Should we rethink arrow spine ?

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Yew Selfbow

Active member
The appropriate arrow spine selection for wooden longbow arrows is a discussion that crops up again and again with different people offering differing suggestions and recommendations.
The common consensus seems to be that the correct (or near correct) spine lies anything from 5lb to 15lb below the draw weight of the bow. But is the draw weight of the bow a correct indicator of the required stiffness of the shaft?
The required stiffness of the arrow shaft is a result of the magnitude of force applied to the arrow on release from the bow. Force is a product of mass X accelleration so there fore would it not make for a more accurate spine indicator if the limb speed (arrow accelleration) were the prime indicator factor and not the force required to bend the bow.
As a simplistic example, take 2 50lb at 28" bows. One has a limb speed of 1meter per second the other has a limb speed of 10 meters per second. The force exerted along the axis of the arrow is increased by the second bow by a factor of 10 so the arrows would need to be proportionally stiffer to resist excessive deflection caused by an increase of accelleration.
Of course it would only be of help if bowyers were able to provide limb speed data for there bows.
 


Flying Whale

New member
The appropriate arrow spine selection for wooden longbow arrows is a discussion that crops up again and again with different people offering differing suggestions and recommendations.
The common consensus seems to be that the correct (or near correct) spine lies anything from 5lb to 15lb below the draw weight of the bow. But is the draw weight of the bow a correct indicator of the required stiffness of the shaft?
The required stiffness of the arrow shaft is a result of the magnitude of force applied to the arrow on release from the bow. Force is a product of mass X accelleration so there fore would it not make for a more accurate spine indicator if the limb speed (arrow accelleration) were the prime indicator factor and not the force required to bend the bow.
As a simplistic example, take 2 50lb at 28" bows. One has a limb speed of 1meter per second the other has a limb speed of 10 meters per second. The force exerted along the axis of the arrow is increased by the second bow by a factor of 10 so the arrows would need to be proportionally stiffer to resist excessive deflection caused by an increase of accelleration.
Of course it would only be of help if bowyers were able to provide limb speed data for there bows.
Draw weight can only be an indication, and a reasonable starting point. This is where an experienced bowyer sales person can help.

My experience is only from recurve, but I have 2 pairs of limbs. The first is 36lbs. I have used them all summer. I decided to buy some lighter limbs for inddors, because I do not need the cast. I bought some 32lb limbs. When I tried them out the arrow tuning was IDENTICAL to my 36lb limbs. The lighter limbs are Border TXG Golds, and I have since been told that they are notoriously fast. It seems the arrows are emerging from the bow with the same speed (confirmed by the fact my sight marks at 60 yards are identical) and the tuning is the same...quite a bonus as I diod not need to buy new arrows.

Sorry to drag recurves in to this section, but I thought it was illustrative.
 


Yew Selfbow

Active member
F.W.
I think you've made a very good point.
Were you given any advice from the retailer as to what would be an appropriate arrow spine for your new limbs?
 


gwynn

New member
Yeah as you say - I spine mine 10lb less than the bow and they work pretty well - saying that I've shot arrows that are 'underspined' and those that are well over [according to the blurb] and the Longbow seems pretty tolerant throughout.
My ex coach, I think it was, just told me to experiment until I found a spine that suited me and my bow.
Helping a friend sort out arrows for a Scythian bow, shot with a thumbring, we found he had to 'overspine' by a large amount.
So yes I think none of this is written in stone - experiment!
 


kernowtom

New member
its all very complicated:)

Static spine is what an arrow does on a spine tester; basically how stiff it is, and that is how we buy arrows... because it can be measured. Dynamic spine is what it does on a loose, and there is no good scientific model of this. The obvious variables include:
1 - the arrow: length, mass, pile weight, fletching drag and weight, nock weight and grip, elasticity (ie not just how stiff it is, but how fast it bends and re-bends)all affect its dynamic spine. Tapering or barrelling will also affect the interaction between shaft and bow.
2 - the bow: weight is what we use to match arrows, but as said above, the limb acceleration is important and on top of that, tillering will affect the acceleration curve. For an extreme example.. compound bows have a different acceleration pattern to other bows (apart maybe from composites with recurves or siyahs), because of the cams. Bow handle width affects the paradox needed.
3 - the string: string mass affects acceleration, but also string stretch affects the acceleration curve applied to the arrow. the nocking point will also affect the vertical torque on the arrow.. wooden arrows are made to be stiffest laterally and irt seems easier to get porpoising than fishtailing.
4 - you... a clean release increases the initial acceleration - any sideways movement of the string at the release point might also be significant.

Ummm.. I am sure others will think of other things. but all that is enough to convince me that the comment about experimentation is the most important in this thread. There probably isn't a "right" spine... there is only what works for you with your bow. Ancient egyptian arrows were hopelessly underspined by modern standards, but killed plenty of people none the less.
BUT....
My challenge for today - does an underspined arrow fly left or right??????
 


Flying Whale

New member
F.W.
I think you've made a very good point.
Were you given any advice from the retailer as to what would be an appropriate arrow spine for your new limbs?
Actually I bought them second hand. It was my local dealer who made the comment about the relative speed. It is nice to have somewhere to go where they happily talk and provide you with tea, even when you have just been and bought 2nd hand kit rather than new from them!!
 


English Bowman

Active member
My ex coach, I think it was, just told me to experiment until I found a spine that suited me and my bow.
Was that me you're talking about there Gwynn?

I have always said for an English Longbow assuming a draw of about 28" start about 2/3 of the weight of the bow, as a starting point and experiment until you get the best flight, it varies so much from bow to bow, and archer to archer that you can't draw a chart that will work for everyone.

kernowtom said:
My challenge for today - does an underspined arrow fly left or right??????
Are you right or left handed?

If you're right handed, and using a Mediterranean Loose, the an underspined arrow will fly to the right. (usually)

Daniel
 


steve58

New member
Hmmm, I have two sets of arrows for my 53lb Bickerstaffe, the heavy ones have 125grn piles and a 50/55 spine, the lighter ones (but only by about 10%) have a 45/50 spine and 100grn piles. 4" fletch on both sets. Outdoors they both come off nice and straight. Indoors at 20yds the lighter ones go right. If I shot this bow regulalry indoors I would use the lighter ones. Experiments are fun! I had some old shafts and built some variations, taper on the front, taper on the back, 100 vs 125 grn piles. I put 5" fletchings on and cut them down as I went along. All the shooting was at 60 yards. My conclusion was that a lighter pile, or a taper on either end, is worth one roll of the rubber band (about 1/4"). 1/2" off the fletching is worth a roll of the band. So if I had a taper (I liked the flight of the rear tapered ones best), a lighter pile and 2 1/2" fletchings rather than 4" I could in theory put the band 1 1/4" higher. This would make a significant difference to me at 100yds. I can see some money heading Hi-Force's way in the near future! Caution, what works for me may not work for you!
 


robtattoo

New member
Slightly off topic, I know, but this is the best arrow tuning explaination I've ever read

http://www.bowmaker.net/index2.htm

I always experiment with any arrows I buy. It seems that a lot of folks in the UK haven't cottoned on to the fact that dynamic spine can easily be altered by changing pile weight & arrow length, shorter or lighter points to stiffen a shaft, longer or heavier to weaken a shaft. I see so many people at shoots with 40-60# ELBs, consistently shooting very weak shafts, when the shaft has been left at full 32" length & fitted with 125gn piles. When you mention anything, all I hear is "I can't warrant buying another dozen arrows, mate"
 


nelly

New member
I agree, arrow length makes a big difference. I only have a 25" draw and shoot a 58# at 25" ELB. Ive long given up using any tables as they cant cope with these kind of numbers and only seem to work on average bows at average draw lengths
 


steve58

New member
And I know some people who go to the money saving lengths of making the arrows too long to start with on the grounds that they can shoot one a bit shorter if it breaks near the point! Interesting to watch!
 


Yew Selfbow

Active member
I agree, arrow length makes a big difference. I only have a 25" draw and shoot a 58# at 25" ELB. Ive long given up using any tables as they cant cope with these kind of numbers and only seem to work on average bows at average draw lengths
Nelly... what arrow spec did you settle on with such a short draw and a high poundage bow?
 


Macbow

New member
I personally don't think limb speed info would help much in choosing the correct spine as there are just too many other variables that affect arrow flight, not least the archer himself. Shafts need to be tuned to the bow and to a lesser extent bow to shaft. For me it's all about perfect arrow flight and that starts with bareshaft tuning. Once my bareshafts are grouping well at 20 yards I will then try and get them to group at 30 yards. It's a long and expensive process when using wooden shafts but as Rob said there is so much to gain by experimenting with point weight, shaft length and fletching. My 47# AFB performs well with arrows spined 35-65 depending on length and point weight. For target shooting short 35-40# shafts and 70 grain field points with 3" fletching makes them fly fast and flat in good shooting conditions and as long as my form is good. But the bow is just as happy with long 600 grain shafts of 60-65# spine with 160 grains or more up front and 5" feathers - very quiet, maximum impact and very forgiving of a less than perfect release. With my beloved carbons the whole equation changes again. With aluminiums anything from 1816 to 2016 depending on length and point weight. A very wide range of arrows can all fly nicely from the same bow. Only through trial and error can you find your perfect combination which may or may not match the spine chart recommendations.
 


nelly

New member
Ive finally found 30-35 (32 to be exact) fly straightest with 63 grain piles. Ive tried 100 grain piles but they didnt make much difference to flight but brought my point of aim to top of target at 100 yards.not the bottom which i prefer. This seams to be another side effect of short arrows that playing with pile weight has less effect than on a longer shaft.
 


steve58

New member
This is a really interesting thread and people are putting up lots of technical detail, which I find very helpful. What strikes me is that it might be possible to have an optimum set of arrows for every distance eg on a York one would need 100, 80 and 60 yard arrows. With a lot of experimentation it might be possible to arrange things so that the rubber band, or point of aim, was very similar for each distance, thus giving greater consistency of form for the archer. Has anyone tried this sort of approach? Of my two sets of arrows I have decided that the lighter ones are good at 80 and 60 yards, but don't go so well below that, the heavier ones are good at 60 and below. (Ironically I prefer the lighter ones indoors! Not sure why, they just seem to go better.) I still don't have a set I am happy with for 100 yards. (I am thinking 100grn piles on a 5/16" shaft with a rear taper to 9/32", and a 2 1/2" fletch might do the business.)
 


Yew Selfbow

Active member
Steve
I have arrows for specific distances. At the moment I have six sets..
1 set for clout
1 set for100 yards
1 set for 80 and 60 yards
1 set for 50 and 40 yards
1 set for 20 yard indoor..
and 1 set for flight..
It gives me exactly the situation mentioned in your post, my point of aim remains the same whatever distance I'm shooting. The difficulty arises when I decide to change bows. I use one specific bow for clout and flight, a different bow for Yorks, another for Westerns and a low poundage bow for indoors.
 


steve58

New member
Yewselfbow
If I have understood your post you use two variables, the arrows and the bow? I assume you use the same bow all the way through a York, and change arrows? Rather than changing bows half way through? I find this interesting, because I am going through a patch where I can't shoot my lighter bow happily, hurting my right shoulder every time I try. I think this may be due to the muscles not recognising the need for correct form with the lower poundage bow. I have now started shooting my Bickerstaffe indoors. It's a pain getting the arrows out of the boss, but I shoot much better and my shoulder doesn't hurt. What I am interested in is how you manage to shoot several different bows and retain consistent form? Do you have any tips, or is this something that you do naturally and never have problems with?
 


Macbow

New member
Steve
I have arrows for specific distances. At the moment I have six sets..
1 set for clout
1 set for100 yards
1 set for 80 and 60 yards
1 set for 50 and 40 yards
1 set for 20 yard indoor..
and 1 set for flight..
It gives me exactly the situation mentioned in your post, my point of aim remains the same whatever distance I'm shooting. The difficulty arises when I decide to change bows. I use one specific bow for clout and flight, a different bow for Yorks, another for Westerns and a low poundage bow for indoors.
WOW! Way too specialised not to mention expensive for me but the great thing about archery is there are so many different approaches to the same thing.
Archery for me is always going to be a compromise. I want to be able to grab a bow and quiver of arrows and go out and hit whatever I'm looking at, paper, inanimate object or whatever. So that means a lot of practice, much of that to burn trajectory & windage information into my subconcious. I consider myself a "gapstinctive" archer as in I know my gap distances for various ranges but don't consciously focus on them. For my system to work I need to use the same set of arrows, each with the same length and same weight. My arrows are a constant, my arrow speed is a constant (same anchor point every time and same draw length) and my windage calculation is fairly constant whether it is 10 yards or 100 yards. The only variable is elevation and through repetition and really knowing your kit, figuring out how much you need to hold over or under becomes easier.
Personally, and this is only my opinion - I am mainly a field archer and not criticising Yew Selfbow's system in any way - I don't like the idea of a 20 yard arrow, a 40 yard arrow etc. I like trad archery because of the simplicity and the specialised arrow per distance thing is just too complicated. My archery hero Howard Hill didn't reach for his 170 yard arrow for a long range shot on a deer or miss a 40 yard boar because he accidentally used a 20 yard arrow. He just shot the same bow and arrows a lot (many hundreds of arrows each week) and learned through experience.
 


nelly

New member
If your looking for max score i think yew selfbows approach or something similar is probably the best.There are big differences on what is required from an arrow at long ,medium and short distances. If you dont change your arrows accordingly you will be fighting an up hill battle. Of course this does assume you are able to adapt quickly to the different performance of each set of arrows when you change mid competition.

All of the above is complete rubbish if your an instictive shooter looking to replicate the more natural archery senario of one man/one bow/one shot. Each to their own.
 


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