Spine tester

dvd8n

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Except they changed those figures from being actual measurements, to being "shaft codes"... (hence the whole 9.3mm debacle)
Oh, yes, I forgot that the ally measurements aren't actual measurements, just codes that were at one time measurements, but are now, due to material changes, just numbers in Easton's catalogue.

I tell you, everybody in the archery industry is perpetually ****-faced. It's the only possible explanation.
 
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dvd8n

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Yes. As in 2317. Which should be 23/64" or 0.3594". Which is less than 9.3mm or 0.3661" which should be legal. But if you measure the shaft a 2317 is actually 0.3690" (*) which is too big to be legal.

On the other hand 2312, 2314 and 2315 are legal. A 2312 has an outside diameter of 0.3634" and a 2314 has a diameter of 0.3568" and the 2315 has a diameter of 0.3649" (*).

To be honest I'm not sure if the codes were ever an accurate indication of size then the measurements drifted, or whether the codes were always approximate. I heard that the sizes drifted to keep the spines consistent as time went on but I really don't know if that's true.


* This was true at the turn of the century when this blew up. Who knows what the measurements are now.
 
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Kernowlad

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There's a story here, I suspect involving embarrassing injuries...
It could have been worse but it still wasn’t fun. The replacement has titanium rails. Far more dependable when looking after ones underside.
 

KidCurry

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I had heard that carbon arrows don't have an even spine due to the lay-up of the carbon and where the edges of the mat fall but I wasn't convinced that it is a real effect. Can you see it on your tester?

Did you make the weight yourself or is it something repurposed?

Did you go to the effort of making it to the ATA standard (28" / 1.94lb) or are you just using what's convenient to spot the variations that you're interested in?
Yes, you can see the spine vary as the shaft rotates. My ACEs show about 0.06mm or 0.0025" deviation which I have yet to translate to spine. Interesting my 1 1/2yr old ACEs are all still within 0.0025" straightness with no load and they have been shot a lot into foam. I'm yet to see if the spine variation aligns with the arrow straightness variation. I'm going to bet it does and will make life a lot simpler :) ACEs are concentric with no measurable deviation.
Compare that to my Easton apollo 610 which has a straightness deviation of 0.13mm 0.006" (6thou) and a spine deviation of 0.32mm 0.016" (16thou).

At present the weight is off my barebow, 1.5lb as I only have 303 stainless bar stock at the moment for customer weight orders and it's a waste to use raw stock 303 for a spine tester. I will make a 1.94lb weight when I get some mild steel, although I have some brass kicking around some where. But I'm really only interested in spine alignment and arrow straightness.
 
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dvd8n

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Yes, you can see the spine vary as the shaft rotates. My ACEs show about 0.06mm or 0.0025" deviation which I have yet to translate to spine. Interesting my 1 1/2yr old ACEs are all still within 0.0025" straightness with no load and they have been shot a lot into foam. I'm yet to see if the spine variation aligns with the arrow straightness variation. I'm going to bet it does and will make life a lot simpler :) ACEs are concentric with no measurable deviation.
Compare that to my Easton apollo 610 which has a straightness deviation of 0.13mm 0.006" (6thou) and a spine deviation of 0.32mm 0.016" (16thou).

At present the weight is off my barebow, 1.5lb as I only have 303 stainless bar stock at the moment for customer weight orders and it's a waste to use raw stock 303 for a spine tester. I will make a 1.94lb weight when I get some mild steel, although I have some brass kicking around some where. But I'm really only interested in spine alignment and arrow straightness.
I'd be interested to know if there's any spine loss to an arrow that's been in an 'incident' (e.g. bounced off a tree) with no visible damage. Or spine change to an ally that's been straightened.
 

dvd8n

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Yes, you can see the spine vary as the shaft rotates. My ACEs show about 0.06mm or 0.0025" deviation which I have yet to translate to spine. Interesting my 1 1/2yr old ACEs are all still within 0.0025" straightness with no load and they have been shot a lot into foam. I'm yet to see if the spine variation aligns with the arrow straightness variation. I'm going to bet it does and will make life a lot simpler :) ACEs are concentric with no measurable deviation.
Compare that to my Easton apollo 610 which has a straightness deviation of 0.13mm 0.006" (6thou) and a spine deviation of 0.32mm 0.016" (16thou).

At present the weight is off my barebow, 1.5lb as I only have 303 stainless bar stock at the moment for customer weight orders and it's a waste to use raw stock 303 for a spine tester. I will make a 1.94lb weight when I get some mild steel, although I have some brass kicking around some where. But I'm really only interested in spine alignment and arrow straightness.
You could go down to your local garage and see if they'll give you a some old lead tyre weights to melt down - or just put in a tub.
 

4d4m

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I've just had a look at the dial gauge on my tester and it's range is 0-0.5" so the maximum spine would be 500. Doh! 🤦‍♂️
Could you make one with a smaller weight and so a smaller max deviation? It would take some trial and error to get the calibration right as it's (probably) not linear but shouldn't take too long to get it agreeing with a known good spine tester.
 

dvd8n

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Could you make one with a smaller weight and so a smaller max deviation? It would take some trial and error to get the calibration right as it's (probably) not linear but shouldn't take too long to get it agreeing with a known good spine tester.
I wondered about that. According to Hooke's law a simple spring should deflect half as much with half the weight. But it's not that simple as the defined simple support method of the arrow at two points means that the spring (arrow) length changes as it deflects, and a smaller weight would change the length by a smaller amount. It's beyond my maths ability to work out how significant that is. I could have worked it out at one point but the knowledge has been pushed out of my brain by useless stuff like the date of my wife's birthday.

I guess the simple solution would be to try it :)
 

4d4m

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I was thinking more of the arrow nearing its elastic limit, a bit like a bow "stacking", but you make a good point I hadn't considered.
Then I thought about it a bit more and concluded given the deviation is so low relative to the arrow's length that for both concerns it be might near enough linear to make little difference. Good enough for a home made spine checker anyway.
 

Rik

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I'd be interested to know if there's any spine loss to an arrow that's been in an 'incident' (e.g. bounced off a tree) with no visible damage. Or spine change to an ally that's been straightened.
Don't know about straightening, but I recall a report of someone measuring an old set of allys which had been used in a single orientation for their whole life, and finding that they had become oval over time.
Also the "exploding X7s" thing. Those were tempered to the point where they would stay straight after a hit which would bend a lesser shaft... but you might find them in bits in your box later, as the internal stresses came out
 

little-else

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with a standard 3 point load test the supports are knife edges or a single roller and a knife edge rather than bearings but a nice thing to build your own one.
For woody shooters you can make a very simple jig out of a plank and a couple of nails and then use a pencil to mark the deflection. Obviously measuing accurately will be a problem but for batching shafts and finding the direction of greatest and least deflection it will work well enough.
With ali alloy shafts the alloy code (say 75XX) tells you both the alloy and treatment process so they dont need to put that on the shaft as anyone who reeaally wanted to know would look it up in an ASTM data book or the like and crib the rest of the stremgth of materials data from there so the 1916 or whetever is enough for most folks.
Where playing with your rig comes in handy is being able to cart it about and use your current arrow data as a benchmark and then try out all of the arrows in a shop before buying. You could find some cheaper ones that match your existing setup or you could discount those that fit the theoretical data given by Easton or the like because the reality doesnt match their charts.
 

little-else

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AS for Kernowlad's bike, the John Percy Group made a batch of hot extruded superlight alloy for Peugeot to use for seat stems for their Tour de France team. The weight saving equated to thousands of calories saved by the riders and that led to less overall weight so less effort to push that person around for a fortnight. funny how a small thing can have a big knock on.
Did some analysis on Russian Ti alloys that came from their helicopters shot down in Afghanistan years back. ended up giving the big bits away to geophysics to use as hammer seismometer plates as they were lighter and tougher than steel so better for students to lug about.
If you want a very stong composite meteial for your bike saddle struts try Morgan Advanced Materials, and see if they have anything in their bin made from a squeeze cast MMC that will suit. Some super combos exist that will beat carbon hands down.
 

Kernowlad

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AS for Kernowlad's bike, the John Percy Group made a batch of hot extruded superlight alloy for Peugeot to use for seat stems for their Tour de France team. The weight saving equated to thousands of calories saved by the riders and that led to less overall weight so less effort to push that person around for a fortnight. funny how a small thing can have a big knock on.
Did some analysis on Russian Ti alloys that came from their helicopters shot down in Afghanistan years back. ended up giving the big bits away to geophysics to use as hammer seismometer plates as they were lighter and tougher than steel so better for students to lug about.
If you want a very stong composite meteial for your bike saddle struts try Morgan Advanced Materials, and see if they have anything in their bin made from a squeeze cast MMC that will suit. Some super combos exist that will beat carbon hands down.
Titanium seems to suit seat rails quite well. I did my Degree dissertation on MMCs; they never really took off as well as I thought they would (Lotus originally used them for Elise brakes) but I know they do have some niche applications.
I’ve got a few carbon bits on the bike; the bars, most of the brakes and some bits of the gear mechs but it’s a good old steel frame (Reynolds finest) which I much prefer to bone shaking aluminium.
The road bike is alu with carbon forks but that doesn’t get smacked into trees very often...
 

dvd8n

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with a standard 3 point load test the supports are knife edges or a single roller and a knife edge rather than bearings but a nice thing to build your own one.
The ATA (AMO? ASTM? Whatever?) regs state that the arrow be supported by rollers (well, a system to allow free axial travel) of maximum diameter 1/4" oriented to allow axial movement of the arrow. Not many testers I've seen actually comply with that, I think.
 

Rik

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Slight sideways step here... does absolute spine matter much? I mean, right ballpark, okay, but the charts are not exactly precise things.

Relative spine, on the other hand: I've thought before that it might be handy to have a simple tool which would take two shafts and show how close in spine they were, for matching. I have this image in my head of something which stresses one shaft against the other and shows the imbalance.
 

dvd8n

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Slight sideways step here... does absolute spine matter much? I mean, right ballpark, okay, but the charts are not exactly precise things.

Relative spine, on the other hand: I've thought before that it might be handy to have a simple tool which would take two shafts and show how close in spine they were, for matching. I have this image in my head of something which stresses one shaft against the other and shows the imbalance.
For people shooting woodies I think it does. It's really useful to be able to sort your bag of dowels into groups.

For people shooting allys or carbons, not really, although it may be a useful tool for spotting spine change due to damage (but that's just speculation on my part).

But I won't be experimenting in the near future - my plans for a combined arrow straightness/straightener/spine tester workstation have just been scuppered by the last electricity bill and a trip to Homebase for insulating and draught excluding material 😭:cry:😭
 

Mark2

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I must admit that when I quickly want an idea of the spine of an ally, I look at the tables and look to see what the spine of the carbons are that are in the same group.
Probably no one cares because they are always bent!
 

little-else

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Titanium seems to suit seat rails quite well. I did my Degree dissertation on MMCs; they never really took off as well as I thought they would (Lotus originally used them for Elise brakes) but I know they do have some niche applications.
I’ve got a few carbon bits on the bike; the bars, most of the brakes and some bits of the gear mechs but it’s a good old steel frame (Reynolds finest) which I much prefer to bone shaking aluminium.
The road bike is alu with carbon forks but that doesn’t get smacked into trees very often...
my bike came out of a skip and weighs about the same as the skip. It gets me to the allotment , post office etc and was free
 
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