# Question on plunger movement



## chrstphr (Nov 23, 2005)

Park Sung Hyun had a plunger that was rock hard from what i have been told. If that is true, then I doubt it would move much. Natalia may be the same. 

In the bottom video the plunger isnt moving much either, if you put your mouse on the end of the plunger. I think the angles makes the last video arrow appear to bend more than the others. 


Chris


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## kshet26 (Dec 20, 2010)

Hmm good points. Interesting to see how little movement is actually imparted on the plunger.

Side question: is the amount of sideways force (the force pushing against the plunger) largely a function of draw weight on properly spined arrows? For example would a 30# draw push the arrow against the plunger less or more than a 50# draw? Or is a function of arrow mass?


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## chrstphr (Nov 23, 2005)

I think the amount of sideways force is based on the spine of the arrow in relation to the draw weight pushing it. But i am not an archery physics expert.


Chris


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## limbwalker (Sep 26, 2003)

Last archer appears to be Alison Williamson of GB


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## Fury90flier (Jun 27, 2012)

the plunger movement in the vids is probably what it took to get that particular arrow tuned to that bow...I wouldn't read too much into it.


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## gjlama94 (Oct 11, 2013)

I've seen the third video before as an example of showing how an arrow flexes and oscillates as it leaves the bow. That one may have an arrow deliberately underspined for effect.


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## ThomVis (Feb 21, 2012)

gjlama94 said:


> That one may have an arrow deliberately underspined for effect.


That arrow is perfectly spined for that bow, you can tell by the way the nock end flexes away from the riser when it passes.


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## Viper1 (Aug 21, 2003)

k - 

It's a tuning parameter, nothing more and both scenarios are correct and usable. 
You typically want about 1/8" of the plunger button sticking out past the rest, to allow for various tuning. 

Viper1 out.


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## kshet26 (Dec 20, 2010)

So clearly if you ignore convention, you can achieve a wide range of dynamically spined arrows using centershot and plunger tension. As long as the arrow isn't breaking or contacting, there is in theory a large window of static spines that could work.


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## Viper1 (Aug 21, 2003)

k -

Sorta technically true, but ...

"Wide" is relative. You might be able to get a "wide" selection of arrows to shoot, but the tunable number will be more limited. 

I do believe that the closer you are to the textbook settings, the more efficient and forgiving the rig will be overall. 
That's why choosing the right arrows has the first tuning requirement.
Then you set the parameters to the textbook setting, and then tweak as necessary - trying not to go to extremes on any one parameter.

Viper1 out.


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## gjlama94 (Oct 11, 2013)

ThomVis said:


> That arrow is perfectly spined for that bow, you can tell by the way the nock end flexes away from the riser when it passes.


I stand corrected. A nice detail to keep in mind for future reference. Thanks.


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## Joe T (Apr 5, 2003)

kshet26 said:


> Hmm good points. Interesting to see how little movement is actually imparted on the plunger.
> 
> Side question: is the amount of sideways force (the force pushing against the plunger) largely a function of draw weight on properly spined arrows? For example would a 30# draw push the arrow against the plunger less or more than a 50# draw? Or is a function of arrow mass?


The sideways force between arrow shaft and plunger is what you are adjusting when you are pressure button tuning. So its value is what it needs to be to balance out the sideways force effects of the bow string on the arrow. - So as long as a piece of string is the answer .

The force is mainly determined by the spring preset. Once the force reaches the spring preset the button moves into the barrel and there is only a minor increase in the force from this point.

A general rule of thumb for spring preset is 8 grams per pound of draw weight. So a 45lb draw weight needs a spring preset of around 8x45= 360 grams force equivalent (3.57 Newtons).

Other factors which add to this value for the overall shaft-button force are the button spring constant and the net acceleration (force*mass) of the plunger itself. The horizontal flex frequency of both the bow (string) and the arrow shaft will effect the depression and the rate of depression of the plunger and so are tied into the plunger acceleration parameter. The archers technique (finger release and bow arm alignment) will also have an effect on the required button force as regards tuning optimization.

I would vaguely suggest that to get an estimate of the shaft to plunger force then use 10 grams per pound draw weight. i.e with a 45 lb draw the button shaft force = 10*45 = 450 gram force equivalent (4.4 Newton).

Not aware of anyone actually measuring the force between the shaft and the button. The following graph is a model prediction (Kooi) of the shaft to button reaction force against time for the arrow power stroke.


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## Mika Savola (Sep 2, 2008)

Joe T said:


> I would vaguely suggest that to get an estimate of the shaft to plunger force then use 10 grams per pound draw weight. i.e with a 45 lb draw the button shaft force = 10*45 = 450 gram force equivalent (4.4 Newton).


So, with a 20 lb bow you should use like a 200 gram plunger, which is quite light? I 've had couple of situations where a youngster is increasing his/her poundage. Current arrows are showing weak and by increasing plunger tension, arrow flight goes much worse than before?!?


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## Fury90flier (Jun 27, 2012)

Tuning by the plunger will only help when you're on the cusp of correct spine...if you're too far out, it won't help---probably the reason the flight got worse. That, or it could be that maybe center shot isn't dialed in, possibly string not centered with limbs/ limbs not on plane.

What happens when you increase the tip weight by 25grn?


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## limbwalker (Sep 26, 2003)

> The sideways force between arrow shaft and plunger is what you are adjusting when you are pressure button tuning


Sorry to be nit-picky Joe, but when you adjust the plunger spring tension, you are only adjusting the amount of RESISTANCE to the sideways force. To adjust the sideways force, you must adjust the bow, arrow, or both.



> The archers technique (finger release and bow arm alignment) will also have an effect on the required button force as regards tuning optimization.


Indeed, but so will stabilization. I would argue, after conducting multiple tests on the affect of stabilization (or lack thereof) on tuning, that stabilization has an even greater affect on tuning than most realize.

For example, with the bow I use for both WA Barebow and NFAA Traditional, I can use the same arrows (full length 400 spine X-busters). Without the 12" stabilizer, I achieve a tune with 120 grains of point weight. However, with the 12" stabilizer, I need to increase my point weight by a full 60 grains, to 180 grains of point weight, to achieve the same tune.

Bare shaft impact changes nearly 14" at 18 meters just by adding or removing that 12" stabilizer.

I demonstrated this at my recent equipment seminar, with about 20 people looking on. The reactions were priceless. It's not something most folks even realize. Stabilization increases the dynamic spine of your arrow.


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## Joe T (Apr 5, 2003)

John 

Apart from the first sentence  I agree with everything you say. Maybe it would have been better put to say that button tuning is adjusting the force between the shaft and the button so anything that affects the tuning will effect what this force requirement is.



> but when you adjust the plunger spring tension, you are only adjusting the amount of RESISTANCE to the sideways force. To adjust the sideways force, you must adjust the bow, arrow, or both


Nope. It's only when you have relativistic effects that action and reaction are not equal and opposite. The force that the shaft exerts on the button equals the force that the button exerts on the shaft. If there was no button then this force would be zero - so what is this "sideways force" for which the button provides resistance only. If you change the bow or shaft then this required force changes (the tuning requirement changes). A good way to think of the button is as a buffer on a rail car - it's a force limiter but with a button the force limit is controllable.


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## Joe T (Apr 5, 2003)

Mika Savola said:


> So, with a 20 lb bow you should use like a 200 gram plunger, which is quite light? I 've had couple of situations where a youngster is increasing his/her poundage. Current arrows are showing weak and by increasing plunger tension, arrow flight goes much worse than before?!?


The rule of thumb (though I don't know its origin) is 8 grams per pound draw weight so with a 20 lb draw a spring preset of 160 grams would be the suggested starting point. Whether this ratio works for very light or very heavy bows I don't know. The actual required spring preset is determined by testing (bare shaft say). A typical clicker exerts under under 100 grams force equivalent on the shaft so 160 grams should be stable. A high plunger preset with a weak arrow is a bad combination as the button starts to effect the dynamic spine - the button effect on the shaft behaviour can, in theory go into reverse.


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## Mika Savola (Sep 2, 2008)

Joe T said:


> The rule of thumb (though I don't know its origin) is 8 grams per pound draw weight so with a 20 lb draw a spring preset of 160 grams would be the suggested starting point. Whether this ratio works for very light or very heavy bows I don't know. The actual required spring preset is determined by testing (bare shaft say). A typical clicker exerts under under 100 grams force equivalent on the shaft so 160 grams should be stable. A high plunger preset with a weak arrow is a bad combination as the button starts to effect the dynamic spine - the button effect on the shaft behaviour can, in theory go into reverse.


OK, thanks for the info. Back in the day, I used to tune my aluminum arrows, with a lack of better knowledge, mostly by plunger tension. I often used weak arrows on a 40-45 lb bow with over 1000 gram plunger and still got pretty good grouping (PB FITA 1256 then), better than with stiff arrows and weak plunger...


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## Joe T (Apr 5, 2003)

I think it was Kisik Lee who made the comment in one of his books that "too much" of anything was a bad idea. Certainly true when it comes to pressure button springs, too stiff or too weak a preset are both bad ideas. Same applies to arrow shafts; weak or stiff are less than optimal - just right (as Goldilocks would say) is what's wanted.


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## shuumai (Nov 23, 2013)

To use the 8 grams per pound of draw weight guideline, I just tried the following procedure. I pressed the plunger against a food scale until the plunger just started to compress, then checked the force. Does that sound right? 

I found that if the spring tension screw was screwed in flush, it needs to be loosened 6 turns to get close to the calculated starting point of 272 grams. (34# * 8g)

My aluminium arrows are scratched down to bare metal starting about 2" from the end of the shaft and ending at about 6.25". It looks like the heaviest part of the scratch is at 3 to 3.25". Does that mean anything other than the fact that metal rubbing against metal isn't the best idea? (I have an inexpensive Infitec plunger like this: http://www.archerytorque.com/image/data/Riser/inficushion.jpg)


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## ButchD (Nov 11, 2006)

shuumai said:


> To use the 8 grams per pound of draw weight guideline, I just tried the following procedure. I pressed the plunger against a food scale until the plunger just started to compress, then checked the force. Does that sound right?
> 
> I found that if the spring tension screw was screwed in flush, it needs to be loosened 6 turns to get close to the calculated starting point of 272 grams. (34# * 8g)
> Hey Shummai
> "My aluminium arrows are scratched down to bare metal starting about 2" from the end of the shaft and ending at about 6.25". It looks like the heaviest part of the scratch is at 3 to 3.25". Does that mean anything other than the fact that metal rubbing against metal isn't the best idea? (I have an inexpensive Infitec plunger like this: http://www.archerytorque.com/image/data/Riser/inficushion.jpg)


Which end of the shaft?
So the assumption is that the shaft is rubbing on the plunger?


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## Joe T (Apr 5, 2003)

shuumai said:


> To use the 8 grams per pound of draw weight guideline, I just tried the following procedure. I pressed the plunger against a food scale until the plunger just started to compress, then checked the force. Does that sound right?
> 
> I found that if the spring tension screw was screwed in flush, it needs to be loosened 6 turns to get close to the calculated starting point of 272 grams. (34# * 8g)
> 
> My aluminium arrows are scratched down to bare metal starting about 2" from the end of the shaft and ending at about 6.25". It looks like the heaviest part of the scratch is at 3 to 3.25". Does that mean anything other than the fact that metal rubbing against metal isn't the best idea? (I have an inexpensive Infitec plunger like this: http://www.archerytorque.com/image/data/Riser/inficushion.jpg)


The method is fine. The actual spring pressure setting is only a rough one. (see Bow setup for various bow setup guides. My own suggests 300-400 grams. When you shoot an arrow the arrow gets torqued by the bowstring and between the draw weight and the center shot adjustment you try to minimize this torque. The button spring is a control to make fine adjustment to (zeroing) this torque so in principle you want the button spring to do as little as possible. You want the button spring to be as close as possible to the correct final value *before* you start adjusting the draw weight during bow set up. (The spring pressure will effect the draw weight value you end up with). It's for the same reason at the start of a bare shaft tune you move the fletched arrows to the target center *before* adjusting the nocking point. The nocking point adjustment (which is interactive with the button spring) is made with the spring setting close to the correct value you end up with.

Endlessly shooting aluminium arrows wears away the anodizing showing bare metal. It's purely cosmetic.


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## ButchD (Nov 11, 2006)

Endlessly shooting aluminium arrows wears away the anodizing showing bare metal. It's purely cosmetic.[/QUOTE]

Right,
Joe,
If it's the fletch end, then it's an indication of button contact at an unwanted time in the shot.


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## Joe T (Apr 5, 2003)

ButchD said:


> Endlessly shooting aluminium arrows wears away the anodizing showing bare metal. It's purely cosmetic.


Right,
Joe,
If it's the fletch end, then it's an indication of button contact at an unwanted time in the shot.[/QUOTE]

4" of shaft scraping at the fletch end then the button setting is the least of your worries :wink:


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## Vittorio (Jul 17, 2003)

Joe T said:


> ....The button spring is a control to make fine adjustment to (zeroing) this torque so in principle you want the button spring to do as little as possible. You want the button spring to be as close as possible to the correct final value *before* you start adjusting the draw weight during bow set up. (The spring pressure will effect the draw weight value you end up with). It's for the same reason at the start of a bare shaft tune you move the fletched arrows to the target center *before* adjusting the nocking point. The nocking point adjustment (which is interactive with the button spring) is made with the spring setting close to the correct value you end up with.
> ...


There is a third very important element to consider in this process, and is the relative angle of the rest to the arrow shaft. The arrow at release not only compresses the plunger ,but also the rest to the vertical. So, considering the rest as a fixed plane (if the rest is "weak" relationships become more complex) with just an inclination to the shaft, it is clear that depending from the weakness of the plunger, the shaft also moves diagonally down at the beginning, by this way influencing/influenced by the nocking point. This is probably the explanation why the traditional system says "set nocking point height first". Only way to limit this variable is to eliminate the inclination of the rest in relationship to the shaft as much as possible, so that at the end adjusting the plunger will only give horizontal movements of the groups/bare shafts and not a combination of the two. So, summarizing, first thing to set is the nocking point height AND the rest parallel to the shaft ... OK, I will have a chapter of THA2 going deeper in these concepts, but this is the summary.


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## Joe T (Apr 5, 2003)

Some thoughts on the rest topic here. Arrow rests


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## Joe T (Apr 5, 2003)

Vittorio said:


> There is a third very important element to consider in this process, and is the relative angle of the rest to the arrow shaft. The arrow at release not only compresses the plunger ,but also the rest to the vertical. So, considering the rest as a fixed plane (if the rest is "weak" relationships become more complex) with just an inclination to the shaft, it is clear that depending from the weakness of the plunger, the shaft also moves diagonally down at the beginning, by this way influencing/influenced by the nocking point. This is probably the explanation why the traditional system says "set nocking point height first". Only way to limit this variable is to eliminate the inclination of the rest in relationship to the shaft as much as possible, so that at the end adjusting the plunger will only give horizontal movements of the groups/bare shafts and not a combination of the two. So, summarizing, first thing to set is the nocking point height AND the rest parallel to the shaft ... OK, I will have a chapter of THA2 going deeper in these concepts, but this is the summary.


Interesting thought. You learn something new often on AT. There is one more aspect to this. If you regard the nocking point position as controlling the arrow rotation in the vertical plane, then because the arrow is at an angle to the horizontal the arrow rotation in the "button sense" of a plane 90deg to the bow plane has a vertical component. So vertical arrow rotation tuning can be affected by the nominal nock height, the angle of the rest to the arrow shaft, the button spring tension, the amount the button depresses and the tiller/stabilization system...ouch!


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## limbwalker (Sep 26, 2003)

It's a wonder we can hit anything with our arrows...

If only we dissected the mental game the same way, eh?


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## lksseven (Mar 21, 2010)

limbwalker said:


> It's a wonder we can hit anything with our arrows...
> 
> If only we dissected the mental game the same way, eh?


John,

Agree. I, for one, would love it if you began to discuss details/techniques/visualizations that comprise 'the mental game' with the goal of readers being guided/nudged/herded down the path to 'mental game enlightenment'.


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## gster123 (Dec 17, 2012)

limbwalker said:


> Last archer appears to be Alison Williamson of GB


Now retired from international competition.


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