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Thread: Binary cam tuning simplified.

  1. #1
    Join Date
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    Bargain Bin Binary cam tuning simplified.

    Syncing cams, setting drawlength, setting letoff and determing exact point of rollover to deliver most mechanical advantage (reflected as speed).

    There's way more to this than you realize. As you add twists to a cable you add more degrees of rotation, thus more draw length. This has to be corrected with the string and the limb pre-load (A to A) can't change as that would increase or decrease draw weight. Of course if you increase draw weight or poundage you will gain speed. We're looking for the perfect sweet spot in the cam. I talked with Michael last night and he spent 8 1/2 hours doing this to his personal bow. With the right tools this time can be greatly decreased. This is why I personally recommend the E.L.P. press designed by Larry Asford who is a PSE Pro Staffer. It has a built in timing machine (vertical drawboard). This is a tremendous help, to be able to use the same machine to press my bow and adjust strings and cables and checking drawlength and synching cams and setting the drawstop. I don't pay any attention to the numbers on the scale on the adjustable drawstop as once the cams are properly synched and the bow is timed for optimum rollover then I simply use a digital scale to determine draw stop setting if I'm looking for less than 80% letoff or a direct measurement if I'm looking for maximum letoff which may not always be exactly 80%. It may be 77% or 78% or whatever. It is the setting which yields the highest letoff and longest valley. Now that I've said all that, do you know how or more importantly do you have the tools. You'll need a press, drawboard of some sort, chrono & digital scale as a minimum to do this right.
    Last edited by Bellows1; January 28th, 2008 at 09:16 PM.
    Matthew 6 : 14 & 15 For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins.
    If God is your Co-Pilot, move over and let Him drive!
    Murphy's Law works even better in the woods!!!
    VaporTrail Pro Staff - Strings, Cables, LimbDriver & Vapor Shield

  2. #2
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    --------------------------------------------------------------------------------

    I'm more than a little amused that BowTech says you can set up one of these bows by simply showing a certain number of dots outside the limb face. Let me endeavor to explain a few things. First the cams on these bows are indeed mirror images of one another but you don't draw from the true center of the string. That alone will negate the idea of tuning perfectly by utilizing the dots. The problem doesn't stop here however as the limbs are graded by deflection numbers. In simple terms their strength or resistance to bending. There are plus or minus specs as regards these limbs, just as there are for A to A and brace height. Now this is getting more complicated. What do you think the chances are of you getting two perfectly matched limbs on your bow? Do you have any idea what the quality control costs would be in perfectly matching limbs? You wouldn't pay it. Now let's look at the bow. One of several things is true. The upper limb is on the plus side of the spec and the lower is on the minus or possibly the reverse of this scenario. Then again maybe both limbs are on the positive side but not perfectly matched or maybe they're both on the neagtive side and not matched. All of these are possibilities. Have you wondered why in looking at the birth certificate of a 70# bow some may be right at 70# and some as high as 71.5# or so. Think about this . If you insist on setting each of these bows up at the same A to A the differences in strengths of the limbs causes these differences in peak draw weight. How many of you have really thought about that before? Now to synching the cams. The cams are in sync when the draw stops on the modules of each cam contact the cables at the same time at full draw. If one draw stop makes contact before the other it begins to bend that cable back toward you until the other finally hits the cable. This in effect shortens the cable which had first contact. This will shorten your valley when the bow is at maximum letoff and reduce the maximum letoff which can be achieved. Your not through yet. To achieve maximum letoff you must set the adjustable drawstop so that it hits the limb face with about a 1/16 inch gap between the draw stops on the modules and the cables. Why? It's simple, observe the adjustable drawstop, you will see that it is covered by a piece of heat shrink tubing with a bulge in the middle. This bulge is caused by an O ring. When you draw hard into the wall this O ring is compressed. If you set the adjustable draw stop up in a way that allows the draw stops on the modules to make contact when the adjustable drawstop first touches the limb you will distort the cables back toward you as the cam rolls over further as you compress the O-ring. When you do this you shorten your valley and reduce your letoff. Now finding the perfect point of rollover on your cam involves making adjustments in the exact point of rollover to get the greatest speed without changing draw weight or draw length. This is done with the help of a chrono, which is the sole judge of your results. When you find this perfect point of rollover, I like to scribe my cams on each side of the limb with a machinists scribe for future reference. Now for the fun part. Yor reference point here is the limb face. Should you somehow have a limb failure and replace one or both limbs with limbs which aren't absolutely identical to the ones removed, your reference points are no longer valid and you will have to rediscover the perfect point of rollover. Take heart though in the fact that it won't be to far away from the original marks you made. It just won't be in the same place.

    That's as far as I'm going in this post. Tuning the bow for center shot and tuning a LimbDriver are another subject for another day.
    Dave Nowlin
    Last edited by Bellows1; January 28th, 2008 at 09:19 PM.
    Matthew 6 : 14 & 15 For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins.
    If God is your Co-Pilot, move over and let Him drive!
    Murphy's Law works even better in the woods!!!
    VaporTrail Pro Staff - Strings, Cables, LimbDriver & Vapor Shield

  3. #3
    Join Date
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    Savannah, Tn
    Posts
    2,718
    Just in case I need it. B1
    Last edited by Bellows1; January 28th, 2008 at 09:26 PM.
    Matthew 6 : 14 & 15 For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins.
    If God is your Co-Pilot, move over and let Him drive!
    Murphy's Law works even better in the woods!!!
    VaporTrail Pro Staff - Strings, Cables, LimbDriver & Vapor Shield

  4. #4
    Join Date
    May 2003
    Location
    Savannah, Tn
    Posts
    2,718
    See above.
    Last edited by Bellows1; January 28th, 2008 at 09:27 PM.
    Matthew 6 : 14 & 15 For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins.
    If God is your Co-Pilot, move over and let Him drive!
    Murphy's Law works even better in the woods!!!
    VaporTrail Pro Staff - Strings, Cables, LimbDriver & Vapor Shield

  5. #5
    Dave has offered his considerable expertise on this subject, if there are any questions, please post them at this link.

    http://www.archerytalk.com/vb/showth...32#post6168932



    Thank you, Bill.
    Last edited by Bellows1; January 28th, 2008 at 09:46 PM.


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