# Arrow Straightness? How is it measured?



## elkski (Feb 4, 2005)

Well all these claims of arrow straightness by the manufactures has me wondering how do they measure it?
I understand they use laser straightness checkers but what does the +/- .001 straightness mean? Does it mean that no part of the shaft will be out of a +/- .001" cylinder tolerance zone over the entire arrow length like it should? or that the arrow can be out .001" per inch?
How do you guys measure your arrows?
I have an Apple arrow checker with the small bearings that are 9.5" apart. I usually put the arrow on it with 15" of arrow sticking off the short end and rotate slowly by pressing directly over the bearing so I dont deflect the shaft and then I look at the long end to see how much movement I see. I do have a dial indicator I can use on the tip but mostly use my calibrated eyeball and the movement on a good arrow is less that .015". I check each end this way. On a typical dozen If I include all the arrows the movement would be more like .030"


----------



## fletched (May 10, 2006)

There is no real standard in measuring arrow straightness. Some measure it by measuring a shorter section or the arrow than others.

Besides, most arrows will be straight enough to shoot accurately. It is the spine consistency that really matters.


----------



## elkski (Feb 4, 2005)

I know that spine is important. Three main things come to my mind when considering consistent arrow flight at 18 m. The degree to what each contributes is debatable till we die and you may have other variables to add to my list. Spine has a pretty clear cut standard of measurement method (requires a spine tester) for arrows. Then you have weight and that is a standard measurement that we all can check with a low cost device, and lastly we have straightness that we cant even agree on how to measure. In the old school days a dimensional feature of bar stock like an arrow was specified in terms of runout which was an ambiguous term even back then that had to be further specified as to its exact meaning. Then came the ANSI standards of 1982 called Geometric Dimensioning and tolerancing. or GD&T for short. The standard has been updated over the years but the basic concept has remained the same. Create a measurement standard that is meaningful and makes real World sense in the hands of the machinist to the inspector. To achieve this each object is given reference planes. The reference planes are usually specified on a good drawing as standard planes or surface a machinist will lay the part on or chuck it up onto. Lets say we have a .5" thick slab of some outside dimension. We really care how flat the top surface is but not really how thick the part is to fit our purpose. So with a simple call out we give a flatness specification to the top surface and reference the bottom surface but then we can give a wide tolerance between them. Depending on what we specify on the bottom surface finish and flatness this might allow the machine shop to just grab a slab of raw stock clean it off put it on the mill table and lop off the top. The bottom surface might only be contacting the ground in 3 small places but it forms a repeatable surface for future machine steps as well as the inspection process. Another way to do this is to specify the thickness tolerance so close that we can control the thickness as well as the surface finish of the final part. We can also extend this concept to the other sides of our slab whereby we might direct the machinist with a simple notation to not only put the slab on a flat surface on the bottom but slide that part to the West to a stop and to the South and locate two holes from those 3 now specified and repeatable physical locations. The concept of GD&T is easy to understand with a slab like this but when you have long round objects it is more complicated.
How do you support an arrow to take measurements where are your reference planes. In the case of the long arrow you surely wouldn't expect the inspector to stand it on its end and make sure all points in the cylinder are within a cylinder tolerance zone. You could specify two v block locations where you tell the inspector to support it there to take measurements but maybe in the real world you cut those parts off anyway. Obviously the longer a raw arrow is the harder it will be to maintain a certain tolerance. I understand that arrows are checked in a laser machine in a matter of seconds. But what these .001" or .005" straightness checkers are measuring I do not know.
I do know with my arrow laying in precise ( how precise is important) ball bearings 9.5" apart I can see a movement of the arrow end that varies of course by how far from the end I am supporting it. I typically leave 15" unsupported and see deviations of .020".
The only way I can see these arrow manufacture claims to be valid is if they are talking about .001" per inch of arrow shaft.
Yes straightness might not be as important as spine or something else but until it is a defined term how do we hold these manufactures accountable?
If anyone has input I would appreciate it.


----------



## elkski (Feb 4, 2005)

Just so you know I also consider the straightness of the nock to the tip to be important also. More specifically it is important for the string to impart the acceleration in a line down the middle of the shaft and to have the CG of the tip on this line.


----------



## bowhunterprime (Jan 28, 2009)

elkski said:


> Yes straightness might not be as important as spine or something else but until it is a defined term how do we hold these manufactures accountable?


Hey man I didn't understand much of your documentary there, but I definately agree with that last statment. I always assumed that straightness was measured over the whole shaft end to end or as a whole cylindar as you were saying. I would definately like to know the answer though because I want to know exactly what makes my GT Expedition Hunters (.006" straightness) cost $50 per dozen bare shafts while the Pro Hunters (.001" straightness) cost $110 per dozen shafts. Is there really enough difference in performance by the arrow to merit that much difference in price? -Chris


----------



## Deezlin (Feb 5, 2004)

bowhunterprime said:


> I would definately like to know the answer though because I want to know exactly what makes my GT Expedition Hunters (.006" straightness) cost $50 per dozen bare shafts while the Pro Hunters (.001" straightness) cost $110 per dozen shafts. Is there really enough difference in performance by the arrow to merit that much difference in price? -Chris


This is probably one of the most debated subject in archery. Regardless, of the static straightness as the arrow comes out of the bow, it is anything but straight. 

The static measurement of straightness is only a guide to the measurement of spine. Generally the straighter the arrow, the better the spine control is. How much does spine vary around an arrow? By the way, I have a spine tester. A really good arrow will usually have around .005 spine variation. I have seen a few aluminum arrows go less. I have seen many carbons with as much as .015 variation. These carbons are best used for paint stirring:wink: Although, with proper tuning they may do OK.

Now, aligning the high spots in the spine helps a lot. However, a whooter shooter helps even more. First the whooter shooter needs to shoot the bow and adjustment need to be made until the bow is shooting a perfectly straight shaft. Then each arrow needs to be individually shot and nocks turned until the arrows are all shooting in the same hole.

I guess, I didn't really answer your question, but in general the more expensive arrow will shoot better for you. However, even then you may find a dud. Also, the arrow shaft should be trimmed with a quality saw from both ends. The majority of straightness variation is on the ends. Personally, if I was going to recommend on arrow shaft over another, I would recommend ACC's. They may weigh more than carbon, but they are generally a better shooting arrow.


----------



## fletched (May 10, 2006)

elkski said:


> I know that spine is important. Three main things come to my mind when considering consistent arrow flight at 18 m. The degree to what each contributes is debatable till we die and you may have other variables to add to my list. Spine has a pretty clear cut standard of measurement method (requires a spine tester) for arrows. Then you have weight and that is a standard measurement that we all can check with a low cost device, and lastly we have straightness that we cant even agree on how to measure. In the old school days a dimensional feature of bar stock like an arrow was specified in terms of runout which was an ambiguous term even back then that had to be further specified as to its exact meaning. Then came the ANSI standards of 1982 called Geometric Dimensioning and tolerancing. or GD&T for short. The standard has been updated over the years but the basic concept has remained the same. Create a measurement standard that is meaningful and makes real World sense in the hands of the machinist to the inspector. To achieve this each object is given reference planes. The reference planes are usually specified on a good drawing as standard planes or surface a machinist will lay the part on or chuck it up onto. Lets say we have a .5" thick slab of some outside dimension. We really care how flat the top surface is but not really how thick the part is to fit our purpose. So with a simple call out we give a flatness specification to the top surface and reference the bottom surface but then we can give a wide tolerance between them. Depending on what we specify on the bottom surface finish and flatness this might allow the machine shop to just grab a slab of raw stock clean it off put it on the mill table and lop off the top. The bottom surface might only be contacting the ground in 3 small places but it forms a repeatable surface for future machine steps as well as the inspection process. Another way to do this is to specify the thickness tolerance so close that we can control the thickness as well as the surface finish of the final part. We can also extend this concept to the other sides of our slab whereby we might direct the machinist with a simple notation to not only put the slab on a flat surface on the bottom but slide that part to the West to a stop and to the South and locate two holes from those 3 now specified and repeatable physical locations. The concept of GD&T is easy to understand with a slab like this but when you have long round objects it is more complicated.
> How do you support an arrow to take measurements where are your reference planes. In the case of the long arrow you surely wouldn't expect the inspector to stand it on its end and make sure all points in the cylinder are within a cylinder tolerance zone. You could specify two v block locations where you tell the inspector to support it there to take measurements but maybe in the real world you cut those parts off anyway. Obviously the longer a raw arrow is the harder it will be to maintain a certain tolerance. I understand that arrows are checked in a laser machine in a matter of seconds. But what these .001" or .005" straightness checkers are measuring I do not know.
> I do know with my arrow laying in precise ( how precise is important) ball bearings 9.5" apart I can see a movement of the arrow end that varies of course by how far from the end I am supporting it. I typically leave 15" unsupported and see deviations of .020".
> The only way I can see these arrow manufacture claims to be valid is if they are talking about .001" per inch of arrow shaft.
> ...


Very good post. I take it you are machinist. Another thing to consider is that an arrow has two surfaces, inside and outside. Some arrows aren't perfectly round either. Acc's don't ever seem to spin very well. I don't think they are perfectly round. I would like to see a standard on arrow measurement so we can get consistent info.


----------



## Stryder (Oct 7, 2009)

Per Easton's website:

*STRAIGHTNESS
Our straightness measurements are actual, and surpass, with a far more stringent straightness requirement, ATA/ASTM industry standard. We measure straightness based on the full length of the shaft, minus two inches, which makes Easton arrows the most accurate in the industry. What we say is what you get — and better*


----------



## bbjavelina (Jan 30, 2005)

*Elkski is dead on here*

However, I don't think he goes far enough. As a machinist of over 40 years I have some concerns.

"Roundess" matters. If the shaft is not truly round, what are you measuring? Also, as mentioned above, spine constistany matters. Even and indicator with the spring removed places some load on the shaft, so, again what are you measuring?

I have long believed that we often fool ourselves by the diffuculty of determining out or round, spine varience, and run-out.

A spine testor does not take into account out-of-roundness.

Checking the OD for round tells us nothing about the ID, and therefor possible spine variance.

Without knowing both of the above, what can we tell about run-out?

What's a concerned arrow assembler (not arrow builder) to do?

I would surely love for the more knowledgeable among you to to allay my fears and tell me how to build the best possible arrow.

As this is one of my favorite subject, I look forward to a lively discussion that will make me a better arrow assembler.

Best of luck to each of you.


----------

