Author Topic: String alignment (bang)  (Read 9397 times)

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Offline DC

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String alignment (bang)
« on: May 12, 2016, 12:45:47 pm »
I've read that as long as the tips and handle line up everything is OK but when I see something like this where the string goes completely outside the bow something in the back of my head says this is wrong. Am I right? The black line hits the other tip fine and the tips and handle line up but it just looks wrong. I'm thinking this is going to cause the limb to twist as it's drawn.
« Last Edit: May 18, 2016, 02:39:20 pm by DC »

Offline Del the cat

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Re: String alignment
« Reply #1 on: May 12, 2016, 01:19:29 pm »
That's fine... but you'll need to tiller it carefully as the limb may want to twist and settle in it's own way at different points along it's length, but overall it's OK.
The limb will probably stiffer in torsion (twist) than it is in bending the way you want it to, so it shouldn't be too bad.
Dunno if that makes sense?
Leave extra width at the tip to allow for any shift and take it slow and steady...
This post from my blog shows a way of watching for twist of a limb during tillering.
http://bowyersdiary.blogspot.co.uk/2011/03/twisting-bow.html
You can use that trick at several points along the limb to see what's happening.
Del
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Offline DC

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Re: String alignment
« Reply #2 on: May 12, 2016, 02:12:45 pm »
Thanks Del  I've seen your method of checking for twist changes but had forgotten. I won't again ;). It's funny you think that the limb will be stiffer in torsion. My gut says the opposite but that's all I've got. I guess because I've noticed that when I'm steaming out twist and bends the twists seem to come out easier that makes me think it will be weaker in torsion. Do you have any better reasoning?

Offline wizardgoat

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Re: String alignment
« Reply #3 on: May 12, 2016, 02:50:05 pm »
Unless it's really bad and obvious I don't worry about alignment till I get a string on it.
Sometimes a super snaky stave will need no correction, and sometimes a stave you thought was dead straight needs a tweak

Offline Del the cat

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Re: String alignment
« Reply #4 on: May 13, 2016, 02:11:25 am »
Thanks Del  I've seen your method of checking for twist changes but had forgotten. I won't again ;). It's funny you think that the limb will be stiffer in torsion. My gut says the opposite but that's all I've got. I guess because I've noticed that when I'm steaming out twist and bends the twists seem to come out easier that makes me think it will be weaker in torsion. Do you have any better reasoning?
Nah, just my gut vs your gut  :o
Well I s'pose maybe the stiffness is the same but the twisting force is likely acting over a shorter distance...
e.g Say the limb is 1" out of line. The force on the string is 36# then there's only 3 foot pounds of torque (36#x1") trying to twist the limb.Whereas the bending force mid limb (24" limb) is 72 foot pounds.
When you steam out twist you use a bloomin' great lever? Yes?
Yeah I know that's a very rough and ready explanation/theory, but in reality the maths/physics is probably near on impossible as the geometry is constantly changing through the draw.
Del
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Offline Pappy

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Re: String alignment
« Reply #5 on: May 13, 2016, 07:39:34 am »
It's hard for me to tell when you look at one like that, I can make it line up any way I want it looking at one like that, I hold it in my hand as if I were going to shoot it, if it lines up down the center of the handle and don't torque in my hand I don't give it anymore thought. :)
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Offline Marc St Louis

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Re: String alignment
« Reply #6 on: May 13, 2016, 08:24:51 am »
Nothing wrong with that
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Offline George Tsoukalas

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Re: String alignment
« Reply #7 on: May 13, 2016, 08:51:50 am »
I've had a few like that. The only drawback is if the stave wants to flip over in the rope and pulley or torques as it has been called.

I usually leave nocks and handle full width so I can cut the nocks deeper towards the handle so the stave does not flip. So if she flips towards me I'll cut the nocks deeper the other way.

Then if she makes it I can finish the nock grooves to be even and no one is the wiser...:)
Jawge
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Offline Pat B

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Re: String alignment
« Reply #8 on: May 13, 2016, 08:57:20 am »
You can't really check string alignment until low brace and the string is under tension. Laying a string or straight edge on an unbraced bow tells me very little about string alignment.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline DC

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Re: String alignment
« Reply #9 on: May 13, 2016, 11:50:14 am »

Well I s'pose maybe the stiffness is the same but the twisting force is likely acting over a shorter distance...
e.g Say the limb is 1" out of line. The force on the string is 36# then there's only 3 foot pounds of torque (36#x1") trying to twist the limb.Whereas the bending force mid limb (24" limb) is 72 foot pounds.
When you steam out twist you use a bloomin' great lever? Yes?
Yeah I know that's a very rough and ready explanation/theory, but in reality the maths/physics is probably near on impossible as the geometry is constantly changing through the draw.
Del

I think you're right. Once I really started thinking about it I realized how short the lever arm is trying to twist it. But I will try your twist test once I get it bending. If I get it bending :D

Offline simson

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Re: String alignment
« Reply #10 on: May 13, 2016, 03:03:18 pm »
You can't really check string alignment until low brace and the string is under tension. Laying a string or straight edge on an unbraced bow tells me very little about string alignment.

What Pat said!
That pic makes no sense at all, you don't know if the stave wants twist, you should look at the three points orthogonally - not with an angle like in the pic.
Simon
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Offline DC

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Re: String alignment
« Reply #11 on: May 13, 2016, 03:32:49 pm »
You can't really check string alignment until low brace and the string is under tension. Laying a string or straight edge on an unbraced bow tells me very little about string alignment.

What Pat said!
That pic makes no sense at all, you don't know if the stave wants twist, you should look at the three points orthogonally - not with an angle like in the pic.

I'm not sure if I follow either of you. What I'm concerned with is the distance between the two red arrows. Maybe string alignment was a bad choice of words? It looks just like this if I'm holding it. This is the belly you're looking at.

Offline bradsmith2010

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Re: String alignment
« Reply #12 on: May 13, 2016, 05:37:04 pm »
they are saying get it strung and then see what needs to be done,, :)

Offline George Tsoukalas

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Re: String alignment
« Reply #13 on: May 13, 2016, 07:33:12 pm »
I've been able to tell if it is going to flip around while on the long string. Jawge
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Offline DC

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Re: String alignment
« Reply #14 on: May 13, 2016, 07:47:13 pm »
OK let me put this another way. Imagine a bow, it's got a big "S" shape but the string goes from the tips right through the center of the handle, string alignment is good. Now brace the bow and turn it around and look at the back. Oh, look, you can see the string because it's such a big "S". Does that matter?