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Discussion Starter #1 (Edited)
I remember someone did a thread on CrossbowTalk where they were checking the deflections on a set of shafts. But I don’t recall if he was using the amount of the major 12 o’cock deflection and comparing it to the shafts to get “matching shafts", or if he was going by the least amount a variance of the 4 measurements on a shaft, and grouping them that way.

I know I should shoot them but I’d like to put my small numbered labels on first and end up with th better shafts with the lower numbers.

Still need to know which way to group “like shafts” or must I shoot them to be sure? Thanks.

fullsizeoutput_c8c.jpeg




I made some small numbers and taped them between the fletching and the nock. We’ll see how it goes.
 
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Static spine is what is used to try to predict dynamic spine. Dynamic spine is how the shaft reacts to the launch and is the actual point that affects your POI amongst other things. Yes, I believe you still have to shoot. Below is quoting a post in AT which is the best explanation I’ve seen.

ron w
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#2 Mar 10, 2013
static spine, is the actual deflection of the shaft as measured by the industry standard of 28 inch support spacing and 1.94 lbs. of weight hung at the mid point between the two supports, expressed in thousandths of an inch and relatively inexpensive to record accurately and consistently.
dynamic spine is the reaction of the shaft when being pushed at one end by a force. it can vary within the same static spine value by several modifying characteristics. it is also very difficult and expensive to record accurately and consistently, so static spine is used to predict what dynamic spine will display.
the relation between the two is that, a static spine value, is simply an indicator of what dynamic spine will be. ie.....a static spine of .400 will bend more in dynamic reaction than a shaft with a static spine of .300, when pushed with the same amount of force , given that both samples are the same diameter. modifying aspects of dynamic spine within the same static spine value will be, wall thickness, construction method and material used to make the shaft. ie... two shafts of the same static spine value with different diameters will display different dynamic spines. generally speaking, the larger diameter shaft will display a faster recovery from the reaction displayed by dynamic spine.
 

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I have had to remark the spine of several Spinal Tapp arrows over the months... even then there is no guarantee they will group with the others. Shooting every individual arrow is the ONLY way to really know what its performance level is.(in my opinion)

Don, have you ever had a "flyer" and pulled the insert and the nock out switched the arrow end for end and reinserted the nock and insert to find it made absolutely no difference???
 

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Discussion Starter #4
Don, have you ever had a "flyer" and pulled the insert and the nock out switched the arrow end for end and reinserted the nock and insert to find it made absolutely no difference???
That would be like shooting it in the opposite direction. 😂
 

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I have had to remark the spine of several Spinal Tapp arrows over the months... even then there is no guarantee they will group with the others. Shooting every individual arrow is the ONLY way to really know what its performance level is.(in my opinion)

Don, have you ever had a "flyer" and pulled the insert and the nock out switched the arrow end for end and reinserted the nock and insert to find it made absolutely no difference???
Nope, I’ve made quite a few arrows for people as well as myself and get very few fliers. But I agree, you still have to shoot them no matter what.
I don’t see that it would make a difference because the flex of the arrow tends to be in the center. Arrows out of the Swat XP are scuffed up in the center.
BTW, I locate cock vanes on the soft area.
 

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That would be like shooting it in the opposite direction. 😂
I bet your teachers enjoyed every single moment with you in class! 🤣🤣🤣
 

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I may have forgotten the strip fletch and refletch part....lol

So you have stiff side between the hens Don?
 

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Discussion Starter #8
BTW, I locate cock vanes on the soft area.
If the stiff spine side is at 12 o’clock, then are you putting the cock vane at either the 3 or 9 o’clock position?

fullsizeoutput_4e6.jpeg
 

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If the stiff spine side is at 12 o’clock, then are you putting the cock vane at either the 3 or 9 o’clock position?

View attachment 183430
When using the Ram Tester you watch the dial gauge. I find the area that gives me the weakest reading. At times there are 2 areas that read the same and I use the largest. The way I see your diagram, of the 2 stiff planes, one will be the stiffest and the other will be the weakest. Much of the info given (like that diagram) is very much over explained as it were, for us mere mortals. I am a simple BMW mechanic that took his apprenticeship under an old world German Mechanic. I am also surrounded by engineers 🙄 including my daughter who has her PHD in engineering who is married to an engineer. There’s more engineers that I’m around. Logic and experience often prevails.
 

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I may have forgotten the strip fletch and refletch part....lol

So you have stiff side between the hens Don?
I put the cock vane in the largest of the softest area. I completely ignore the stiff area. I would rather have arrow bow up in the Center on launch rather than have the front end point up and lack the guidance of the flight groove. Not sure if it makes any real difference though. Right or wrong, that’s how my mind works.
 

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Discussion Starter #11
The way I see your diagram, of the 2 stiff planes, one will be the stiffest and the other will be the weakest.
So cock vane at 6 o’clock then? Thanks.

On my last set of Tapps from Jerry, there was a short 1/4” long mark on the underside - inline with the cock vane.

They used to come with a “dot” painted on the shaft in front of and in between the hen vanes.

Could be just a method to always orient the shaft in the fletching jig for the cock vane location and is the same as the stiff side being between the hen vanes.
 

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So cock vane at 6 o’clock then? Thanks.

On my last set of Tapps from Jerry, there was a short 1/4” long mark on the underside - inline with the cock vane.

They used to come with a “dot” painted on the shaft in front of and in between the hen vanes.

Could be just a method to always orient the shaft in the fletching jig for the cock vane location and is the same as the stiff side being between the hen vanes.
Yes, right or wrong, I put it at 6, opposite of the stiffest. It works for me and my customers.
 
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BTW, buy a Swat XP and lose your cock vane location worries 👍
 

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I remember someone did a thread on CrossbowTalk where they were checking the deflections on a set of shafts. But I don’t recall if he was using the amount of the major 12 o’cock deflection and comparing it to the shafts to get “matching shafts", or if he was going by the least amount a variance of the 4 measurements on a shaft, and grouping them that way.

I know I should shoot them but I’d like to put my small numbered labels on first and end up with th better shafts with the lower numbers.

Still need to know which way to group “like shafts” or must I shoot them to be sure? Thanks.

View attachment 183427



I made some small numbers and taped them between the fletching and the nock. We’ll see how it goes.
First let me first say there is no better way to identify how to orient arrows than shooting them and rotating nocks.

But if you plan to use a testing process I think you need to start by understanding the proper way to test.

If you put arrows on a spine tester, zero the dial gauge then hang the weight to measure static spine deflection you are testing the arrows incorrectly

There is only one way to accurately identify true spine and that is to test the arrow to identify the stiffest point, then remove the weight, rotate the arrow 90 degrees, zero the meter then hang the weight and take a reading.

Static spine and Dynamic spine are at the same location on ALL arrows no matter what material as long as they are a hollow tube. If you are shooting a solid fiberglass fishing arrow then that is another subject all together.

The dynamic spine of an arrow is not along the weakest point it is always 100% of the time 90 degrees from the stiffest static point of the arrow. matter of fact the weak static spine has zero to do with arrow flight.
 

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Yes, right or wrong, I put it at 6, opposite of the stiffest. It works for me and my customers.
The reason it works is dynamically the stiff point located at 12 is also located at 6 during flight. There is only two spine deflections in an arrow during flight. There is the stiff plane located at 12 and 6 and the neutral plane located at 3 and 9. Arrows flex 100% of the time along the neutral plane during flight

If you could test an arrow dynamically you would find that the deflection 45 degrees right and left of 12 and 45 degrees right and left of 6 are the exact same deflection. Likewise the dynamic spine deflection 45 degrees left and right of 3 and 45 degrees left and right of 9 are the weaker dynamic spine
 

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So cock vane at 6 o’clock then? Thanks.

On my last set of Tapps from Jerry, there was a short 1/4” long mark on the underside - inline with the cock vane.

They used to come with a “dot” painted on the shaft in front of and in between the hen vanes.

Could be just a method to always orient the shaft in the fletching jig for the cock vane location and is the same as the stiff side being between the hen vanes.
We use a number of marks during the build process depending on what arrows we are building. As long as you put the static stiff side inline with the cock vane or between the hen vanes the arrows are properly indexed.

The Dynamic stiff plane is 180 degrees through the shaft and the dynamic neutral plane is 180 degrees through the shaft
 
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When using the Ram Tester you watch the dial gauge. I find the area that gives me the weakest reading. At times there are 2 areas that read the same and I use the largest. The way I see your diagram, of the 2 stiff planes, one will be the stiffest and the other will be the weakest. Much of the info given (like that diagram) is very much over explained as it were, for us mere mortals. I am a simple BMW mechanic that took his apprenticeship under an old world German Mechanic. I am also surrounded by engineers 🙄 including my daughter who has her PHD in engineering who is married to an engineer. There’s more engineers that I’m around. Logic and experience often prevails.
The diagram you are referring to is a dynamic spine depiction not a static spine depiction

Statically the weakest point of a shaft can be 180 degrees from the stiff side but dynamically no it is not ever there as I have stated above dynamically 12 and 6 are the exact same dynamic deflection. 3 and 9 dynamically are where an arrow will flex 100% of the time during flight this location is called the neutral plane
 

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If the stiff spine side is at 12 o’clock, then are you putting the cock vane at either the 3 or 9 o’clock position?

View attachment 183430
Let me explain this in a slightly different way

The picture depicts dynamic spine

When an arrow is launched the 12 and 6 positions repell the energy toward the center of the arrow and it exits the arrow along the 9 and 3 o'clock plane in the form of flexing

So you can place the cock vane at 12 or 6 it does not matter dynamically

Remember static testing on a RAM is for one purpose only and that is to identify the static stiff point

No other measurement matters
 

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Discussion Starter #19
If you put arrows on a spine tester, zero the dial gauge then hang the weight to measure static spine deflection you are testing the arrows incorrectly

There is only one way to accurately identify true spine and that is to test the arrow to identify the stiffest point, then remove the weight, rotate the arrow 90 degrees, zero the meter then hang the weight and take a reading.
Thanks Jerry, I’ve been doing it wrong evidently.

So if I hang a weight and continue to rotate the shaft several times, and if the stiffest point continues to show in the same spot - isn’t that spot suppose to be in the middle of the hen vanes?

Stiff side is the stiff side to me - then do the 3 readings 90 degrees apart just show the variations of shaft to shaft? Thanks.
 

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I tune my carbon shaft crossbow arrows by shooting at a target a usually 25 yards and taking a sandbag type rest instead of just standing and shooting. (a rest will be more consistent when testing for grouping)
(you can use blunted field tips for the initial group testing and fine tuning of the nocks)
When i have a arrow that is not grouping with the others I take a marks a lot pen and mark the position of the moon nock in relation to the arrow shaft and then take a pair of smooth jawed hose clamp pliers and turn the nock (usually moon nock) 180 degrees) and usually the arrow will go to a completely different place on the target and if not with the other groups I keep testing at 90 degree internals of the nock and when it get close I can then usually fine tune the nock at 1/8 inch turns. Any arrow that will not ever come in close with the majority of the others I use that arrow as a unloader arrow.
Sometimes you will come up with a completely different cock fletch down arrow, just use a marks a lot and re-color/re-label the cock fletch.

Try turning the nock in the arrow and you will get some surprises as to how a arrow groups on target.
 
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