Deflection-based spine chart for wood arrows

[Don Stokes]

I put this on another thread, and decided to make a new thread for it. I've been meaning to do this for a while.

This spine chart was based on a couple of years of bare-shaft testing that Dan Quillian, my brother and I did in the early 1990's, traveling to shoots all over the eastern US and getting people to shoot our shafts with their bows and gathering data. We were preparing to launch the Superceder arrow shaft business. We carried around a full set of our barrel tapered bare shafts, in three lengths tipped with 125 grain points, and a big soft target to shoot. When we had a few hundred data sheets, I plugged the data into a computer program and it fit a mathematical equation almost perfectly, a 5th order polynomial. I'm not that much of a mathematician, but the computer was!

The spine chart is in deflection numbers rather than pounds, because that's how we marketed our shafts. One of these days I'll convert it to the "pound scale", even though the pound scale only really applies to self bows. To do the conversion yourself, compare the bow draw weight column to the self bow column. The deflection number listed in the self bow column is the high end of the range for the corresponding bow draw weights, so that 45-50# draw weights have deflections of .570-.520", based on a classic Adams spine tester. Here's what it looks like:

 

PS- the phone numbers are no longer valid.

The chart works for other species and parallel shafts, too. It won't be perfect for everyone or every bow, but it will get you close. Enjoy!

[Shaun]

Good stuff Don. There are a ton of "what arrow for this bow?" threads on TG. This chart is the result of some serious data collection - not "guestimating".

If you use this system you will have arrows that fly like darts.

[Fletcher]

Thanks, Don.  I'll probably play with this a bit.  I can remember using deflection in thousands rather than pounds many years ago.  Most folks find pounds easier to work with as it gives something to relate spine to.  We could probably be more accurate working in the actual deflection, tho.  Good stuff.

[divecon10]

Always look forward to u’r info but u’ll have to excuse the ignorance with u’r timbers.
On another post you mentioned these superceders as being barreled Magnolia (yellow poplar). Did I get that right? I’m asking here as I didn’t want to hijack and the other post was a different Q. Were these the ones u sent me a couple of yrs ago? They are straight an weighty, a terrific shaft. Well I sent a few to my bowyer here, telling him they were cedars. as he enjoys playing with such and although he wasn’t sure he thought because of the weight they may have been rock maple as they had a 270 spine which he said was popular many yrs ago.
Unfortunately those shafts I got from u are diminishing in number and as u mentioned u have sold on the gear u used to make them. Does this mean u’r at the bottom of the barrel?
Cheers

[snag]

Seems a little stiff for Recurve category...?  The 50#-55# recurve say .330 deflection.  As I recall some translate by dividing that into 31.5 which comes out to 95.45# spine weight.  I usually can bareshaft woodies from 75# to up 85# real nicely.

[Jeremy]

That chart is based on the AMO spine measurement (26" centers and a 2#weight) NOT what they're using now.  A .330 deflection is 78.8#      

The conversion is: 26/deflection = spine weight in #

[Don Stokes]

Divecon, yes, I sent you these same shafts, barrel tapered yellow poplar, which is really a Magnolia, not a true poplar. And yes, I'm at the bottom of the barrel. I have some long ones (33") between 65 and 80#, some light stuff up to 45#, and a few shorter shafts (29") from 95-110#. The fellow who bought my equipment will producing barreled shafts with it, but I'll let him break the news when he's ready.

Snag,that translation isn't right.  A deflection of 330 on my scale, which is the range of .350 to .330, is 75-80#, right with your experience. I love independent confirmation! Look at the self bow numbers and compare to the bow draw weight numbers for the right conversion.

[divecon10]

Don
I am unsure if what I am asking is credible or not. With reg to those shafts. Is there a reason with barrelled shafts that one would leave them long at 33” for the flight character etc? I have cut one down to 29”. I haven’t finished this little experiment yet but to give a little extra grain weight to the one arrow I drilled an put in a nail. So I have yet to compared the lighter 33” to this modified heavier 29”one in flights over shorter and longer distances. I’m waiting for lull in the wet to go for a ride and pick up some concords or blackstumps, made locally down the track from me but am wondering.
 I’m  also wondering if it would be better to have the ones that are made at 29” as they have the fullness of the taper and are heavier anyway? Are the ones u mentioned 95-100# spined, any heavier an arrow, or the spine is the 4” reduction in length what would u perceive the difference to be out of 70+# bows”
Cheers

[Bowferd]

Don, I've been using the 70-75's for most of my bows and they have been working fine. But I'm a bit confused as probably a lot of others with limited experience.
So let me throw a question out here.
I sent you a list of my bows and their wieght range earlier but am beginning to wonder if I may not be properly spined.
Let's use the Strunk selfbow for example.
66" 53@28. My draw length is 28 1/2. The shafts I am currently using are finished at 31" BOP.
So adding 5# per inch would put me in the 65-70 range on your chart. I also would need to add because I'm generally loading the front end with between 200 to 300 gr.
The 70-75's seem to be performing fine but according to the charts I should be showing stiff.
I do not bare shaft my wood arrows because I've broken too many doing that.
Because of front loading, should I actually be ordering a heavier spine?
Fred

[Shaun]

Bowferd - your calculations should be close with the above chart. Self bow about 55# at your draw length, plus 5lb for each inch over 28"bop (3 x 5) plus add for heavier than 125 point (5-10lb for 200-300 tips) and you are in the 75/80lb spine range. If you are like me you may even have a FF string on that self bow - add another 5.

[snag]

Got it...sorry. Just trying to figure it out.

[Don Stokes]

Divecon,if I understand what you're asking, if you cut the 33's down to 29", they will shoot much stiffer. Also, the reason we offered three lengths was to allow archers with different draw lengths to select the one closest to their draw, to keep the barreling as intact as possible. It complicated our production considerably, and I would do it differently now, and only offer one or two lengths. And yes, the higher spined shafts are heavier in weight. For modern longbows and recurves, for a 70# draw you will need something in the 95-110# range, depending on setup.

Jeremy, thanks for that conversion. Remember, this chart is almost twenty years old, and AMO was the standard. It's not exactly AMO, but it's close, and based on our actual test results.

Fred, Shaun is right on. If you don't bare shaft tune, shooting your broadheads will tell you if the spine is right. With field points you can be one or two spine classes off and the feathers will correct the flight so you don't notice it, but the broadheads will tell the tale. If you want to do some testing, I'll hold off on preparing the 70-75's you ordered. I feel sure the 75-80's would work too, especially with some front loading.

I know what you mean about breaking shafts while testing- it works best for me with a very soft target. I use a big soft cube of furniture foam, like the cushions of a sofa are made from. It absorbs the energy of the arrows without breaking them.

[Don Stokes]

One other thing, Divecon. I've found that I can cut up to two inches from each end and still get the barreled performance- you still have seven inches of taper on each end. Any more than that and it's hard to fit a hand-held taper tool to the shaft for point and nock tapers. I shoot 28" arrows, and I sometimes use 31" shafts and cut two inches off the point end when I'm making them for broadheads, to beef up the point end a bit.

[Bowferd]

Don,T
The first 2 dozen I purchased from you a couple of years back I had made a terrible mistake. I ordered the 29" shaft thinking they would be perfect for my 28" draw length.
I didn't take into consideration the amount I'd lose using glue on points.
Prior to this I had been using aluminums and carbon and this was my first attempt at making my own wood arrows.
I forgot to compensate for the loss of length on the front with the point taper.
The 29" shaft ended up being too short. I ended up selling them after they had all been finished.
I corrected the error on my next purchase and ordered the 31" and 33" shafts.
The 31's have worked out great.
The 2 dz 33's are stained and sealed in my rack but I've never finished them.

[Don Stokes]

Fred, when I was selling them for a living, my literature pointed that out. I guess I should mention it on my current list of available shafts. Thanks for reminding me.

[Bowferd]

Don, What do you think for the Quillian Longhunter and the Mosshorn? Both 52#@28.
Should I try the 75-80's? FF on both of them.
The RWH's all perform well with the 70-75's but all 3 of them are 45-49#'s
I always appreciate your input.
Fred

[Don Stokes]

Fred, the 75-80's shoot well in my 55# Bamboo Longhunter with 28 1/4" arrows. Not sure about the Mosshorn, but I'll guess that they'll work for it too.

Keep in mind that you can also tune your bow to your arrows if necessary. For instance, if they're a little weak, you can put on some heavier string silencers, more strands in the string, add a bow quiver, build out the strike plate, etc. You can even shoot a lighter shaft by raising the nocking  point, if everything else is perfect. Dean Torges has an article about doing this sort of thing on his web site, I think.