point weight effecting stiffness?

bolerus

Member
There are many of the technical aspects of archery that go way over my head, and here is another one

so what I was wondering, if somebody knows how much point ( and nock ) weight effect the stiffness of an arrow

I have 2 scenarios.

I am shooting a 40lb recurve with about 41.5 on my fingers. measuring my draw to the button I get about 27 inches, which fives me just a tad short of 29" draw length.

I have 2 sets of ACE arrows, one I bought ( second hand) for my recurve and one set for my compound.

One set are ACE 570, with 28.25 shafts, pin nocks and 85 grain screw in points ( the inserts are the 39grain ones and the points are 46grain)

I was thinking about putting heavier points in to try and cut through the wind a bit better, but would that weaken the spine ( effetively) too much and make them too whippy? also how much would the heavier point effect my sight marks?

I did a shoot at the weekend and beat my handicap score with the 570s so they cant be too bad, but the wind was effecting them, and I noticed a couple of shots, the back end kicked out a bit, but it was only occasional, so more likely a bad release than a bad arrow.



The other arrows are ACE 470 at 28 inch shafts, currently with easton G Nocks and break off points that are weighing in at 118 grain.(whihc are quite long so make the arrow effectively longer) so overall the 470s are only a couple of mm shorter than the 570s

So the other option would be to put the pin nocks and lighter points in the 470s but would that bring the stiffness down enough to shoot on my recurve ( the 470 are, according to the chart in the 44lb + range) but then would that mess them up for cutting through the wind.

I am on a really low budget at the moment ( which is why I am trying to sell my compound and other gear) so cant afford to go get some 520s which is really the correct choice.


I know a lot of this is guess work, and the only real way is to do it and see, but I would people opinions if at all possible.

Thanks

(my other arrows are 540 ACGs but I couldnt reach 100yards without aiming high, hence the change to ACE)

edit:
I only put the pin nocks in last week, before shooting, and havent done any bare shaft testing since, maybe they have already stiffened them a bit?
 

Rik

Supporter
Supporter
Technically, the point weight doesn't affect the stiffness of the shaft at all - it can't, that's a property of the shaft.

But what most people mean is: how does it affect the arrow match? And it's not a simple answer.
Something like (for example) a 20 grain change in point weight may not change the match noticeably. It may not be detectable in setup (bare shaft, walk back etc), unless the match was somewhat edgy in the first place. So if you start out with a weak match and increase point weight... I don't know how to call that.

I'm not sure what you're trying to say about the 470s... if they are currently too stiff, then there's no way that reducing point weight would help. Swapping pin nocks out and replacing with something lighter might.

My personal experience: increasing point weight on a set of ACE 670s, from 100 to 120, made no difference except to vertical sightmarks. Setup tests detected no change.
 

Timid Toad

Moderator
Staff member
Supporter
Fonz Awardee
Ironman
On the other hand, I *do* find changing point weight changes tune. But only a little. If you've got the wrong spine, you've still got the wrong spine, I'm afraid.
 

jerryRTD

Well-known member
second thoughts

Suck it and see. Buy three or four heavier points put them in the 570 spine arrow (make one of the shafts the bare shaft) and see if there is any difference when you tune. Ignore your draw length the only important measure is arrow length. as long as the arrow will stay safely on the arrow rest when you are at full draw you arer ok.
 

KidCurry

Well-known member
AIUK Saviour
The other arrows are ACE 470 at 28 inch shafts, currently with easton G Nocks and break off points that are weighing in at 118 grain.(whihc are quite long so make the arrow effectively longer...
Actually the points do not make the arrows longer in terms of matching to the spine tables or the bow :)
 

Aleatorian

Member
Weight changes to the back of an arrow changes dynamic stiffness more than weight changes to the front.

Adding weight to the front reduces dynamic spine (acts weaker) and the inverse.
Adding weight to the back increase dynamic spine (acts stiffer) and the inverse also

Putting pins and the 85 grain into the 470's which are already stiff would make them act even more stiffer
 

bolerus

Member
Actually the points do not make the arrows longer in terms of matching to the spine tables or the bow :)
correct because that is spine. but they do make them longer in terms of length, in other words the tips are no closer to the arrow rest. they are well within safe distance anyway
 

bolerus

Member
Weight changes to the back of an arrow changes dynamic stiffness more than weight changes to the front.

Adding weight to the front reduces dynamic spine (acts weaker) and the inverse.
Adding weight to the back increase dynamic spine (acts stiffer) and the inverse also

Putting pins and the 85 grain into the 470's which are already stiff would make them act even more stiffer
thanks, that was what I was trying to say ( although did i get it mixed up) I think based on my last shoot adding the pin nocks may have brought the 570s dynamic spine up better.(I also had quarter of an inch taken off - funny how i forgot about that)

I was also wondering / thinking about adding the heavier points to help them cut through the wind but maybe that will make that act too weak again. Ideally I would buy some 520s and set them up but right now that is way out of budget
 

geoffretired

Supporter
Supporter
When you add weight to the arrow the first thing we notice is it travels more slowly and we get lower sight marks.
The extra weight also slows the bow down, which gives the arrow more time to go through its flex and wave oscillations.
Matching arrows to bows is about matching the flex and wave oscillations to get the arrow in the best position at the point where it leaves the string.
Adding the weight at the front, puts more bend in the shaft as the inertia is increased,( we think that is good if the shaft is too stiff) but the resulting slow down can work against the benefits.( stiff arrows usually need faster bows not slower ones)
Adding weight at the back is usually a smaller weight, but it slows the bow down without adding to the amount of bend, and can help with weak arrows.
 

Rik

Supporter
Supporter
On the other hand, I *do* find changing point weight changes tune. But only a little. If you've got the wrong spine, you've still got the wrong spine, I'm afraid.
I suspect that error margins have something to do with it as well... The better (more consistent) someone is, the more likely they are to spot relatively small differences in setup. It's probably true that small changes in my setup would be swamped by "noise"... :(
 

Mark31121

Member
Ironman
Is it the weight change or the inserts (either the pins or the internal part of the pile) that make the biggest difference?

for example, if you add a pin at the back you're effectively shortening the shaft by half an inch as there is very little bend in the pin itself.

The same goes for break-off points, by reducing the weight you're also increasing the bendable part of the shaft.
 

Rik

Supporter
Supporter
Is it the weight change or the inserts (either the pins or the internal part of the pile) that make the biggest difference?

for example, if you add a pin at the back you're effectively shortening the shaft by half an inch as there is very little bend in the pin itself.

The same goes for break-off points, by reducing the weight you're also increasing the bendable part of the shaft.
well,
adding weight at the back: it doesn't appear to matter whether you add it to the shaft (pin) or the string (brass nock point) - same effect.

Adding weight to the front... that's more complex, but bending isn't really the point (pun intended). Matching isn't really about how much the shaft bends, it's about when it bends. shaft stiffness is used as a proxy for the timing of the bend (reaction of the shaft), a slightly shorter effective beam, assuming a longer insert, probably has a slightly higher frequency, and it's moving forwards slower, which should be a double effect... but there's lag in the whole thing - more bend at the back initially, which may reduce the perceived effect on matching. Basically, the whole thing is a morass of maths, and any simple answer is likely to be inaccurate :)
There is modelling of it - James Park's PhD thesis springs to mind.
 

bolerus

Member
so, by taking quarter of an inch off the front, and adding pin nocks is effectively the same ( in terms of stiffness) as taking abotu 3 quarters of an inch off the arrow ( because the pin stops some of the arrow bend)


What I really shoudl do, at some point is do some more bare shafting to see how it is.

Another sort of related question. how important is the batch code. mine are G series. As I only have 9 I was thinking of buying a set of 4 from clickers ( ?92 ) but i imagine it unlikely they will have the same series.

Anyway, thanks for your time guys, I certainly understand it all a bit more, as long as I dont think about it too hard lol
 

bolerus

Member
Ok things have gotten a bit more complicated.

so, I bought a grain scale last week, and decided last night to weigh the ACE 570s to see how much of a difference I have based on the 3grain per dozen tolerance thing... just because I was curious.

I only have 9. 6 of them weigh within 2 grains , so well within .

3 of them are 8 grains lighter. and on closer examination, those 3 have the writing mostly rubbed off, and the other 6 look considerably newer. My guess is the 3 lighter ones are older and possibly a differnt C number , but cant see it at all.

is 8 grains enough to worry about, and also, as they have screw in points, i could just buy 3 point inserts that are slightly heavier to bring them in line, would that work to bring the weight together?
 

geoffretired

Supporter
Supporter
You could shoot them and see if the lighter ones land higher. The lighter ones may have lost material from constant shooting into hard bosses.
You could take out the points and weigh them and try the heavier points in the lighter shafts, to see if you can get more arrows closer together in weight.
I suppose you could try filing a little off the insert end of the heavier piles and try to match the weight that way.
 

Rik

Supporter
Supporter
Ok things have gotten a bit more complicated.

so, I bought a grain scale last week, and decided last night to weigh the ACE 570s to see how much of a difference I have based on the 3grain per dozen tolerance thing... just because I was curious.

I only have 9. 6 of them weigh within 2 grains , so well within .

3 of them are 8 grains lighter. and on closer examination, those 3 have the writing mostly rubbed off, and the other 6 look considerably newer. My guess is the 3 lighter ones are older and possibly a differnt C number , but cant see it at all.

is 8 grains enough to worry about, and also, as they have screw in points, i could just buy 3 point inserts that are slightly heavier to bring them in line, would that work to bring the weight together?
Or weight the current inserts with a little melted solder? Though if the shafts are significantly worn, you've probably got a good deal more variance than just the weight.

Just a thought: did you check that point/insert is the same size on the older shafts? 8 grains could be a combination of wear and different shaft codes...

For comparison: I had a set of Navigators a few years back, that I took care to set up with a sub 1 grain range of weight across the set. I weighed them a couple of years later and found the weight range had expanded to close to 7 grains. It made me realise: it takes vigilance and maintenance to keep a set of shafts tightly matched, and unless you're chasing points it doesn't matter much. Do I still get anal about matching up shaft weights...? Well, duh... :)
 

bolerus

Member
Rik. I took the "lighter" points out and measured them, they are the same as the others.

although one of the new arrows had a heavier point in ( only 5 grain) which I have already swapped for one of my spares.

long term I will need to buy some more, but at the moment I think I will try the solder trick.


I will try to shoot the lighter ones mixed in and see if they are going noticeably higher. I am not that good that things need to be critical, If I can keep them in the red ring at 80 yards I will be happy.

Thanks again for your advice guys :)
 

bolerus

Member
thanks again Rik, nipped to the local diy shop and picked up some solder, all my arrows now weigh the same (288 grains) with a couple just over 289. no more excuses for bad groups lol
 
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