Pressure buttons - how do they really work?

4d4m

Member
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.
Thanks, some interesting videos but they aren't any higher res or framerate than some posted earlier in the thread, so it's hard to see detail of the exact moment the arrow comes off the button, and whether the plunger has ceased its travel or not. I had in mind a closer shot of the button with higher res and at least 20k fps. Something like The Slow Mo Guys use. I appreciate that's a serious camera that not even archery manufacturers would have lying around. That said, an extreme close up of that area with a 6k fps cam might do tha job.
 


geoffretired

Supporter
Supporter
This is an interesting topic.
I have to ask, what the differences would be if the button was fully extended or not at the point of separation from the arrow.
Would it be the same for all arrows on all bows? Or could it be that one situation is good and the other is bad?
 


4d4m

Member
This is an interesting topic.
I have to ask, what the differences would be if the button was fully extended or not at the point of separation from the arrow.
Would it be the same for all arrows on all bows? Or could it be that one situation is good and the other is bad?
Well I guess it would show that some damping of the button motion was happening and so the button wasn't doing (as) much to "bounce" the arrow away from the riser. My speculation, and the idea that prompted this thread, is that there is little or no damping and the net effect of the button being able to compress and rebound is no different than having a rigid button (set to the right centre shot for the tuned bow). With no damping, if the button was absorbing differences in arrow pressure caused by variations in release, then it's only going to "give them back" a millisecond or two later. In other words the arrow would rebound just the same. A lot of people are stating this isn't the case but I've not seen either evidence or a description of a physical principle that would support the contrary position. I don't have an axe to grind here, I'm happy to be proved wrong. If the answer is actually "nobody really knows" then that's fine too. I just want to know how things really work.
 


KidCurry

Active member
I don't have an axe to grind here, I'm happy to be proved wrong. If the answer is actually "nobody really knows" then that's fine too. I just want to know how things really work.
I doubt you will find an academic proof. But you could spend the next year with a matchstick instead of a spring and see what it does to your scores. My view is it does not dampen. It absorbs some of the energy from the arrow and returns very slightly later keeping the arrow on its intended path. Without the spring the energy in the arrow flex would bounce the arrow off its path. It effectively reduces the amount of paradox needed to keep the arrow on its path to the target.
 


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geoffretired

Supporter
Supporter
James Park did a lot of work on this. The bouncing off was his reason for rewriting his set up guide without the matchstick/solid button at stage 1.
Having a sprung button not a rigid one,must make some difference. we keep reading about softening the button to make the arrows fly along a different path. Where the arrow is ( from left to right )during the power stroke is difficult to determine. Not just because it is travelling quickly; but because of the flexing and waving side to side. It is a complex movement. But, the arrow follows a different path if the tension in the spring is changed.
I am a bit unclear on what we are talking about when you say "Damping". Does that mean the bend in the shaft is reduced by the button? Are you saying the solid and sprung buttons will have the same effect on the bending in the shaft?
 


geoffretired

Supporter
Supporter
4d4m, it is good that there are people who want to know how and why. I think this is a good place to find out answers to such questions. I also think that if we don't know the answers we can, between us, find something that is reasonable.
If I write out what I think in detail, everyone else can pick holes in it and we will all gain from that.heehee!
Imagine a shoot through riser with a very wide "keyhole" to shoot through. Rest the arrow on the flat shelf, no rest or button. Draw and release as normal.I am going to assume that the arrow at the sharp end positioned itself in the middle of the keyhole, so well away from anything solid to either side. The force of the release will push the arrow forwards as normal. It will bend, as normal ( almost) and it will veer off to one side... but with no restriction it will go off as far as it wants to. To the right for a right hander. This veering off to one side isn't obvious in normal conditions because the bow, or button prevents it.
If a rigid button or similar restricts the veering off, it will change the flight path. The restriction will prevent the tendency to veer off, by putting pressure on one side of the shaft. At the same time, the shaft is pushing against the restriction and will take a bend as a result. It is the equivalent of a glancing blow on a target stand.
At the same time as the bending is happening due to pressure against the button, the flex in the shaft, due to column loading, is trying to bend it the other way. I think the net result is that some bend is taken out of the shaft compared to being shot with no side restriction.
The amount of bend put in and the amount of reduction will depend on many things; point weight being one of them.
If the restriction is sprung,then the veering off is less restricted; so the bend put in by that veering is reduced.
The bend in the shaft caused by column loading is the same and in the same direction as the unrestricted shaft.
The net result this time is, the shaft bends slightly more compared to a rigid button, but the veering off is greater than with a rigid button.
As for the point of separation; I cannot work out whether or not it is fully extended. It will be fully extended if its returns faster than the arrow can flex away from it. The veering to one side changes as the flexing and forward travel progresses. So in some cases the veering could be moving the shaft away from the button, and the flex could be in the same direction or the opposite.
I think the return stroke of the button will be pushing the shaft off to that side, but how strong that effect is will be too complicated for me to guess at.
 


geoffretired

Supporter
Supporter
Just looked at the video again and the separation happens at much the same time as the button reaches its full extension. In the last stage you can see the shaft is flexing away from the button and only the front edge of the button is touching the shaft. As they separate the tip of the button flicks back towards the camera but doesn't continue to extend further from the barrel.
Also, the point at which the button starts to push back out coincides with the point where the arrow flex turns the other way. It's as if the button is playing catch up; not the button forcing the arrow to move to one side.
 


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4d4m

Member
I doubt you will find an academic proof. But you could spend the next year with a matchstick instead of a spring and see what it does to your scores. My view is it does not dampen. It absorbs some of the energy from the arrow and returns very slightly later keeping the arrow on its intended path. Without the spring the energy in the arrow flex would bounce the arrow off its path. It effectively reduces the amount of paradox needed to keep the arrow on its path to the target.
Well that wouldn't really tell either of us much as I've done a total of one scored target tournament in my archery career. I'm not counting our club Christmas fun shoots as that's with beginner bows and arrows :D

Most of my archery these days is really just plinking and a little bit of field, with trad style bows, instinctive aiming. My competitive spirit is catered for by FT with air rifles, and archery is relaxation for me.

You may be onto something with your last point though. So the button keeps the arrow centre shot in the right position at launch, while allowing it to briefly flex past centre (by pushing in the button) during the shot, thus reducing the overall deflection off the straight path. I can see that, thanks.
 


4d4m

Member
I am a bit unclear on what we are talking about when you say "Damping". Does that mean the bend in the shaft is reduced by the button? Are you saying the solid and sprung buttons will have the same effect on the bending in the shaft?
Geoff, I mean simply that if it was damped, the button wouldn't spring back as quickly. Your car's "shock absorbers", or dampers, are oil or gas filled pistons which mean when the suspension springs (the real "shock absorbers") are compressed, the wheels don't bounce back into position quite as quickly. This stops the car being bounced all over the road when it hits bumps.
 


geoffretired

Supporter
Supporter
Ahh, I follow that now. I think in that case the arrow would leave the button as soon as the flex direction was away from the button. At present, the shaft flex reverses and the button goes out to keep up with it. I don't think it is the button pushing the arrow away. It might be pressing lightly, but not the controlling force.
 


4d4m

Member
It's unlikely to be the major force, I accept that, but any force would contribute to moving that arrow further out than if there were none.

Thanks to Kidcurry I had a minor eureka moment and I can visualise that a sprung plunger allows the arrow to flex past the centre position very briefly, absorbing some of the deviation caused by arrow flex. When well tuned this should keep the arrow on a straighter flight than without a sprung plunger. I guess the timing is critical, which would be affected by fine-tuning the spring rate and centre shot.

Thanks all who contributed. I've downloaded the PDF of James Park's study for further light reading. :D
 


Hawkmoon

Member
Set you button so it is solid, put a D-loop on your string and shoot with a release aid, then shoot the same setup off the fingers and you will see exactly what a button does and why it is often call a cushion button.
 


geoffretired

Supporter
Supporter
It's unlikely to be the major force, I accept that, but any force would contribute to moving that arrow further out than if there were none.
Yes indeed. It seems to me that the button and the shaft act together to produce a flight path. Change the button in any way and the flight path could change as a result. The shaft presses on the button; and the button presses on the shaft. they both affect each other to some extent.
I wrote out my observations with some comments regarding what I saw. I think the arrow is in charge; and after all , it is what the arrow does that concerns us when setting up the button. What the button does is of interest; so a damped button would probably change the flight path compared to an undamped one. I would guess that whatever changes resulted from changing to a damped one, could be reversed by changing its settings. The button is simply restricting the left/right movements of the shaft while the two are in contact with each other.
Is the contact between them seen as helpful.... or is it interference??
I would say more helpful than interference. It could be seen as interference if the shaft was bounced off the button, or if the shaft bounced against the button at speed when it has already flexed away of its own accord... a second contact in other words. The undamped button does not seem to bounce the shaft away; it seems the button reaches its outer limit with the shaft still in contact and the shaft continues to slide over the tip until its flex causes a separation; like a plane taking off.
 


geoffretired

Supporter
Supporter
Yes indeed. It seems to me that the button and the shaft act together to produce a flight path. Change the button in any way and the flight path could change as a result. The shaft presses on the button; and the button presses on the shaft. they both affect each other to some extent.
I wrote out my observations with some comments regarding what I saw. I think the arrow is in charge; and after all , it is what the arrow does that concerns us when setting up the button. What the button does is of interest; so a damped button would probably change the flight path compared to an undamped one. I would guess that whatever changes resulted from changing to a damped one, could be reversed by changing its settings. The button is simply restricting the left/right movements of the shaft while the two are in contact with each other.
Is the contact between them seen as helpful.... or is it interference??
I would say more helpful than interference. It could be seen as interference if the shaft was bounced off the button, or if the shaft bounced against the button at speed when it has already flexed away of its own accord... a second contact in other words. The undamped button does not seem to bounce the shaft away; it seems the button reaches its outer limit with the shaft still in contact and the shaft continues to slide over the tip until its flex causes a separation; like a plane taking off.
OOPs pressed send twice
 


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