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Discussion Starter · #2 ·
Top left graph.
Standard DFC. the area under the graph shows the stored energy. (potential for throwing arrows down range)

as you can see there is a outward bulge. in the initial part of the draw. and an unward dip in the latter half of the draw.

the "inflection" point is where the graph goes from bulging outwards. to bulging inwards. here on this graph it looks like around 23"

this graph also shows you what your holding weight would be at each inch of the draw. so at 27" or at 29".

its a very informative graph and is the bread and butter of bow making.

known as the F/D Curve or the DFC. (force draw curve, or Draw force curve)
 

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Discussion Starter · #3 ·
Top right.

this graph shows the stored energy as a factual number. its directly related to this bow and its draw weight.

it shows you how the energy climbs as you pull the bow back.

as you can see the energy climb is more steep at the back end than the front end of the draw, meaning that you will get more stored energy per inch of draw, than you would only holding 2lbs more.
 

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Discussion Starter · #4 ·
Lower left


This is where it starts getting complicated. this graph is what we call the smoothness graph.

it shows you the relationship between the current inch of draw and the last.
so if a bows draw weight in the DFC went 2lbs, 4lbs 8lbs.
then the resulting pounds per inch gained per inch of draw would be 2, 4. as in 4-2=2 and 8-4=4lbs.

this is how much the bow is going to climb in the next inch.
so if your holding 40lbs. and the next inch gains at 3lbs then the next inch will be 43lbs.

this is where the rule of thumb that the bows gain 2lbs per inch of draw.

as you can see this isnt quite true. this bow starts at 7lbs. and this is called preload.
preload is good energy storage.
stack would be when the last inch is 7lbs. and the next graph explains why.

as you can see in this graph though. it REALLY emphisis the "inflection" point on the DFC.
showing you the change from bulging outwards to bulging inwards.
as you can see this inflection point is clearly not 23" its 22".
if you want to see how this inflection point can be easily measured, read my sticky on "smoothness" at the top of the main section here on TT.
but this graph also clearly shows you that the 2lbs per inch at peoples draw lengths are clearly visable... from 27" to 30" this bow is hovering around the 2lbs. which is right for a 40lbs bow.
stack would be when the bow is above this 2lbs...

this is all a generality. but its near enough on the right tracks.
 

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Discussion Starter · #5 ·
lower right.

this graph shows you SE/PDF.
Thats stored energy (upper right graph) devided by the holding weight (upper left graph)

this is a VERY interesting graph when it comes to bow design.

as you can see, the energy climbs at a nice constant rate untill the preload stops. preload stops when the inflection point flips and stack officially starts.
as you can see here, the stored energy per pound of draw weight standardises the energy stored. it shows you here that stored energy per pound held becomes greater, with longer draw lengths. irrespective of poundage.
so this bow has a stored energy of about 0.9 at 28". so thats 0.9X40lbs at 28 = 36ft/lbs of energy.
but at 30" its closer to 1.0 so, if the archer also held 40lbs but at 30". they would be storing closer to 40ft/lbs, not the 36ftlbs of the 28" draw.
but basically the steeper the graph the more energy the design stores. and the smoother the draw. the less the graph tails off. Nast stack would be a heavy tailing off of graph. where the poundage climbs MUCH faster than the energy is stored.
 

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The only other bow I have shot is this Viper longbow.

This Pinnacle Winex Feels real "smooth" to me, but then again it is the only recurve I have shot. I am not sure how much difference I could feel with the 1 vs. 2#/inch at the last part of the draw. Then again I'm pretty new to all this!

If it helps you decipher the graphs, the string leaves the limbs at 19" and 18". I think on your newer Border limbs the string only leaves the limbs at 23/24"?

This is the Viper graphs so you can see why my new rig feels so good. I'm drawing a shade over 28.5 with the longbow as opposed to 29.25" with the recurve.
 

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Discussion Starter · #8 ·
Zulu. As you can see the lack of smoothness means that the SE/pdf is decaying at about 23" onwards on the LB leading to a little kick of stack from 28 onwards.
the new Covert lifts at 27" on average. but thats a different topic.

the SE/PDF if that bow at 28" is 0.86 by the looks of things.
 

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Strange the transition is also around 23" on the LB. Seems like this is a standard measurement with the normal recurves/ longbows.

I will look up some of Hank's other graphs.
 

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Discussion Starter · #12 ·

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Discussion Starter · #13 ·
Force Draw curve for my Caribow recurve, that I bought 14 years ago..

Mine is 59# @ 28 inches.

One can see why I can draw to 30# inches with absolutely no stackig....
Thats a nice clean looking dfc.
So if you work out the stored energy per inch. And at each inch devide it by the poundage held. You will get the se/pdf value.
28" seems standard. Even though thats wrong for longer limb lengths.
 

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I get your point that a SE/pdf is dependant on draw length, but not on bow/limb combinations setup for a 28" draw. I'm with you that that's the key to a fair evaluation, but it's not that hard to figure out. I think you have a recommended combination for 28" draw length? That's why it's important to match the bow you are testing to the test parameters.
 

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Interesting.

Since when did 2# per inch become stacky? It wasn't more than a few years ago that anything under 3# per inch was considered pretty good and 2# was super smooth.

Also, what happens to performance when you short draw a bow that lifts at 27"? If a guy normally pulls 28" but can't get to full draw in a treestand for some reason how does that affect said bow?

I shoot longbows so I'm just asking for informational purposes...
 

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STR8,

It seems 3 things happen when one short draws. Of course, the total draw weight goes down but more importantly, the total power stroke is reduced and just as critical, the release is likely poor.

I sometimes practice with a chronograph to see how consistent my form is. Pulling against the back wall of a stacking longbow or conventional recurve makes it pretty easy to stay within 1-2 fps shot on shot. To do the same thing with my Hex 6 limbs I have to really focus on expansion and a clean release. Just flinging arrows I will see 2-3 fps spread and this is without a short draw.

Rasyad
 

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Just so everyone knows, I got the labels reversed on the Winex charts. I fixed it on the original post. Just swap limbs bolts in and limb bolt out.
 

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I like to think of the SE/PDF curve as the bow's intrinsic ability to store energy. It is far from rigorous but is a good way to think about it, especially, since we are so focused on draw weight as a key measure. We forget that force only tells you what it takes to move the string, but it is energy that our body must put into the bow. We will encounter different magnitudes of force along that journey, which is represented in the DFC. What that means is that it takes me more energy, at my long 32 inch draw length, to pull a bow to full draw at 40 pounds holding weight, than someone with a 28 inch draw length. So 40 pounds is harder for me than it is for someone with a shorter draw. On the flip side, I get more energy out of the bow, and consequently, more speed. So why do we mark limbs in pounds rather than energy? Because it is easier to measure and people understand pounds better than energy.
 

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Interesting.

Since when did 2# per inch become stacky? It wasn't more than a few years ago that anything under 3# per inch was considered pretty good and 2# was super smooth.

Also, what happens to performance when you short draw a bow that lifts at 27"? If a guy normally pulls 28" but can't get to full draw in a treestand for some reason how does that affect said bow?

I shoot longbows so I'm just asking for informational purposes...
That's why I hunt with a longbow ;-)

Matt

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Team Montana - we are coming for your quarters ;-)
 
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