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String Stretch


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#1 1Ranger49

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Posted 06 September 2007 - 07:54 PM

How far will a string stretch or settle? I have a Mathews Switchback and never had it checked if the string has stretch or settled. It looks like the cam rotation is off. Does string stretch effect the draw length, ata and brace height? Just how far will a string stretch or settle? 1/4, 1/2 inch or more? Will the string be able to be twisted to get it back in specs? I guess the best bet would be to take it back to the pro shop,( which I am not to thrilled about the guys that work there) to have it checked to get it back into specs. Would it be wise to have new strings and cables installed or will the original string and cables still hold up?

Thanks for any advice.

#2 Leo

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Posted 09 September 2007 - 11:01 AM

Different strings "stretch" more than others. I wouldn't worry too much about it unless the string looks bad, is real old or the bow is strangely inconsistent.

Once the bow has settled down with a new string I leave it be until a replacement is needed. Unless it's settled way out of spec don't complicate your life by monkeying with it ;)
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#3 1Ranger49

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Posted 09 September 2007 - 08:16 PM

Thanks for the reply leo. The string looks fine as I see no wear. The only thing I might have checked if the bow is out of spec a little. The bow still shoots where I aim, but my aim isn't always that good.

#4 Rowdy Yates

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Posted 10 September 2007 - 11:58 AM

1ranger49 get the timing checked. Even solo cam bows like Mathews having timing issues with the cam. Your Mathews dealer should easily show you how to check it, especially if it has gone out a bit from its original specs. Good luck with it. ^_^
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#5 Jeremiah

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Posted 10 September 2007 - 06:34 PM

Trust me when I tell you that all strings "settle". The only difference is in the amount and in the amount of shots it takes to stop settling. (The really bad strings will just outright stretch like gum bands and have a higher rate of "creep" which is basically when a string keeps all or some of the length it stretched to while under load when removed from load instead of springing back.)

Break out a tape measure and measure from Axle To Axle and from the center of the Berger Button (rest bolt) hole in the riser to the string for the Brace Height. They should be 33" and 7" respectively. If the bow is out of spec due to string/cable stretch, the ATA length will generally read long and the BH will read short. Unless the specs are way out of range, the strings can usually be twisted down to return the bow to factory specification. (Zebra recommends no more than one full twist per inch of string. So, if it take considerably more twist than that you know it's time for new strings.)

Single cam bows have an optimum cam rotation, not a sync or timing issue. Optimum cam rotation on most Mathews bows is set by aligning two small holes in the cam to be parallel to the bow string when the limb bolts are maxed. On a Switchback, it should ideally look like this...
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As for setting the bow back to factory specs, I will usually begin with the cable and add twist to the end near the cam until the ATA length is close to spec with the limb bolts maxed. At this point, the inner cam rotation hole will likely be pointing toward the bow string. Add equal numbers of twist to each end of the string to maintain the balance/peep location as best as possible. Basically, twist and check, twist and check. The bow is in spec when the ATA length is 33" and the BH is 7" with the cam rotation holes looking as they do in the picture above. Also, the peak poundage of the bow will almost always read between 2 and 5 pounds over the limb sticker rating on a Mathews bow set to factory specifications.

As always, remember to check all specs and cam rotation with the limb bolts turned all the way in (maxed). If you back the bolts off for shooting, the specs and rotation will naturally change slightly. Simply let everything fall where it may if you do so. The specs should not be reset where the limb bolts are backed off to. Furthermore, Mathews recommends turning limb bolts out 5 full turns before pressing. You can probably guess that most folks do not do this when setting specs because they need to be checked with the bolts maxed. But, I would be out of line to not at least mention it.

Happy twisting... :)

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#6 Leo

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Posted 11 September 2007 - 08:14 AM

Single cam bows have an optimum cam rotation, not a sync or timing issue.


This is a probably one of the MOST ignored things on single cam bows. I absolutely concur with Jeremiah on this point.

The reason it is so often ignored is often the bow can be "tuned" and still shoot quite consistently. You do loose performance but many shops take that loss in performance in favor of an adequate tuning job. The rotation position of the cam is bow model and cam specific. It's extremely difficult to be "up" on all the different iterations. This is one of the reasons going to a "certified" for that manufacturer pro shop is so important.

Each bow should have this information in it's manual. You know. That pamplet no one ever reads. If you don't have one usually the company website allows you to download one from their website.

You are usually MUCH better off if you have the cam rotation set properly BEFORE you start to tune. Changing it afterwards can totally obliterate your tuning efforts.
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#7 1Ranger49

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Posted 12 September 2007 - 03:31 PM

Okay, took a few measurements. Limb bolts maxed out. ATA, 33" BH, 7" to the center of string from center of berger hole. Well, as close as I could figure. Now the cam rotation is leaning toward the rizer and away from the string. How many and what direction do I twist the string? I am sure it would be trial and error and a redo. If I twist the string to get cam rotation will this affect the ATA and BH? I guess I will take it to the bow shop but I would like to know for sure if he is doing it right according to your info. That way I can watch him work on it and make sure it is done right. I want to be armed with as much info as I can before I take it in. Not real sure how well he is on working on bows and not that many Mathews dealers close to me.

Thanks again

Edited by 1Ranger49, 12 September 2007 - 03:34 PM.


#8 Jeremiah

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Posted 12 September 2007 - 04:27 PM

Don't touch the string. With the specs already pretty much on and the inner cam hole tipped toward the riser, the buss cable needs twisting. Try adding a twist or two at the cam end and see how things look then. A couple twists to the cable will not noticeable change the ATA/BH. It will change the poundage, however, as the buss controls peak poundage. (Remember, when properly set the bow should peak at least 2 pounds over what the limb sticker reads.)


Less Likely:
If, by some strange chance, the peak poundage of the bow is already several pounds over the limb sticker rating now, then you will want to remove twist from the string instead of adding twist to the cable. (Always add or remove twist from the string in equal numbers from both ends to maintain the balance.) I'd say something like remove one full twist from each end and see what it does.

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#9 1Ranger49

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Posted 14 September 2007 - 08:19 AM

Thanks for all the info. If I had a bow press I think I could fix it myself with all the help and support here.




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