Recurve bare shaft- effect of spine change

mbaker74

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Assuming you are shooting at 30m, if x spine gave a 30cm gap between fletched and unfletched groups showing the shafts to be too stiff, how much smaller would that distance be by changing down one spine group? This assumes the bow is set up for the new arrow and everything else is equal.....
 

geoffretired

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What a great question. It's a bit like saying " my bare shafts are 30" away at 30m what spine change will bring them together?"
I would guess the 30" in your case would be halved.... but that is only a guess. But someone will be better able to give an accurate answer.
Perhaps ,though, the differences change as draw weights change; or arrow lengths.
 

Rik

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You could test this...
wind your weight all the way down, do a bare shaft test. Wind the weight up to the top (same settings) repeat the test.
But I suspect the results are not so easily predictable and may be non-linear...

One potential answer "30cm or more" - assuming the lower spine group is a match... if it isn't a match then the answer might be "zero difference" - assuming the 30cm is a limiting case at the distance you're using for the test. But if the button offset etc are reset for the new shaft then grounds for comparison are already gone. If that basic setup is not done then the test isn't done properly :)
 

Rik

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Well, if the aim is to see what the result of a change in the match of the shafts is, then it's probably more useful to know how much you can improve the match by adjusting the draw weight...

The rest of the comments are to do with the mechanics of the thing:
If the shafts are way too stiff, then the next size down may also be way too stiff, so there may be no visible change in results. If the next size down is supposed to be correct, then you'd expect to be able to bring the bare shafts and fletched together, hence could be the whole 30cm different.

Thing is, you tend to be changing things to minimise the group placement difference. Draw weight, button settings. Which makes the comparison between two sizes of shafts indirect at best.
 

geoffretired

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Hi Rik, Thanks for that. I follow what you are saying.
I was looking at this as a beginner might(not mbaker74)

"My bare shafts are XXX far from the group, do I need one spine weaker or two?"
It seemed to me to be a question we often get posted but rarely in those terms. They tend to ask about the distance between fletched and bare shafts and whether that is too much or can they do anything with the button etc etc.
Mbaker's wording seems like a useful way of asking for help with spine.
I also see the use of knowing what weight adjustments can be made. Sometimes draw weight changes seem like the obvious way to go, but then I have to bear in mind, I am not the one drawing the string with 2 lbs extra to struggle with.
 

AndyS

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Enough lurking!
Last year my ACCs were wearing out (aluminium starting to show near the point !) and as I suspected that my 3-28 (500) were too stiff, I bought a couple of 3-18 (560) and another couple of 3L-18 (620) to experiment with over a couple of weeks.
With the rear of the bare shafts taped up to match the weight of the impulse vanes I was using at the time, at 30m I found that whilst the 560s were consistently fairly close to the central fletched shafts, the 500s were about 10" from the left hand edge of the boss (RH archer), and the 620s occasionally hit the right hand edge of the boss, but most were in the green :)
This was typical, but wasn't totally repeatable across several sessions - sometimes the differences were significantly smaller, and the variability must obviously have been down to the pink bit at the back, and the unforgiving nature of bareshafts. There were actually sessions where I wondered if the 620s might be an option, but others where I could barely keep them on the boss, however the 560s were consistently good whatever I did.
When I fletched all three spines, there wasn't much difference to be seen.
Out of interest, I did experiment with taped vs untaped on the 500 bare shafts, and the difference (for me) was typically around 4 to 5 inches with the taped showing a little stiffer as you might expect.
In the end as the 560s seemed consistently good, I went with 540 ACGs with XS vanes (slight rear weight reduction and weakening effect compared with the impulses), and with a slight tweak of the limb bolts I'm really happy with how they fly (most of the time)
So for me last season, one spine seemed to equate to around half a boss at 30m.
From my experience, bareshafts seem to be very sensitive to quality of the shot - I've just updated my riser and did a bit of bareshaft tweaking last week, and whilst well-shot bareshafts are now in the group, slightly poor quality shots can be an easy six inches out of the group - for reference I shoot at a fairly consistent Bowman standard.
With the new riser, my bareshafts initially were probably showing somewhere around 30 cm stiff, but after winding in the limb bolts to give around another lb, well-shot bareshafts are now nicely in the group.
If you think your shafts might be too stiff and the budget will run to it, it might be worth getting a couple from the next spine weaker to play with before you bite the bullet - I'm glad I did.
 

AndyS

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Sorry, obviously not clear, yes I did. The fletched versions of each spine where pretty consistently close to each other around the centre of the boss, but the differences I was trying to describe were for the bare-shaft of each spine, with the rears of the bare shafts taped to replicate the weight of the vanes I was using.
So at 30m I was typically seeing bare shaft 500 spine approx 10" from the left edge of the boss, bare shaft 560 spine central in with any fletched group, and the bare shaft 620 spine very close to the right hand edge of the boss.
Like I said, some sessions the spread was smaller which I put down to my release being a little cleaner on those days, but those differences were fairly typical of what I saw.
 

geoffretired

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Hi AndyS thanks for that. So, if I put this in my own words, I should be explaining what you observed, yes?
All three spines of fletched arrows landed close to the centre of the boss. The bare shaft weak ones(620) grouped well right and the bare shaft stiffer ones( your old 500)well left, and the bareshaft mid spine ones(560) in the centre.
The weaker ones were further from the centre than the stiffer ones even though they were same spine difference from the 560.
It is interesting that the best spine match and the other two, still group in the same place as each other , when fletched.
It seems that you could have shot just the bare shafts and found the best match.... once you knew where to set the sight etc having used one set of fletched arrows to confirm. I find that a bit interesting, too.
 

Rik

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Bareshaft is sometimes a little less useful than you would like... I had this experience recently where I could get 3 sizes of shaft past a bare shaft test. But one size (the stiffest) consistently produced groups 2 to 3 times larger than the others.
Ultimately, how they group is more important.
 

AndyS

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Yes that's pretty much it. The three spines when fletched did show small differences, but these were pretty insignificant when compared to the bare shafts. So yes it did look like I could just have selected from the bare shaft positions, and that's effectively what I did once I'd established that the fletched versions showed very small differences. Since then I've done the standard tweaking of limb weight and button pressure with the new arrows, but the best "starting" spine was fairly obvious once I'd done the comparison.

Yes the stiffer shafts being further out than the weaker, despite the same spine difference did seem odd, but the stiffer shafts were also the old, worn ones that had definitely lost carbon around 1 to 1.5 inches from the point, so I wonder if this might have weakened them slightly (I didn't have any new 500s to compare). Interestingly, on the sessions where the overall spread was smaller, the weak shafts actually moved in closer than the stiff ones - but I only saw this on one session.
From what I've picked up in the three years I've now been shooting, the general advice seems to be that a slightly stiff spine is more forgiving, and certainly the too-weak spine gave me more variation in bare shaft position than the too-stiff, which tends to support stiffer being more forgiving - at least for my standard of shooting.

The whole exercise was a bit of an experiment to learn from first hand, and I did also experiment with 10 / 20 grain point weight reductions on the weak spine to see how much that would stiffen it up - I don't have any figures, but I do remember thinking that adding tape at the rear of the bare shafts to simulate the fletching weight seemed to have much more effect on the bare shaft, than making a larger weight change at the front.
 

AndyS

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Sorry Rik, was replying to GeoffRetired and posts overlapped.
I've no doubt that groups are more important, but didn't have the funds to buy complete sets of each spine to compare, so thought a couple of each would be an interesting exercise that I might learn something from. I've since had favourable comments from more experienced archers at the club about how well my arrows fly, so maybe for the wrong reasons, but I'm happy with the selection I made.
 

Rik

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Sorry Rik, was replying to GeoffRetired and posts overlapped.
I've no doubt that groups are more important, but didn't have the funds to buy complete sets of each spine to compare, so thought a couple of each would be an interesting exercise that I might learn something from. I've since had favourable comments from more experienced archers at the club about how well my arrows fly, so maybe for the wrong reasons, but I'm happy with the selection I made.
Oh yes. The only reason I could do it was having a mixed bag of odds and sods that I've picked up from people over the years. If I had to buy anything, it wouldn't have happened...

But my point really was: bareshaft is a bit of a lottery. I've had setups where I couldn't get it to work at all. Now I'm in one which seems to show a wide range of matches... Overall, I've had far more reliable results from walkbacks (ignoring the nonsense about curves and straight lines).
 

geoffretired

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I still remember, as a beginner, shooting a friend's x7's when my own arrows were 24 SRTX.
My own arrows came out with a wiggle and the X7's came out beautifully. I Robin Hooded one of the X7's and my friend had just brought them out to try for the first time; a Christmas present from his wife!! I was mortified!
I can also remember the feeling that I had before the accident, seeing the arrows flying so well.It seemed right that arrows should fly like that. I felt better about my shooting; it was as if I had improved.
I have seen archers shoot great scores with arrows flying not so well, so I know good flight isn't everything. There is a still a feeling lurking inside that wants me to get better flight when it isn't as good as I would like.
 
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