Bare shaft tuning - what went wrong?

KidCurry

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68inches, 44lb, ACE 430, 31 inches, 100gr points, string 20 strands. 30m.
Okay, so I did some bare shaft tuning the other night. Having gone up to 44lb I expected my arrows to be a bit weak. They were. Trimmed 1/4 inch of my test ACE arrow and hay diddly back in the group at 30m. So back home trimmed all my arrows. Back on field at 30m and bare shaft now going 15 inches to left of group. What have I done wrong?
 

dvd8n

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Were you simultaneously trimming your test arrow and your bare shaft when testing?
 

KidCurry

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My test arrow is my No. 13 ACE bare shaft arrow. I use it for tuning so I don't screw up my dozen. I shoot 3x fletched and 3x bare shaft. The results tell me to shorten or lengthen my test shaft. It has always given correct results in the past. This time I changed something which really screwed things up and it was nothing to do with the arrow. Even my test arrow was now 15 inches left of the group that only the day before was in the group.

What I did was change my initial 652 20 strand string to a 8125 20 strand string :) Only at the end of my head scratching did I revert to my FF string and all bare shafts went back in the group :)
When I weighed my strings the FF was 105gr and the 8125 was 138gr. The extra weight was slowing the bow. I weighed 1m of FF straight off the reel at 2.6gr/m and the 8125 at 3.15gr/m. The 8125 is heavier and has a lot more wax. I don't know if this is a consistent difference or if it is a one-off. So, in future, I will be weighing my strings as well :)
 
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Stretch

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Different BCY 8125 colours have different levels of wax. Some colours are not bad some colours are very heavily waxed. Silver was terrible stuff - left the serving tool covered in grey sludge. Best that I tried was medium green. I don’t know why they do this as the material doesn‘t need that much wax to hold the colour and their old Dynaflight was way less waxy the Brownells FF.

Some folks have been known to strip the wax off the string with Acetone while it is still in the jig. I did do it a couple of times and it certainly shortened the shoot in time for the string… and didn’t do any harm. If you leave the string very waxy it will take a long time to stabilise for weight.

I changed to Angel products which have a whole different set of quirk.

Stretch
 

albatross

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I never even considered the amount of wax on a bow string could have an effect on the way arrows shoot. Not that it matters much at my 'hobby' level.
 

bimble

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Okay, so I did some bare shaft tuning the other night. Having gone up to 44lb I expected my arrows to be a bit weak. They were. Trimmed 1/4 inch of my test ACE arrow and hay diddly back in the group at 30m. So back home trimmed all my arrows. Back on field at 30m and bare shaft now going 15 inches to left of group.
I just want to get this right in my head.

You shot trimmed your 13th arrow to bring it bareshaft back into the group, which were all at their original length. So a shortened bareshaft was grouping with longer fletched arrows.

You then trimmed those arrows.

Are you sure it's the 13th bareshaft that's now moved, and not the now trimmed other arrows moving away from that 13th bareshaft?
 

KidCurry

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That's why you remove the excess wax before serving the string.
I have now removed as much wax as I can from the strings before weighing. The results are:
8125 = 3.15 gr/m
8190 = 2.9 gr/m
652 = 2.6 gr/m

I just want to get this right in my head.
You shot trimmed your 13th arrow to bring it bare shaft back into the group...
Yes, I know what you mean. By taking off the 1/4 inch it moved the bare shaft from the black 9'oclock into the gold. The fletched shafts moved about 2 inches left when shortened. I'm not overly ambitious when bare shaft tuning and getting bare shaft and fletched in the gold at 30m I'm happy with shooting bare bow.
Everything thing seems good again as I'm now back to 330+ at 30m.
 
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albatross

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That's why you remove the excess wax before serving the string.
As it happens I do put a loop of serving thread around the served string to remove access wax, especially on 8125 strings, but mainly to make it round and to compress the strands. I never had to do it with fastflight 652.
 

KidCurry

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I read my bow tuning book when I started barebow three years ago. Just re-read it. It states "string weight is the most overlooked element in bow tuning". Should have written that bit down :)
 

Geophys2

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I found that polishing the string can make a big difference, when I used sights it changed point of impact at 70m by about 150mm. I found this particularly important when putting a new string on a bow. I used to use the plastic shaft from a cotton bud, but now these are all paper I use nylon line from a grass strimmer. With the string on the bow, after applying wax to an old string, or when fitting a new string, wrap the strimmer line a couple of times around the string and vigorously run it up and down the string, the string should end up polished with the strands nicely bedded in and smooth plus any excess wax will be squeezed out. When making a string I also do this before applying the centre serving.
 

tabashir

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Thanks for the thread and updates @KidCurry . I've not experimented with strings much (I just use a Carrera SK99 16 strand) and would never have thought that change of string, or even excess wax, would make that much difference. One more thing to keep in mind when tuning in future!
 

Senlac

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…. What I did was change my initial 652 20 strand string to a 8125 20 strand string :) Only at the end of my head scratching did I revert to my FF string and all bare shafts went back in the group.
Jake Kaminski has an interesting video about bow string materials. He doesn’t cover string weight, but he does talk a lot about 8190 -> 8125 -> FF. He concludes that FF are the best for him (and for some Koreans too)
 

Mark2

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That was an interesting video by JK (not Rowlings). It convinced me to try BCY's 652 (fastflight that was, or still is, I lost track over the years) and I must admit I wouldn't bother going back to 8125. And half the price of 8125 with a stupid range of colours. PS. I don't work for BCY but...
As I mentioned to Kidcurry off line, weighing your string may be worth a punt, but was not expecting such a difference.
I've never been a good string waxer, and I'm not sure if anyone still uses bees wax. I wonder if anyone out there is experimenting with other string dressings?
 

KidCurry

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Was helping a fellow archer tune their bow yesterday. They were looking at a new set of ACCs as the bareshaft was about 12 inches to the left (RH - too stiff) at 20 yds. They didn't want to go up in draw weight so I suggested replacing the 8125 string with a 652 string following my recent experience. Result was bareshaft in fletched group and archer very happy :)
 

geoffretired

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I keep wondering if the weight of the string effects things in two ways. One is the speed of the string travel changes, and therefore the speed of the arrow changes. But also... the flexing( side to side) of the string should change and that in turn will impact on the position of the shaft in relation to the its alignment with the intended direction of travel.
 

Mark2

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It is most likely some of both. In some years when I was shooting less often than usual I would drop my bow weight. However I struggled to make 100yds, si i would shoot a thinner string as it noticeably helped get the extra range. I would suspect the speed of the bow is likely influenced more than the deflection off the fingers, but I can't be certain.
 

geoffretired

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I wasn't thinking of the deflection off the fingers as much as the frequency of the oscillations changing with the change in weight of the string. That would affect the point at which the back of the arrow left the string and its apparent stiffness or match with the bow. It's a plucked string and would produce a different "note" if it was on a musical instrument. Separation would happen at a different point on the phase due to the change in speed forward and change in phase side to side.
 

Cereleste

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I wasn't thinking of the deflection off the fingers as much as the frequency of the oscillations changing with the change in weight of the string. That would affect the point at which the back of the arrow left the string and its apparent stiffness or match with the bow. It's a plucked string and would produce a different "note" if it was on a musical instrument. Separation would happen at a different point on the phase due to the change in speed forward and change in phase side to side.
The frequency of the string does change, but the range over which it changes isn't huge though. I normally get about 108 Hz with a 110 grain string and otherwise similar conditions to the first post. If I switch it for a 70 grain string at the same brace height (therefore same length that's able to vibrate, and same tension in the string) that measured frequency increases to 149 Hz, which is within a few Hz of what I calculate using the equation for the frequency of a standing wave on a string. If I were to increase the mass by 33 grains to replicate the heavier string then I'd expect to decrease the frequency to 96 Hz. A string at 96 Hz takes 10.4ms for one cycle, while one at 108 takes 9.4ms.
That's for plucking the string though, which is the same frequency that the string vibrates at after the arrow has left.

However when the arrow is being accelerated, the string doesn't get to choose how quickly it goes from side to side. In the videos of people like Park Sung Hyun, the time for the string to go from far left (right after leaving the fingers) to far right (right before the arrow leaves) is about 10ms, or the time that it would take for the string to vibrate left to right and back all the way to where it started if that pesky arrow wasn't involved and if the tension on the string (which determines the frequency, and which is at its lowest at full draw) wasn't changing.
The change in mass of the string does have the effect of slowing everything down slightly which is where the effect on the tune comes from. That in turn changes where the arrow is in its bending cycle when it leaves the string very slightly - but it's not because of the change in the string frequency (which doesn't really exist as such during the time that the arrow is being accelerated because the tension and effective length of the string are also changing significantly which both affect the string's natural frequency).
 

geoffretired

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Cereleste, Thank you for all those details and numbers.
Apart from the arrow bending and running through its cycle of flexing; there is also the fact that the string tethers the nock to some extent. That imparts a side to side swing/rotation into the arrow, making the front end sway more as it is free of string restriction.
Small speed changes can affect the tune of the system as the cycles of flex and sway are rapid. What I am thinking is that the weight change of the string will change its forward speed, and affect the tune; but also the weight change will alter the string's flex rate a little, too.
I don't think it takes much of a change to alter the tune.
I understand that it is difficult to measure changes in flex rate and probably more difficult to find what changes they make to the tune.
My feeling is that it is more than a forwards speed change giving the arrow more or less time to go through its cycle. I think there is a change at the string/nock end of the arrow which changes the alignment of the arrow at the point of separating.
 
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