Dumb spine question?

[razorsharptokill]

So I have a set of spine test cedars from 3 Rivers. I left them full length. 35-40 40-45 45-50 50-55. My draw length is 27".  Spine is measured at center between 26" on a spine tester so it seems that it would stay the same spine unless shortened past 26" correct?
It seems like it would make sense to trim them all to 29" perhaps, and then re shoot them then trim 1/4" until flight improves. Get them closer to my draw length. Right now I have about 5" of arrow left at full draw according to pics.

[McDave]

Static spine stays the same regardless of arrow length.  That’s what you measure on a spine tester.  Dynamic spine varies with length and point weight.  Dynamic spine is more important than static spine, but static spine is easier to measure and how wood arrows are sold.  Since I use the point of the arrow to aim, it makes sense for me to have all my arrows the same length, which is 29” for a 28” draw length.  I’ve never had any problems getting an arrow to tune (dynamic spine) by either changing the (static) spine or the point weight.  I could tune just as easy if I had chosen a length of 30”, but it helps my aiming to have them all the same length.

[slowbowjoe]

Jim, what's the draw weight, and what sort of bow are you shooting? Before you start cutting...

[razorsharptokill]

48 @27" selfbow not centershot but shelf and window cut.

[Pat B]

The spine indicated is for an arrow 28" long with a 125gr head. Each inch longer weakens the spine by 5# and each inch shorter stiffens the  spine by 5#. You can also adjust the dynamic spine by 5# by reducing or increasing the point weight by 15 to 25grs.

[razorsharptokill]

I should know this but I have shot carbon or carbon/aluminum arrows out of my recurve for a while. Just getting back into the selfbow realm. So oddly the 35-40 flies the best and it should be REALLY weak.

There may be some limb timing or a stiff limb on this bow that I also need to investigate as has been pointed out on the Bowyers bench.

[slowbowjoe]

I think even 1/8" shy of center would lower dynamic spine by around 5 pounds,bringing the 35/40's close.

[razorsharptokill]

Just leary of cutting it roo deep and weakening the handle.

[pavan]

I find that wood arrows cut closer to the actual draw length with bows that are outside of center are easier to predict.  My two go to hunting bows are both 3/8" outside of center the charts would call for spines at my 27" bop length and point weight to be 35-40 for the one and 40 for the other. Dang near had a test arrow pile up against the bow. Both bows are glassed bamboo and shoot fine with arrows that are technically over spined. With outside of center bows the first bend the arrow takes is into the bow whether you shoot with fingers or a release aid.  it is the arrow resisting acceleration and the bow limbs driving the string back to center.  My pig nut self wood is about 70 pounds when it is first strung, but it is less after it has be strung for a couple of hours.  Thus the the arrows it likes when it is first strung are stiffer than the arrows it likes two hours later.  It likes 50-55 27" bop with 160 grain heads.  The one deer that I shot with it, came in on my wrong side, so I went from right hand to left hand and killed the deer.  It sounds about right that a 35-40 would be the correct spine with a bow that is 3/8 to 1/2 inch out from center at your weight and draw length at about 28" bop.  I would simply fine tune with the brace height and point weight with a finished wooden arrow.  A 35-40 cedar can seem pretty wimpy on the structural side if it is a 5/16" shaft, a 40-45 11/32" with a heavier point may be a better alternative.

[Msturm]

None of my self bows have cut in shelves, so my arrows are all pretty weak.   Keep in mind that doing a bunch of math will get you to a starting point but you need to shoot the arrows to see how they fly. Selfbows are tough to tune arrows to. I get a general idea and tune from there. For example. My 54lb @28 vine maple bow shoots 45-50lb POC arrows. My 62lb @28 Yew bow shoots a 50-55 spine shaft very well. All shafts are 31 inches. Tip weights are different but I don't remember what they are right now.