Tuning with Cam Lean

In a previous edition of Bow International magazine I wrote about the steps I go through in order to tune my bow. I mentioned that paper tuning is just a starting point, and that I put much more weight on the French tune being perfect.

The French tune is generally set using your arrow rest, but even a perfect French tune does not ensure perfect arrow flight. Once the French tune is complete I would recommend heading back to the paper tune to see what you’re left with. If your paper tear is now out there are steps you can take to correct this. This correction can be done by moving the position of the string left and right in order to perfect your paper tear.

What you’re aiming for: a perfect bullet hole on the paper test

This method will only help to correct a left/right tear and will not have any impact on your vertical tear through paper. The string can be quite simply adjusted left to right by adjusting the angle of your top cam or wheel using the yoke cable.

Most modern compounds are designed with a cable that runs from the bottom cam up to the top of the bow. Approximately six inches from the top, the cable splits into two, and the two cables are attached to either side of the top limb. This split cable is called the ‘yoke’ cable. By twisting each side individually it will allow you to adjust the angle of the top cam or wheel in relation to the riser. By moving the angle of the cam, you will automatically cause a slight adjustment to the position of the string in relation to the riser.

There is a common myth that your top cam or wheel must be straight up vertically in order for it to be set correctly. However, I would always use true vertical as a starting point when setting up my bow, as it does not have to remain straight to get a good tune. You should think of adjusting your cam angle no differently to the way you would think about a small adjustment to your rest. I have shot some great scores with a slight angle on my top wheel. This small adjustment can also help to offset any issues you may have with your grip or anchor.

Use a straight edge like a parallel shaft to determine your top cam angle, and start with it in the vertical position

Firstly, you need to ensure that your cam or wheel is set in a true vertical position to begin with. This is done by laying a straight edge against your top cam. A straight parallel arrow is perfect for doing this check – I wouldn’t use a bent arrow, or a barreled shaft, to do this as it will throw you off. Holding the arrow against the cam, it should cast a line down the centre of the limbs and riser. Do not compare your arrow to the string, as the string will be slightly off due to its fitting position on the bottom cam. If the top cam leans left, put some twists into the right-hand side yoke. If the top cam leans right, put some twists into the left-hand side.

A left-leaning cam

If you get a left tear, try putting twists into the left side of the yoke cable

Once you are certain that your top cam or wheel is up straight, shoot another arrow through paper. I would do this at about five yards back from the paper. If your tear is now perfect, then you have nothing further to worry about.

A right-leaning cam

If you have a right tear, this means that the nock and fletchings are clearly visible to the right of where the arrow point is. To correct a right tear you should put two twists into the right hand side yoke. Then shoot another arrow through paper and see if there’s any change or improvement. You may need to add or remove twists to get the hole perfect.

If you get a right tear, try putting twists into the right side of the yoke cable

If you have a left tear through paper this means that the nock and fletchings are to the left-hand side of where the point has passed through the paper. To fix this, put two twists into the left-hand side of the yoke cable.

This process is very much a case of trial and error. There is no fixed formula to say anything like, for example, that one twist equates to three millimetres of tear. It is very different for each individual bow. A bow with larger diameter cams will naturally lean more with the same number of twists than a bow with smaller diameter cams, so the adjustments will be finer. On a bow like a Mathews C4, the idler wheel is very small, so it will take a larger number of twists to move the wheel alignment and see an impact on the paper tear.

One thing to be careful of during this process is to make sure you put no more than six twists in each individual side of the yoke cable. If you lean the cam too much there is a risk of the string leaving the track and the bow de-railing, so when you have found true vertical for the top cam never go more than six twists in either given direction.

In my experience, this method of cam leaning works extremely well on any bow with a large diameter cam. This method will not fix everything, and perfect form is still the best head-start to getting a perfect tune. However, it will help to eliminate a small amount of error in your arrow flight and can just put that finishing touch in your tuning that you have been looking for.