Max spine at front or rear?

[Del the cat]

Normally spine is measured between two supports at say 28",and calculated as distance between the supports divided by the deflection. I use 24" (for convenience for short flight arrows), but sometimes 21".
I'm making a 32" flight arrow and have been looking at the spine using the 21" centres to measure the spine at the front 21" vs the rear 21".
My view/theory is that the rear needs to be stiffest, (which is what I have on the arrow I'm making) as the sideways deflection/force the arrow is maximum just before it leaves the string (point of maximum paradox... eg. a straight line from string position at brace past the side of the bow is angled substantially to the left).
Or putting it another way, the arrow is travelling relatively straight early in the loose.
Does anyone have have a view on this? Either for or against this theory.
Del

[Del the cat]

I couldn't bear the silence as the Tumbleweed rolls across this thread, so I thought I'd reply to it myself   
Del (disappointed of Harlow )

[mmattockx]

I can't say about your theory, but the Easton X10 target arrow is weaker in the back half and is considered to be more forgiving of a bad release due to this. Since part of the challenge of flight is getting the arrows to fly straight as soon as possible maybe weaker spine in the back is the way to go?


Mark

[Hawkdancer]

That might explain the rear taper on some premium shafts.
Hawkdancer

[Del the cat]

Ah, some interesting observations, but is that because "normal" shafts tend to be too stiff, with relatively heavy points (opposite of a flight arrow), so the back needs to be weaker?
S'pose what I should do is make a shaft that can be reversed and try it both ways round 
Del

[Don W]

i always assumed the measurement would be the back. That comes from thinking about how you taper a shaft to reduce the spine and when you barrel a shaft you barrel it forward. Also the middle is what flexes around the bow, so the front could theoretically be to stiff and not matter, but if the back was to stiff it would never paradox.

[Del the cat]

i always assumed the measurement would be the back. That comes from thinking about how you taper a shaft to reduce the spine and when you barrel a shaft you barrel it forward. Also the middle is what flexes around the bow, so the front could theoretically be to stiff and not matter, but if the back was to stiff it would never paradox.

I see what you mean... that makes sense if you are starting with a heavy arrow... but from my perspective I'm starting with an arrow that is pretty much minimum weight to start with... so the question is where can I remove stiffness/weight without reducing it too much.
Del

[Don W]

I would assume there would be a point forward where weight wouldn't matter, but I think arrow diameter would. To some degree, arrow diameter changes center shot. In practice however, that point may be far enough forward to not matter.

If the arrow is already on the verge of to light, I would think anything center  would have a dramatic effect, and a less effect as you neared the ends with some sliding scale where the back has more effect than the front. The back gets the brunt of the force, where the weight of the arrow causes the front to feel less trauma, so it could theoretically be lighter.

But I'm still on my first cup of coffee, so there may be a caffeine deficiency flaw in there.

[Badger]

       
         Del, keep in mind my arrows have not been one of my strongest points but most of that is because I don't put any time into them. I always do them at the last minute. But what I have found in practice and seeing other successful flight arrows is that they tend to have a slight front to back taper. Seeing as how the front of the arrow has no weight and it tapered forward You don't really need to include that in your sprine measurement.So this would throw the spine to being weaker at the rear but I think the primary goal is the weight distribution and the taper, spine is just a side effect of that. As far as a starting pine would go I figured you are shooting about 80#
and the bow is about 1 1/8 wide. I think about 40# measured at 24" with the back of the arrow on one of the supports, should get you pretty close.

[Del the cat]

       
         Del, keep in mind my arrows have not been one of my strongest points but most of that is because I don't put any time into them. I always do them at the last minute. But what I have found in practice and seeing other successful flight arrows is that they tend to have a slight front to back taper. Seeing as how the front of the arrow has no weight and it tapered forward You don't really need to include that in your sprine measurement.So this would throw the spine to being weaker at the rear but I think the primary goal is the weight distribution and the taper, spine is just a side effect of that. As far as a starting pine would go I figured you are shooting about 80#
and the bow is about 1 1/8 wide. I think about 40# measured at 24" with the back of the arrow on one of the supports, should get you pretty close.

Cheers
Del

[Buckeye Guy]

Any up dates Del