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FOC calculations...method in question

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FOC calculations...method in question

Old 05-29-2004, 01:07 PM
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Default FOC calculations...method in question

Eastons Tuning guide says to measure from the v in the nock to the insert...not the head. Well it doesn't "say" it but that's what the diagram indicates.

Bow Jackson says to the tip of whatever head you use.

Which is correct and why?
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Old 05-29-2004, 08:19 PM
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Default RE: FOC calculations...method in question

I have just started to look into the FOC for my setup. It only makes sense to me that you measure the entire arrow tip of point to end of nock. This is the entire weight of the arrow. If you exclude the broadhead or field point you will get the FOC of the arrow without a tip and I would never shoot my arrow that way. This is why the FOC can change if you switch from a 100 grain bh to a 125 grain.

Maybe I am missing something but that is the only way the FOC makes any sense to me. Hope this made sense and helped.
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Old 05-29-2004, 08:48 PM
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Default RE: FOC calculations...method in question

I agree with the Easton way.It gives you foc in regard to spine and that is the most important reason for measuring foc,along with arrow flight.


Steel or solid aluminum will not spine the same as carbon or aluminum arrows so why would you add the tip in when trying to get an ARROW foc right in relation to spine and flight.


I do agree that with a mathematical equation that adding the total point length would be correct but this isn't a mathematical equation for mathematical sakes.It is for spine and arrow flight sakes.


Besides,Easton kinda makes up the rules for this don't they.They should know how their arrow performs best and why they reccomend certain foc for different kinds of shooting.
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Old 05-30-2004, 08:03 AM
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Default RE: FOC calculations...method in question

I see the point for spine issues, but I thought most used it for insight into flight characteristics or arrows "Balance" in flight and how it performs downrange?

If it's just spine Ithan I can see that weight would be the only factor and length wouldn't be pertinent.
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Old 05-31-2004, 10:13 AM
  #5  
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Default RE: FOC calculations...method in question

mark the balancing point of the arrow
measure the arrow from the throat of the nock to the end of insert, this is your cut length.
devide the cut length by 2 to get physical center.
mark the center and measure the distance of the balancing point to the center of shaft.
multiply this measurement by 100
then divide that number by the cut length of the arrow
this will give you the foc %

do not try to determine foc% by components because it is very inaccurate method
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Old 05-31-2004, 12:31 PM
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Default RE: FOC calculations...method in question

I agree with Rack Buck for the most part, but one thing that should be clarified on the instructions, you must determine the balance point with your field point or broad head inserted into the arrow shaft. Also, do not measure past the cut point. The length of the arrow you are concerned about is from the groove of your nock to the end of your arrow shaft excluding the field point or broad head length.

The reason you do not care about measuring to the tip of the broad head is that you only care about the Moment Arm (engineering term, Moment = (Force)*(distance)) created by the weight of the broad head or field point at the insert point of the arrow. If you look at all of the broad heads on the market today some are short, some are very long but they come in the standard 75 - 150 grain weights. To remove all of that nonsense from the equations you treat the weight of the broad head as a single point load at the end of the arrow opposite the nock. If you were to hang your broad head from the very end of your arrow using a string, you will get the same balance point as you would when the head is inserted.

Basically do what Rack Buck said, but when you calculate the balance point for your arrow the field point or broad head must be inserted and only measure to the cut point. For instance, without my field point/broad head in place my balance point is 11.6 inches with a FOC of -5.3 %. That does not make any sense. With my field point inserted my balance point is 15.6 inches resulting in an FOC of 10 % which is not too bad for producing level arrow flight.

My whole set up is a Beman ICS Trebark with a 26 inch length (center nock to cut), using 100 grain muzzy broad heads and 4 inch veins. My total arrow weight with broad head is 398 grains. Yes, I know I have a very short draw, I am only 5'7".

Also, I trust and use the Easton FOC and KE program included on their download page.
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Old 05-31-2004, 02:32 PM
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Default RE: FOC calculations...method in question

OH redneck

which rack buck are you talking about?
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Old 05-31-2004, 02:37 PM
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Default RE: FOC calculations...method in question

whunter you must balance the arrow with the point or broadhead on the arrow but the method of getting your FOC% must be done by the method I listed anbove to get a correct FOC%
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Old 05-31-2004, 05:09 PM
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Default RE: FOC calculations...method in question

Sorry about that, I was refering to the post by Big Papa Scout.
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Old 05-31-2004, 05:30 PM
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Default RE: FOC calculations...method in question

Thanks guys for clearing that up for me. It does make sense and I will be checking my FOC now. Sure am glad I checked back.
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