Help me calculate a spine weight, please

[SamIAm]

I want to make some matched arrows for my granddaughters longbow and  I need assistance calculating the recommended spine weight.  The draw weight of the youth bow is 25# @ 28" but she only pulls it to about 25."  Sorry don't know what the actual draw weight would be at 25."  The longbow does not have a shelf, shoots around the handle.  I've looked up a few charts but none of them go down to that light of a bow.  Also as part of the question, what weight field tip would you recommend for her arrows?  Some say the heavier the tip the faster the "limber" arrow will straighten up and fly straight.  The arrows will also be cut to about 29" (unless yall tell me otherwise) because I've also read that the longer arrow will help stabalize the flight.  Thanks for the help.

[Danzn Bar]

Well....you could lay an arrow shaft (1/4" dowel) between two nails 26" apart, suspend a 2 lb weight in the center of the shaft and you should have about 1 5/16" of deflection in the shaft.  The way I come with that is.... I always take 26 divided by the bow poundage at the draw length. that equals the deflection of the shaft or spine to start with.

For that light of bow  I think 2# per inch less the bows rating would be close. sooo 3" X 2# = 6, 25# - 6 = 19#.    therefore 26/19= about 1 5/16".
But, I have found that for light weight bows. Using a 1/4" diameter poplar or hardwood dowel with a 50 - 75 grain weight tip with 4" feathers cut 29 -30" long would probably work.

This is just my experience,  good luck.
DBar 

[SamIAm]

Thank you very much Danzn.  Just what I needed.  That's even lighter than I thought it would be.  Since posting this question I've been thinking about trying to make some arrows for her bow out of river cane....got a lot of it around here and should be able to find some the right size that would spine in that range.  I'm in your debt.   

[Davesea]

River can would work great.  I use cane for youth arrows. Here are some specs based on your granddaughters bow and draw length.  This should  give you a guide to get you in the ball park.  If you can find some cane with a lower spine you can cut them shorter and use a lighter point.  I have some 5/16 Sitka Spruce shafts which have the specs shown in the image shown.  I specialize in youth arrows so if you have any questions don't hesitate to PM me.
Dave
Seattle

[PEARL DRUMS]

I like the 1/4" dowel idea myself. There really isn't any spine at work with such a light, 15-18# bow.

[SamIAm]

Thanks.  Lots of help here, appreciate it.  Sam

[Davesea]

Problem with 1/4" dowels is that they don't stay straight.  If you want to give her the best experience possible, your answer is Eason Jazz, 1214.  At least three Jazz arrows will give her the consistency in an arrow that she needs to work on form.

[SamIAm]

Thanks Davesea.  That is obviously what I want, consistency in an arrow so she can work on form.  And nothing succeeds like success.  Nothing brings you back to the range like shooting good groups.  I would like for her to learn to appreciate the beauty of primitive archery though, so the river cane will probably be my first arrows for her.....and they're so good lookin'.

[Davesea]

Here are a few matched Phragmites (Apache hybrid) arrows I made for youth archer (25# @ 28" with 24-25" draw) that weigh in at 250 grains which is very light.  They are 26" BOP.  I used a parallel screw on point (tophat) 5/16" and 85 grains.   I glued and tied on the feathers and then sealed with tree resin/Beeswas/earth pigment mix.  Also crested with the natural resin/pigment mix.

Thanks to Jackcrafty for the very nice Phragmites canes he sent me.  Such a light material for arrows although fragile compared to bamboo.

Dave
Seattle

[SamIAm]

Very nice.  What's BOP stand for?

[Pat B]

back of point

[Jay]

So a 50# bow should have an arrow that delects .52"

26 / 50 = .52"

Is this correct?

Thanks!

[Danzn Bar]

Jay,
Yes a 50# bow at your draw length......
That's a good starting point.  You will still need to try some things.... Length of arrow, point weight, and how far off center shot the bow is all plays a part in fine tuning.

A shorter arrow is stiffer, a longer arrow is weaker
More point weight makes the arrow weaker, where less weight stiffer.
A cut in shelf can handle a stiffer arrow where a bow with no cut out needs a lighter spine arrow.

DBar

[Jay]

Thanks Danzn,
That all makes sense. I am shooting a 50# elb and am having some troubles, so i went down to my 40# flat board bow to work on form

The arrows I'm shooting were made for the 50# elb.Mmy arrows must be to stiff for the lighter bow, thats why i'm shooting 12" left at 20 yards when i used to be able to hit a coffee cup.

I need to go back and make some lighter arrows. then work on form.

  Thanks!!
jay