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Cam Lean



By: HuntinHabit
Posted: 22-Aug-10

I've been playing a little today tuning my Switchback. I read a few post on AT and the Mathews forum about setting cam lean by adjusting the yoke, and I'm not sure if I understand how to know if it's set properly.

So tell me, how do YOU set the lean? If you were putting a new string on, how do you know how much to twist each side of the yoke, then how do you test?

*EDIT - Sorry, I should say idler lean, not cam lean.


By: Bowfreak
Posted: 22-Aug-10

HH,

Take an arrow and place it flat on the idler wheel and have it run down toward the nocking point on your string. The arrow should be parallel to the string for the entire length of the shaft. If not, pull on one side of the yoke to see the effect it has on the idler. By doing this you will see which side of the yoke needs to be twisted to straighten out the idler wheel. Press, twist the yoke and recheck. Eventually you will have it perfect by just following this process. I hope this makes sense. Good luck.


By: HuntinHabit
Posted: 22-Aug-10

Thanks Bowfreak. That is how I would have done this before I started searching for more information. And that is what I found on the Mathews forum. But, the below is from a post on AT that seems to contradict setting the idler in line with the string:

"Now you have to paper tune your bow. Your center shot should be somewhere near 13/16" (center of arrow to side of riser near the riser hole. If you have to stray from this more than 1/16, you need to adjust the idler wheel lean. Lots of guys are having "unfixable" left arrow tears because the cam lean is not set properly. Take an arrow (preferably carbon) and place it flush on the left side of your idler wheel. As a starting point, the field tip on the arrow should point near the center of the string at your nocking point (initial nocking point is set where arrow is perpendicular to string when arrow is on your rest). My arrow tip ended up being about 1/4 inch to the right of the string (looking from bow string to riser), but it may be different for each person. You adjust the wheel lean by twisting or untwisting the left side of the cable yoke (that's why you only measure ATA on the right side)."

"If you are still getting a horizontal tear with the idler set here and the arrow centershot set at 13/16", then you need to start twisting one side of the yoke or the other (depending on the tear direction) until the tear goes away (or gets close to going away and then centershot can be adjusted slightly). Should be just a few twists. The tip of my arrow when the arrow is flush with the idler wheel is pointing about 1/4 inch to the right of my string at my nocking point. There is no noticeable idler lean."

"To get rid of a tail-left arrow you should twist the left side of the yoke, causing the top of the idler to lean to the left (can't really see the lean though). Just a few twists should do it. Again, try and start idler alignment with your arrow point on line with the sting and work from there."

I normally don't paper tune much, other than to get close, then broadhead tune. But I do have a constant left tear, so I thought I'd play with this a bit. I did correct that left tear by having my idler lean the way described above, but it just doesn't seem right.

So should I just ensure that the string is in line with the idler, or is there any truth to what this guy says?


By: WapitiBob
Posted: 23-Aug-10

Set your idler to run parallel to the string at full draw. That will take the "induced" left tear out.

Shoot in your center shot, shoot groups at 60, go huntin.


By: YukonJack
Posted: 23-Aug-10

Just something I learned after a few years of doing what you are now (repetitively) - Paper tuning is an approximate thing. Bullet holes are great, but they don't mean your bow is tuned. Broadhead tuning is a better indicator of bow tune.

Once you get your idler lean straightened out, Shoot 4 arrows - two Broadheads and two field points. If they all group together, you're in tune. If not, move your rest from Broadheads to Fieldpoints.

When they match, you're tuned.

This saves me a whole bunch of time when tuning.


By: HuntinHabit
Posted: 23-Aug-10

Thanks guys, but I understand broadhead tuning and how to set the idler lean parallel to the string. Maybe I'm taking this further than is neccessary, but I am trying to find the perfect lean before continuing to tune.

From my understanding, if you set it parallel at rest, it will lean at full draw. If you set it parallel at full draw, it will lean at rest. Ideally you should find those two points and split the difference. This provides the least amount of horizontal string movement when the arrow is realeased.

I have not had anyone around to help me look at the lean at full draw, but I played with it back and forth yesterday. I can't imagine having the arrow 1/4" to the right of the string as described above. I set mine about an 1/8" to the right and got a good bullet hole, but it seems to lean way too much, almost to where it seems unsafe. This can't be right. I'm going to play again tonight, maybe I'll learn something...


By: Bowfreak
Posted: 23-Aug-10

From what I gather in the AT post above. The guy above just sets his rest at 13/16" and then tunes his paper tears out with the yoke. I can't imagine that a Mathews bow has that much play in the idler wheel that it differs that greatly from brace to full draw. Personally, I would set it dead center at brace and let it eat but I have never owned a Mathews so I am by no means an expert on their stuff.


By: Florida Mike
Posted: 23-Aug-10

The difference between at brace lean an full draw lean is very very small. Get it anywhere in that range then tune the rest by walk back tuning. Once you've done that if you still have problems look at form, spine, etc... Mike


By: x-man
Posted: 23-Aug-10

I set it at brace too. It doesn't usually move much until almost full draw when the cable guard tension is it's highest. When you shoot, you want the horizontal nock travel to stop before it gets to brace(and the arrow leaves the string). This won't happen if you split the difference with the lean.

You'll also want to experiment with twisting and/or untwisting the entire cable to help eliminate vertical nock travel too.


By: HuntinHabit
Posted: 23-Aug-10

"You'll also want to experiment with twisting and/or untwisting the entire cable to help eliminate vertical nock travel too."

Great, throw something else at me to make me wonder... 8^)

Seriously, I appreciate all the input. I set the idler lean back to parallel at brace, one turn of the left yoke from where it was originally. ATA is now perfect, it was off an 1/8" before. Cam rotation is adjusted to dead on which was also off, and brace height is about 1/16" short. But, I have a custom grip so I'll blame the BH difference on that. 8^) I then reset my nock point and arrow rest height, and set windage to 11/16" from riser. Paper tuned to check for vertical tear, one slight adjustment and it was good. I now have probably a 1/4" left tear compared to 1/2"+ before.

Now, to the range tomorrow night for some walk back and broadhead tuning. I was getting frustrated shooting this weekend. Although broadheads and FP were grouping last time I shot broadheads, too many things just weren't right and my groups were inconsistent. I came home and stripped the bow completely to start over. It was time, and I feel much better after getting the bow back to spec.

So x-man, tell me more about eliminating vertical nock travel.


By: Gray Ghost
Posted: 23-Aug-10

HuntinHabit,

I've spoke with engineers at Mathews at length about this issue.

The true sweet spot for most idlers is not perfectly parallel at brace. It should have a slight lean in the opposite direction that it gets pulled by the cable guard at draw. In other words, the right side yoke should be twisted slightly shorter (right-handed bow).

This is how Mathews sets most of their solo-cam bows at the factory.

I use a laser pointer and a homemade jig to test cam/idler lean at brace, and at full draw, on my bows. I usually know immediately when I've found the correct spot. The bow will be noticeably more quiet, and usually much easier to tune.

GG


By: WapitiBob
Posted: 23-Aug-10

You have a single cam, the rotation will never be "perfect" unless you have the exact draw length the cam was designed for, and that's unlikely.


By: Bowfreak
Posted: 24-Aug-10

I was looking at a Q2XL last night that is my co-workers. One thing I don't understand on this bow as at a glance the cam and idler seem to be shimmed to a different plane. Basically....the string groove on the cam was closer to center than the idler. A Mathews guy in the shop told me that is the nature of the beast.

Is this true?


By: Gray Ghost
Posted: 24-Aug-10

Bowfreak,

Yes, it's true. I think they do it for fletching clearance. The Conquest was the same way.

I always found that my Conquests and my Q2XL shot better when I switched the shims on the cam, making the string more parallel with the riser.

Now you also know why I level my bubble to the string and not the riser. ;-)

GG


By: Bowfreak
Posted: 24-Aug-10

That is odd to say the least. But, obviously they still perform quite well. Honestly I know less about one cam systems than any other system out there. I have never owned one.


By: Purdue
Posted: 24-Aug-10

The adverse effects of cam lean are way over emphasized IMO. The horizontal movement of the string is frequently no more than the unremovable vertical movement from non-straight and non-level nock travel, yet "perfect" tunes are obtainable from these bows.

Should finger shooters worry about cam lean? They induce far more horizontal string movement by shooting fingers than cam lean will cause, yet are not they also able to tune there bows?

I'm not saying that minimizing of both horizontal and vertical nock travel does not help, it's just over emphasized. I would put it just above arrow FOC in importance. Shooting or building your hunting skills will be a better use of your time.


By: Gray Ghost
Posted: 24-Aug-10

Double post. Sorry.

GG


By: Gray Ghost
Posted: 24-Aug-10

Purdue,

We disagree. I think cam lean is under-emphasized. Take a look thru the newsletters on Spot Hogg's website. They've done extensive study on cam lean and its effects on nock travel using high speed cameras and shooting machines.

I think their findings will surprise you.

GG


By: Purdue
Posted: 24-Aug-10

I was not as impressed with the article as you.

The article gave no specifics as to how much better or how much more consistent arrow flight was. It reminds me of "new improved Tide" or Crest that whitens and brightens "Better"

In one part he states,

"We had discovered that cam lean definitely had an affect on the shootablity (forgiveness) of a compound bow."

In the same paragraph he says,

"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."

Will it help a bow that was most likely built out of spec. like the 7 degree example he gave? Yes. Will an arrow come off straighter from a bow which has minimal cam lean? Of course it will. Is it necessary to get a bow to tune. No...no more than perfect vertical nock travel is necessary in order to tune a bow.

Concentrated practice has FAR more effect on how you shoot than this minutiae.

When finger shooters of compound bows and traditional shooters even shooting off the shelf can tune their equipment, you are going to have a hard time convincing me that cam lean is critical to tuning a bow or for what is generally considered accurate shooting .


By: Gray Ghost
Posted: 24-Aug-10

Purdue,

Terms like "perfect tune" and "accurate shooting" are subjective, and depend on the individual. Some think pie plate groups at 30 yards is "accurate shooting", but I don't.

To me, a "perfect tune" is a bow that is set to exact factory spec, AND is shooting as efficiently as it possibly can. That means that I strive for the straightest launch I can achieve, which means cam/idler lean is critical to my "perfect tune".

Your mileage may vary.

GG


By: x-man
Posted: 24-Aug-10

Finger shooters have side pressure on the arrow because of the induced side nock travel. Release shooters do not(usually).

With drop aways over-taking market share, it is more important now to have the nock travel as close to perfect as can be achieved on each bow. Especially with most guys arbitrarily setting drop aways up to fall within 4-6" of forward travel. It's never going to be "perfect" without a shoot-through cable system, but we should all get it as close as possible. IMHO


By: Purdue
Posted: 24-Aug-10

"Terms like "perfect tune" and "accurate shooting" are subjective, and depend on the individual."

I know, that's why I put perfect in quotes. I was also giving examples of that from Spot Hoggs article. Words like "shootability", "forgiving", and "straighter" were peppered throughout, but nothing was defined or quantified. This was left up to the imagination of the reader.

"Finger shooters have side pressure on the arrow because of the induced side nock travel."

The horizontal movement of the strings lasts throughout the distance that the string travels (about 22") from a finger shooter. The side pressure is only present for about 4" of arrow movement. The bow is still tunable and accurate despite violent horizontal motion of the string and arrow. (see link)


By: Gray Ghost
Posted: 24-Aug-10

Purdue,

I assume you're still talking to me, even though you haven't addressed me by name or handle.

I'm not arguing that a bow with horizontal nock travel can't be tuned.

What I am arguing is by eliminating as much horizontal nock travel as you can, a bow becomes much easier to tune and shoot. You can discount it as "minutiae" if you want. But for me, it makes a world of difference, therefore I will continue to recommend it for those who want the optimal performance from their bows.

GG


By: x-man
Posted: 24-Aug-10

If he arrow is spined correctly, it will snug the cushion plunger almost all the way out. That video link is not a "good" example. I hope you didn't really believe that to be a properly tuned setup. Properly spined shafts will be finished flexing before they get five feet from the string. The wooden arrow in that videp clip probably flexed for twenty yards.

If I'm not mistaken, that clip is from the Bob and terry Ragsdale instructional archives as an example of what NOT to have happen. If you watch the whole instructional video, they go through proper and improper arrow flight footage to illustrate the importance of a properly tuned setup.


By: Matt
Posted: 25-Aug-10

"I'm not arguing that a bow with horizontal nock travel can't be tuned."

If you won't I will - depending on your definition of "tune". Back in the day I hot-rodded a Darton Maverick in a way that accentuated the lean inherent in a single/hybrid cam system. The cam on that bow twisted so badly at full draw you could honestly see the side of the cam if you looked down. No matter what you did, you couldn't get BH and FP groups to coincide due to the horizontal travel. It shot small groups with each, but eh BH groups were 4-5" left of the FP groups at 40 yards. This is a perfect example of how exaggerated horizontal nock travel made a bow untunable, at least to my standards of tuning.


By: Gray Ghost
Posted: 25-Aug-10

Matt,

I had a General that was the same way. No amount of tuning would eliminate the horizontal difference in POI. Like your Maverick, the lean was very noticeable at draw.

Since there's no way to twist out cam lean on the binary system, I was just about to sell the friggen thing. Fortunately for me, they had a recall on the limbs, and I got a new set for free. With the new limbs, the cams don't lean nearly as much, and the bow tunes like a champ.

GG


By: Bowfreak
Posted: 25-Aug-10

GG,

The only thing you can due on a Binary is to swap limbs. When I got my Exceed 300 out of the box I slapped a rest on it and started tuning. I realized quickly that my center shot ended up so far inside that my rest had no more horizontal travel left. So....I immediately put the bow in the press and broke it down. I swapped the limbs from top to bottom and put it back together. The bow tuned right down the middle perfect. With the 2 track binary that is your only recourse.


By: Purdue
Posted: 25-Aug-10

"If he arrow is spined correctly, it will snug the cushion plunger almost all the way out."

x-man, I can not find one video that supports your statement. (unless by "snug" you mean stays within 1") And I think you are mistaken about the source of the video as well.

http://www.youtube.com/watch?v=Sx3weOYdBYE

http://www.youtube.com/watch?v=48R2ajWx3rY

http://www.youtube.com/watch?v=xkpmgdv6h_0

http://www.archerycoach.com/

I guess none of these people know how to correctly spine an arrow.


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