Main Discussion Area => Arrows => Topic started by: Jjpso on November 11, 2014, 07:06:21 pm
Title: Question on arrow length and spine
Post by: Jjpso on November 11, 2014, 07:06:21 pm
Hello there.
I have been reading about things that affect spine and i got a dougth If you arrow spine is, for example 45#, this is only true if the arrow length is 28 inches. But If your arrow is for example 30 inches long the spine will only be 35#. Is this rule true, despite you draw length?! For example, my draw length is 25, if i have 40#-45# spine and are 30 inches long, in reallity they will be 30#-35# spined?
I hope you can understand what i mean...
Thanks,
Joao
Title: Re: Question on arrow length and spine
Post by: Pat B on November 11, 2014, 08:11:28 pm
Yes, that is correct. The shaft will bend at its center, not the center of your draw length. Tip weight will also affect spine. The 45# spined arrow should have a 125gr point on it. Heavier head will reduce the spine, lighter will increase it.
Title: Re: Question on arrow length and spine
Post by: Danzn Bar on November 11, 2014, 08:14:27 pm
Jipso, I think your confusing true/static and dynamic spine.... True or static spine is what the shaft is when it has been placed on a spine tester no matter how long the shaft is. Dynamic spine is the way the arrow responds when shot. When we say spine is reduced 5# for every 1" over 28" we are talking about dynamic spine. Hope this helps DBar
Title: Re: Question on arrow length and spine
Post by: duke3192 on November 11, 2014, 08:57:46 pm
D. B. If spine is reduced 5# for every inch over 28", why are spine testers set up for 26" centers.
Title: Re: Question on arrow length and spine
Post by: Danzn Bar on November 11, 2014, 09:23:39 pm
Duke, Not all spine testers are....Remember for static or true spine..... Modern shafts (carbon, aluminum) are spined according to the modern standards (ASTM F2031-05) an arrow's spine deflection is measured by hanging a 1.94 lb. weight in the center at 28". Traditional/Primitive shafts (wood, cane, bamboo, shoot etc.) is usually expressed using the old AMO standard of 2 lb. and 26".
Why, I don't know. But when we talk about reducing 5# for every inch over 28" we are talking about how the arrow reacts when shot using 28 just as a starting point. There is really no correlation to the 26" used for static spine and 28" when expressing dynamic spine.
I hope I answered your question :-[ DBar
Title: Re: Question on arrow length and spine
Post by: Jjpso on November 12, 2014, 04:47:12 am
Pat b and Danz bar, Thanks for the help, my dougth came because my draw length is just 25, 26 the most, and i was not sure that the rule applied the same way. Now i get it.
Thanks, this is really a Nice forum!
Regards from Portugal
Joćo Pedro
Title: Re: Question on arrow length and spine
Post by: BrokenArrow on November 25, 2014, 11:47:49 am
Does the 28 inch spine referred to here include the length of the field point?
Title: Re: Question on arrow length and spine
Post by: Grasshopper Mouse on November 25, 2014, 12:36:41 pm
Arrow length is typically measured from the throat of the nock, where the string rests, to the back of the point.
Guy
Title: Re: Question on arrow length and spine
Post by: Buck67 on November 25, 2014, 12:58:48 pm
Static versus Dynamic Spine. There's always something new to learn.