# Measuring offset/helical vane placement??



## gofor (Feb 4, 2013)

How do you measure the amount of off set or helical in degrees?

I thought I knew the answer: Compare the line of the vane to a line straight up the center of the arrow shaft.

Turns out this doesn't work. I commonly see the phrases "3 degrees offset" and "5 degrees helical". Drawing it out on a piece of paper, a 3" vane at 3 degrees would have the nose of the vane clear off the side of a normal carbon .295" diameter shaft. No way it would have enough contact to glue onto the shaft.

So then I thought it may be radial degrees. For a .295"d shaft, that would work out to about .008" (about 1/125") for 3 degrees. Very doable, and using that, I could see getting 5 degree offset on a short vane without too much problem. I also read a thread where someone mentioned that the JoJan mono helical clamp (which is what I use) gives an 11 degree helical according to the factory. However, he did not state for how long a vane that was. The 11 degrees radial is very close to what I am getting on a 3" vane (actually, my imprecise measurements showed 10 degrees), but the clamp will do a 5" vane, which would increase the amount of radial twist to about 17 degrees. Using the other method of measuring, I have just slightly more than 1 degree of offset.

This is really just a theoretical question for me, because with the JoJan helical clamp, there is only one setting to get the shaft to fit the curve for good adhesion, but the numbers I see tossed around here sometimes do not seem realistic.

So, I am confused whether it is

Choice 1: An angular measurement compared to the long axis of the arrow, in which case the degree would remain the same regardless of the vane's length, but a shorter vane could have more offset and still get adhesion.

Choice 2. A radial measurement with which the amount of degrees would increase with the vane's length.

Choice 3: Something else entirely.

Just trying to learn, 

Go


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## jameswk (Aug 23, 2014)

Tag I'm interested too


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## gofor (Feb 4, 2013)

Well jameswk, it appears we aren't the only ones in the dark on this matter. LOL.

With all the scrutiny of arrow spine, flex, vane shape, FOC, etc, I thought surely someone would have info on what is the most effective amount of offset for a given use (target, 3d outdoors, long distance, hunting) beings the vanes/feathers are one of the most basic parts of an arrow. I have seen that no offset is the best for long distance due to drag, but would think someone has researched what is the best spin rate to drag ratio for things like 60 yd antelope shots with broad heads, or 30 yd cross-wind 3d shots.

Guess not. Makes me wonder how many other numbers cited in many posts are just PFA (pulled From Air) and not based on on measureable fact.

Occasionally I see threads where someone is finishing a college course, etc, and wants an archery-related topic on which to base their final research presentation. Looks like this might be one such topic.

Go

Of course, it could just be no one likes the looks of my buddy in my avatar.


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## jameswk (Aug 23, 2014)

Someone has to have an answer


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## bbjavelina (Jan 30, 2005)

Helical is not measured in degrees anywhere but on AT.

Helical is referred to, in the real world, by pitch. That is, the amount of turns per inch, foot, meter, or whatever. A 1/4 X 20 bolt has 20 thread per inch, a 1/2 X 13 bolt has 13 threads per inch. The same is true of boat propellers, or aircraft props, or feathers on a shaft. 

The degree thing has more to do with the offset of your clamp than the pitch of your fletch. If you take two nearly identical fletching jigs, one with a 4" distance between the pivots, and one with a 3" distance, the degrees will not be the same, but the pitch may be. 

It's obvious that the degree offset can be measured pretty closely by drawing a straight line along the shaft forward from the back of the fletch and measuring how far the front of the fletch is offset. Pretty simple math can give you a degree amount. Pitch? Not very many of us can come up with a number for that. 

For me, it's pretty simple. I shoot feathers. I offset the clamp as much as I can while maintaining full base contact with the shaft. 

Hope it all works out well for you.


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## gofor (Feb 4, 2013)

Thanks bbjavelina. I have been setting mine with an eye toward where I get the best contact of adhesion. For the helical, this is pretty much determined by the curve of the clamp. However I do have some leeway with my straight camp.

Up 'til now, I have been putting in as much offset as I can, and trying different vane sizes to adjust drag. However, as I become a bit more accurate at distance, I am beginning to re-think the "more is better' rational may not be valid. Part of the reason for me re-thinking it is due to the discussions I have read on here. That is when i started questioning "how do I measure the degree of off set". Guess I do too much reading/thinking, LOL, but it also brings into question the credibility of some of the posts when a figure is stated without a standard way to measure it.

By the way, as near as I can tell, my helical would give me about a 1/90 to 1/100 pitch (1 turn per 90 to 100 inches), From what I see shooting on a sunny day, it appears to me the actual arrow spin is way less than that with the 3" vanes. 4" rotate faster than 3", to be expected by the increased area, and I really can't tell with the blazers I have because the shorter vane is very hard to see from the back. However, when I say "it appears", I do know that its hard to really see the spin well from the tail end of the arrow.

Thank you for the reply. I appreciate your common sense answers.

Go


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## bbjavelina (Jan 30, 2005)

gofor said:


> Thanks bbjavelina. I have been setting mine with an eye toward where I get the best contact of adhesion. For the helical, this is pretty much determined by the curve of the clamp. However I do have some leeway with my straight camp.
> 
> Up 'til now, I have been putting in as much offset as I can, and trying different vane sizes to adjust drag. However, as I become a bit more accurate at distance, I am beginning to re-think the "more is better' rational may not be valid. Part of the reason for me re-thinking it is due to the discussions I have read on here. That is when i started questioning "how do I measure the degree of off set". Guess I do too much reading/thinking, LOL, but it also brings into question the credibility of some of the posts when a figure is stated without a standard way to measure it.
> 
> ...


Maybe a few things to consider. 

Fletch is about drag. Shorter, or taller, fletches can impart the same amount of drag as longer fletches if they have a bigger "bite" on the air. This is the only thing that really keeps to pointy end in the front. Otherwise, it would be a knuckle ball. 

When used correctly, drag can be used to impart a spin to the arrow. I believe this to be important if your arrows are not very straight, or if you're shooting broadheads. 

Years ago in my traditional days the recommendation was to shoot an arrow into the sky at a pretty steep angle. As the arrow gets to its apex and turns over to come back to earth observe it's flight on the coming down side. If it's parachuting (hanging on the fletch with the head wobbling back and forth) it may be a sign that you have more fletch than you need. 

And then there's this -- excepting something like Turbonocks, the arrow does not begin to spin immediately. It takes some distance (time) for the bite of the fletch to overcome the angular momentum of the arrow. Try this -- providing that you use a cock fletch. Say you shoot cock fletch up -- at one yard you'll not likely see any spin. At 5 yards it becomes noticeable. Try it at 10, 15, 20, ad infinitum. As best I can tell it takes at least 50 yards before the arrow spin stabilizes to a reasonable degree. It's surely not linear. 

No such thing as reading/ thinking too much. Life's a learning process. Good decisions are based on previous experience. Poor decisions in the past lead to better decisions in the future. 

Best of luck to you.


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## bfisher (Nov 30, 2002)

Good explanation Javi. As long as I've been shooting I have never given a thought to the degree of offset or helical. Like you guys, I adjust my jig so there is maximum contact between the fletch and shaft and live with the results. We do know that you can't change the clamp itself. What I like is how you explained how to check just how much rotation is imparted to the arrow. Never gave a thought to shooting fixed distances and check how much rotation there really is. Cool!!

I'm also glad to see that you suggested that the only place you read about "degrees of offset" is here on AT. My Bitz jig is just about 40 years old and has notches for noting offset, but no marks designating "degrees". Made me wonder how all these guys figured out how many degrees they were setting their jigs for. No I know. They're guessing.


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## bbjavelina (Jan 30, 2005)

bfisher, I've always enjoyed your post both here and on the old Martin forum.

" They're guessing." No one could have said it better. I don't really have a problem with folks referring to the helical in degrees, but I think it'd be best if they understood they were referring to the degrees of their jig rather than the fletch itself. If anyone is unclear about this, I like feathers. 

I reckon the most important thing is that we all hit what we're aiming at. 

Best of luck to you, my friend.


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