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"Stacking" - trying to understand the exact meaning

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aluminated

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Discussion starter · #1 ·
I fear I may never get to complete understanding due to the many definitions and interpretations of the actions of bows, but here goes:
If I have a recurve bow that at the following draw lengths, exhibits the following draw weights, at what point is it said to be "stacking"?

@26": 25.93#
@27": 27.40#
@28": 29.22#
@29": 31.19#
@30": 33.22#
@31": 35.45#
@32": 37.88#

Or is it perhaps that this bow, even if it had a consistent 2# per inch increase, would be said to be "stacky" vs. another bow with a 1.5# per inch increase (if there is such an animal)? This would seem to be two different applications of one term, but I believe some feel each way is the correct usage. I've looked at previous threads on the matter and I am left still wondering.
Thanks for your time.
 
#2 ·
Stacking for me, beyond math and formulas, is when my capacity to draw the bow is running out of gas. I am shooting this year #70 bows, and going back to my #55s none is stacking even if I draw them beyond my draw length (+28"). It's more a feeling due to draw weight and string angle around my fingers than something very defined that I can put the finger on it.
 
#4 ·
It's what Border's don't do. LOL. Last inch of draw on a 7.5 I believe is .7 and 8's are .4. I'd call that awesome, but the term is used so much that now it's just mediocre. I'd call it stupendous. But they're SR's.

For a regular recurve I think 2.5 pounds is acceptable in that last inch of draw. If it hits 3, I notice it. And that's only a half pound.

If I may ask, how long is the bow your stats are from?

Bowmania
 
#5 ·
a -

A bow stacks when the number of pounds the draw weight increase per inch begins increasing.
A 20# bow will (on average) increase 1# per inch of draw length. When that number goes above 1#/inch, stacking is beginning.
A 40# bow will (on average) increase 2# per inch of draw length. When that number goes above 2#/inch, stacking is beginning.
A 60# bow will (on average) increase 3# per inch of draw length. When that number goes above 3#/inch, stacking is beginning.

There are several physical reasons for stacking and you look those up if you like, but in the simplest terms, you reached the compression limit of the face or the expansion limit or the back of the limbs AND/OR either the limb is no loner being bent, but being pulled apart (the latter is an extreme case).

However, this is still a trad forum, and "stacking" is often confused with just being over bowed ;)

Viper1 out.
 
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#6 ·
stacking only occurs on bows with short riser or short limbs. Really short recurves even 1 piece one tend to all be short draw and are only meant for tree stands or blinds . When you draw a bow and it feels like you hit a wall and the bow can no longer be drawn back comfortably , that is stacking.

Short limbs or short recurves could be drawn past even 28-32 inches on machines and jigs , but it would most likely break or damage the limbs.
 
#7 ·
Technically that bow is stacking between 28" and 29". Whether you notice or care is relative.
 
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#8 ·
A perfect lever has a linear draw force curve. As you increase deflection, the lever will eventually deviate from linearity, in an accelerated fashion. Archery takes this simple concept of physics and calls it stacking. What I have found from detailed recurve measurements is that stacking becomes significant when you start pulling the limb tips closer together. This is after the point where the string loses contact with the limbs (the lift point). Up to the lift point the effective length and leverage of the bow increases. Longbows are a bit simpler. They become non linear for large deflections, same a recurves, but without the counteracting influence of the bow getting longer as the string rolls off the recurve of the limbs.
 
#9 ·
Taking your example (rounding numbers)


@26": 26#
@27": 27.5# -> 1.5
@28": 29# -> 1.5
@29": 31# - > 2
@30": 33# -> 2
@31": 35.5# ->2.5
@32": 38# -> 2.5


Pretty linear -- could be considered slight stacking, but generally not.

If your numbers were like this. It would be considered stacking at 30" were the force draw curve takes an uneven increase from the previous measurements

@26": 26#
@27": 27.5# -> 1.5
@28": 29# -> 1.5
@29": 30.5# - > 1.5
@30": 34# -> 3 **********
@31": 37# ->3
@32": 41# -> 4
 
#10 ·
When the pounds per inch starts to increase over the previous inch the bow is stacking…and with an adult bow this would generally be somewhere beyond the sweet spot, which is the neighborhood of 28”.

You can see this clearly in Draw Force Curves…and Blacky Schwarz has several posted on line. http://www.archeryreports.com/

I just grabbed one, for example: BEAR “Grayling Green” Super Kodiak 60”.

At approximately 26” the pounds/inch increases at a steady rate out to just past 28” (possibly 29). That couple of inches is where the bow is sweet…and beyond that the stacking will commence to build.

Bows vary and the sweet spot could be longer on some bows. That sweet spot could start earlier or later…which would cause it to extend further beyond the 28” and be of benefit to those with a longer draw length.

As I’ve never seen a DFC where 28” wasn’t within the sweet spot, people drawing 28” or less should virtually never experience stacking. Rick.
 
#11 ·
rickstix said:
When the pounds per inch starts to increase over the previous inch the bow is stacking…and with an adult bow this would generally be somewhere beyond the sweet spot, which is the neighborhood of 28”.....
Click to expand...
That's how I would define it. For the numbers given in the first post, mild stacking begins between 29 and 30".
From 26 to 29", each inch adds less than 2#. For numbers above that, each inch adds more than 2#.

Here's the link to that graph of the Super Kodiak: http://www.archeryreports.com/index...ditionalbowreports/item/bear-grayling-green-super-kodiak-60.html?category_id=72
 
#13 ·
I've always considered it where the weight/inch of draw begins to increase more exponentially rather than linearly. If you're going up in weight relatively consistently, you're not stacking yet. Once the weight begins to jump higher and higher, that's when you're stacking.
 
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#14 ·
Several definitions which all seem problematic.

If a bow has an average pull of 2lbs per inch. Anything more than that is stack. So anything greater that the average pound increase.

Anything where the the dfc flicks from bulging outwards to anything bulging inwards.

Or anything where the next pound is higger than the previous


Stack is what your used to. Greater climb at the back end will always feel tough. If thats a bow with a utterly flat DFC at the back end, then 1lbs gain will feel odd.
2lbs gain over a 1 will feel stacky.
3lbs gain over a 2lbs gain will feel stacky.

Its not a measure of the stress in the limbs. Its a measure of the design running out of geometry.
Stack is also a great indicater of energy levels.
Smoother bows store more energy.

These are all good rules of thumb. Though the definition of stack depends on your level of technology.
 
#15 ·
I measured my Border yesterday. 24"-46.5 25"- 47.3 26"- 48.2 27"-48.4 28"-48.9 29"-49.5 30"-50.2 31"-51.3 You will notice that it does start to stack by a tiny bit at about 29". My draw length is about 29 1/2 on this bow so it is just about perfect for me. When the draw hits 26" it feels like you are pulling but not really exerting to pull. You get used to it.

The best definition of stack to me is when the draw weight increases by a greater incremental amount per inch of draw when compared to the prior few inches of draw. Say that your bow is fairly linear at 2 1/2 pounds of gain per inch of draw from 8" to 28" then jumps to over 3# gain per inch. The bow begins stacking at 28"
 
#16 ·
norton850 said:
stacking only occurs on bows with short riser or short limbs. Really short recurves even 1 piece one tend to all be short draw and are only meant for tree stands or blinds . When you draw a bow and it feels like you hit a wall and the bow can no longer be drawn back comfortably , that is stacking.

Short limbs or short recurves could be drawn past even 28-32 inches on machines and jigs , but it would most likely break or damage the limbs.
Click to expand...
Not exactly... It depends upon the riser length and limbs length in combination. A long riser (25") and shorts can be shot at greater draw length than a 17" riser and shorts. Always check with the bow maker so you don't sell yourself short on performance or over-stress the bow. One size does not fit all
 
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#17 ·
aluminated said:
I fear I may never get to complete understanding due to the many definitions and interpretations of the actions of bows, but here goes:
If I have a recurve bow that at the following draw lengths, exhibits the following draw weights, at what point is it said to be "stacking"?

@26": 25.93#
@27": 27.40#
@28": 29.22#
@29": 31.19#
@30": 33.22#
@31": 35.45#
@32": 37.88#

Or is it perhaps that this bow, even if it had a consistent 2# per inch increase, would be said to be "stacky" vs. another bow with a 1.5# per inch increase (if there is such an animal)? This would seem to be two different applications of one term, but I believe some feel each way is the correct usage. I've looked at previous threads on the matter and I am left still wondering.
Thanks for your time.
Click to expand...
In my opinion, stacking is the point in YOUR DRAW that the force required of the DRAW disproportionately increases from that required getting to that point... :grin: Your illustration doesn't give example of that... :laugh:
 
#18 ·
Sid brings up a definition that addresses how a bow feels to an individual. If you are strong enough to power through the stack, it is therefore not there, or the stack occurs later when you are no longer able power through without notice.

This is a valid, but not a very precise definition. Stack becomes defined by the observer rather than the bow itself. But perhaps this is why the non physics term -- stack, is used.

We can quantify the increase in draw force using a power series.

Take the force equation F=a +bx +cx^2 +dx^3 +.... to infinite terms.

At small deflections you get an ideal beam F=a+ bx. The force is proportional to the displacement.

As you pull further higher order terms, second, third, forth powers, etc. become significant and the bow force ceases to be proportional to displacement.

From a purely analytical perspective, it is at this point that the bow can be considered to be stacking. It may not feel like it is stacking to all observers.

We know looking at DFC's that bows show apparent stacking properties early in the draw cycle. This geometric effect is because we are not flexing a simple lever, but rather a more complex geometry.

So while the answer is not simple, we can assume a simple lever model and say that stacking occurs late in the draw cycle and describes an increase in the pounds/inch of draw, ignoring what happens earlier in the cycle.

This may not address how stacking feels. Going from 2 to 3 pounds/inch near full draw may not be that noticeable to some folks. So the point where two observers determine the onset of stacking may vary significantly.

This is where connecting things you can measure, with things that you feel, becomes complicated. So is the exact meaning something you can measure, or something you can feel?
 
#19 ·
Now it is complicated more by Border's Hex 8 limbs. They "un-stack" and draw weight diminishes over the last few inches of draw.
So often I see too much thought and effort going into things that are of little or no consequence.
 
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#20 ·
Bill 2311 said:
Now it is complicated more by Border's Hex 8 limbs. They "un-stack" and draw weight diminishes over the last few inches of draw.
So often I see too much thought and effort going into things that are of little or no consequence.
Click to expand...
Ironically. They make hex7.5s feel a little stacky.
Definatly make the 6s feel like they stack. But the 6s make conventional limbs stack.

Stack by definition is limited to your personal experience level.

But for transfering experience independent data over the internet.
Pounds per inch at full draw will help you understand.
Last couple of inches of draw. 3lbs gain is considered stack.
2lbs in normal
1.5lbs was virgin territory
0.7lbs utterly bizzar.
So the last 4" of draw on a 50lbs bow to be within decimal places of each other. Where 24" and 29" for a 60" bow, 17" riser are equal. Makes 0.7lbs gain look like stack.
Yet compaired to convention at 2lbs. Ive no idea how to discribe 3lbs.

https://youtu.be/CWGO20UTfUQ
 
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