Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on May 12, 2016, 12:45:47 pm
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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.
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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 (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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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?
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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
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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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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. :)
Pappy
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Nothing wrong with that
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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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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.
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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
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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.
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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.
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they are saying get it strung and then see what needs to be done,, :)
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I've been able to tell if it is going to flip around while on the long string. Jawge
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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?
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it won't do that,, it will kind of line up better than laying flat like you have it,, but if it did,, it would not matter,, :)
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DC, now I see what you are asking for.
Asuming that s- shape bow:
here you will get a torsion in the limbs, upper opposing to the lower. So string alignment is correct when both limbs travel the same amount.
your bow (only one limb C-shaped):
Think on the cross section where the curve makes the greatest wave. Looking from bellyside you should leave the material at the inner curve slightly thicker than at the outer curve. This will prevent twisting.
Hope this is useful for you
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I don't get what people are talking about here. I've made several bows with jogs in the limbs like this and as long as the bow is well tillered then there will be no twisting. Look at this one that has the grip area fully off to one side making it fully center shot
(http://img.photobucket.com/albums/v355/Marc-St-Louis/Selfbows/Plum/Plum%20D%20Bow/Character%20D%20Bow.jpg)
There is no twisting here and the bow shoots great. I've also seen many bows posted with such character
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Like said earlier from some.Get it at a low brace.See what ya got.I have bows with the string off to one edge of limb one way or the other too at brace.They shoot fine.I'm sure you've seen this too.
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I'll add do not narrow/reduce the handle area at all until it's braced. Then you can assess what is going on better and shape the handle to the string. Much easier than trying to steam or such.
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Here it is on lowish brace. You can see how much outside the bow the string goes in the third picture. I seems to pull OK out to about 10-12" @ 40# and that's as far as I've pulled it. On lower brace it wanted to torque in my hand a touch but that seems to be gone with the higher brace. Any suggestions or should I just keep on keepin' on :D
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yes get the limbs bending, ,what a crazy piece of wood,, I bet it will shoot great,, go slow and keep the taper even on the roller coaster,,
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That's ok.......about the string where it is.40#@ 10 to 12 inches....You got plenty of wood yet.I like it.It's gonna be a bow people will scratch their head about why it shoots so well.Believe me.Your top view taper looks good I think.Now you need to slowly get your thickness taper then get to your drawweight.This one will take a little time.Remove ,bend/remove ,bend etc. slowly and when your done I'll vote for it.
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I chickened out a bit and bent it a little in the direction of the arrow. The handle is kind of canted perfectly for a lefty, which I am but I shoot righty so the string was off a bit. Hopefully the bend I just made will just correct that. If not I may have to do the same on the other limb.
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Huui, That is an interesting piece for sure!
I see two possibilities (looking at the last pic)
first: as I mentioned above in my post, make the cross section in the lower limb asymmetrical, thicker at the inner curve and thinner at the outer curve where the red arrow is.
second: heat that big curve (or the most of it) out, when you have done that you have to correct with a second bending in the handle portion
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orientate the handle or point toward the string,, then see which limb is up,,or which limb the bow shoots the best at ,, up,, once you start to shoot the bow,,, you will see you don't need to bend it,, if it won't shoot ok, bend it,, but I think its gonna shoot like it is,,,, leaving part of the bend thick like simson said ,, seems like a good idea,, :)
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I would just carry on, I have built several somewhat like that with no problems, it seem the limbs are close to opposite each other so they will off set any twist in your hand. I would get it shooting and go from there.
Pappy
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Personally that's more of a gap than I use. I do as GEORGE said cut the knocks in deeper to the other side of where the arrow will lay, shelf or hand . This will make better alignment. If I think it's still to much out of line. I 'll been the handle some to help out.
But if it's file in deeper tips. If I think this makes the alignment close enough. Then I'd just use it but I'd turn the bow to make it more center shot.
How close the alignment has to be out of line. I build all my bows center shot. So if you can turn the bow over. If it's with in a 1/4 inch of center shot. It'll shoot OK if it's not that close I'll been the handle. Then I'll make it center shot. If it's OK the the owner.
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I have an ocean spray that is way off like yours, but crosses the handle. Its just fine and doesn't torque at all, and shouldn't torque at all. My only concern with this project would be tillering that bugger. I aint scared of bow wood, but that one gives me the heeby geebys.
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I'm going to have a tough time with the one I think. It is my first Cascara and I don't have any idea what to expect. Vinemaplebows has doubted that it will work, he says cascara isn't that strong in tension and this is a high crowned stave. Add to that the lumpy back. With that in mind I am proceeding with hope but without expectations. I've got it to brace height so that's a start. Listen closly, you may hear a bang in the next few days :D
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if you are really worried ,, you can always reduce your target weight and shorten the draw,,that will help overbuild the design,, if it works ,, you can be more aggressive on the next one,, no need to push it, if you don't know what the wood will do,, or if you are in doubt :)
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It's a full 72" so that will take a lot of strain off I hope. My big concern is that I haven't seen another Cascara as twisty as this around here. Most are pipe straight. I just stumbled on this one when I got way off the beaten path. What happens, happens. It won't be the end of the world.
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I think it will make it,, :)
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This isn't supposed to happen, is it? I got it to 40#@26, so I exercised it a bit, then it was 40#@27 1/2 then this. I never heard a tick, but I may have missed it(hearing aids). Anyway I can't see an obvious reason. Looks like tension break right on top of the crown to my uneducated eyes. It is in an area that got a bit of steaming but there isn't many areas that didn't get steam. To bad, it would have been an interesting bow. Better to have it happen now than after all the finishing. I was that close.
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Its highly reflexed there and the only area moving, by looking at it.
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Can you re-write that PD? It seems to be missing a few words.
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I think new meant it was the only area moving
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Yes sir. That 18" of flatness after that area did nothing but dish all its work load off on that already strained 8" area. Pop goes the splinter!
I told you I was scared of that one, and I aint skeered of very much bow wood :)
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I was suspicious of that area on both limbs but just a few scrapes before this I clamped a splinter to the flat area on the back so I could see if it was moving. It was but probably not enough. I was going to not scrape the big bends and then all of a sudden I was at weight and then break. First time with Cascara I was surprised how much wood it took to get weight. It was .70" thick where it broke. It was the only piece of Cascara I had so I can't jump back on the horse.
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Wood bows break tell me about it, I shot 800 arrows thru my last one., she broke. :( enough is enough, I rest my case/
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Gone over to the dark side Dean? ;D
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DC.....I had a red cedar indicate to me to be losing draw weight as the draw length got longer before it broke.I know now that's an indication the wood is breaking down.At least it did it on the tree for ya.Mine did too.
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Is that the cambium that broke. It looks darker than the wood below.
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Is that the cambium that broke. It looks darker than the wood below.
I was kinda wondering the same thing Pat.
Patrick
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That is what my steamed shellac looks like. I shellac the back of everything and when I steam it turns dark. It's old shellac, that may have something to do with it. It also stays sticky for quite a while and picks up a layer of crud.
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That's why these character bows are so hight valued by those of us who make bows*, they are not easy 'cos it's so hard to see the bend.
Del
* Joe Public just doesn't understand, they just think they are bad bows.... ::)