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Discussion Starter #1
Being the curious learner that I am, I am trying to understand the different bow tuning parameters. I've done some searching, but can't really find what I'm looking for.

Just about all of the tuning "guides," books, and threads state "Set the Brace Height to the manufacturers specification."

Why do they specify a specific range?

What exactly does that mean?

Does it make a difference with short/medium/long limbs?

Does it make a difference with a 21"/23"/25"/27" riser?

What effect to tuning/arrow behavior does a higher brace height have relative to a shorter brace height?

Thanks in advance.

Dave
 

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Discussion Starter #3
Normally, a lower/shorter brace height gives more speed, and a higher/longer brace height gives a more stable/softer shot feel.
Being an engineer, I'm still interested in why? I can understand the speed issue - longer on the spring/string - kind of like a longer rifle barrel. However, I don't get the stable/softer comment.

What will the dynamic consequences be? If all I want to be is faster, why would I stay close to the mfg specs? I could drop BH to a point where I am just barely tensioned when the bow is at it's dynamic limit (and won't lose the string off the limbs).

I'm actually not really interested in speed, execpt academically. I'm really interested in the cleanest (I guess you could say most stable) arrow flight indoors.


Dave
 

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Being the curious learner that I am, I am trying to understand the different bow tuning parameters. I've done some searching, but can't really find what I'm looking for.

Just about all of the tuning "guides," books, and threads state "Set the Brace Height to the manufacturers specification."

Why do they specify a specific range?The MFG knows that a specific range works well however they can't know all the rest of the parameters in the tune process

What exactly does that mean? Brace height tuning has to do with trying to find the optimum time for the string / arrow release.

Does it make a difference with short/medium/long limbs? Yes

Does it make a difference with a 21"/23"/25"/27" riser?yes

What effect to tuning/arrow behavior does a higher brace height have relative to a shorter brace height? see below

Thanks in advance.

Dave
BH Tuning has to do with how the arrow/nock releases from the string. Since Paradox begins the minute we release the string from full draw, as the arrow flexes and recovers the angle that the nock would be released from the string changes. The goal is to have the string and arrow separate when the throat of the nock is in line with the direction of travel of the string at the moment the string stops moving forward.

While changing BH can and will change dynamic spine of an arrow by changing the length of the power stroke (lower BH will mean a longer power stroke) you are also lowering the "preload" of flex on the limbs so some of the gain is lost. We have found that it does affect dynamic spine to some degree but I would prefer to use this as a last ditch effort to get a good tune.

Mfg's give a range primarily to guide archers with a starting point. Technically most of us would set the BH at it's lowest point in the range and slowly twist up the string to raise the BH. Shooting end after end and raising the BH between each set until we find where the bow is the quietest and has the least vibration. When you really start to work at this, you can find that it's the difference between one or two twists where the bow gets real quiet. This final location can be outside the MFG range.

The effect to arrow behavior is that a cleaner release means less energy being spent trying to "pop" the arrow off the string and thus better transfer of energy to the arrow. Also if the nock is releasing from the string at an angle, you are pushing on one side of the nock harder than the other. or pushing the nock end to the side. any variance in your (shooter) release can affect the amount of paradox and direction of string movement as well as the timing of said nock/string separation so finding the cleanest separation time would be more forgiving to these variances in our shooting.
 

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Discussion Starter #5
Thanks you dchan. I really appreciate this explanation.

So how do I really tune the BH to get the best angle of separation/separation timing? Does that truly correlate to sound/vibration level? I'd assume there are many other factors when tuning for S&V, including amount of recurve, string diameter relative to nock size, actual nock design, etc. Would you generally use a higher brace height with longer limbs, or does that not really matter?

Is the only way, to really get this in-line release tuned correctly, a high speed video session? Is there another method that works (almost?) as well?

Thank you,

Dave
 

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Thanks you dchan. I really appreciate this explanation.

So how do I really tune the BH to get the best angle of separation/separation timing? Does that truly correlate to sound/vibration level? I'd assume there are many other factors when tuning for S&V, including amount of recurve, string diameter relative to nock size, actual nock design, etc. Would you generally use a higher brace height with longer limbs, or does that not really matter?

Is the only way, to really get this in-line release tuned correctly, a high speed video session? Is there another method that works (almost?) as well?

Thank you,

Dave
I'm going to go out on a limb and say shooting bareshafts is the best, practical way to optimize brace height. Assuming a properly spined arrow for your draw weight and a consistent, clean release, a bareshaft arrow will fishtail or rotate longitudanly (think that's a word) until a proper brace height is set.

I speak only from my own experience here as I recently went through some tuning issues where the only way I could stop my bareshafts from fishtailing was adjusting brace height. Plunger settings, centershot and other parameter adjustments made no difference. I would also recommend shooting from as far back as comfortable, as initially I thought I had it at 20 yards but upon moving back to 35 it was obvious I still had issues.
 

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The best way to tune for BH is shooting and listening (unless you have a very high speed camera, like 10kfps) You will find that there is a pretty loud "snap" that disappears when you reach that sweet spot.

gjlama94, shooting a bare shaft changes the dynamics quite a bit. the change in weight, along with the slight drag of the vanes can affect the timing some..

Every one of the tuning guides I've looked at all recommend setting the bow up a specific way (if it's centershot and hard plunger or slightly out from centershot and stiff plunger) and doing the BH tuning FIRST, before any other adjustments. The reason for this is the nock/string release and how clean it is along with the angle of this, will affect every other part of your tuning process.

This is why MOST coaches and techs that do a lot of tuning and understand the relationship between all the steps and physics, start here and go back to this before making other changes. If they have to change BH for some reason, they go back through all the other steps AFTER they have set the BH.
 

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So how do I really tune the BH to get the best angle of separation/separation timing? Does that truly correlate to sound/vibration level?
The sound does correlate..

There are often several different things you are hearing at the end of the shot but the separation sound is distinct. I'm not sure I know how to describe it.

Other things you might hear, some sort of contact between the arrow/riser. This would be checked by doing clearance tests.
String impacting the limbs as they hit the recurve (this is generally a lower deeper sound)
if you don't have any twists or not enough twists in the string, as the string billows out and the strands come back together you will get a snap as the strings slap together. Hard to describe this one also. think of cracking of a whip or belt.

and of course the string/nock release. The best way I can describe it is a sharp pop with very little reverberation. Probably because part of the pop is created by an item traveling away from you at a very high rate of speed so you don't continue to hear the arrow reverberate.

DC
 

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Discussion Starter #9
Thanks again.

One of the reasons I'm asking is that I'm tuning new aluminum arrows for indoors. I like the carbons for outside, but they just "flutter" too much indoors for me. I like the feel of something more substantial. I don't know how else to describe it. Kind of a "Zen" thing for me.

I've gotten the bare shaft to tune to the same impact point as the fletched arrow. Or, rather the vaned arrow - AAE Waves on a 2114 doesn't seem to be enough. I've got some Truflight 4.5" feathers on the way.

I'm seeing the bare shafts fly really well- straight and perpendicular to the target. It's the vaned arrows that are landing slightly nock left maybe two inches tip to nock over a 29" arrow length at 18M. Again, same impact point. I don't have that issue with the carbons. I'm also seeing that my FOC is not nearly as far forward on the Aluminum vs. Carbon arrow. I've ordered heavier tips to check that out as well. The BH is 1/6" to 1/8" less on the 14-strand string I'm using for the aluminum vs. the 18-strand I use with the Carbons. Only reason for that is that could be string build inconsistancy (mine) and not actually counting the number of twists.

I guess, seeing as I'm conversing wht THE dchan, I'd better elaborate my setup:

Me:
Intermediate Olympic (I like to think intermediate/advanced)
Indoor 500/600 on a Fita target
57 years, RH
Learned to shoot in 1980 (taught by MN state champ at the time), laid off for 30years, been shooting again for 1.5 years - limited coaching
Can't say I'm shooting NTS, but I was amazed how well I understand the steps and agree with them.
I don't shoot a clicker yet - too much work. I've ordered a Formaster, we'll see if that changes things.

Equipment:
25" Sky TR-7 Riser,
Sky limbs, long, bamboo core, 40# at 29.5" DL measured
BCY 8125 string .014 Majesty center serving
30" stab, 4"ext., 12"side rods w/dampers Krossen Vegatus
Aperture sight, Shibuya Ultimate (not carbon)
Beiter button, Champion II rest
Viper tab
Easton X7 2114, 78gr nibb points, AAE Wave vanes
Carbon Express Nano-pro 600, 100gr tip

My groups, even with this tune - the nocks left - are tighter than the CX's. I like the feel, but I don't have the confidence with the arrow strike. It disturbs my Zen.

Thanks,

Dave
 
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