Guess we'll have to agree to disagree on this one. I couldn't give a physics formula to explain they how's and why's, but I can say, from experience, that some arrows in a given spine have not flown the same as other arrows in the same spine, but a different material.

For instance, when I shot ash arrows I had to go up in spine. I have a couple of theories, but nothing solid except the results I got. Possibly the heavier over-all weight of the shaft acted somewhat like a heavier point; or maybe the recovery time was slower; or it could be some other factor-- but that's the way it worked for me.

I think the point Jakes was trying to make (correct me if I'm wrong Jakes) is that there are some variables that you cannot predict, primarily release. Take two people with identical bows and identical draw lengths, and they may still need different spined arrows if there is a big difference in their release. However, it shouldn't be a big difference in the arrow spine they need, so the "if it works for me, it should work for you" will normally get you in the ball park. Nobody can say exactly what spine will work best on a given bow every time, because you can't put a formula on an individual's release.

A pound of feathers weighs the same as a pound of steel, but there is a difference. If you don't think so, drop each one from 6 feet onto your big toe and see it that doesn't change your mind.

Chad

LBR,

If I dropone pound of feathers or anything that equals one pound on my foot it will have the same result because the potential is the same.

one pound of feathers or steel that is elevated one foot will have 1 foot pound of potential energy. If I elevate it 2 foot it will have 2 foot pounds of energy.

Obvious you would have less steel to acheive 1 pound than you would feathers. It would also be harder to keep the feathers concentrated into a 1 lb unit.

The same is true for arrow material. A carbon arrow that has a spine weight of 69 lbs will weigh less than a POC that has a spine weight of 69 lbs. It takes less of the carbon material than POC just like it would take less steel than feathers.

In regards to your ash arrow example. Ash is more dense than POC so if the spines were the same the Ash arrow would weigh less. It would take less of the ash material to equal the same spine as POC.

We can agree to disagree on many things. For instance we can agree to disagree that 2 + 2 = 4, but it will not change the correct result. I can not argue that someone may have had an experience in which the result was 5, but I know that he achieved the answer by doing something wrong.

The laws of physics are called laws because they are the same every time, other wise we would refer to them as opinions of physics

O.L. Adcock has a pretty good page on his site dealing with arrow selection and bow tuning. A lot of good information.

http://www.bowmaker.net/index2.htm

Milton, in a way you make my point for me. Yes, on paper 1lb is 1lb, regardless if it's feathers or steel. However, saying that the results would be the same with either one? It doesn't take a genious to figure that out.Let's take it a step further--say the 1# of steel is a cylinder with a sharp end, and thesharp endis pointed down--still won't make a difference? It's still 1# vs. 1#. That's the difference between an equation on paper and the real world--the real world has variables that don't always show upon paper.


On the arrows, I don't claim to be an expert, but I'm not a novice either. Just for giggles, I pulled three different arrows made from three different woods and checked the weight and spine. Here's what that not-so-scientific test showed.

Port Orford Cedar, spined 75-80, weighed 566 grains
Sitka Spruce, spined 75-80, weighed 644 grains
Ash, spined 80-85, weighed 750 grains

Why else would folks tout certain arrows for added weight? Maple, ash, and hickory all will weigh a lot more than spruce, cedar, or fir in the same spine. Nobody has to take my word for it--ask anyone that deals in wood arrows, especially those folks that make a living at it, and see what answer you get.

Simply put, density does not always equal stiffness when you are talking about different woods. Shoot, you build bows--do you ever use laminations from a particular wood that are lighter, but stiffer than a different wood? Why would you think that wouldn't apply to arrows also? Now, if you are comparing apples to apples, that does usually apply to some degree. A Port Orford Cedar shaft that spines out 85# isgoing to weigh more than another POC shaft of the same diameterthat spines 40#, but that rule doesn't apply when you are comparing POC to Ash.

The ash arrows are, by the way, leftovers from a bow I no longer own that was about 10 lbs lighter in draw weight than the one I currently shoot. They spine weak on the bow I shoot now, even though the old bow was cut past center and the one I shoot now is cut to center. Spruce and POC that isspined 10# lighter than the ash shoots just fine.

The bottom line is everything about this sport can't be figured out on paper with a calculator and a slide rule. The laws of physics do generally apply, but certain variables have to be considered. Unless of course you are a bumblebee, who doesn't pay any attention to physics at all.

I don't agree with everything O.L. says either, but he does have some good info. on tuning. I like his info. because it's based on the results you get, which is all that matters in the end.

Chad

The point I was making with feathers and steel is that 1 pound is 1 pound, no matter what material makes up that 1 pound. We had better drop the feather and steel analogie, because I can see that it is confusing the issue.

The point is, is that if one arrow no matter the material has a certain amount of deflection with a 2 pound weight hanging from it, and another arrow (same length) made of a different material has the same amount of deflection they will both clear the bow the same.

In tuning arrows to your bow the thing that is to be accomplished is for the arrow to clear the bow without being bumped off it's flight path.

If it was not for this bumping off the flight path any arrow would work. Just like a pendulum swings equal distances on each side of the center and will eventually come back to the center. (the law is that for every action there is an equal opposite reaction).

An arrow swings similar to the pendulum except that it has two ends that are swinging simultanously (tip end and knock end). The amount of swinging action (parodox) is determined by the amout of potential energy that is dumped on to the arrow when the string is released. If the two arrows of different material (mentiond above) have the same amount of deflection with a two pound weight, then they will have uniform deflection no matter what the weight.

Tuning an arrow is all about timing. The aim is to time the arrow swings (bending nodes) so that the arrow passes the shelf of the bow without bumping the shelf.

To be continued....

Most of that I can agree with--the rub comes in with the speed of recovery with a given material.Feathers vs. steel isn't a difference in recovery, but it does show that there is a difference in materials and their effect even when they weigh the exact same.

Also, the point weight or anything else that effects the amount of resistance from a given arrow will affect the amount of paradox, regardless if they spine the same. It's just my guess that an extra heavy arrow shaft, such as ash, acts similarly to a lighter shaft with a heavier point, which gives more resistance and has to be stiffer to get the same amount of paradox. How much difference this makes probably varies with bow weight and draw length. I have a long draw and shoot fairly heavy bows, so it might be showing up a lot more for me.

Chad

continued from last post...

An arrow moves so quickly it would be hard to know for sure if this bump was happening.

By bare shafting an arrow it will tell you if the arrow is clearingcleanly or not.

I agree with adcock in that bare shafting is the best way to tune the arrow to the bow and the archer.

I differ with adcock in determining the bare shaft results. I feel that an arrow that tunes to a particular bow and archer will have the nock lined up with the point when bareshafted into a bag target. He (adock) describes some means of comparing bare shaft impact point with fletched arrow impact points. I have never felt compelled to try this comparison method, but many of my customers have told me that it left them frustrated and gave up on bareshafting.

Once you have got an arrow to bareshaft properly for you then the next step is to measure the length of the arrow and the spine or amout of deflection.

For exampel let say that it was an arrow made of POC that was exactly 29" long and and had a deflection of .360"which is a spine weight of 72# (26/.360). This arrow had a 125 grain tip weight.

Armed with the above knowledge a person would not have to guess what arrow to purchase if he wanted to change to aluminum or carbon. However he would have to know the deflections of the aluminum or carbon that he wanted to switch to.

He could get an easton 2018 and cut it to the same length of 29" and it would bareshaft the same. Spine on a 2018 is 72#.

He could get a Gold Tip 3555 which spines at 69# but he would have to cut is slightly shorter if possible.

He may be able to get a Gold Tip 5575 which spines at 90lbs but it would probably have to be left at full length and possibly add a bit more tip weight.

The main point is that since he knows what bareshafts pefectly out of his bow for him, he will know what will work or not.


Why Bareshafting?

You can put enough feather on any arrow and get good flight out of it, but excessive feather kills energy prematurly. A major objective is to get as much kinetic energy to the point of impact as possible.

LBR,

Please consider,

How will a heavy pendulum swing in comparison to a light pendulum.

Example,

You mentioned bows in a previous post, so I will use that to try and make my point.

When I use carbon on a bow I use it directly on the back (tension side) of the bow. By using carbon in the above mannor it allows me to build a bow with a limb that is thinner from belly to back, than if I did not use carbon or sandwiched the carbon between other laminates of the limb.

The thinner limb recovers quicker because the limb has less virtual mass. A quicker recovering limb translates into greater arrow speed.

I can build the thinner limb due to the properties of carbon, but the laws of physics that dictates the bottom line, is that the limb has less virtualmass.

In terms of a carbon arrow;

Less carbon gives greater spine. If that carbon arrow still bends or deflects the same amount as that great big wooden arrow, the way it clears the window will be dictated by amount of bend and length of arrow. I will concede it may be possible that down range it may come out of the bending nodes (parodox) sooner.

Does the above make sense?

I get what you are saying, and I don't doubt what you have experienced.

My experience has been thattwo arrows that spine the same but are of a different materialmay or may not fly the same. Centershot of the bow, how well within the bow's spine tolernace you are, difference in shaft diameter, material flexibility/recovery,etc. can make a difference. Maybe not so much with carbon and aluminum, but definately with wood. I have shot wood arrows almost exclusively for the last 10 years or so, tinkering with several different types of wood anddesigns--laminated,paralell, tapered, and barrel tapered shafts. Like I said, I'm no expert, but I do have a bit of experience with them. It's like strings (don't even get me started there!)--some bows just "like" some string materials better than another. Danged if I know why, and it can vary from one shooter to another, but it happens. Some of this stuff doesn't make any sense on paper, but it works all the same.

Chad