Beginner question about spine and length for flatbows.

chuck

New member
I'll probably end up answering my own question, and I have read up as much as possible. I'd really just like some one to confirm my thoughts before spending any more on shafts.

I've recently started making my own woodies for my flat bow, it's 45#, so the shafts I purchased and built were rated for 50-55. They shoot straighter than a laser when I leave them at full length, however, when I chop them down so they only stick out an inch longer than the front of my bow, they have a funky flight pattern. They kick out to the side before coming back in straight.

Am I right in thinking I need to purchase a lighter spine? Will I be at a huge disadvantage if I just leave my arrows long? (They stick at least 4 inches past the front of my bow)

Thanks in advance for your help.
 

lbp121

Member
Unless you are a target archer with a clicker, there is no disadvantage with over length arrows except weight and therefore cast. This will effect the maximum distances you can achieve. A good method of tuning is to gradually alter length which in turn alters apparent stiffness.

You could think in terms of roughly an inch of arrow is worth about 5lb bow weight. Any reason why you ended up with 55lb rated shafts? As a flat bow is less efficient than a recurve I would have thought you were more likely to order shafts spined lower than bow weight if the actual correct spined ones are a little stiff. (by the way, if the full length shafts fly as straight as a laser, I suggest you get a better laser!)
 

chuck

New member
I had read that with flatbows its best start with a spine 5# heavier than the bow, however I think the amount I've cut off has changed the spine to be too high for the bow. I had just presumed that the spine rating was at a 26" shaft length so chopping off a few inches wouldn't matter.

I'll look around for a site that sells shafts in quantities less than a dozen and give them a try.

And I find that my laser, much like myself, is starting to get a bit droopy. :)
 

lbp121

Member
If you think about a broom handle, it is quite bendy but if you cut it in half each half is very rigid. This is the same as arrow length. Small changes can be made by adding weight to the front or back but all these things only change the dynamic spine, or how the arrow behaves when hit with the force of the string. Static spine, which is the way they are sold, is purely a system to indicate how some shafts are stiffer or weaker than others.
Cutting 3 inches from the arrow shaft would make them suit a bow up to 15 lb heavier than before or maybe 65lb bow.
 

lbp121

Member
As far as I'm aware the measurement is taken on a 29 inch shaft with supports at 28 inches apart. A 1.94lb weight is hung from the centre and the deflection noted. This figure is translated in charts to suit certain bow types. As I say it is purely a comparison system. If you can get a bunch of shafts to match then you can set the bow to shoot them
 

chuck

New member
A bunch of shafts is basically what I've got. I found 30 shafts cheaply on eBay, all 50-55 spine, and then matched them by weight into sets of 6. Like I say, they fly well at 32 inches, even during bare shaft tuning. Its only when I trim them to length.

You say I can set up my bow to shoot them? How do I got about that?

- - - Updated - - -

Also, my bows shelf is cut to centre, if that matters.
 

lbp121

Member
Setting up a basic bow involves twisting string to alter length (brace height) perhaps using more or less strands to speed up or slow down the bow, trying to alter height of nocking point to give best grouping and getting the arrow spine to match these other areas so the arrows fly true and quietly.
I haven't done this personally but if you were able to rotate shafts in a drill and sand down the diameter, you would weaken the shafts. Archery shop would probably have alternative spine shafts to try.
 
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