How to Fine-Tune Your Bow's Cam System

Despite all the technological advancements in today’s archery world, few things can improve accuracy more than a well-tuned bow. It doesn’t matter if the bow is new or old, a bow that cycles arrows smoothly and consistently can make all the difference in world with improving an archer’s confidence and success whether punching bull’s eyes or the vitals on a big buck.

The key, of course, is doing the necessary work to ensure the bow’s eccentrics are functioning as a complete unit. When the “system” is not in harmony, the arrow’s launch pattern becomes erratic and indirect. In other words, the arrow’s nock is whipped up or down, or from side to side, vibrating the arrow profusely as it moves across the arrow rest. The arrow’s fletching eventually helps spin and stabilize the shaft a few feet from the bow, but at this point, the arrow is already misguided, causing all sorts of accuracy issues, especially when using broadheads.

In contrast, when the system is in synch, the bowstring follows a smooth, high-speed motion, keeping the arrow’s path in a straight, level line. There is no excessive whipping of the shaft as it glides across arrow rest and out through the bow. The result is less vibration and maximum control and repeatability. This leaves the archer with a highly accurate, forgiving bow that seems to shoot dead-on no matter the conditions – helping his or her mindset ooze with confidence.

Here are some simple techniques designed to fine-tune any bow’s cam system, so it’s optimized for consistency.

Step 1: Review the Bow’s Specs

To begin the cam-tuning process, be sure to review your owner’s manual, or a technical bulletin offered by the manufacturer, that outlines the bow’s setup and operating parameters. This will specify the correct cam orientation (the position of the cams in the undrawn position) and center-shot location of the arrow.

This step is important because engineers usually refine every bow’s cam system using specific setup guidelines. Staying within these parameters will ensure the arrow and cams are lined up perfectly with the bowstring’s power-path, producing the sweetest, fastest arrow tune possible.

Step 2: Synchronize the Cams

With this step, you’ll need a quality bow press that safely compresses the limbs and relaxes the bowstring and harnesses. Then you’ll need to assess how each cam rotates in the full-draw position. In other words, do the cams bisect each draw stop at the same time? If not, then some adjustment will be needed.

There are two ways you can analyze cam synchronization: 1. You can draw the bow back and attempt to ease into the full draw position, while a friend or family member assesses the positioning of each cam’s draw-stop location. 2. Or, better yet, you can put the bow in a draw board or shooting machine and slowly crank the bow to full draw while micro-analyzing each cam’s roll-over point. Both methods work, with the latter clearly being the best way to synch-up the system.

With adjusting, twist the buss cable end-loop on the cam that strikes the draw stop first — before the opposing cam. This will “slow” the cam’s rotation compared to the other. Make ½-turn twists until each cam strikes the stop at the same time. Sometimes it’s good to make the twists, then shoot the bow a couple times to help the newly twisted cable to settle in across the string peg, then check synchronization again. Continue this process until the cams are rotating in unison.

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Once cam synchronization is corrected, be sure to double check the bow’s draw length. Oftentimes, when twisting/untwisting cable harnesses, the draw length is changed slightly, depending on the number of alterations made. When making draw length changes, DO NOT alter the buss cable/power cable lengths, only twist/untwist the main bowstring and/or modify the cam’s draw length modules. This will allow you to dial in draw length without altering the cams’ synchronization.

If you are using a one-cam system, rather than a two-cam or hybrid-system, you don’t need to perform this step, only the first step to ensure the bottom cam’s orientation is in the proper undrawn position as suggested by the manufacturer.

Step 3: Examine Cam Alignment

If the cams aren’t positioned vertically, straight up and down, the bowstring will cause undo resistance and torque as it rotates through each cam’s outer groove. This disrupts the bowstring’s natural power stroke and the arrow’s ability to launch smoothly out through the bow. The poorer the alignment, the harder the bow becomes to tune.

Ideally, cam lean is checked using a draw board, then by laying an arrow across the outer surface of the cam to see if it’s in line with the bowstring. If it points to the left or right of the bowstring, then it’s off center. If a draw board is not available, you can have someone stand behind you while at full draw, then look to see how the cams are positioned with the bowstring. A slight amount of cam lean is acceptable, depending on the setup. However, too much lean is generally bad, causing problems with accuracy and tuning.

To fix cam lean, you’ll need to relax the bow and begin to adjust the string-yoke harness(es) by twisting one side or the other in attempt to equalize the limb tips while under load. If the cam’s bottom lobe is pitched to the left, make one full twist to the left side of the split-yoke harness. If it pitches to the right, do the opposite. Make one twist at a time until the cam position is more or less straight up and down with the bow’s riser. This will bring you to a solid baseline position. Additional adjustments may be needed as you fine-tune the system using the next steps.

Step 4: Check Arrow Flight

Paper tuning is the best way to examine an arrow’s flight pattern. I use a large PVC-type paper tuning rack for this step. However, a picture frame or cardboard sheet with a large opening, along with some painter’s paper taped tautly across the gap, works just as well. Position the paper a couple yards in front of a solid back stop, stand about six feet from the paper, then shoot an arrow through it to examine the arrow’s flight.

For this procedure, I prefer using an arrow without fletching attached, since it exposes the smallest imperfections in arrow flight, plus it eliminates fletching contact issues with the rest or riser. To keep arrow weight and balance the same, wrap 3 to 4 inches of electrical tape around the shaft where the fletching is glued.

When paper tuning, correct vertical tears first, then horizontal. Move the arrow rest or D-loop up or down, depending on the tear, in 1/32-inch increments until the vertical tears are eliminated. If a persistent high-tear remains, try twisting the top cam buss cable one-half to one full-twist. If a persistent low tear remains, try twisting the bottom cam buss cable in the same manner. Some cam systems may shoot best with one cam hitting very slightly before the other, so it doesn’t hurt to experiment.

With a left tear, you can try moving the arrow rest to the right 1/32-inch at a time until the tear is eliminated. With a right tear, try moving it to the left. Typically, moving the rest to the left or right only works with fairly small tears. Also, when adjusting the arrow rest, be sure to stay within the manufacturer’s center-shot alignment. This will ensure appropriate clearance for the arrow’s fletching and optimum performance from the bow’s cam system. Large tears will usually require additional tuning procedures as outlined in the following steps.

Step 5: Sweeten the Tune

By yoke tuning and/or moving axle spacers to position the cam(s) in a different spot on the axles, you can micro-tune the bowstring’s power-path, correcting slight imperfections in arrow flight.

To perform yoke tuning, be sure to make one twist at a time until you achieve a perfect paper tear. With consistent left tears, twist the left side of the yoke and untwist the right. Continue in this fashion until the tear is corrected. With right tears, twist the right side of the yoke and untwist the left side.

With large or persistent left or right tears, “shimming” one or both cams will eventually eliminate the tear, but I prefer to yoke-tune first before moving on to adjusting the cam(s). When repositioning the cam, always move the cam in the direction of the tear. If the tail-end of the arrow rips to the left, move the cam to the left. If it rips to the right, move the cam to the right.

With shimming, all your doing is adjusting spacer thickness from one side of the cam to the next. For example, when moving the cam left, you are decreasing spacer thickness to the left side, and increasing spacer thickness to the ride side. The opposite is done when moving the cam to the right. To keep things simple, only move one cam at a time, typically the bottom cam, then recheck arrow flight. If a poor tear persists, move the other cam as well.

Some bows are equipped with spacers that have different thicknesses, which allows you to swap spacers as needed to achieve proper tuning. However, some bows don’t come with this capability. In this case, you may have to purchase new shims to make these adjustments. Lancaster Archery and Last Chance Archery sell relatively inexpensive spacer kits and tools for this type of tuning, or, better yet, contact the bow’s manufacturer to request an assortment of shims custom designed for your bow.

Don’t be overly intimated with yoke- or spacer-tuning. Both steps may seem highly complicated, but in reality, they aren’t all that difficult to do. Just take it slow and easy and you’ll be amazed at the effectiveness of these tuning steps.

Once you achieve the perfect “bullet hole” rip in the paper using the bare shaft, shoot a fletched arrow next. The tear should still be clean as well, but only now with additional slits caused by the vanes. If the tear is irregular or large, then you know fletching contact is the issue. Spray the fletching area of the shaft with aerosol foot powder, shoot into a firm backstop, then examine the arrow for where the contact is occurring. Twist the arrow nock until the fletching passes cleanly through the arrow rest. If the contact persists, no matter what you do, you may have to switch to lower-profile vanes or try a different style of arrow rest.

Cam-tuning is critical for optimum arrow flight, efficiency, and shooting consistency. By performing these step-by-step procedures, you’ll enjoy the benefits of a sweeter-shooting setup, improving your effectiveness as an archer and bowhunter.