Spine and FOC

[mudSwine]

If you add weight to increase FOC does that change the spine of the arrow ?
   If so does it increase or decrease the spine of the arrow ?

  Thanks

[moebow]

It decreases the effective spine of the arrow.

[George D. Stout]

Adding tip weight requires less force to bend an arrow, so it reduces arrow spine.

[joebuck]

Depends on where you add it.

Weight added to the BH itself will greatly effect spine in proportion

Weight added inside the shaft behind the insert.......very very little effect.

If your current arrow is flying like a dart and you want FOC or Extreme FOC..add weight inside.

Today one can buy BHs from 100 grains to 300+ so adjusting the weight on BH does have a limit.Plus you can add weight with steel BH adpaters if your heads take those.

[mudSwine]

Ok one last question.
  Does any one know or have a chart that can tell you how much it changes it ?
  25gr added to a 30" arrow will decrese the spine by  XX amount.

  I know that's asking a lot.

  Thanks

[Blackstick]

Try Stu Miller's Calculator.

 http://www.heilakka.com/stumiller/

[joebuck]

My testing has been 75grains you start to see.

Heres why I do not agree with the calculator above
....for example the following arrows both have a total weight the same.

2315 with a 125 grain head and 175 grain added behind the insert
2315 with a 300 grain head and no internal weight added

Now take these two arrows and shoot bareshaft at 12yards...........uuuummmmm

the 2315 with 300 gr. head will shoot weaker thus spine is affected more although both arrows have same total weight with weight added up front. But where up front is the important Key here.

So in short, the calculator above just lumps point weight together ( inside and outside the shaft)....however it makes a tremendous difference......
IMO the calculator should not be used. Instead use basic backyard tuning with a bareshaft at short distance.

[George D. Stout]

Adding insert weight works both ways...it adds weight but effectively shortens the working shaft a tad.  Just think while you are doing and you should be okay.  Points is points...inserts is inserts, and they will have separate effects as to how much they affect spine.

[Bill Carlsen]

When I was making wood arrows I would recommend an additional 5# of spine for every 25 grains of additional point weight over 125 grains.

[Kris]

"If your current arrow is flying like a dart and you want FOC or Extreme FOC..add weight inside."
joebuck

Is this what you meant to say?  

Adding weight 'inside' as in a weight tube, will NOT increase your FOC.  Adding weight near the front of your arrow, by whatever means, will.

Kris

[wtpops]

Originally posted by Kris:
"If your current arrow is flying like a dart and you want FOC or Extreme FOC..add weight inside."
joebuck

Is this what you meant to say?  

Adding weight 'inside' as in a weight tube, will NOT increase your FOC.  Adding weight near the front of your arrow, by whatever means, will.

Kris

I beleve he is talking about adding weight to the back of the incert. Adding a weight tube  will not in most cases increase FOC

[joebuck]

I never said "Tubes"......don't like em...i add my weight behind the insert....Alaskan Bowhunting Supply (Screw in Brass) weights are great.

Kris's comment is my whole point.. you can add weight to the point or to the inside of the shaft at the insert to achieve FOC........but be careful where you add it because it could throw your spine out if to much is added to the point ( outside the insert and shaft)

[artifaker1]

Thanks George Stout, you just explained what I haven't been able to figure out on my own.
Heck I have close to three inches of weight in the front of some of my heavier arrows. I was amazed when I caned my weight tubes and put the same weight up front and the arrow still worked in the same bow. With maybe just a tad less spine than it had. Not enough to shorten for though. But the shaft being that much shorter effectively would explain a lot. That will be cookin for a day or two.

[xtrema312]

I use the calculator, but if I have a long brass insert or shaft ID size weight behind it I reduce the effective shaft length by the extra length of what I have in the end.  I get real close on spine with that change.  I still work down to what the calculator says to see for sure.