Tuning the Tac 15

Discussion in 'PSE TAC 15/15i Crossbow Hunting Forum' started by ablebakercharlie, Jul 26, 2011.

  1. ablebakercharlie

    ablebakercharlie New Member

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    Mar 16, 2011
    Had a limb split on the TAC after about 700 shots. PSE sent new limbs to my local (nearest) authorized repair shop and they replaced all 4 limbs, string (tune-up kit), and 4 arrows that had eaten the nock... no charge. Very pleased with their response.
    Problem is, it's tricky for a bow novice (like me) to tune and tweak this instrument back to the consistent accuracy I had before. I finally got it set, but to paraphrase Thomas Edison, "I found a thousand ways not to make a light bulb." Setting the D loop and whisker biscuit is tedious, but do-able if you have enough patience and paper. My main difficulty was with the cam alignment. The repair tech had said that the cams should be in line and level with the string. He did a few twists at the cam axles and tested it indoors at 20yds. So far, so good. But when I got it home and stretched out to 50yds I was shooting 4 inch groups instead of the "same hole" accuracy I used to get. Looking carefully at the bow I noticed the double limbs were not being compressed equally and the cam lines were about a strings width off. String/cam clearance was reaching minimum tolerance as well. I felt like isometrics were more crucial than perfectly level cams, so I undid the twists at the cam axles and got the cam marks spot on with the string. Now the cams both tilt slightly down toward the sled rail. It worked for me.
    For the first time in 2 months I'm shooting same hole again. Although I'm sure that will change when I shoot my first broadhead... hope this isn't anotherlightbulb
     
  2. Buzzard Bait

    Buzzard Bait Well-Known Member

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    Jul 25, 2010
    ablebakercharlie.......21 threads below is the thread Tac 15/15i Basic Unpublished Information.......a great source of info on tuning your Tac.
     

  3. OkieBowie

    OkieBowie Well-Known Member

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    Aug 28, 2010
    I am throwing this out there, only if you run into more trouble tuning your TAC-15, and your down to pulling out your hair (exhausted all other possibilities).
    There is the remote possibility one of the replacement limbs is different (stronger/weaker) than the others. I have seen serious tuning problems on a non-Xbow because it had mis-matched parallel limbs.

    If you are really into bow tuning of non-Xbows, then you have worked with something called a "Drawboard". However, a standard "Drawboard" is meant to show vertical knock point variations towards the wheels/cams (limb tips) as the bow is drawn and released. Unfortunately, a parallel-limb bow can also have horizontal knock point variations left or right when the limbs are not matched. I would liken it to having a bent cam/wheel that leans left/right at rest, but leans right/left at draw.
     
  4. ablebakercharlie

    ablebakercharlie New Member

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    Mar 16, 2011
    Thanks for the insight. I have a new cable replacement kit handy and, after reading your reply, decided to compare the 2 new cam strings with each other. They are slightly different lengths! That means unequal kinetic energy will be stored left/right limbs when drawn. The bow is shooting great now at short range w/field points, but longer ranges (especially w/broadheads) could really amplify an un-equal left/right release force. I'll also check the cams more closely for synchronization.
    Anyway, thanks again, 4-10 over & under - charlie out.
     
  5. jon.henry755

    jon.henry755 Well-Known Member

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    Dec 16, 2010
    Hi ablebakercharlie,
    Another note worth mentioning to you is to be very careful when changing over to broadheads. I've found out that regardless who's broadheads you are using there's a considerable difference in weight on each broadhead by the same manufacturer.

    As an example, I'm currently using the Terminator Phat Head 100 grain broadheads. The weight deviation from the lightest head to the heaviest in a group of a dozen heads in as follows: 99.0, 99.1, 99.1, 100.1, 100.4, 100.7,102.5, 103.3, 104.5, 105.0, 105.1, 105.7 grains. This is a considerable weight difference and will cause elevation changes at longer distances.

    I remove the extra weight and balance the heads through a sharpening process on the blades, but the point is you should have an electronic grain scale that can measure gains of weight down to the tenths of a grain. This would be as listed above and I try to keep the weight deviation between my heaviest and lightest arrow in a dozen arrows to be not greater than one tenth of a grain in either direction. Even two or three grains is not going to have much of an effect in elevation up to 100 yards, but the closer you match them, the better your performance will be.

    Regards,

    Jon