Spine matching arrows to my new bow.

[jitsuka]

Hi everyone

Just got a new bow. One piece wooden recurve with arrow shelf and cut away making it nearly to centre shot. Its a 40# bow so I made up some arrows with spines from 38 to 45. They all fishtailed.

Its a slightly different style to my last bow. I'm holding the grip rather than doing the Olympic style open hand thing. I think I made things a little better by changing how I was gripping the bow but I'd have thought if I was torquing on release I'd sent it off target but not make it fishtail.

I also thought I got them to fly a little straighter if I made sure I was really pulling to my absolute fullest draw, but even with that they all still fishtailed.

They ended up to the left and the 38s seemed to be the best. Now I think that means I need to drop the spine a bit but I thought that centreshot style bows would need stiffer arrows not bendy ones so I am wondering if I am doing something wrong.

The arrows are 5/16 or 11/32 with 100grain points. 29.5 inches long measured from tip of nock to tip of point.

Any thoughts all welcome.

[Del the Cat]

Your thoughts seem fine to me. However I'd say the variation from 38 to 45 is a bit small to show much difference. Get some arrows a bit more Extreme and the effects may show up better...maybe try a 30lb spine and a 60 ! It will help to convince you which way you need to go.
Sometimes all the theory in the world is no help, but a quick test can show a lot.
Have you watched anyone else shoot it?
Good luck
Del

[jaselpool]

Hi - what's your draw length? Is the bow marked 40lb @ 28"?

Jason

[steve58]

Is this any help?

Bowhunting With Wood Arrows

Or this?

http://domino.htcomp.net/bhn/Columni...f?OpenDocument

[nutterforlongbows]

Hi, Give Richard a call, he helped me allot in choosing my shafts, `Richard Head Longbows` 01225 790452 or just google his site

[soundo26]

Hi;

I had a thought when reading your post! Not sure how experienced you are so forgive me if I'm teaching grandma to suck eggs here but I believe you are trying wooden arrows, have you checked the direction of the woodgrain of your arrows before fletching for your spine tests? If this is not done and the index fletching not stuck with the grain at 90 degrees to the string, you will get different results from arrow to arrow! You probably already know this, if so just ignore this reply!

[Del the Cat]

Originally Posted by soundo26

Hi;

have you checked the direction of the woodgrain of your arrows before fletching for your spine tests? If this is not done and the index fletching not stuck with the grain at 90 degrees to the string,

Great point, it's easy to forget that in this era of glue on nocks, (a self nock obviously needs to be the right way to the grain).
Or to put it another way...whoops I'd forgotten that...just as well I'm not a good enough shot to notice the difference
Del

[robtattoo]

From experience, I'd say you were way too weak on your spine. Weak enough that you're getting a 'false' reading.
The formula I've always used (& it's about 99% right) is to take the draw weight of the bow (40#) add 5# for every inch over 28 (+7.5#) add 5# for a centre cut bow, add 5+ for a fast fight string & finally add 5# if you're using a point over 125 gn. so for you, I'd suggest an 29.5" arrow of 60/65# spine as a starting point. I'd bet you all my bows that this is about right! (I'm assuming you're using a FF string)

Centre-cut bows will need a far stiffer arrow than you'd think! As an example, my Morrison Recurve is drawing 63# at my 30" draw. I'm shooting a 32" arrow with 160gn points & 4x4" fletches. My arrows are spined at 92#!

[Dreadnaught]

To follow on Soundo26's point, I have often found that even if the cock feather is on at 90 degrees to the grain the arrow can have a very different spine if rotated 180 degrees. In other words check spine both sides of 90 degrees from the grain before putting on the cock feather.
Good luck
Dreadnaught

[Igor]

Originally Posted by robtattoo

take the draw weight of the bow (40#) add 5# for every inch over 28 (+7.5#) add 5# for a centre cut bow, add 5+ for a fast fight string & finally add 5# if you're using a point over 125 gn.

Hi Rob, when you say 'for every inch over 28', do you mean draw length or arrow length? And does it work the other way round - do you need to subtract if under 28"?

I will soon have a flatbow which will be 38# at my draw length of 26" (this is the AMO 'true draw length' - from nock groove to pivot point, i.e. inside of the grip.) The arrow length will be 1.5-2" longer, so you could say 28".

Bearing in mind it's a flatbow, so almost centre-cut, and the string is 8125, what would your formula suggest? I make it 48# spine (?).. And since shafts are sold in spine bands, does that mean trying the 45-50lb band?

The bowyer suggested 45# spine arrows (but again - which band?) and 75gn points...

Thanks for any advice!
Igor

[robtattoo]

Hi Igor, to clarify (sorry!) you should take the draw-weight at your drawlength & add 5# for every inch over 28" of arrow length.
Yes, it also works the other way around. If you're shooting a 26" arrow (for example) you'd take your bow weight & subtract 10#, then add or subtract for all the other variables.

'True' drawlength is a bit of a misnomer & plays very little part in bow/arrow tuning. The length you need to know is from the string to the back of the bow. I'd guess tht this will be about 27" in your case. You'll probably be drawing around 41# at 27" If you wat to shoot 75gn points on a 28" arrow, would suggest starting with a 40/45 spine. You may need to up your point weight to 100 or 125 gn, or leave yourarrows a little longer (I'd suggest starting at 30" and cutting them down if they show weak)
Having 3 or 4" of arrow hanging out the front is no detriment at all, if it means they spine correctly. Try not to get too hung up on arrow length & you'll be fine!

[Igor]

Hi Rob, many thanks for your reply. A curse upon all the confusing ways of measuring draw length and arrow length! I don't mean this to become yet another discussion about it, but this AMO standard (pdf) is what the bowyer asked me to refer to when quoting my measurements (see bottom of p.9). 26" is exactly my distance between nock and back of bow. In any case, I should actually be holding 38# on my fingers - that's what I asked for - although I am going to re-measure it with bow scales to know exactly, and I'm going to experiment with different anchor points which can add a bit to the draw length. My arrow length needs to be about 28" just to be safe, but I hear you about it not having to be that length.

So for 38# on fingers, does your advice still stand - 40-45# spine band? Because according to your formula, for let's say a 28" arrow, I think we're looking at 38 + 5 (centre cut bow) + 5 (fast string, 8125) = 48# spine... I'm just worried about getting 40-45# shafts, finding they are too weak already and being stuck with them!

I'm sure I'm over-thinking this, but money is money and I'd rather try and guess it right before getting the shafts!

Thanks again,
Igor

[robtattoo]

Hey Igor.
Just to be safe, go with a 45/50# shaft. Leave it full length to start with & use a 125gn point. If this is too weak, try a lighter point. If it's still too weak, start shortening the shaft 1/4" at a time. To be honest though, I think that you'll be somewhere around the right area. Unless you want to start bareshaft tuning for perfect flight (CHECK THIS OUT) you'll be pretty good to go from a 45/50.

[steve58]

Originally Posted by robtattoo

Hey Igor.
Just to be safe, go with a 45/50# shaft. Leave it full length to start with & use a 125gn point. If this is too weak, try a lighter point. If it's still too weak, start shortening the shaft 1/4" at a time. To be honest though, I think that you'll be somewhere around the right area. Unless you want to start bareshaft tuning for perfect flight (CHECK THIS OUT) you'll be pretty good to go from a 45/50.

That's a good link Rob, cheers