Limb string groove

PeD

New member
Whilst my son was trying out a new set of limbs I noticed on my sons usual limbs that the lower limb string grove has been extended by nearly an inch.
It would appear that the string is cutting into the limb I assume after the release. There are no marks on the upper limb.
The loop serving is longer than the groove so it must be the serving doing this.

At rest the string does not contact the limbs below the groove on top or bottom. There is no noise on arrow release.
Bracing height is at 9? . The tiller measures 7 4/8? top and 7 2/8th? bottom. Giving 2/8ths tiller on the top limb.
The riser is a 27? Hoyt Factor with X Tour long limbs 38lbs.

Ive experimented with a different set of limbs with some tape in the lower groove and the string also leaves marks on this tape
below the groove. So I don?t think it?s a difference in the limbs
Would this mean that the lower limb is working more or less, than the upper limb even though the flight of the arrows are good and group. I would have thought that if the limb setup is right any the marks on the limbs would be the same top and bottom.
We?ve tried a higher bracing height during tuning but it always seems to work best at 9?.

I was surprised to find that on winding the limbs fully in and measuring the tiller top and bottom, that the tiller measurement were not at zero to each other. So I assume that that?s due to the riser geometry and built in.

We could of course leave ?sleeping dogs lie?.
 


mbaker74

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You are at the bottom end of the recommended brace height at 9", might be worth wniding it up to 9.5" and repeating the tape exercise. This would prove if its a low BH issue?
 


geoffretired

Supporter
Supporter
I noticed on my sons usual limbs that the lower limb string grove has been extended by nearly an inch.
When you say "Extended" do you mean the groove is longer than the one in the top limb? Or is the bottom groove getting longer over time? Does the extra length in the lower groove look like recent wear or could it have been made longer by the factory.( accidentally perhaps?)
 


Del the Cat

Active member
Generally a lower limb is adjusted to be slightly stiffer than the upper (by tightening the limb bolt a little more). This would make the string contact the limb for a longer distance.
I don't think its an issue, the grooves are possibly filed in manually.
Does the string sit nicely in the groove after a shot? If so there is no problem. The groove is only there to discourage the string from working it's ways sideways off the limbs during the vibration at the end of the shot... it's one of the perils of highly recurved limbs.
Del
 


PeD

New member
The string sits in the groves top and bottom with no problems. I just wonder why the lower limb has more wear than the upper.
 


Del the Cat

Active member
The string sits in the groves top and bottom with no problems. I just wonder why the lower limb has more wear than the upper.
My previous post supplies the answer... it's the fact that the lower limb is generally adjusted to be stiffer.
Face it you can't expect the behaviour of two limbs in a bow which by it's nature is slightly asymmetric* to be identical!
Del
* If you grip at the geometric centre the string and arrow pass are above centre. If the arrow pass is at the centre then the grip is below.
The fingers on the string are also not symmetrical with respect to the arrow or the grip.
 


Rik

Supporter
Supporter
Winding the settings all the way in may not show you the riser geometry. It may just show you the differences in the limbs. They tend not to be made in pairs, in mass production methods, and mfrs rely on people being able to adjust kit to fit...
 


geoffretired

Supporter
Supporter
The string sits in the groves top and bottom with no problems. I just wonder why the lower limb has more wear than the upper.
I can see why you would want an answer to that; I would, too.
If you look at the bow when it is strung, there may be some clues.
Are the string grooves the same length on both limbs? Does the string sit in both grooves nicely? By that I mean does the string want to settle centrally in the grooves or is one tending to be off to one side? Are the notches on the sides of each limb tip, level with each other and equally deep? Is the serving that is rubbing away the limb, a bit rough?
If you can hold the bow upright, really firmly, or get some one to hold it, try to push the nocking point up and down, and pay close attention to the way the limb tips curl and uncurl. You may detect a rubbing at the bottom that doesn't happen at the top.
I have seen damage of this sort on an old beginners' bow. The damage looks as if the serving windings have dug through the varnish. By that I mean there appears to be short lines across the grooves as if something has rubbed side to side. When the grooves are made, the file would be pushed up and down along the groove, so the damage is at right angles to that sort of rubbing. That might indicate that the limb tip was twisting side to side in the last few vibrations before the bow becomes still after a shot.
That might happen at both ends, but if the varnish is a bit thinner at the bottom, it could wear through sooner.
 


Timid Toad

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Ironman
My guess, without seeing the bow, either static or being shot, is that your tiller is out a little.
The lower limb moves forward and stops earlier (wrapping the string further round the limb) than the top. The top then catches up and yanks it back, maybe causing a little friction, hence the wear. This might be a consistent thing, but it is something that someone with an inconsistent hand position can produce. Pushing down with the heel of the hand will be different to shooting with the grip up in the web of the thumb.
So two options; consider a tiller tweak and/or see what your son's hand position is like.

Of course, your son, with a birthday coming up, may take the view that the limbs are on the way out and it's time for a new pair ;)
 


PeD

New member
My guess, without seeing the bow, either static or being shot, is that your tiller is out a little.
The lower limb moves forward and stops earlier (wrapping the string further round the limb) than the top. The top then catches up and yanks it back, maybe causing a little friction, hence the wear. This might be a consistent thing, but it is something that someone with an inconsistent hand position can produce. Pushing down with the heel of the hand will be different to shooting with the grip up in the web of the thumb.
So two options; consider a tiller tweak and/or see what your son's hand position is like.

Of course, your son, with a birthday coming up, may take the view that the limbs are on the way out and it's time for a new pair ;)
Thank you for your answer. I?m beginning to think it?s a tiller a little out of whack.

Bit worried though you realising his birthday is coming up!
 


Timid Toad

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Thank you for your answer. I’m beginning to think it’s a tiller a little out of whack.

Bit worried though you realising his birthday is coming up!
Entirely a tongue in cheek guess... It's always a teen's birthday coming up.
 


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