"FOC"...Front of Center

Discussion in 'General Archery Forum' started by Pinky, Jun 13, 2004.

  1. Pinky

    Pinky Senior Member

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    Quote Chris:

    FOC stands for Front of Center. It's the a measurement that shows at what point your arrow balances. You can find the balance point easily, just use a pencil and try to figure out at what point your arrow balances. You want your FOC between roughly 7-15%. Some documents even say for broadheads you want to be 11% or more.

    Find the exact center of the arrow measured in inches and mark with a pencil. Then find the balance point of the arrow. Take the difference of the balance point from the center point and divide by the total length. This will give you the percentage.

    Lets say the arrow is 30" in length (including the tip or broadhead and to the throat of the nock). The center is then 15" but it balances 3" closer to the tip than the center of the arrow. The FOC is 3/30 or 10%.

    End Quote.

    I have tested my arrows and here are the results. Please feel free to give advice here.

    My hunting arrows are Easton Kinetic A / C 340's with four 3 inch feathers. They measured 30.8125 inches from the throat of the nock to the point of the 100 gr. Steel Force broadhead. They balanced 2.625 inches forward of the the centerline. If my calculations are correct, the FOC is 8.5%. (2.635 / 30.8125 = .085)

    My target arrows are Gold Tip Pro X-Cutters with three 4 inch feathers. They measured 30.875 inches from the throat of the nock to the point of the 85 gr. field point. They balanced 3.5 inches forward of the centerline. Using the same formula, the FOC is 11.3%.

    If I add the new Quick spin vanes to my hunting shafts, weight will be moved back. Where do I go from here?

    THX in advance for any tech help.
     
  2. Chris

    Chris Administrator Staff Member

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    The FOC on the target shafts if fine. I would have to look up the actual weight differences of the quikspins but my guess it that you would be ok to change them.

    The hunting shafts are little light on the FOC. I would be real curious to see how they would balance with 125gr heads. The 340 is a pretty stiff shaft. You must be pulling about 65# or more with a 29" or more draw length? By the way, what bow and cam are you shooting?
     

  3. Pinky

    Pinky Senior Member

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    Here's the bow specs of my hunting rig Chris.

    My hunting rig is a 2003 model Bow Tech Patriot with the single cam. The module has "DS2" embossed on it. Draw weight is 57# and my draw length is 29.5 inches.

    I picked up the 340's at a steal. I was warned that they might be "over spined". But a dozen of them for $20 was too good to pass up. Thus, I cut them long in hope of overcoming the stiffness. The arrows launch at 238 fps on the rig with the 100 gr. broadheads. They bury in deep on my 3-D targets. They fly well too. But, my tests have been at 20 yards. 30 yards is "way out" for hunting for me. My preferred hunting shot range is 15 - 25 yards.

    My questions arise from the fact that I want to switch over to the quikspin vanes for hunting this year. From what I have been told, and have read, the better you can spin a broadhead the better the arrow flight will be. The rumor is that the quikspins make it happen. This is the first time in many years that I have attempted to maximize my hunting rig. I still have plenty of time to make it go before the season opens.

    Feathers are feathers. They get wet. And, add to that, the whisker biscuit seems to fatigue the feathers after repeated shots. This is my first year using the biscuit. The rest is awesome in my opinion. The biscuit should be the rest of choice for youth and newbies. My plan is to give it a thorough work out this season. I am thinking that vanes will be the way to go with the biscuit.

    I would have no problems switching over to a 125 gr. broadhead. My oldest son, 12, will most likely hunt deer this year with me. The 100 gr. broadheads will fit nicely into his rig. I am not a "speed freak" at all. I will sacrifice speed for accuracy any day of the week for hunting.

    Any help would be appreciated here.
     
  4. Chris

    Chris Administrator Staff Member

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    From the specs you provided, the arrows are WAY too stiff. Even when I switch down to the 400 size, these are even stiff for your setup. You mentioned accuracy over speed. I would really consider getting arrows that are spined to match your bow setup.

    Now, some bows like a stiff arrow so you may have no trouble with it. Just don't be surprised if you struggle to get them to fly well or group well.

    If you really want to try these arrows, I would put the 125 grain heads on and the quik spins. Adding both will soften the spine a little. Go out and see how they fly.

    With the Whisker Biscuit, just make sure you put the quik spins on straight or with a very slight right offset.
     
  5. bow-regard

    bow-regard Member

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    When measuring FOC do you include the length of the broadhead or just measure the shaft?
     
  6. ptcruz421

    ptcruz421 Member

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    You definitely measure from the tip of the broadhead to the throat of the nock.
     
  7. Pinky

    Pinky Senior Member

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    THX Chris for the info on the hunting rig. I am gonna do a thorough test on the 340's with the 100 gr. broadheads. I'll post my results soon. I have decided to stick with the four 3 inch feathers for the test. Like I said, this is a new set up that I have only tested with target points.

    One more thing.........

    When test shooting broadheads, I shoot each arrow at a different spot. Then observe the hit of each arrow and get a gouping from that. I usually only fire 3 arrows, then pull and repeat that 3 times at each distance. I do this at 10, 20, and 30 yards.

    Is this a decent way of measuring a group?

    THX in advance.
     
  8. Chris

    Chris Administrator Staff Member

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    That's not a bad way to test. I prefer to get my field points and broadheads to group very close to each other. I can usually get them within 1/2".
    When I can do this, I only need to shoot my broadheads to know they are flying good a couple of times. After that I just shoot the field points.

    If you have broadheads with practice blades you can group test at 30 yards usually without worrying. More times than I care to admit, I have shot multiple arrows at them same spot. I then walk to the target to find shaved vanes on the ground and blades stuck inside of other blades. It's not pretty.

    The method you are using is a good method and will preserve your arrows. Just keep track of where each arrow is hitting. Just make sure you mix them up so you are not shooting the same arrow at the same spot all the time.
     
  9. Chris

    Chris Administrator Staff Member

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    I was told today that Eastons tuning guide suggests you only measure from the throat of the nock to the end of the shaft (do not include point or broadhead).

    So I called them. Their response, "we feel this gives a more accurate result". I asked, then why measure from the throat of the nock and not the end of the shaft. "This is just the way we have always done it and this is where the arrow starts". :confused:

    I'm not sure I agree with their methods but I just thought I would pass on the information.

    In the FOC calculation, it just seems odd to me that you take into account the weight of the point but you ignore the fact that total length of the arrow could be increased by an inch or more.
     
  10. Pinky

    Pinky Senior Member

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    Man....THX Chris.....you went the extra mile with the phone call.

    I can understand Easton's thinking in a way. From their engineer's point of view, it is important to eliminate variables. With the wide array of points available, it is probable that the most accurate and generic test results would arise from data collected without regard of point length. Thus, a baseline recommendation can be offered.

    I agree that the addition of a point/broadhead increases the OAL (over all length) of the arrow. Maybe the OAL, created by the addition of a point, is not as important to the arrow's properties as is the FOC based on point weight versus point length.

    Pretty cool.......

    THX Again
     
  11. jcmorgan31

    jcmorgan31 Prodigal Son

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    I think FOC is overated. Just pick a cool looking arrow, slap some vanes and a point in it and have at it.....:peace:
     
  12. BUNNYMAN

    BUNNYMAN I pray for you!

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    old thread again....your not very good at this......

    hope your deer heads come out better than your attempt at fooling us.....:noidea:
     
  13. poorman

    poorman And thats no lie !

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    In this case FOC stands for


    Full



    Of



    Chit
     
  14. jcmorgan31

    jcmorgan31 Prodigal Son

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    I'm not trying to fool anyone. This was a very informative thread. :noidea:
     
  15. BUNNYMAN

    BUNNYMAN I pray for you!

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    very informative yes, your intention.......NO:biggrin1:
     
  16. Ronhop

    Ronhop RIP

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    What's with the digging up of old posts ???
    I don't get it... :bowl:
    Can't anyone come up with new material ? :noidea:

    Ron
     
  17. BUNNYMAN

    BUNNYMAN I pray for you!

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    bored???:noidea:
     
  18. Foc

    To find the correct Front of Center you measure the arrow from the bottom of the nock groove to the end of the shaft( NOT THE END OF THE POINT) and divide by two(2). Put a mark there. Find the balance point by balancing it on a pen or pencil. Put a mark there. Divede the distance between the two(2) marks by the length of the shaft. Example; 3.125 divided by 28.5=
    .1096491 move decimal point two(2) spaces to the right and you have 10.96491 %. If you include the point in your measurement your length will change when you go from a field point to a broadhead but you will change the actual FOC by VERY little like .1 percent but your numbers will be better with the longer point. The way Easton says to do it is correct.