Primitive Archer

Main Discussion Area => Arrows => Topic started by: DC on September 04, 2017, 09:39:43 pm

Title: Spine question
Post by: DC on September 04, 2017, 09:39:43 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?
Title: Re: Spine question
Post by: BowEd on September 04, 2017, 10:00:25 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.
Title: Re: Spine question
Post by: Pat B on September 04, 2017, 10:43:46 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.
Title: Re: Spine question
Post by: DC on September 04, 2017, 11:20:49 pm
Yes, I realised that. I just wanted to make an arrow that was the same spine no matter how it was oriented.
Title: Re: Spine question
Post by: Pat B on September 05, 2017, 06:46:11 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.
Title: Re: Spine question
Post by: BowEd on September 05, 2017, 09:42:42 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.
Title: Re: Spine question
Post by: DC on September 05, 2017, 10:26:46 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.
Title: Re: Spine question
Post by: DC on September 05, 2017, 11:28:13 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?
Title: Re: Spine question
Post by: willie on September 05, 2017, 01:00:21 pm
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
Title: Re: Spine question
Post by: DC on September 05, 2017, 01:06:25 pm
So you're scraping the compression side when the arrow is stiffest, Can you remember why you chose to scrape that side?
Title: Re: Spine question
Post by: willie on September 05, 2017, 01:41:28 pm
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?
Title: Re: Spine question
Post by: Aaron H on September 05, 2017, 02:27:36 pm
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?
Title: Re: Spine question
Post by: DC on September 05, 2017, 02:41:00 pm
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.
Title: Re: Spine question
Post by: DC on September 05, 2017, 02:46:12 pm
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.
Title: Re: Spine question
Post by: Pat B on September 05, 2017, 02:56:18 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.
Title: Re: Spine question
Post by: BowEd on September 05, 2017, 03:27:08 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.
DC......Now Pat B is explaining with edge grain or split timber shafts there is a rift[feathering out side]and an edge gran[straight lined side].You want the edge grain against the bow and the rift side on your knuckle side with the points pointing at you.In case the arrow does brake the points can't stab your hand.
Title: Re: Spine question
Post by: willie on September 05, 2017, 03:43:18 pm
Aaron, that does make sense, all other things being equal, but as dc point out, a bit hard to determine beforehand. I suppose out of round would be a bigger factor as is the case with some of my bamboo.
My previous replies were not "bamboo specific", just generalities I guess.

Quote
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


DC, I am having a bit of a difficulty understanding. Are you describing the left/right orientation of the way the arrow sticks in the target? How are the groupings  relative to your aiming point or the groups of fletched arrows?
Title: Re: Spine question
Post by: DC on September 05, 2017, 04:20:36 pm
 the left/right orientation of the way the arrow sticks in the target. I can't really go by grouping. My"groups" usually take the whole face of the target. I can't count on any consistency.
Title: Re: Spine question
Post by: willie on September 05, 2017, 05:05:20 pm
well, I should have not questioned you so much, your earlier description seems just fine. It's just that I was reading a bareshaft method that is more about group locations than knock orientations. 
Code: [Select]
http://www.acsbows.com/bareshaftplaning.html
For a selfbow, I would find point on aiming to be more desirable than having perfectly straight nonfletched flight at extremely close range. That might just be something for the centershot/plunger button guys.
Title: Re: Spine question
Post by: Aaron H on September 05, 2017, 05:20:38 pm
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.
Haha, I guess I meant to use it to help you with the others
Title: Re: Spine question
Post by: DC on September 05, 2017, 06:14:42 pm
Mostly what I was after was why do we reduce the compression side? I was sure that we would reduce the tension side.

But wait... Since we are dealing with one arrow the compression side for bending it one way is the tension side for bending it the other way. My head hurts, I gotta think this through ;D ;D
Title: Re: Spine question
Post by: willie on October 02, 2017, 06:31:48 pm
Mostly what I was after was why do we reduce the compression side? I was sure that we would reduce the tension side.

But wait... Since we are dealing with one arrow the compression side for bending it one way is the tension side for bending it the other way. My head hurts, I gotta think this through ;D ;D

DC

you gave me second thoughts with your question, and said you were going to think this through, so I was just wondering which side?

and for wood arrows? the same?
Title: Re: Spine question
Post by: DC on October 02, 2017, 07:08:42 pm
Thanks for bringing this up again Willie (I think ;D). I had put it out of my mind cause I finished the arrows I was working on and wasn't making any more. Now after my "stiff side" post it looks like I'll be rebuilding about half of my arrows so I'll have to think this through. I only use bamboo so I don't know about wood.
Title: Re: Spine question
Post by: Hawkdancer on October 03, 2017, 01:32:44 am
Things to garner from this thread!  1. Have a sip or 2 of your favorite beverage.  2. Check spine.  3.  Stiff side to the bow.  4. Scrape stiff side a bit to check spine.  4. Check spine.  5.  Sip beverage.
  6.  Scrap stiff side.  7. Check spine.  8. Sip beverage!  9.  If spine has gone below expectations, go to step 1.  Continue with step 1 and step 1., and step 1! >:D. There ain't no arrow making emoji!
Actually, pretty good information - I'm on step 1!!!  I find working the stiff side tends to bring spine into line.  But you guys have broken more arrows than I have made or repaired!
Hawkdancer
Title: Re: Spine question
Post by: DC on October 03, 2017, 11:24:33 am
I think I'm going to go with Arron's suggestion. All I can think of is that boo is tension strong. If the wall is thicker on one side it would increase the compression strength the same amount as the thickness increase. Maybe when it's in tension it's already so strong that the thickness increase doesn't matter that much. It seems a little far fetched but if the boo is so strong that all or most of the bend comes from compression it starts to make sense. I think this is going to have something to do with a shifting neutral plane. I don't know how this would effect solid wood arrows or shoot arrows with a pith.