brucelanthier

From what I have learned adding or removing weight from the front or rear has no effect on the static spine BUT it does have an effect on the arrow's dynamic spine.So, I would agree with you in one respect, no effect on the static spine, but disagree in that it does effect the dynamic spine. And, since we are shooting the arrows, the dynamic spine is the end result and the one we need to be mostly concerned with.

ijimmy

Spine and foc are 2 completly diferant animals , trying to get both to work in your favor , with an arrow , is fun

Paul L Mohr

I think you have that backwards Mobow. Less FOC makes the tip of the arrow want to wander and the fletchings don't work as hard. More FOC actually forces the fletchings to work harder which is why they stabilize faster and have more control. That's the way I have always seen it anyway. I will admit I'm not a physics major though. If one tells me different I guess I will have to go with that. I think I have been wrong once before, so it is possible I guess.

I have shot a lot of bareshaft arrows both with lots of FOC and a few with negative FOC and have never had one tumble on me. I have also shot fletched arrows with negative FOC or very little FOC. They don't group very well and are very bad in the wind. And forget about using a fixed blade one.

And when we talk about spine, we are almost always talking about dynamic spine. Adding weight anywhere to an arrow will not effect static measured spine, unless you add it where you are measuring it. Static spine is simply a measurement that lets us reference and compare different arrow shafts. Dynamic spine is how the arrow reacts to force as it leaves the bow. And anything in your set up can effect this.

Everything I have read says that adding or removing weight from the back of the arrow effects spine. But like Arthur I have yet to see it have a great effect on tuning. I think you would have to really alter the weight to make a difference. It is much more noticeable when changing the weight in the front of the arrow since it holds the resistance to forward travel.

Paul

brucelanthier

Well, I will agree that most changes in the rear of the shaft do not have a great effect but he said they have no effect.Personally, I think the front and rear setup kind of go together, what you have/want in the front helps determine what you have in the rear. Anyway, I think we are just splitting hairs now so I'll stop.

Paul L Mohr

You have to keep in mind Arthur deals in the practical world, not physics. he is giving practical advice based on years of experience. Not what someone says will work on paper with a bunch of math calculations. If someone asked me the same thing I would give the same response on most cases. It really doesn't effect anything. Technically I guess it might, but it probably won't be enough to notice. I have never had changing the weight on the back of the arrow effect tuning to where it showed a spine issue. And I have tried some crazy stuff.

Many can argue that changing FOC effects arrow forgiveness because you changed the spine, not the FOC. Bob Ragsdale is one of them if you read his site.

I have found though that when using both extremely under spined or over spined arrows an increase in FOC makes the arrow more stable. So the relationship to front to rear balance must make a difference. Otherwise you would get the opposite reaction with the two extremes.

Paul

Straightarrow

Paul, how did you get an arrow with a negative FOC. That would require tip weight (including insert weight) to be less than about 30 grains. This would seem improbable with any semi-normal setup.

ijimmy

Mobow got it right , if your tip is heavy , high foc , your fletchings leaverage is greater , providing a stable projectile

but thats foc , not spine , the thread header

Arthur P

No tip + No insert = Negative FOC. I've managed to do that a time or three... Have an insert pull out in a target and not notice it until I shot that arrow again. They certainly didn't fly straight though, even fully fletched.[&:]

Straightarrow

LOL, I gotta admit. I've done it once myself. It resulted in the arrow hitting the frame on my target holder, and breaking like a tooth pick. The best part - it not only didn't have a tip, but it didn't have feathers. I was bareshaft testing with a recurve and I forgot to put a tip in the bareshaft. This is somewhat easy to do, because I'm usually testing the shafts with several different tips and/or insert weights.

Just curious, with no tip , but having fletching, did the arrow fly tip-first?

AllenRead

Arthur, we've all heard and read that adding or subtractingweight on the nock end makes the arrow spine act stiffer or weaker. It has always been one of the things that "everyone knew".

There are a lot of things in archery that "everyone knows" and later turn out to be not exactly right.

I'm interested in your take on this. Can you discuss it a little more?

Thanks,
Allen