Author Topic: Bow design and development  (Read 3781 times)

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Online Bayou Ben

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Re: Bow design and development
« Reply #120 on: November 08, 2018, 09:46:51 am »
Many good points to ponder Ed.  And those bows are sweet!

Offline Halfbow

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Re: Bow design and development
« Reply #121 on: November 08, 2018, 01:29:08 pm »
Ed those are some wonderful looking bows you've got there. I admire your skill, and I fully respect that you guys have experience with extremely reflexed bows, and I do not. The most extreme bow I've ever made ended up with a little over 6" of reflex and was 60" long. Not so extreme. So I'm not telling you guys you're wrong, I'm just looking to understand better. I'm reading your post closely.

To tiller out a bow such as C that you showed it would be like tillering a wildcat.Linear and lateral stability would be an issue especially more so if the bow was very narrow.I've been there and done that and it an be done.

Tillering bow C would be a nightmare, for sure. I can't imagine the process of even just getting it to brace. I had enough trouble getting my bow to brace. The fact that people can tiller a bow like bow C without computer controlled machines producing nearly full draw ready limbs straight off the factory floor... it's amazing that you say it's possible.

The difficulty of tillering makes sense to me, because a huge part of the tillering process has to happen while the tips are beyond the handle, and are pointing away from the direction the string wants to pull them, leading to intense lateral instability.

Quite frustrating really with no added benefit but still very unstable as Badger stated even after tillering it stable.

If I'm understanding you right, this is where you lose me a little bit. If we picture bow C on a tillering tree, once you get to the stage where you can finally pull those tips down past the handle (which would be when you've tillered it like 60% of the way to full draw (A)), then I imagine things become much easier and much more stable. I am very familiar with this transition from the reflexed bows I have made. In the tillering tree, while the tips are above the handle, the bow is doing all kinds of weird things and desperately wanting to flip. After the tips are below, ahh sigh of relief, things are in control now. From that transition point on, the farther you draw it, the more stable it becomes. That's the point that I'd expect a reflexed non-recurved bow to start behaving more like a sane bow. I hope I'm understanding you right, but I think you're telling me this isn't the case with bow C. You're telling me it would remain unstable even after the tips are past the handle and pointing down. I'm having a hard time understanding why that would be.

In fact the bow would stack at the end of the draw then.A  bow such as C should have retro bent tips pointing straight down the last 6" in the profile you've shown.

I'm not sure what you mean by tips pointing straight down. If you mean that a bow like C would automatically come out whip tillered, I'd have to disagree. If it came out whip tillered, then I'd just say whoever tillered it did it wrong. They should've left more material on the outer limbs. It's perfectly possible to have bow C come out to the circular full draw profile I've drawn.

I do agree that bow C would stack more than many recurved bows. Recurves, of course, add a lot more energy storage. But I think C would stack less than A and B, which was the point of the exercise. To distill out the effect of reflex without muddying the water with extra variables like recurves.

But sure. Add recurves to all 3 bows and they'll all stack less, and bow C will still stack less than the other two. I'd imagine that something like bow C with big recurves would start getting in to levels of energy storage that would make compound bows start worrying about competition. But that would be crazy unstable.

My expectation would be this: for bows with recurves, especially recurves that are extreme enough to point away from the belly side at brace (a.k.a. string contact somewhere along the limb), more string tension means less lateral stability. To a high degree. The string is trying hard to pull that recurve out of line. So for recurves, the more reflex the less stable in use.

Conversely, for a bow with no recurves, I wouldn't expect increased string tension to have nearly the same effect destabilizing effects in use. It will have some destabilizing effects, just because of the general increased tension everywhere. Like if I imagine limbs that are nearly as thick as they are wide, then yeah, there will be problems. But I wouldn't expect it to be too much for a reasonably wide limb. And to take that farther, if bow C were to taper in width like a modern fg recurve, with very wide and thin limbs staying quite wide and thin all the way to the tips.. I have a hard time imagining lateral problems. Perhaps my expectations just drastically underestimate the forces involved?

But in short, I'd expect recurves to have an extremely destabilizing effect on a high tension bow. However, I do see that shortening the working area will have a stabilizing effect. I'm with you guys there. But I'd think you'd only really need to do that to counter the destabilization from recruves. In addition, you can shorten the working area without recurves.

But every extremely reflexed bow I've ever seen has had some form of recurve. If the tips aren't pointing away from the belly at brace (string contact), then they're pretty damn close to being in line with the string. This makes sense because people are chasing that power. But it also means it makes sense that people have this association of more reflex = a bow with less lateral stability to a high degree. If you know of or have made any extremely reflexed bows with no recurve, I'd love to see them and to know more about them and how they failed.

A boat shape type profile with the reflex mostly on the outer half of bow will be much easier.With not so much up close reflex to tiller coming from the fades but if reflex is in fades more so should be put in the outer half of limbs yet.
More reflex can be put on the last 6" of these bows here too with a bit more benefit but this profile is easier for me to brace with just a primitive stringer the way it is without the use of tepeliks.They are still very stable bows.The extra reflex on the outer limbs puts more pressure or strain closer to the handle which is stiff which helps stabilize the limbs better.Making static recurves have the same effect of pressure on a self bow.

I fully understand you here and my expectations agree. :) It's interesting to note that it would be possible to make a bow that had your boat shape when unbraced, but had a perfectly circular tiller (identical to bow C) at full draw. What would your thoughts on that be?

Again, I respect your experience with this, I'm just contrasting my expectations with what you're saying in hopes that I can understand better. I'm actually wondering if our thoughts on this are as different as they seem to be.

Offline PatM

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Re: Bow design and development
« Reply #122 on: November 08, 2018, 01:35:13 pm »
You'll hear of cases where strung reflexed bows have reversed themselves despite the tips being past the handle.

 With the built up stresses the bow is looking for the tiniest bit of weakness to one side and that can  be almost totally unapparent.

Offline Halfbow

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Re: Bow design and development
« Reply #123 on: November 08, 2018, 01:39:47 pm »
Yes, on recurved bows. I've battled the effect myself. Once a bow flipped on me so hard it jammed my wrist, just from holding the handle while it happened. Scary stuff. But I've never heard of a bow without recurves unstringing itself, unless a nock broke or something. I don't understand how that could happen without some kind of total collapse of the material.
« Last Edit: November 08, 2018, 01:43:56 pm by Halfbow »

Online Badger

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Re: Bow design and development
« Reply #124 on: November 08, 2018, 01:51:26 pm »
Half, bows with a long static reflexed outer limb will flip in a heartbeat if they have some reflex. The low string angle for a long section of the limb creates a huge amount of stress.

Offline Halfbow

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Re: Bow design and development
« Reply #125 on: November 08, 2018, 02:00:01 pm »
Ah, yeah, I mean terms get fuzzy here. When you say reflexed outer limb, I assume you mean it has some curve. It's that curve away from the string (at brace and after) that I'm suggesting really makes a flip more likely. Low string angles, however they are achieved, also help encourage it for sure.
« Last Edit: November 08, 2018, 02:04:01 pm by Halfbow »

Online Badger

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Re: Bow design and development
« Reply #126 on: November 08, 2018, 02:12:04 pm »
Not necessarily and curve just a kink in the limb a little past mid limb will do it. I stay away from those and prefer long sweeping gently curves.

Offline Halfbow

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Re: Bow design and development
« Reply #127 on: November 08, 2018, 02:14:25 pm »
Yeah, a better way for me to say it would be: any concavity to the back of the bow at brace makes a flip much more likely.

Offline BowEd

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Re: Bow design and development
« Reply #128 on: November 08, 2018, 02:56:27 pm »
Whenever the recurves I made have their tips aligned I have no problems of it twisting.This is at brace and full draw.They don't neccassarily have to look that way at rest yet either but it is preferrable.
The reflexed area on the outer limbs should be closer to not farther from the string at brace for good stability and lower stacking.
Making these type bows takes patience amoondo compared to a self bow.Extreme power and tension to deal with.As said it looks for the weakest point fold.
That's good you got one to settle with 6" of reflex.What reflex did you start with before tillering?
Making bows like ones shown takes me as much time planning on paper as constructing it,it seems.The best materials used is a must.
BowEd
You got to stand for something or you'll fall for anything.
Ed

Online Badger

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Re: Bow design and development
« Reply #129 on: November 08, 2018, 03:07:26 pm »
  A recurve just aacts like a heavier shorter bow until you draw it out. If the outer limb has about 10" of straight limb pointing straight out almost parallel with the string that is when the forces get crazy and unstable. I have never seen a way to stabilize them without curving them.

Offline BowEd

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Re: Bow design and development
« Reply #130 on: November 08, 2018, 03:47:31 pm »
Yes I would have to agree.Shooting a bow should be a fun & safe experience.Each of us has our own degree of fun I guess.There's a lot more safer ways to have fun.
« Last Edit: November 08, 2018, 04:18:59 pm by BowEd »
BowEd
You got to stand for something or you'll fall for anything.
Ed

Offline Halfbow

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Re: Bow design and development
« Reply #131 on: November 08, 2018, 03:52:43 pm »
Ed - I don't remember how much reflex my bow started with. I shortened the siyahs at some point in the process, so it's hard to say.

You can maybe see the reflexed angle the (straight) limbs originally came off the handle, but after set that reflex is pretty much gone. I made a thread about it not too long ago. The one called Bamboo Asiatic horse bow, if you're curious to see more. And yeah there's no doubt that stable highly reflexed and recurved bows are possible. My lowly example certainly is very stable. I'm a big proponent of that, and was never meaning to suggest otherwise. But it did take some fine tuning to get it there. I was just suggesting that the recurve would increase tendencies toward instability, amplifying alignment issues when compared to not having it.

Badger - You touch on an interesting point there, that string contact has a stabilizing effect... up until the one unlucky time the string misses the limb and it flips. But yes I agree, 10" on the end nearly parallel to the string will be very unstable. But you're not going to get that unless the back of the limb has some concavity before the straight section. (Unless your brace height is next to nothing or your bow super long) So I maintain that concavity on the back (convexity on the belly) increases likelyhood of flipping. This is what I was meaning on in my long post up there when I said, "But every extremely reflexed bow I've ever seen has had some form of recurve. If the tips aren't pointing away from the belly at brace (string contact), then they're pretty damn close to being in line with the string."

You're making me realize that by "recurve" I've just been meaning any concavity of the back/convexity of the belly at brace. Whether in a working section, or stiff, or angled siyahs, or just at the tips, or through most of the limb. I was calling all those things recurves. Probably wasn't using the word quite right. ><

Offline BowEd

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Re: Bow design and development
« Reply #132 on: November 08, 2018, 04:17:53 pm »
Yes I remember that bow now.Using the power fibers of bamboo on the belly.Very articulate joints made also.A very well crafted durable bow.A lot of thought went into the making of that bow.I would'nt call it a lowly bow at all.We don't see many like that.You made alignment of limbs a no problem project as a 5 piece bow.I'm sure it shoots very well for you.
Recurves do have tendencies to be more unstable than your regular straight gently curving self bow.It's the nature of the beast,but for those who like them it's what it is.
« Last Edit: November 08, 2018, 04:38:42 pm by BowEd »
BowEd
You got to stand for something or you'll fall for anything.
Ed

Online Badger

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Re: Bow design and development
« Reply #133 on: November 08, 2018, 04:40:33 pm »
  I don't think recurves are unstable at all, I hope I didn't give that impression. Like any design they have to be done right.

Offline BowEd

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Re: Bow design and development
« Reply #134 on: November 08, 2018, 06:57:35 pm »
By unstable I mean a bit more work to make is all.
« Last Edit: November 08, 2018, 07:57:33 pm by BowEd »
BowEd
You got to stand for something or you'll fall for anything.
Ed