Author Topic: Spine question  (Read 397 times)

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Online DC

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Spine question
« on: September 04, 2017, 06:50:31 pm »
I'm messing with a bamboo arrow trying to get it to bareshaft nicely. Nock is cut and I marked one side as the potential cock fletch side. If I shoot it cock side out it hits nock left. If I shoot it nock side in it goes nice and straight. I put it on my spiner cock up and it spines as 40#, cock down its 35#. If I decide I want to scrape one side to reduce the 40# to 35# which side do I scrape, the tension side or the compression side?
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Offline Beadman

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Re: Spine question
« Reply #1 on: September 04, 2017, 07:11:13 pm »
Pat B might chime in here as to which side of bamboo a person normally puts against the bow with his experience with bamboo.Why not put your cock feather on the side where it shoots straight and call it good?Usually your stiffer side is against the bow on a shaft.
You got to stand for something or you'll fall for anything.
Ed

Offline Pat B

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Re: Spine question
« Reply #2 on: September 04, 2017, 07:54:34 pm »
The stiff side of cane and hardwood shoots goes against the bow. I have still had a few arrows shoot better with the cock feather in towards the bow but generally the stiff side of the shaft goes against the bow.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Online DC

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Re: Spine question
« Reply #3 on: September 04, 2017, 08:31:37 pm »
Yes, I realised that. I just wanted to make an arrow that was the same spine no matter how it was oriented.
Vancouver Island

Offline Pat B

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Re: Spine question
« Reply #4 on: September 05, 2017, 03:56:59 am »
You can do that. Art Butner, the guy that taught how to make arrows would scrape cane so his arrows had the same spine on all sides. I don't go that far but it can be done.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Beadman

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Re: Spine question
« Reply #5 on: September 05, 2017, 06:53:30 am »
DC...Seems everyone has their limits but if an arrow is within 5#'s of a difference in spine from 1 side to the other I call it good enough.The arrow will fly good enough for me.Of course balanced is best.If it is 10#'s difference I've taken it off the compression side to balance them a little better.
It has to be done right away as the shaft is a bit too heavy as if it is done later towards the finish the shaft will get too weak.
You got to stand for something or you'll fall for anything.
Ed

Online DC

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Re: Spine question
« Reply #6 on: September 05, 2017, 07:37:34 am »
Thanks guys. This was just an experiment to see if it would fly any better. What it did do was sort out in my mind what PatB means when he says stiff side to the bow. I never knew for sure what that meant. I'm pretty sure now that it means that the arrow is weakest in the direction that it has to bend to get around the bow.
Vancouver Island

Online DC

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Re: Spine question
« Reply #7 on: September 05, 2017, 08:39:01 am »
I would like to talk about this a bit more. :D Initially I was surprised that an arrow could be stiffer one way. I expected that if you bent it, measured the deflection and then rotated it 180 degrees, it would be the same deflection. Nope. Then I had to decide which side to scrape to equalise it. I guessed it would be the tension side. I took a few scrapes and measured it. It seemed to be getting worse but rather than ruin an arrow I started this post. Ed says he scrapes the compression side. That seems to fall in line with what I've seen. I'll try that after I finish my coffee. Pat, do you know what side Art scraped? Do we have any theories why it's that way?
Vancouver Island

Offline willie

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Re: Spine question
« Reply #8 on: September 05, 2017, 10:11:09 am »
If I place the point of an arrow on a smooth table top, holding the nock end with one hand while pressing a bend into the shaft with the other hand ... and roll the arrow back and forth, I can easily find the stiffside and the weak side.

I scrape the up-facing side when the arrow is the stiffest. I could be doing it different from everybody else however.

Often it seems like the arrow is only stiff on one quadrant, and weak on the three other sides.

I only need to scrape for stiffness in the middle third of the arrow for spine, and as  jeffp51 mentioned in the other thread, reduce the outer thirds for weight reduction

Online DC

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Re: Spine question
« Reply #9 on: September 05, 2017, 10:17:13 am »
So you're scraping the compression side when the arrow is stiffest, Can you remember why you chose to scrape that side?
Vancouver Island

Offline willie

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Re: Spine question
« Reply #10 on: September 05, 2017, 10:52:16 am »
I cannot remember why, just that it's what I do. Perhaps it does not matter which side gets reduced, but we seem to prefer to do reductions on our bows on the compression side, so maybe just a force of habit?

Offline Aaron H

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Re: Spine question
« Reply #11 on: September 05, 2017, 11:38:24 am »
I would think that with bamboo, the difference in stiffness lies in the uneven wall thickness.
Maybe try an experiment on a particular shaft where there is drastic difference in stiffness from one side to the other, mark the stiff side, then cut the bamboo shaft in half lengthwise along that stiff side line. When you open it up, see if there is a noticeable difference in wall thickness from the stiff side to the weak side (possibly using a set of calipers). If there is a difference, I would then use that to determine which side to scrape. It would make sense to me that you would want to even out the wall thickness for consistency.
Does that make sense to anyone?
But those who put their trust in the Lord will find new strength. They will soar high on wings like eagles...     Isaiah 40:31

Online DC

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Re: Spine question
« Reply #12 on: September 05, 2017, 11:51:48 am »
I cannot remember why, just that it's what I do. Perhaps it does not matter which side gets reduced, but we seem to prefer to do reductions on our bows on the compression side, so maybe just a force of habit?

It definitely matters. That's what's bothering me. I've got this arrow just about even now. It shoots a little nock left no matter which way I shoot it. Scraping the compression side of the strong bend is bringing it around. I've had to shorten it twice and I'm about to run out of draw length but I'm learning stuff.
Vancouver Island

Online DC

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Re: Spine question
« Reply #13 on: September 05, 2017, 11:57:00 am »
I would think that with bamboo, the difference in stiffness lies in the uneven wall thickness.
Maybe try an experiment on a particular shaft where there is drastic difference in stiffness from one side to the other, mark the stiff side, then cut the bamboo shaft in half lengthwise along that stiff side line. When you open it up, see if there is a noticeable difference in wall thickness from the stiff side to the weak side (possibly using a set of calipers). If there is a difference, I would then use that to determine which side to scrape. It would make sense to me that you would want to even out the wall thickness for consistency.
Does that make sense to anyone?
Once I split it in half it's a bit late to scrape :D I see your point though.
Vancouver Island

Offline Pat B

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Re: Spine question
« Reply #14 on: September 05, 2017, 12:07:06 pm »
DC, Art(artcher1) went all out with arrows. He understands arrows and arrow making like nobody else I know. Unfortunately his health isn't good and he hasn't been around for a few years now. Art scraped the whole cane shaft so they were the same stiffness all around.
Not only cane but hardwood shoot arrows also need for the stiff side against the bow. If possible, Art told me to put the second stiffest side to the shelf(down). That isn't always possible though.  Even doweled arrows have a stiffer side which is along one of the grain edge sides. With dowels you also have to consider the grain "flames" so if the arrow breaks when shot it doesn't drive the broken shaft into your bow arm.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC