Published by archerchick on 08 Feb 2011
Fine Tuning The Compound ~ By Roy Hoff
At First Glance, One May Feel Only A Graduate Engineer Stands A Chance, But Here’s The Step-By-Step Technique!
DURING RECENT MONTHS, BOW & ARROW has received many
requests on how to tune a compound bow. Upon receiving this writing
assignment, a thought occurred to me that often is expressed in race horse
parlance: “If you want to know if a certain horse is going to win a race, go
to the horse and get the dope straight from the horse`s mouth.”
This is exactly what I did! Only, the horse was Jennings Compound Bow, Incorporated.
If the owners, Tom Jennings and John Williamson, do not know how to tune a
compound bow, then there just is no way! As we seated ourselves in comfortable
chairs in Tom’s immaculate office of their new manufacturing plant in
Castaic, California, I recalled an embarrassing incident I experienced during our
We were warming up prior to taking to the hills. I shot a practice arrow and my
bowquiver shed a sharp broadhead that, in its fall to the ground, severed my
bowstring. This was years ago, when I was shooting a conventional bow. At
that time it was hardly worth mentioning. I had a spare string in my pocket, which
put me back in business in a minute or two.
Suppose this had happened to my compound bow. How would I or you ~ have
been able to replace the string and fine-tune the bow back into the condition it
was when received from the manufacturer? Following are the answers, as told
to me by the aforementioned partners of Jennings Compound Bow, Incorporated.
Step No. l: Loosen jam nuts on weight bolts. Most archers keep jam
nut only finger tight so it may be loosened in the field without a
wrench. Apply counterclockwise force on the nut with fingers of left hand
and simultaneously turn the weight adjustment bolt — using allen wrench
supplied with your bow — counter- clockwise and jam nut will loosen. Do
not, at this point, loosen or turn tuning keys.
Step No. 2: Before you go hunting or attend a tournament, you should
mark the limbs along the side plates at your favorite draw weight. This is in
case you lose count of the end-bolt turns, or the end bolts come all the
way out, Loosen end bolts approximately eight turns — will vary some
depending on the draw weight of your bow by turning end bolts counter-
clockwise. Cables and string should be loose, but not out of the tracks in the
Step No. 3: Lay the bow on its side with string facing you and sight
window up. Turn right eccentric end wheel clockwise until it snugs the
cables, then drop your allen wrench in the lighting hole in the wheel that is
closest to the back side of the limb. Turn left eccentric counterclockwise
and drop a pen, pencil, small stick, nail, etc., in the lighting hole nearest
the back of the limb. This will keep the eccentric wheels from turning and
letting the cables tangle on the tuning keys or come off the idlers. The string
should be loose at this point and come unhooked easily. Unhook the string,
noting double—loop hookup on S hook. Replace new string in the same manner
on the S hooks.
Step 4: Remove allen wrench and other pin from the eccentrics. Make
sure cables are in the tracks. Take up end-adjustment bolts approximately
half the number of turns you let off. Examine end wheels to make sure
cables are in the tracks. Examine cables at the idler wheels. Examine
cable at the tuning keys to make sure the cable is not crossed. Cable must be
laying even and not overlapping at any place on the tuning key. Cables should
be easy to move into correct position; however, if they are too tight, loosen
end bolts enough to take off tension. When cables are right, take up end
bolts to line on limb or the correct number of turns.
Step No. 5: Replace nocking point, kisser button, peep sight, etc. A bow
square is necessary for this job if you want to do it right. Hunters should
have a prepared string, complete with nocking point, with them in the field
at all times.
How To Change A Cable
Step No. l: Lay bow down with sight window up and string facing you.
Measure tiller height. Measure both.
Step No 2: Loosen lock screws in tuning key of cable to be changed. Turn Grover-type
key counterclockwise to loosen and cap screw—type of key clockwise to loosen. Loosen
key until all wraps are off the reel.
Step No. 3: Grasp cable one-half-inch from hole in reel and push cable
into hole and keep pushing until stop swage comes out the end of the reel.
At times. it is necessary to probe with a thin instrument ice pick, scribe,
etc. — into end of the reel to dislodge stop swage. Snip stop swage off cable
with sharp cutting pliers. Pull cable out of reel. Unthread cable off idler
and out through the slot in the limb. Turn eccentric wheel until set screw in
center of the wheel is opposite end of limb. Remove this set screw completely.
Use small, round pad to protect cable from being cut by set screw.
Save this pad.
Step No. 4: Unhook string from S hook. Remove cable from eccentric.
You might have to out—shrink tubing from cable to pass through hole in
eccentric. Your replacement cable will come with S hook installed, new
shrink tube and new stop swage. Drive a finishing nail into a board. Hook the
old cable and the new cable on the nail by the S hooks. Make ninety-degree
bend in the new cable exactly the same as the old one. The factory does
not pre—bend the cables, because this varies with the size of wheel, draw
length, etc., of your bow. Feed new cable into eccentric wheel in the same
direction you removed the broken cable. Replace round pad in set screw
hole. Screw set screw in until it makes contact with cable. Make one—quarter
Step No. 5: Slip on shrink tube and feed cable back through idler in the
same direction as you removed broken cable and into the hole in the reel of
the tuning key. Pull cable out of end of reel and pull until eccentric stops
turning. Measure four inches from the end of the reel and cut cable with
sharp cutting pliers. Slip on copper stop swage and swage with tool
supplied. Pull swage back into reel as far as it will go and bend cable slightly
to hold. Turn the Grover tuning key clockwise until you have two turns on
the reel. Cap screw tuning key counterclockwise. Re—hook string,
making sure cable with S hook. extending out of eccentric, is wrapped
around eccentric through slot in limb before you hook up string. Take up
several turns on end-bolt adjustment screws to take slack out of cables and
string. Note; If your limbs are not marked. be sure and keep track of
turns so you can return to your favorite draw weight.
Step No. 6: Take up on new cable tuning key until eccentrics balance
with each other. Do this by observing the distance between the cable near
the S hook in relation to where the cable goes into the eccentric. Take up
only the tuning key where you re- placed the cable. Do not turn the
other key, as it should stay in original position for a single-cable change. Fine
tuning is done by feel. Shrink the shrink tube with a match, torch or any
other movable source of heat.
Fine Tuning Your Tournament
l. Check the tiller heights. To re-fresh your memory, the lower-limb
tiller should be one-eighth—inch less than the upper.
2. Test draw your bow to check roll—over of the eccentric cams. lf they
don’t roll together, adjust by means of the tuning keys mounted on the side
3. Install a handle center—reference point. To do this, place a two—inch
piece of masking tape between the upper side plates on the inside of the
handle so you can see it when bow is held at arm’s length. Mark an accurate
center line between the two side plates that can be seen from five or six feet.
This will be used as a visual center reference.
4. Install a squeeze-on nocking point, do this gently, as you might
be moving it later. Locate it five- eighths of an inch above ninety
degrees from the arrow rest. This set-up is for nocking point over the
arrow, one-fourth-inch Bjorn nocks and ledge-type release-aid Finger
shooters, using a leather tab, usually prefer to nock slightly lower by
approximately one-sixteenth of an inch. Nocking points, of course, are
personal and require slight adjustment by the individual archer.
5. Clamp bow in vertical position ina padded vise. Nock arrow and place
on arrow rest.
6. Adjust your cushion plunger or adjustable rest in or out until the bow-
string bisects the arrow from point to nock when the string is aligned with
the center line mark on the masking tape A pasted between the two upper
side plates. Stand back several feet to do this aligning. Double check nocking
point height and that your cushion plunger — if used — strikes center of
7. Stand at shooting mark, approximately six feet from a unidirectional
backstop — excelsior bale is good — placed at shoulder height. Shoot with
your best technique. Should arrow enter nock right — right—hand shooter
— increase bow poundage. Left entry, decrease poundage. Work one pound
at a time — one-fourth turn. Re- member, both limbs exactly the same.
lf arrow enters nock high, lower nocking point. lf it enters nock low,
raise nocking point. Finger shooters may require a cushion plunger or
adjustable arrow rest set slightly out- side of center.
8. When you have acquired good arrow entry at six feet, try several at
twenty to thirty feet. lf you get extreme deflection, either you are too
center-shot or you are striking your fletchings Adjust center-shot out just a
little. If you think you are striking the lower hen-feather fletch, rotate nock
on the arrow.
9. The best hand position is a straight wrist with the back of the
hand flat, bow handle load carried on the base of the thumb — not the
thumb. The less thumb contact with the handle, the better. lf you shoot
with a low wrist, turn your hand so the knuckle line is diagonal to the
vertical line of your bow.
10. With a release-aid, you can shoot bow weight — holding weight — down
to fifteen pounds or less with good arrow flight. Some finger shooters find
it difficult to get good arrow flight under thirty pounds — holding weight.
Since you are always holding and releasing a lighter weight with a com-
pound bow, a good, relaxed release will have to be developed. The more
you shoot your compound the better your release will become. You will
learn to relax your fingers after the peak load, which occurs at mid—draw.