Time,
crossbow@... writes:
If you shorten your string to have a higher brace height, the limbs are
more flexed because of the shorter string, when you pull it to the same
point, the limbs will be even more flexed that they would have been with
the longer string, and therefore the poundage will have increased.

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

Siegfried

This is one of those subjects in archery where everyone is saying the same
thing, but using different terminology to describe the effect. In this case, I
believe Carolus to be correct.

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

What is different is the amount of time the string is in contact with the
arrow, which is what fools a lot of folks. The lower the brace height (within
good operating parameters for the style of bow) the more of the stored energy
makes it into the arrow, increasing arrow speed off the bow. The higher the
brace height, the less time the string is in contact with the arrow, slowing the
arrow speed. These differences can be quite dramatic and allow the shooter to
fine tune for things like over/under spine in the bow and arrow relationship.

Again, the net effect is the same as both of you have described it, but the
mechanism for getting there is as described above. The poundage does not
change, per se, but the amount of energy transferal increases and decreases
according to brace height.

Regards,

Andras Truemark

[Non-text portions of this message have been removed]
• NO [Non-text portions of this message have been removed]
Message 6 of 24 , Apr 1, 2004
NO

[Non-text portions of this message have been removed]
• ... Same amount of available energy? maybe. Different draw weight? maybe. Different geometry? certainly. Someone with a bow-scale, a measuring tape, graph
Message 7 of 24 , Apr 1, 2004
atruemark@... wrote:
>
> In a message dated 4/1/04 1:46:03 PM Pacific Standard Time,
> crossbow@... writes:
> > If you shorten your string to have a higher brace height, the limbs are
> > more flexed because of the shorter string, when you pull it to the same
> > point, the limbs will be even more flexed that they would have been with
> > the longer string, and therefore the poundage will have increased.

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

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

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

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

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

-- Fritz

will go into a 'special' mailbox reserved for spam. See below.

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

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

"Clutter"? This is an object-rich environment.
• I agree with Carl that my earlier explanation was simplistic. It s also true, in the same way that saying a chunk of lead is solid, which it is in a real
Message 8 of 24 , Apr 1, 2004
I agree with Carl that my earlier explanation was simplistic. It's also
true, in the same way that saying a chunk of lead is solid, which it is in a real
world kind of way. On an atomic level, however, it isn't - in fact, it's full
of space and in no way a solid. So to with brace height vs poundage. My
earlier explanation is true, in a general, real world sense. Technically,
however, all sorts of factors come into play - bow profile, materials, even the mass
of the string. This is from Archery; The Technical Side, of the Legends of
the Longbow series compiled by Glenn St. Charles, in an article written in
March 1931 by C.N. Hickman.

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

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

Regards,

Andras Truemark

[Non-text portions of this message have been removed]
• 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 9 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
>
> Siegfried

________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
• 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 10 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 11 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/

---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!
• 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 12 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<---------------------------------------------
> 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]
>
>
>
>
>
• 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 13 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]
>
>
>
>
>

---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!
• 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 14 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 15 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 16 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 17 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

________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
• What numbers have you recorded? Carolus On Thu, 08 Apr 2004 23:22:25 -0400 Siegfried Sebastian Faust ...
Message 18 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

________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
• 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 19 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

________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
• 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 20 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
>
> ________________________________________________________________
> 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]
>
>
>
>
>
>
>

--
Ex Tenebra, Lux

http://web.raex.com/~obsidian/index.html
• ... 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 21 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 22 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 23 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

________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
• ... 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 24 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/
Your message has been successfully submitted and would be delivered to recipients shortly.