Arrow spines

[Cryogenic]

I recently discovered that I really enjoy archery, and specifically shooting a longbow.  Eventually I wish to hunt with it, but of course I need a lot of practice before hunting even becomes an option for me.

I have done much reading, but I cannot seem to make heads or tails out of this issue:  For a "center cut" shelf on a long bow, how much does the arrow actually flex upon firing?  I have a Howard Hill (for sale) with a shelf that's certainly not on center, so I can see how the arrow might flex or bend around the bow when fired.  On the other hand, a bow with a center cut shelf like a Martin of Bear it seems to me that the arrow would not flex much at all.

Second and last question:  Many arrows have a specific draw weight range marked on them.  For example, I have a GoldTip Traditional arrow with a 5575 marked on it, noting a 55# to 75# draw weight.  How critical it it that a 55#-75# bow shoot the arrows, or could a 50# bow do it just fine?  Or is it an issue of testing to see what works best?

Thank you all for the help.

[Austin]

If you already have 5575s i would recommend buying a variety of field points (3of each 125g and up) and testing them out to see what flies the best.
There are some other variables to consider besides center cut-
Assuming nock and brace height are correct, the most important things are arrow lenght and draw length. The longer the arrow the weaker the spine. A longer draw increases poundage and gives a longer "power cycle" (the amount of time the arrow is being directly propelled by the string). These require more spine. If the arrows are full length they'll be more flexible than the rated spine. For tuning, heavier points weaken spine, arrow wraps marginally increase it.

[Cryogenic]

I see.  That helps a lot.  I have a few different points that I can try, and I just cut my arrows down from full length to something that fits my draw length.

Thanks for the help!

[Orion]

All arrows flex to some degree when they're shot, both horizontally and vertically.  High speed photography has documented this.  The less cut to center the riser is, the more the arrow has to bend, i.e., the weaker spined it must be.  A bow cut to center or past center can shoot a stiffer spined shaft, all other things being equal, because the arrow doesn't need to bend as much.

I have some 55-75 Gold Tip hunter XTs.  They actually spine 80 plus pounds on my spine tester.  As Austin said, you can soften the dynamic spine by adding point weight.  By cutting them shorter, you have effectively increased the dynamic spine and it might not be possible to weaken them enough with additional point weight.  

You don't say what your draw weight is, but unless it's at least 70#@28 inches, the 55-75s likely are going to bee too stiff for you.  If you're drawing 50#@28,  35-55s would be a better choice.

[Cryogenic]

I am currently shooting a 50#.  It sounds like some new arrows are in order.

[sweeney3]

If you put some freakin' heavy points on those 5575s, they can be made to work, although with a non center shot bow they will take a lot of weight.  With a Hill bow, you might want to try some wood arrows, as they tend to flex more readily than does carbon.  Carbon works great out of a center shot bow.  

Of course, if you ask a dozen guys, you'll get at least three dozen opinions.     :D

[Fanto]

I started out with 3555s and 125gr field points, 55lb bow cut 3/6 past centre

i now have a 60lb cut 3/16 past and a 75lb longbow which is not cut to cents, about 1/8 before centre.

I now shoot 5575s with 100gr inserts and 175gr field points.

they were tuned for the 60lb bow. they shoot exactly the same out of the 55 as the 60, and actually shoot beautifully from the longbow also. For a while i thought that the recurves shot a little to the right of how the longbow shoots but I think it may be "all in my mind"

my advice, don't pay too much attention to the charts, guidelines and calculators. my arrows should be hopelessly underspined but fly straight and true and consistently.

I now hand over to the other 11 guys for the 33 other opinions...

[Austin]

Oh Btw, nothing wrong with shooting full length arrows, if you haven't cut them yet you could still mess around with point weights and see what it takes to tune them.

[far rider]

Not trying to hijack a thread, but I too have been playing with a Hill and arrow spine. I have tried several cedar spine trying to narrow it down, with little satisfaction.  I had six Trad GTs sitting around that I picked up somewhere 55/75, screwed some 125s on the end and.....WOW! They shot perfect!
Here is my question....I really like cedar shafts, but how do I find out what the "spine" of my GTs are at full length with 125 gr tips and my draw weight/length so as to buy a set of cedar that directly relate???  Any suggestions?

There are several videos on youtube showing some amazing slow motion of the archers paradox with a longbow. My understanding of it is that a center cut or over center cut bow will shoot a wider variety of arrows.


Tim

[Orion]

Far rider:  I'm going to work at this backwards, but it might be a pretty easy conversion depending on the variables involved.  Your 55-75s have a static spine of 80#, plus a little.  If they shoot good for you at their current length with a 125 grain point, a cedar shaft of the same length about 10# less static spine should work.  

Less spine is needed for two reasons.  First, the cedar shaft diameter is larger, which moves the center of the shaft further from the center of the bow and requires a bit more flexible shaft to bend around the riser. (Minus 5# of spine)

Second, there is at least a 25 grain aluminum insert in your carbon shafts so you have at least 150 grains up front.  You'll have 25 grains less up front with the wood shaft, which means you need to soften the spine a little bit more as well, thus the subtraction of another 5# of static spine.  

On the other hand, if you also have 100 grain brass inserts in the carbon arrows, the extra weight is really softening the dynamic spine.  To get a comparably dynamic spined wood arrow, you would have to subtract at least another 10# in static spine.

So depending on how your arrow is constructed, you would need cedar shafts of about 70# (compared to a standard insert and 125 grain point) or 60# or less (compared to standard insert, 100 grain brass weight and 125 grain point).
 
Rather convoluted, huh.  And substantially different physical arrow weights could affect the wood spine needed as well.  Actually, would be easier to recommend an appropriate wood spine if we knew your draw weight at your draw length and the amount of center cut on your bow. I expect your Hill is cut 1/8-inch from center.

[snag]

That's a good way of going about it Orion. I would just have to put out there that IF he does have a 100gr insert that he may have to go down another #5 in spine weight for wood. Test arrows are a good way of going about this.  Also when talking about how a bow is cut in the shelf some forget to add another 1/16" for some strike plates.

[AkDan]

Good tip 55-75 spine at 75lbs on my spine tester.   You've got to remember diameter is going to change dynamic spine also.  Essentiall the larger dia shaft is pushed farther away from center. A narrow one is closer.  It's he same ifthe site window moved in or out and shaft dia was consistent.

Longbows are more forgiving of shooter flaws but the acceptable window of perfect arrow flight is smaller due to the distance short of center shot.  How many of us are shooting machines like Hill?   The reality is striving for perfect arrow flight is everyone's goal.  I am sure Hill or the Wilhelm brothers weren't shooting apples off people's heads with anything less than matched arrows!!!

Other things play like strings and the shooter themselves.

The right answer.  It takes testing and usually tweaking to get there.   Charts and opinions get you in the ball park.....usually!  I'd start with full length and start working back from there. If its weak cut it down.  If its stiff try heavier heads.   With carobs u can use weights on either end to help but realize they have other effects both good and bad depending on what u do.  If u have a shaft material picked you like and a broad head design you want to go with it starts to help fill in the blanks on where to start.  If not different weight heads is a good start.   And making a decision on type of shafts is all u have to worry about initially.

[AkDan]

[AkDan]

Dbl post sorry

[Orion]

Agree on all points, Snag.  

AK Dan, my tester may be a bit off.  I spine with 2# and posts 26 inches apart.  I believe the convention for carbons now is 28 inches and 1.96#. The latter does give a bit softer spine.

[AkDan]

I also use an older spine tester (agincourt archerys by Roy Day) with a 2lb lead and 26" centers if I remember right (on the centers).  I'll have to check one tonight if I have one  laying around just to double check.  I do know mine's been off a pound or two to a dial indicator modle (rogue rivers).      I do have the conversion tables at home to get the spine based on deflection or visa versa but dont remember it off the top of my head.  one of those age things   .     Easy way to calibrate them as is aluminumnumnumnumnum shafts.  


 to op....If they are short and too stiff, add weight up front...you can do it with washers, heads, and THAN add the weight inserts to get you the weight if you want/need to shoot a lighter head.

ps, sorry tried posting and editing on my phone earlier....blasted smart phones LOL!

[far rider]

Thanks Orion and Snag,
Custom Hill Wesley pulling right at 55lbs @ 30 1/2". My GTs have standard weight inserts, are full length, and I pull them right back to the point if I get a proper anchor.

Tim

[Orion]

70# woodies should do it.  Most wood shafts are 32 inches.  An inch taper for the point still leaves you 31 inches.  Nock also adds an eighth inch beyond the taper.  Good luck.  Let us know how it turns out.

[Flying Dutchman]

Carbon shafts are spined in a different way as woodies. Often carbons have an indication in inches, like: 0.500”. This is the amount of inches the shaft flexes at a lenght of 26" and at a weight of 2 lbs. In other words: the normal method to measure the spine-value of a shaft.

If we want to calculate this back to the normal, AMO value, (Archerey Manufacturers and Merchants Organisation), this can be achieved in a simple way: divide the 26 inches through the amount of flex and multiply this with the constant factor for carbon and aluminium, being 1,2115.

In this way a carbon shaft of 0,500” has an AMO spinevalue of : 26/0,500 x 1,2115 = 63Lbs.

Woodies are spined in steps of 5 lbs, carbon isn't. Most manufacturers work in steps of 20 lbs!
This is: 15-35, 35-55, 55-75, and 75-95 lbs, or, in other words:  0.600”, 0.500”, 0.400” and 0.300”  

However, dont be decieved by those values, they come from the compound world and have nothing to do with traditional archery. Don't think: "I have a bow from 50 lbs, so I should use a shaft of 35-55. It doesn't work that way!

A short overview of the most common values:

15-35  0.600” becomes: 26/0,6 x 1,2115 =  52,5 lbs
35-55  0.500” becomes: 26/0,5 x 1,2115 =  63 lbs
55-75  0.400” becomes: 26/0,4 x 1,2115 =  78 lbs
75-95  0.300” becomes: 26/0,3 x 1,2115 = 105 lbs

Should you be used to shoot a woodie from the 50-55 range and you want to move to carbon, then you would need a shaft from 0,600" which is saying, very misleading, 15-35!

Hope this helps!

[AkDan]

the only gt 55-75 I have at home has a 23/64ths poc shoved up the back end of it.  But those numbers are pretty spot on with what I found FD.   I thought the 35-55's were a little lighter in spine than that though either way its close to my old findings and I didnt put any value to remember it.  The 55-75s flew well but needed more weight and I wasnt into changing from wood to carbon so when they were gone they never got replaced.  I dont mess with them anymore so I'm flying by memory and when I did it was more of an experiment than anything fun to do but their not for me.