Shimming Cams, Swapping Limbs

[Antlerquest]

Hello EAF. Hoping a few can set my mind at ease. I've read quite a bit where some have had difficulty gaining proper clearance to achieve l/r center shot. Suggestions have been to shim the cams to draw the string toward the riser, or the reverse, push it away. Another frequent response is to swap the limbs top to bottom.

I've done all of my bow tuning for 20+ years, but can not afford a new compatible press AND a GT500 at the same time. Therefore, I will be forced to rely on a shop and shop labor to tune the bow after I have it shot in. Not looking forward to that. Therefore, I want to have sufficient knowledge of the bow to ensure that it is correct the first time. This brings me to my questions:

1) How commonplace is this concern? Is it routine to need to adjust the orientation of the lims and/or cams?

2) What is the root cause in bows that need additional modification?

.....A) Are the limbs machined out of square from the attachment at the pocket?

.....B) Are the cutouts for the cam machined off center?

.....C) Is the deflection different across the face of the lims causing the cam to move off center from a twisting or torquing of the limb?

3) Is there a way to check the bow at rest to determine if there is a likely issue before purchase? In other words, is there a standard value that the center of the arrow SHOULD be set at from the face of the riser with a corresponding center shot measurement to the center of the string? I am guessing that if the measurements were begun in reverse- at the rest based on spec, (rather than off the bowstring) AND the cams were skewed left or right, then the center shot would be considerably off when measured back to the string, right?

I know all bows (and shooters) are individual, and slight variances are normal. I'm looking for big-picture knowledge here. Thanks to all who might help settle my concern.

[archer58inPA]

The short answer to your question is the limb inconsistency between the forks. It's basically a problem caused by the limb vendor.
The shim change is necessary to tighten the cam between the forks and move the cam closer to the center of the riser.
The tighter shims eliminate cam lean also.

There are a lot of GT500's and Z28's that need to have them. If your CS is past 7/8"(or real close) and you can't get a bullet hole at that CS , you can figure you need shims.

[shootstraight]

Yeah, what he said. The only thing you can do before you buy it is to papertune with the rest at 7/8, if it will tune there or very close to that you should have no problem. The one's with a center shot issue wanted to have the rest over an inch center shot causing sight and rest problems. The shims can be a fix but some have need to swap out the limbs, both of mine (GT500 and XLR) I swapped the limbs and it fixed it. I had a Z28 that was perfect from factory.

[Maybee-R]

Mine is just past 7/8 center shot. its fine. I dont think it common to have to shim or swap limbs. swapping limbs though has been done for years by tuners its not new. shimming cams also.

[Arky1cam]

The deal is with Binary cams that there is no cable or strings hooked to the limbs. So to adjust any minor limb twist (I mean minor) you have to shim the cams a few thousanths one way or the other to correct. It has the same effect as twisting a Yoke on other popular brands (mathews, Hoyt etc.)

There is just a small % of these bows that even need this done, and your dealer should take care of all of this.

Almost every Mathews I have ever tuned and worked on had to be pressed and have idler lean induced to make it stop left tearing. This is the same thing, it is just done a little different becasue of the way the binary cam is.

There is just to many small variances in manufacturing to have them all leave the factory perfect. That is what the dealer is for !

[Antlerquest]

Thanks to all so far. Starting to understand it a bit better I believe. New to binary cams, but love the feel of the Revolution. It's like magic. Last bow was ughhum, a single cam. Have no interest in buying half a bow again!

[out west]

So is the limb swap done to counter limb twist?

[vhunter]

I think half of the trouble you hear are due to fletching contact or bad form. It seems people read about the spacer issue and that is immedaitly what they blame it on.

[Arky1cam]

I think half of the trouble you hear are due to fletching contact or bad form. It seems people read about the spacer issue and that is immedaitly what they blame it on.

AMEN ! Like I said, Very small % with actual problems ! And when there is it is a very easy fix !

[Daniel Boone]

Thanks to all so far. Starting to understand it a bit better I believe. New to binary cams, but love the feel of the Revolution. It's like magic. Last bow was ughhum, a single cam. Have no interest in buying half a bow again!

I did notice attaching anything to the cable can change center shot as well. Atleast this was the case for me. My cam has a small cam lean at full draw on my gt500. Sure isnt effecting the center shot or groups while shooting. Im now shooting a launcher blade on a Trophy Taker. Put the bowplane tool on it last night and my centershot is real close.
DB