Pressure buttons - how do they really work?

LionOfNarnia

Supporter
Supporter
So, buttons exist so that arrow makers can produce a smaller range of spines then?

- In that case, maybe we are getting the better part of the deal for once. Even a 'premium' plunger is massively cheaper than a set of shafts.
 


jerryRTD

Active member
There are some of us here that were shooting before the advent of the berger button. lots of layers of tape were used to space the plastic arrow rest. The one thing that changed was the way the bow reacted to a slightly different loose. with a fixed arrow rest and no button you have to be far more consistant to get good results, when the button came along a shot that was a 7 without a button became an 8 with a button fitted.
My preferred button is the Cartel triple, the spring was strong and a finger loose 60lb peak draw compound and a heavy arrow needs a strong spring.
 


4d4m

Member
Hmm lots of food for thought there, thanks.

So the "shock absorber" theory seems to me to have merit. My concern with it is, or was, that car "shock absorbers" are actually dampers, and without them a car would bounce around all over the place. It's the springs which soak up the initial push from a bump in the ground and the dampers allow the suspension travel to reset, but slowed down so that the car doesn't straight bounce back up and lose traction. I can't see any damping going on in the buttons I have.

Two thoughts occur in response to this train of thought:
1. Perhaps all the damping that's needed is in the mass of the plunger itself and the small frictional losses of sliding in the tube.
2. Or, after watching the slow-mo vids many times, I'm wondering if in fact the system does not need to be damped as such, and the bounce back is a good thing, to kick the arrow shaft clear of the riser and reduce contact?

From the vids it does seem that the button contact is a very short period in the initial part of the power stroke.
 


4d4m

Member
Actually it's not a safe assumption...
A pressure button is just a quick convenient and probably more reproducible way of making the adjustments without resorting to experimentation with layers of leather. That doesn't mean that the leather wouldn't give as good a result.
Del
Interesting, thanks. Leather is resilient but not quite as springy as some other materials, so I wonder if that is why leather was better for traditional bows (thinking of my damping theory)? Shooting identical shafts from the same bow, what in your experience would be the difference between a rigid arrow pass and a leather one? In physics terms it's basically the same question as why a sprung plunger vs a solid button.
 


LionOfNarnia

Supporter
Supporter
the "shock absorber" theory
I'm drawn towards the idea that rebound damping is unnecessary because either

- The rebound is essential to stabilising flight

or (my fave atm)

- The shaft flex is beyond plunger reach before the rebound anyway.

...but I am starting to wonder if a non-linear (multi-stage?) spring system might be advantageous?
 


geoffretired

Supporter
Supporter
I think James Park mentioned the arrow kicking off the rigid button rather like a contact with the riser with a badly matched arrow.
The spring button gives a longer contact which is more like a glancing blow as opposed to a sudden jolt.
 


Del the Cat

Well-known member
Interesting, thanks. Leather is resilient but not quite as springy as some other materials, so I wonder if that is why leather was better for traditional bows (thinking of my damping theory)? Shooting identical shafts from the same bow, what in your experience would be the difference between a rigid arrow pass and a leather one? In physics terms it's basically the same question as why a sprung plunger vs a solid button.
I've only used a leather arrow pass on a flight bow where the arrow is subject to harsher forces than say a longbow... probably more akin to a modern recurve.
The leather is more forgiving and less likely to damage the arrow (than a bare wooden or horn arrow pass), which is still having to flex substantially. Leather has the advantage of showing a mark where the arrow is rubbing (especially if the arrow is chalked or painted), this allows further adjustment of the arrow pass by lifting off the leather carefully filing/rasping the wood and reapplying the leather. A spring loaded button presumably does much of the work for you, but of course with a wooden self bot it is unlikely to be strong enough to allow it to be cut beyond centre to allow a spring loaded button to be fitted.
The following is just my opinion of course and I reserve the right to be wrong!
There is an art to actually tuning a wooden bow which makes the adjustments on a modern bow seem a bit too easy to fiddle with. Ironically doing it the old fashioned way requires more care and consideration and thus may arguably result in a better appreciation of what's happening?
Del
 


Hawkmoon

Member
From what I understand, if you used a release aid in theory you could have a solid button, but because the string needs to go around your fingers it will have a lateral vibration and so to stop the arrow pushing itself off the button and going left (for a right handed archer) the button "cushions" the arrow and absorbs that lateral movement.
 


4d4m

Member
From what I understand, if you used a release aid in theory you could have a solid button, but because the string needs to go around your fingers it will have a lateral vibration and so to stop the arrow pushing itself off the button and going left (for a right handed archer) the button "cushions" the arrow and absorbs that lateral movement.
I get that but my point was without any damping the spring-back of the plunger is going to launch the arrow away with the same energy it would have done if it was rigid; the arrow's own elasticity providing the spring. In both cases it's an elastic collision and total energy is retained.
 


geoffretired

Supporter
Supporter
I think a rigid button makes a difference to the arrow's launch path. A rigid button means the arrow bending pushes that arrow further away from the riser. With a spring button the arrow's path is closer to the riser. Some of the early travel of the shaft starts while the button is compressed and that gets things started before the button springs back. By the time the button is springing back out, the shaft is well on its way and the bend is away from the button, so the pressure from the button is not having so much of an effect.
 


KidCurry

Active member
If you watch closely the video of Park Sung Hyun the arrow barely touches the button; compression maybe 0.5-1mm max. She could probably shoot with DtC's leather pad for hours with no problem. But at some point she is going to fudge her release and the button will get her out of trouble.
 


jerryRTD

Active member
I get that but my point was without any damping the spring-back of the plunger is going to launch the arrow away with the same energy it would have done if it was rigid; the arrow's own elasticity providing the spring. In both cases it's an elastic collision and total energy is retained.
You assuming the arrow stays straight, it does not. Given that the bow is correctly matched to the arrow shot ; then the arrow will flex pushing the arrow into the button. As the arrow flexes the other way it moves away from the button. At this point it is difficult to say whether or not the arrow beats the button by moving faster or not but I don't think that the button spring will have the effect you think it does. Yes there will probably be some plunger launch but that is necessary to align the nodes of the arrow. the rear of the arrow (and its node) is moved away from riser when the string moves around and brushes aside the fingers upon loose. The right amount of button flex will put the front node back in alignment. If it does not then the arrow will come off the bow with the nodes misalinged and the bare shaft will not impact with the fletched shaft
 


Hawkmoon

Member
So, buttons exist so that arrow makers can produce a smaller range of spines then?

- In that case, maybe we are getting the better part of the deal for once. Even a 'premium' plunger is massively cheaper than a set of shafts.
No they exist to allow for the variation in your release, shoot with a solid button and you will get more variation in your shot, if you then tried the same thing with a release aid you would get a far more consistent group.
 


4d4m

Member
You assuming the arrow stays straight, it does not. Given that the bow is correctly matched to the arrow shot ; then the arrow will flex pushing the arrow into the button. As the arrow flexes the other way it moves away from the button.
No I'm not assuming that at all; I know it flexes, in fact I said as much in the post you quoted: "the arrow's own elasticity providing the spring "

At this point it is difficult to say whether or not the arrow beats the button by moving faster or not but I don't think that the button spring will have the effect you think it does.
I think we'd need to see much higher speed slow-mo to be sure but I suspect the arrow could not possibly "beat the button". The mass of the plunger will be fractions of a gram, even the lightest spring available in a button will cause huge acceleration of that tiny component.

If you hold an arrow loosely in your finger and thumb by the nock end and tap the middle of the shaft against a rigid object it will flex then bounce back, the arrow providing all the "spring". If you do the same against a sprngy object it will also bounce back, this time some of the give will be from the arrow and some from the object. Once again with a resilient but more damped object (say, your fingers) again it will bounce back, but probably a little less as the damping absorbed some of the energy. In each of those three cases there will be differences in the distance, speed or timing of the bounce back. I'm trying to understand what the button spring does, but as above I find it hard to believe that the arrow bounces off the button before the button comes to rest.

Yes there will probably be some plunger launch but that is necessary to align the nodes of the arrow
Why is "plunger launch" necessary? If it was necessary then how could a bow with a rigid arrow pass ever be in tune with any arrow?

the rear of the arrow (and its node) is moved away from riser when the string moves around and brushes aside the fingers upon loose. The right amount of button flex will put the front node back in alignment. If it does not then the arrow will come off the bow with the nodes misalinged and the bare shaft will not impact with the fletched shaft
Yes but the front node could still be aligned by a solid button adjusted further away from centre shot. I'm trying to understand what is the benefit of allowing it to flex under spring pressure.[/QUOTE]
 


geoffretired

Supporter
Supporter
Do arrows have nodes as such when one end is still trapped on the string? I thought the nodes were there when an arrow was in free flight; the nodes being the bits of the shaft that don't move side to side when the shaft is flexing.
 


malbro

Supporter
Supporter
Do arrows have nodes as such when one end is still trapped on the string? I thought the nodes were there when an arrow was in free flight; the nodes being the bits of the shaft that don't move side to side when the shaft is flexing.
The arrow remains attached to the string during the initial movement of the string from full draw to the point of release, during that time the rear point of the arrow is effectively fixed to the string, which will initiate oscillations in the arrow as the string moves. The arrow will thus still have nodes but not necessarily at the same place as they will be when the arrow is in free flight.
 


jerryRTD

Active member
Do arrows have nodes as such when one end is still trapped on the string? I thought the nodes were there when an arrow was in free flight; the nodes being the bits of the shaft that don't move side to side when the shaft is flexing.
Yes because the string is free to move left to right . If it were not then how would the string go around your fingers when you loose? and if the arrow was held by the string then the node would be at the nocking point.
As soon as the arrow starts to flex it has nodes.
 


jerryRTD

Active member
No I'm not assuming that at all; I know it flexes, in fact I said as much in the post you quoted: "the arrow's own elasticity providing the spring "


I think we'd need to see much higher speed slow-mo to be sure but I suspect the arrow could not possibly "beat the button". The mass of the plunger will be fractions of a gram, even the lightest spring available in a button will cause huge acceleration of that tiny component.

If you hold an arrow loosely in your finger and thumb by the nock end and tap the middle of the shaft against a rigid object it will flex then bounce back, the arrow providing all the "spring". If you do the same against a sprngy object it will also bounce back, this time some of the give will be from the arrow and some from the object. Once again with a resilient but more damped object (say, your fingers) again it will bounce back, but probably a little less as the damping absorbed some of the energy. In each of those three cases there will be differences in the distance, speed or timing of the bounce back. I'm trying to understand what the button spring does, but as above I find it hard to believe that the arrow bounces off the button before the button comes to rest.


Why is "plunger launch" necessary? If it was necessary then how could a bow with a rigid arrow pass ever be in tune with any arrow?



Yes but the front node could still be aligned by a solid button adjusted further away from centre shot. I'm trying to understand what is the benefit of allowing it to flex under spring pressure.
[/QUOTE]
If you want to undersrand what is going on then you need to look at the Werner Beiter web site and look at 'the way to the center' video clips 'The bow window' is the one that will be the one that shows the most. they are shot at around 6000 frames per second I think you will be surprised at how fast things happen.
 


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