A question for Hank to answer.
But I’ll add something more to think about. Since we are talking about ILF adjustable bows, let’s use a comparison of two limb sets, one where when the limb bolts are fully tightened to give 50# @28” and another when the bolts are fully out to make the same 50# @28”. Now which do you suppose will be smoother and less stack.

 

bolts out T . "smoother & less stacking".
I worked a lot with a 17" riser and a set of extra short limbs.
My DL is 28".
they went way high with bolts in.
turned bolts out all the way, counted turns back, figured out that at 6 turns out I still had a lot of bolts left in riser.
I forget the numbers, I will find them and report in, I posted up on it, but with bolts out 6 turns, limbs scaled 44# at 28" DL.
YES turning bolts out can reduce OR ELIMINATE STACK.
NOT SAYING for people to go run bolts 6 turns out. it was a test.
I had LOC DO make me a special extra short riser with 22* angles for that set of limbs, for a seated hunting SHORT bow that was 52" AMO.
EDIT - here's the link from my old thread where I detailed the stacking and the fix.
https://tradtalk.com/forums/showthread.php?t=49913

 

Are you getting less stack or or are you getting less weight at full draw?

 

Interesting question. Do you think that varying limbpad angles on different risers may also be a factor?

 

These charts came from some tests I did back in 2015. I'll see if I can find the original thread where the discussion took place. I am not sure which forum it was on. These charts have been discussed in several threads over time. This shows the impact of changing tiller position from all in to all out, and brace height from high to low. This was before I had my shooting machine so I did not have performance data to go with it. These also extend out to long draw lengths.

Below are some observations from the charts.

The impact of brace height is to facilitate more energy storage early in the draw cycle.

Brace height impact on final holding weight is small. It has a larger impact on stored energy which is was translates more directly into performance.

Low brace height result in a slight increase in the minimum of the first derivative curve and a delay in the on set of stacking. By this objective measure, that would mean that the bow is slightly smoother.

Click to expand.

 

I here what your saying Carbo.With the bolts all in I would think the pressure on the limbs would be more balanced,where as a limb with the limb bolts out the force would be more near the limb buts.The limbs buts are not where you want the bend so this is where you get stacking.

 

Maybe. but the key issue Im thinking about is the limb/string angle. As that angle increases it takes more energy toy draw the bow a given distance do to decreasing mechanical advantage.

 

@ Hank
We would need to see a given riser and limbs measured at with bolts in and bolts out to know this.

There many ways to change brace height. Obviously simply moving the whole limb back(the same as not drawing it as far) is going to make a for a smoother bow with any conventional limb.

In contrast if you could simply change the limb angle without change the string length or brace hate it would make for a less smooth bow.

But changing the bolts on an ILF bow does both.

 

@ Hank
We would need to see a given riser and limbs measured at with bolts in and bolts out to know this.

There many ways to change brace height. Obviously simply moving the whole limb back(the same as not drawing it as far) is going to make a for a smoother bow with any conventional limb.

In contrast if you could simply change the limb angle without change the string length or brace hate it would make for a less smooth bow.

But changing the bolts on an ILF bow does both.

You have to apply some constraints for the experiment to make sense. I used the same riser and limbs, which meant that I had to adjust the string length to keep the brace height constant when I changed the limb bolt position. If you keep the string length constant then you will have to change the riser in some way, like changing the grip position. You would need something like the Olsson Variable for that. The complexities of bows are in the details. Gross properties, like how things change when you adjust variables, pretty much stays the same. Breaking these patterns takes some advanced engineering, such as the Border HEX9, where drawing further, at some point, actually results in a holding weight reduction. But for the most part, we can assume that if you draw the bow further the holding weight will increase, until the bow starts to fail.

 

Apologies Hank. I misread or wasnt paying enough attention those charts when I first looked at thos charts.

The 3rd one is what I was asking.
Do you have a similar chart for a more conventional recurve limb?

 

I have not done a conventional limb yet. I plan to redo these tests using my full performance test panel but probably not until after I retire in a couple of months. It takes a lot of time and I need to clear some room to re-setup my lab space. I have been reorganizing at home and my draw board and shooting machine are packed away.

 

Worded that incorrect.Of course there is no bending where the limbs connect to the riser.You are shortening the working part of the limb with limbbolts all out thats why you have to draw the bow further to reach the same speed.

 

Has any one taken in account for grip/deflex and limb lift/length.

 

For the purposes of bow mechanics adding deflection from the grip is the same as reducing the draw length by subtraction.

Shortening the riser length(all else being equal) essentially condenses the curves by a multiplier.

 

I think its the opposite. Lengths draw.

 

Deflex is when the the you move closer to the shoulder away from the grip.

So deflex with respect to draw curves is the same as having a shorder draw length.

 

Deflex is when the the you move closer to the shoulder away from the grip.

So deflex with respect to draw curves is the same as having a shorder draw length.

http://www.merlin-bows.co.uk/article...r Deflex.pdf

Let's just make a clear definition of what constitutes each design. First of all, draw an
imaginary line between the points on the riser where the limbs exit at each end. Now, the
position of the throat of the grip in relation to that line determines the amount of reflex or
deflex you have. If the grip is in front of the line, towards the target, then it is deflex. If it
is behind the line towards the bow string, then it is reflex.

Its saying the same thing I said.

 

< - deflex

> - reflex

 

http://www.merlin-bows.co.uk/articles/Reflex or Deflex.pdf

 

So lets agree that reflex riser with a larger brace height would give then the same characteristics as a deflex riser of the same brace height.

 

Im not talking about compound bows. Maybe some some of this carries over - but I dont know. So Im not getting into that.

If you are talking about recurves - your question doesnt make much sense.
A reflex riser(all else being the same) will have a a smaller brace height than a neutral or deflex riser.