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Confusion on spine tester usage. (Ugh!)

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riarcher:
Almost have another (indicator style) "tester" done. (first in years) Presently most parts are cut and ready to assemble. Been looking (Searches) to verify what I thought was the way to use it and now I'm so completely confused,,, I wonder if I was ever right in my usage.  :-\

Planning on setting it up with 26" and 2# weight. (thinking now 28" & 1.94# maybe? does it matter?)

Okay, for the sake of this discussion, Let's use a bow that reads 50# @ 28" Shooting an arrow measuring 30" from bottom of nock to back of 125 gr. head.
Actual draw is 28 1/2" with 1 1/2" allowing for clearance on back of bow.

Commonly I see 5#/inch as an acceptable rule (personally, I've felt 2 1/2# / inch is closer - but we'll use the 5#)

Using the 26" centers, I would deduct 10# for the 2 inches to get down to 26 from the advertised 50# @ 28". That would make it a 40# @ 26" bow.

Now take the 26" away from 30" and that would give me 4 inches or 20# bringing the (theoretical) actual up to a 60# spine reading on my 26" centered spine tester.

(In reality I'd go with the 2 1/2# / inch and go with a 55# spine.)

I'm thinking this should get me pretty close to the ball park but still need some fine tuning (don't they all?)

Anyways, after searching and trying to confirm / disprove this I got soooo lost I don't know anything anymore!  :o :-[ (Totally confused)

First use will be to spine out some test Boos, after which it'll simply be a comparative thing.

However, as I weed out what I can use from what I can't I'd be offering them to club members to play with. I'd like to pass on acceptablly spined pieces for them to play with. (Right guy gets the right group thing)

Feeling I'm probably wrong,, what is the right (simplistic) route for going this way?
Not expecting the perfect spine from this, just a close starting point.

I swear I learn more and more, about less and less every day. Pretty soon I'll know everything about nothing!   :o

Pat B:
For the standard deflection table you want the uprights set 26"(inside to inside) apart and a 2# weight to indicate the deflection. This standard is for arrows cut to 28" with a 125 gr. point. Any deviation from these values will affect the deflection differently from the standard.
 so...an 50# spined arrow cut to 30" with a 125gr point will shoot like a 40# spined arrow.
  Now, for cane and hardwood shoot arrows you can subtract 10# from the actual spine weight for the natural taper of the shaft....so the 50# spines cane arrow is now 40# spine because of the taper, cut to 30" and with a 125 gr point makes it shoot like a 30# spined arrow.
   These things can get confusing.  ???  Try this, make some cane arrows cut to 30", find the stiff side and place that against the bow, fletch them and shoot them. I think you will find most will shoot well. For the ones that don't shoot well try them with the cock feather in towards the bow. Those should shoot fine this way. If they don't, set them aside and shoot the others.  ;D 

riarcher:
Thanks Pat.  ;D
You're saying the 26" centers are compensating for the 28" length and I do not need to convert?

My intent is to do a "Bare shaft planing" test on the boo for flight.
Problem is, the boo I have ranges anywhere from 1/4 to over 3/8" on the skinny end.
Was looking to save some time (and grief) by selecting some that are reasonably close (like within 15-20# spine?) Diameter does not always equate to (felt) stiffness on these either.

Is the bare shaft flight test a bad idea?
I've only edged around this "Primative" before. This is like new to me.
Keep getting into trouble trying to relate it to carbon and glass.  ;)
Much more interesting / satisfying than sticking feathers on aluminum!  :D

Pat B:
One of the hardest aspects of building "primitive" archery stuff is trying not to relate it to what you know, ie glass, aluminum and carbon.  Try this...imagine yourself in a survival situation. All you have is your bow and a knife. cut some shafting. In your case you already have the cane. Straighten a few, make up arrows and make them fly well for you. Start out longer than you need and shoot it. How does it fly?  Cut off an inch from the point end, reinstall the point and shoot it again...and so on until you get a feel for what will work for you as arrows.
  Start with canes that are about 3/8" at the base(big end/point end) and cut them to 30" and make up your arrows. Don't worry about spine or anything else remotely modern. You will want the bud scar (they alternate sides up the cane) either against the bow or 180 degrees out. If the arrow doesn't fly well with the cock feather out, flip it over so the cock feather is in. It will generally shoot well for you this way. This all can be simple or as complicated as you want to get it. For me, the more simpler the better, but still being effective for hunting. 
  Once you find a length and diameter that works well for you, you can set up a simple spine indicator with 2 nails set 26" apart. Place your "good" arrow on the nails, hang a 2# weight on it and mark the deflection. Now you have a basic spine test to get you into the ballpark with your cane shafts.

aero86:
pat b, i was told something different.  that the stiff side will be 90 degrees out from the node branch, in either direction.

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