Arrow spine

[babbott]

When you are choosing arrows to shoot from your warbow, how does the spine number correspond to the bow weight?  For modern bows, this is a 1-to-one, a 75 lb. @ 28" bow gets arrows spined at 75lbs.  Now, as I see it, there are two factors at odds with that when talking about a warbow.  Firstly, we are drawing our arrows more than 28".  If an arrow is spined to be stiff enough for 28", if you leave it 32", shouldn't it now be too whippy?  Imagine the arrow was 48" long, it would bend like crazy when shot!  Secondly, the archer's paradox has to work harder on a warbow, because the grip is wider than a modern recurve where the arrow passes.  This would mean that the arrow needs to be spined lighter to curve around the extra bow width.  So how do you reconcile these two opposing factors?  Let's say that you have a warbow, and for the sake of the math, let's just say that it draws 100# at 32".  You get on the phone with someone that sells arrowshafts.  He says to you, "what spine arrows would you care to buy?"  What is your reply?  100#, 110#, 90#?
Thanks,
-Ben

[JackCrafty]

Not long ago I had trouble understanding spine.....and how to read the charts.
I found that I had not done enough reading and research (on this forum and other places).  I also didn't realise that there are two different types of spine (actual and effective or static and dynamic).

So, when the arrow shaft salesman asks, "What shafts do you want to buy?"...you ask,"What shafts are good for 100# @ 32" draw?"  If he can't answer your question (and back it up with a guarantee) then go elsewhere.   

(Ask the question regardless of your knowledge level.  If you already know the answer, then you're just double checking.  )

[SimonUK]

I think you're right about the arrow behaving more 'whippy' when you have a longer drawlength.

Once your 32 inch arrow has travelled 4 inches forward, it's like loosing a 32 inch arrow from a 28 inch draw.  That extra 4 inches poking out in front gives it a lower dynamic spine.

Some guys in the UK keep it fairly simple:  For draw weights of up to 100 lbs, use a 3/8 inch shaft (of e.g. ash) and above that use 1/2 inch shafts.  I'm not experienced enough to know if this provides sufficient accuracy.

[Rod]

The problem is that spine testers are not always made to go that high.
What you need is a shaft that will stand in the bow and as with any bow, a shaft that is a little too stiff is far and away preferable over a shaft that is too weak.
One, because it will not break or fishtail and two, that it will shoot to the side that you can see.

The basic rule of thumb principle for measuring spine is that with a bow that is not too wide at the pass you can take the draw weight and add 5 lb for every inch of shaft over 28", and add 5 lb for 100gn of point weight over 50gn.
If the bow is particularly wide you might deduct 5 lb for the additional offset.
If you go up in shaft diameter, likewise.

If you have a shaft that shoots well for you, you can always record it's deflection under a given weight and use this as a means of comparison.
Or learn to assess the shaft by feel.

Rod.

[grantmac]

You can always use a 4lb weight in your spine tester and divide the deflection by 2 to get the true spine. At the other end of the scale you can use a 1lb weight for kids arrows and multiply the answer by two.
           Cheers,
                  Grant