What's The Formula For Matching Bow Poundage to Arrow Spine?

[erron]

I know I asked this somewhere a while back, and promptly lost the formula. Can anyone please supply it? It went comething along the lines of adding 5 lb. for FastFlight etc.

thanks,



Erron

[ozlongbow]

I'd be interested to hear it too - c'mon guys!
Lindsay

[erron]

Okay, dug around a little, and as far as I can make out this is how it goes:

1) start at zero
2) add your bow weight
3) for every inch your drawlength exceeds 28, add 5 pound
4) for every inch your drawlength is under 28, subtract 5 pound
5) add 5 pound for a broadhead
6) add 15 pound for fastflight strings (are other strings in this high performance category?)
7) add 5 pound for high performance bows

for example, the woodies I’m shooting out of Jeff’s 44 pound longbow are only 50 pound spine, and aren’t great results wise. I was given a carbon to try, which rates 65 pound on my spine meter. Better flight characteristics of carbon notwithstanding, the carbon is far more accurate than the woodies. It seems I have to make some higher spined arrows,as the following formula appiles here:

bow: 44 lb
drawlength 29 inches?, add 5 pound: 49 lb
add 15 pound for fastflight string: 64 lb.
add 5 pound for high performance bows (not sure about this, Jeff?): 69 lb.

So, the carbon should outshoot the woodies anyway based on the fact the spine is in the correct range of 64-69 lb.

Any thoughts, anyone?

Erron

[Stickbow Hunter]

Erron,

The very first thing you must realize no matter what bow you are shooting is that you should shoot an arrow that flies perfect for you. This means it is matched to your bow and shooting style. It doesn't matter that someone else can't get them to fly good out of a similar bow, only that they fly perfect for you.

Once you find that arrow, spine it, and then match any others to it. Changing the arrow shaft material, shaft diameter, broadhead weight and so on can all effect arrow flight as these things change the dynamic spine of the arrow (refer to a thread called Concorde broadheads I think) where this is discussed.

To get a rough guesstimate of where to start to find the correct spine you can apply the criteria you listed in your post. The first four I agree with but not necessarily the others. Number 5 will apply if the broadhead is heavier than the 125 grains (standard) or reverse if the broadhead is lighter. Number 6 I would think 10lb would be enough for a starting point. Number 7, well I think most modern laminated bows are not that much apart and I don't think you would need to worry about it.

As I said this will only give you a gesstimate and I would order a few different spine shafts under and over your gesstimate and shoot them all a number of times and see which spine group flies the best.

Knowing that bow of yours Erron and roughly how you shoot (not saying you shoot roughly ), I would suggest a starting spine of about 55 - 60 lbs.

Jeff

[erron]

Thanks for that Jeff, i was coimg around to that sort of poundage as a starting point too!

Erron

[Dennis La Varenne]

Erron,

Could I also suggest that after a time of shooting a batch of arrows, you re-spine them.

Wood seems to suffer from a kind of elastic failure from repeated violent bending such as with paradoxing. You may find that with repeated shooting, their spine decreases even though their weight does not. I had this happen to me fairly often when I did a great deal of practice in my target shooting days.

The resilience of individual arrows will vary with quality of course. The spine meters are only a guide. Both Jeff and I use considerably overspined arrows and never really had a problem with arrow flight, even at close range that I can recall.

We think that canting makes a longbow very tolerant. My cant is only marginal - less than 10 degrees, but I have no problems. Jeff's is far greater and neither does he.

We both have trouble understanding the problems everyone else seems to have. My only problem seems to come from arrows spined 5 lbs or more under spine.

Dennis La Varenne

[woody]

Archery Action magazine had a work shop project many years back on how to build a spine jig, and this came with a sort of slide rule calculator.
When you measured the deflection rating of the shaft, you factored in arrow length and point weight, and then used the calculator to see if it was right for your bow weight.
Maybe this article could be reprinted or someone may have an old copy or back issue. Does any one have this article, because it was an excellent project and well worth revisiting.
My rule of thumb was to always start 5 or 10 lbs on the heavy side and experiment from there.

[erron]

Woody, I think I made my jig from those plans, which someone sent me. If they okay it, I could dig them out and copy them for anyone who'se interested, or even scan them and post them on the site. Not sure of the legalities etc....

Dennis, thanks for the tip, I'll respine some of the ones I've thrashed, although I tend to kill or lose them befoe they get to a decent age

cheers,

Erron

[Preston]

Woody, I think I made my jig from those plans, which someone sent me. If they okay it, I could dig them out and copy them for anyone who'se interested, or even scan them and post them on the site. Not sure of the legalities etc....

Dennis, thanks for the tip, I'll respine some of the ones I've thrashed, although I tend to kill or lose them befoe they get to a decent age

cheers,

Erron

Hello Erron, I would love to read the article.....

[perry]

Like others have said a great many variables rough rule of thumb start around 15 pound over. I think it's a good idea to Bareshaft Tune from there, if the Arrows stiff lightly Sand the last 1/3 to half of the Shaft to Taper it slighly until it flys showing very slight underspine, Fletch it and it will be fine. You can also use different String Materials, more or less strands etc to change the Spine you require. Obviously if it's underspine from the Start, make / buy a stiffer shaft , use a lighter point, use a heavier String etc .Then put it aside or record it's Spine degree of Taper etc so you always have a Reference.

I do wonder if Modern Archers are to clever by half though. It's a modern thing to cut your Arrows short. The shorter an Arrow is the more finicky Spine gets, leave them long and Spine is less finicky - look to the past for Answers and ask yourself why so many Archery Cultures around the World used too long by Western standards Arrows.

regards Jacko