spine - need help!

[stuckinthemud]

To avoid hijacking a thread, I'll post my question here. I have good Welsh legs, that is to say at 5'6" I am blessed with shortness! I draw 24" and my preferred draw weight is around 35#.  The arrows I have fletched so far have had sharpened tips, re-enforced with a triangle of bone or antler, so super-light-weight, and fine against targets - no hunting in the UK.  So, how would I calculate the spine for that - a 24" barrelled shaft with 2" feathers and a 1/2cm triangle of antler inserted in a sharpened tip bound with cotton soaked in ca  let into a shallow rebate (rabbet) ? I usually shoot elb

[DC]

Because you have almost no tip weight your arrow is going to behave like it's stiffer so you can have less static spine. Your arrows can be lighter, faster. Like Pat said in the other thread it's about 5 lbs spine for every 25 grains of tip weight but if you do the math it says that you would want to reduce your spine by 25 pounds.(starting at a 125 gr tip) Your draw weight is 35# ,start 10# under that and minus 25# for no tip weight. That means that your spine should be 0#. Simple, and you get to use rope for arrows This points out the problem with rules of thumb. The further you get from the norm, the less accurate they are. I would start with 30# and see how it goes. I read somewhere that Easton doesn't make shafts under 30# spine(I think) because once you're that low it doesn't make any difference.

[stuckinthemud]

Thanks DC, that is really clear but how light an arrow can I go before its like dry-firing?

[Pat B]

You can also decrease spine weight by adding length. Like I said in the other thread I shoot 30" arrows but my draw is 26" so I can start with heavier spined arrows and still get good arrow flight. There is probably a variable with shorter and longer draw lengths(under/over 28") but I'm not aware of what it would be.

[stuckinthemud]

Slight digression but I cant reliably get my draw length locked in,  as I tire my draw shortens slightly, how do you keep your draw length dialed in with longish arrows?

[DC]

Maybe even more digression. When I started I could pull 40#@27". I figured that I would make each bow a little heavier and then my strength would build. After about a year and maybe 15-16 bows I took a picture for a bow I was posting. There was a lot of arrow sticking past the handle. I measured my draw length with a marked arrow and found that my draw length had dropped 2" so now my bows were 45#@28"  but I was only drawing to about 25". That equalled about 40#. My muscles were smarter than my brain. Still the same anchor point but my bow arm was swinging to the right just enough to limit my pull to 40#.

[bownarra]

Slight digression but I cant reliably get my draw length locked in,  as I tire my draw shortens slightly, how do you keep your draw length dialed in with longish arrows?

Can't means won't! Put a wrap of tape around the shaft and practise. It should be more about feel than some draw check anyway.

[willie]

Slight digression but I cant reliably get my draw length locked in,  as I tire my draw shortens slightly, how do you keep your draw length dialed in with longish arrows?

use a clicker in practice sessions to help develop muscle memory?

[Todd Mathis]

To avoid hijacking a thread, I'll post my question here. I have good Welsh legs, that is to say at 5'6" I am blessed with shortness! I draw 24" and my preferred draw weight is around 35#.  The arrows I have fletched so far have had sharpened tips, re-enforced with a triangle of bone or antler, so super-light-weight, and fine against targets - no hunting in the UK.  So, how would I calculate the spine for that - a 24" barrelled shaft with 2" feathers and a 1/2cm triangle of antler inserted in a sharpened tip bound with cotton soaked in ca  let into a shallow rebate (rabbet) ? I usually shoot elb

I am a bamboo arrow maker, so there may be issues involved with other wood shafts which may alter this, but here is what I would tell you.  If I understand you, you draw a 35 pound bow.  Your draw length is 24 inches.  There is nothing that says you have to shoot an arrow the same size as your draw.  You might consider a 26 or 27 inch arrow.  If you shoot an arrow shaft which has a deflection of 35 pounds, then I assume this was done on a spine tester, which is normally measureing a 26 inch length.  Since it is unlikely to be easy to measure a 26 inch shaft on a 26 inch spaced spine tester, I will assume you might be slightly longer then that. 
The comment that your are not shooting a head which is light needs to be clarified.  Just how heavy (in grains) is the head?  If the balance points (FOC) are reasonable...anything above 10% would certainly qualify...then the comment by DC is an excellent one.  My suspicion is that your are shooting an arrow with a static spine of one number, but whatever that number is, YOUR DYNAMIC SPINE will probably be higher.  At least this is what I suspect.
Here is what I think I know.  You shoot a bow which is rated at 35 lbs @ 28 inches.  If that's correct, then you are shooting perhaps a 28 - 30 pound spine..  Have you ever measured the static spine of these arrows on a good spine tester?
This is an interesting question.   Here is what I want to know...
1-what are your arrows spined at?   What is the spine tester which is used?  Is it for traditional arrows on a 26 inch length or is it one of those spine testers designed for carbon arrows which use a different length?

2-What is the actual draw weight of your bow at 24 inches, and at 26 inches?  (this can be done at any bow shop)

3- what is the weight (in grains) of your arrows, and as a seperate number, what is the weight of your bone/antler tip? 

4- lastly, when you shoot these at 20 yards, where and how tightly do they group.  If you give me that info, I can give you a better opinion.
Great question...too many unknowns....Best of luck!