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Cam Lean - Does it Really Matter?
By Steve Johnson
Aug 13, 2007 - 6:07:04 AM

About 10 years ago we called a bow manufacturer about the lean of the cams on one of their bows. At rest, the top cam was very noticeably leaning (not parallel with the string). At full draw, the cam leaned a lot more. We were told that as long as the string and cable stayed on, the cam lean didn�t matter. The bow would shoot accurate and consistent, if we were having a problem it certainly was not the bow�s fault. We were told the problem was in us, not the equipment.

BULLSHeeT!

So, we made a tool to check the axle hole squareness of the limb. The axle hole was over 7 degrees out of square with the length of the limb. We started checking all the limbs we could get our hands on. None were as bad as that first one. In fact, the most perfectly square axle holes were on a set of limbs made by the same manufacturer that we had called in the beginning.

We decided that it would be easier to fill the axles with JB WELD (a filled epoxy glue) and redrill the holes rather than deal with the manufacturer. So we did (both limbs). The improved shootablity of the bow was so dramatic that we now check axle hole squareness of every bow we work on.

We had discovered that cam lean definitely had an affect on the shootablity (forgiveness) of a compound bow. So began a very long journey to find perfect cam lean. Using ourselves as the guinea pigs, we tried all sorts of different setups. But the going was slow. Often, a great deal of time was spent shooting a new setup with a different cam lean, without any clear results. Shootablity and forgiveness are very hard to measure. Especially when we are in such desperate need of both.

We soon found that measuring the cam lean by �eyeball� produced different results depending upon whose eyeballs were used. So we made a tool to measure the cam lean by projecting a laser dot to the opposite cam that would show if the cams were parallel to each other. This also gave us an indicator for how far they were out of line with each other.

So with our trusty laser tool, we started working on finding the perfect cam lean. We found that even if the axle holes were square in the limbs that cam lean still existed, and varied from one bow to another. There wasn�t much we could do about it until we discovered the split-harness cabling.

Split-harness cabling is not to be confused with the split cable setup. The split-harness hooks on the outside of the limb and ties together about 6 � inches down the cable. The split cable setup requires shooting between the split and it seems to aggravate cam lean. But the split-harness setup (standard on most bows today) makes it possible to manipulate and minimize cam lean simply by shortening (twisting) one side of the harness and not the other. This gives such good control that we converted all our bows to this and won�t work with anything else. (Unless something new comes along that might work better. We are always looking.)

We started lining the cams up with each other (using the laser tool and the split-harness) so that at rest the cams would be in perfect alignment with each other and parallel with the bowstring. We noticed that the best shooting bows also had the least amount of change in cam lean as the bow was brought to full draw. Few bows were able to maintain a parallel alignment of the cams as the bow was drawn to full draw. But, the ones that had the least amount of change in cam lean gave better arrow flight, more consistent accuracy, and didn�t seem to always be changing how it shot when compared to those with a lot of change in the cam lean.

To find out what was going on, we started comparing how the arrow was being delivered by the different bows. Using a shooting machine and a high-speed digital camera, we discovered that the bows with the least amount of change in cam lean always had less left and right nock movement as the arrow was being delivered (less string oscillations). We found that if we balanced the cam lean, so at rest the cams would lean one way and then at full draw the cams leaned the other way, then the change in cam lean was less and the string oscillations were less. The arrow was delivered straighter.

Hot on the trail and smelling blood, we started repositioning the cams on the axles, shimming limbs, playing with the cable guard, anything we could think of to reduce the change in cam lean. As the arrow delivery got better so did our shooting. One hunting bow went from a state of the art piece of garbage, to the sweetest most forgiving hunting bow (it killed an elk this year).

We could not seem to do much about up and down nock travel (seems mostly dictated by cam design). But, minimizing the change in cam lean certainly reduces the string oscillations from side to side.

The arrows are delivered straighter (equals better arrow flight and better broadhead delivery). The launcher prongs will wear more evenly (equals more forgiveness). The cam bushings will not wear out as fast (equals longer consistency). The limbs are less twisted (equals less limb fatigue).

Most of the discoveries were made on dual cam bows. But we found that the top idler wheel of a solo-cam bow had the same effect on string oscillations as the top cam did. The solo cam on the bottom had the same effect as the cam did on the bottom. The only difference is, there is no way to control the change in cam lean on the cam of a solo-cam. The idler wheel generally has a split-harness and is not a problem. But, to align the bottom solo-cam does not and cannot have a split-harness. What you buy is pretty much what you get. We have found that some are better than others, but even two of the same bow (that are suppose to be identical) will not always have the same change in cam lean.

When we use the laser dot to measure cam lean and change in cam lean, we have found that different bows need to be judged differently. High-energy storing bows always have the most change in cam lean and are the least forgiving. But any bow (dual-cam or solo-cam) where the laser dot moves more than an inch (top or bottom) when drawn, we fix or abandon until we can figure out how to fix it. (We have quite a few gathering dust).

Our best shooting bows have less than � an inch of laser dot movement (top and bottom) when drawn. We need all the forgiveness we can get!

Good Shooting!



Spot Hogg

 

Great write ups.

 

Article is spot on. While cam lean is "important", the mere fact that the cam is "leaning" is not necessarily detrimental to accuracy. I also agree with the explanation for why cam lean occurs, which is unequal/shifting limb tip loading during the draw cycle. Riser twist, limb twist, and offsetting both cables to the same side play a part, but they are not the primary causes of cam lean.

 

People here on AT go by the shock and aw factor and bandwagon up a topic. Cam lean, bare shaft tuning, ect. It's just a mechanical device that will shoot the same place each time if you let it.

I shot a 30 inch ata hunting bow yesterday. Draw length was too long for me and I had a floating anchor so I centered the peep and scope each time before shooting. The top cam was four twists behind the bottom cam. I had over a one inch right tear through paper at three feet, and I was using an old crappy wrist release that had to be moved and hinged to open instead of just having a trigger that tripped a sear.

I shot five six arrow groups and they all landed in the white on a five spot target at 20 yards.

Did I know that was going to happen before hand, heck no. Did me and the guy at the shop laugh about it, you bet. It was the perfect example to why people shouldn't get so up in arms about tuning. Just be repeatable.

Sure tuning builds in forgiveness when we mess up, but that's for us not the bow.

 

I learned a lesson years ago that some people have not learned yet, many guys believe that there is only one setup that is going to produce good arrow flight in their bow and that they are basically on a treasure hunt to find it with optimal spine and prelean on the cams and some center shot measurement that only the stud tuners know.

This is not true!!!!

You can get good arrow flight from many different settings on the same exact bow.

The key here is to get that good arrow flight using a setup that compliments your arrow choice and your shooting form and the type of shooting that you are doing. Many of us who are advanced shooters have specific goals that we want out of our bow so we tune our bow to cover these goals and we end up with a bow that compliments our shooting and therefore makes us a more forgiving accurate shooter. When you are restricted in your tuning abilities then you don't have the ability to specifically approach and take care of anything and just seeing good arrow flight is your only concern.

 

I am going to let you in on something and to my knowledge I am the originator of this concept and someone will patent it and take credit but it was mine a while back, the next evolution of bows will come from the company that has yokes above and below such as bowtech.

They are going to make a micro adjustible windage type system that moves a cam left and right between the limbs so that you can set a cam to no cam lean and basically shim the cam left or right. This will serve the same tuning purpose as yoke tuning but the yoke tuning in this system will be there to maintain perfectly no cam lean and the arrow flight will be changed by the movement of the cam left or right on the axle.

Right now yoke tuning and shimming are separate, on a hoyt you have yokes up top and none on bottom where the shims are at. On a bowtech you have yokes on top and bottom but you don't have shims. Bowtech is the perfect company to do a little thinking and add the micro adjust to their bows to move the cams left and right between the limbs.

Bowtech right now has their cams slaved to the axles so the micro adjust has to be on the limbs and move the axle left and right between the limbs a little since there are not spacers like on most bows but I think it would be easy to make a micro adjustment.

Pse has a nice limb pocket leaning thing that moves the whole cam left or right but I don't like it because the axle gets leaned as the limb pocket rotates.

 

Since split limbs wont be leaving anytime soon why doesn't companies make it so each limb can be adjusted at the limb pocket, like the PSE Moneymaker was, if one limb was stiffer than the other it could be weakened just by backing out the limb bolt on the stronger limb. I might be wrong but wouldn't that help since most of the time most problems with cam lean are cause by a missed matched set of limbs.

 

Correcting a "weak" limb doesn't necessarily solve issues with cam lean. The cam is still going to change it's lean orientation as the load shifts from the string side (left limb tip) to the cable side (right limb tip) as the bow is drawn. Increasing or decreasing the deflection of one limb can certainly reduce cam lean at brace, but it will make it worse at full draw (and vice versa). The article states the issue correctly, cam lean cannot be eliminated on any conventionally cabled compound bow because the left/right limb tip loading shifts from the string side to the cable side as the bow is drawn. All else being equal, greater letoff produces a greater load shift, and therefore a greater variation in the amount of lean at brace vs full draw.

 

Yokes on both ends have been around for ages already, though, so I think your idea has already been stolen . Quite a few wheel bows in the past were dual-yoke designs and I still shoot a dual-yoke wheel bow myself today. It's a bonny design too, since it allows you to align the wheels/cams perfectly without having to tolerate one or the other being cockeyed whether you like it or not.

But in my experience, by the time you're actually taking the bow apart to fix a tear, you're not shooting enough. 9 times out of 10, my unresolvable tears were shooter-related and it wasn't until I found the problem through shooting enough for it to finally come up, that I was finally able to fix what I was doing. Probably all bows made these days come out of the box in shootable condition with only minimal tuning required. So when guys start taking limbs off and swapping them around, or reshimming cams and such, I usually suspect they're tinkering with the bow when they should be outside shooting it .

I don't think I've found a bow yet that did something where the fix wasn't me. I do have bows that I shoot better than others, but none that are ill-behaved by themselves...

lee.

 

I don't think I've found a bow yet that did something where the fix wasn't me. I do have bows that I shoot better than others, but none that are ill-behaved by themselves...

lee.

Cuz folks REFUSE to drop the draw length..even when they put enough twists on a yoke leg, to nearly derail the string off the top cam..even when they have to move the arrow rest sooo far to the right, the arrow is touching the riser, to fix a "left tear that won't go away"..even when they try shimming the top cam sooo far left, the cams are rubbing the left split limb, to fix a "left tear that won't go away". Couldn't possibly be too long of a draw length...couldn't POSSIBLY be a form issue. Nah.

 

I agree, Correcting a weak limb will have a effect on the cam lean but the issue becomes right now that we are leaning cams to tune the bow so cam lean in a way is a good way.

When you have the cables pulled over to one side to give room for the arrow to pass by you are going to always have cam lean present at some level. A few years ago i actually put my bow in a draw board and studied the cams from start to finish and I figured out how to set them so that they had the most minimal effect. I basically set my cams at the half way point because the cams start out with one amount of cam lean and then by the time you get to full draw they end up at a different place. Most people either set their bow to have no cam lean at the start before you draw or the set them so that they have no cam lean at full draw. if they are that kind of tuner anyway.

When I was doing this setting the cam lean thing at the half way point it gave me a more average setting where the cam started out on one side of the center line and ended up on the other side of that center line. This made the distance from the cam being off center more minimal. Then I tuned the arrow flight without changing the yokes at all. This was my method that I used for a year or so before learning to yoke tune. It worked really good but was very time consuming and once I learned to yoke tune I stopped.

 

Well one reason I like wheel bows is the super duper squishy back wall. That makes the draw length adjustment with the mods a little less critical. With my particular execution method I pull into the back wall anyway so as long as it's not too long, it can be a little short and it'll mush into just the right length around the time the release goes off....

lee.

 

tagged

 

This OCD over cam lean came more from short ata bows than long ata bows.

Always big on long ata bows I never worried about cam lean. In fact, one of favorite all time bows (ata of 38 3/8") has enough cam and wheel lean to make most sit down and cry. This bow also has a floating yoke. It deadly, pin point accurate from off the point of the arrow out to 80 yards.

Of shorter ata bows, I have a 33 1/2" ata hunting bow and it has cam lean, not bad, but some. Binary cams, no yokes. I don't believe in shimming. I figure the R&D department knows more about shimming than I do. The bow has proven accurate out to 60 yards. I haven't shot longer.

 

Good to know!