Author Topic: Bow design and development  (Read 36665 times)

0 Members and 1 Guest are viewing this topic.

Offline Bayou Ben

  • Member
  • Posts: 661
Re: Bow design and development
« Reply #135 on: November 09, 2018, 07:51:52 am »
To illustrate Steve's point, this one flipped twice on me at low brace with all of that limb touching the string.  Very unstable.

The second pic is at full brace and it's much more stable.  Almost no part of the limb is touching the string.

Offline Badger

  • Member
  • Posts: 8,119
Re: Bow design and development
« Reply #136 on: November 09, 2018, 09:24:42 am »
Ben, that is exactly what I was talking about. That particular one looks like it might stabilize with a slightly higher brace but any straighter than that just doesn't work.

Offline BowEd

  • Member
  • Posts: 9,390
  • BowEd
Re: Bow design and development
« Reply #137 on: November 09, 2018, 09:59:14 am »
Good illustration Ben.A picture is worth a thousand words as they say.I can see why by those pics.
To add here....A higher brace height is needed especially on those Egyption angular bows so they don't invert when the string slams home from release from what I've seen.
« Last Edit: November 09, 2018, 12:23:00 pm by BowEd »
BowEd
You got to stand for something or you'll fall for anything.
Ed

Offline DC

  • Member
  • Posts: 10,396
Re: Bow design and development
« Reply #138 on: November 09, 2018, 10:01:01 am »
Flipped on release or drawing? Do you have an unbraced picture? How much reflex does it have? Sorry for all the questions but I wouldn't have thought that was unstable. I must be missing something. You sure got my attention ;D
« Last Edit: November 09, 2018, 10:22:02 am by DC »

Offline Bayou Ben

  • Member
  • Posts: 661
Re: Bow design and development
« Reply #139 on: November 09, 2018, 10:49:28 am »
DC, that's the same bow I'm working on in my tiller help thread.  It flipped or reverse strung itself the 1st time right after I braced it and the string was a little off center, and the 2nd time when I was putting the bow on tree and the string touched the cradle.  Just that little bit of sideways/lateral force caused it to reverse string itself.  But that was all while it was at low brace (~4", 1st pic of previous post) and the string was contacting a large portion of the limb.  Now at full brace it's a lot more stable (the 2nd pic of my previous post).
 

Offline Badger

  • Member
  • Posts: 8,119
Re: Bow design and development
« Reply #140 on: November 09, 2018, 10:53:38 am »
Ben, you did a pretty good job on that one keeping the limbs tiller rounded, you do have a slight kink near mid limb, that same design with the outer limb straight and slightly more reflex in the kink makes for a very unstable bow.

Offline Halfbow

  • Member
  • Posts: 133
Re: Bow design and development
« Reply #141 on: November 09, 2018, 10:55:50 am »
Good example Ben (and nice looking bow). Just want to point out that it was my point too. :)

Offline DC

  • Member
  • Posts: 10,396
Re: Bow design and development
« Reply #142 on: November 09, 2018, 11:09:59 am »
Is this one going to be a problem? I started it a few years ago and got it too thin so it sat in the corner of shame until last week when I put a belly lam on it. I thought it would make a good tillering exercise. It's only an inch wide. I've been having trouble getting it to bend(it's flipping) but I thought it was just string alignment. I've been doing minor heating the correct that. haven't trid it today.

Offline Stick Bender

  • Member
  • Posts: 2,003
Re: Bow design and development
« Reply #143 on: November 09, 2018, 11:10:09 am »
Looks awsome Ben what target draw weight are you shooting for ?
If you fear failure you will never Try !

Offline Badger

  • Member
  • Posts: 8,119
Re: Bow design and development
« Reply #144 on: November 09, 2018, 11:15:56 am »
Is this one going to be a problem? I started it a few years ago and got it too thin so it sat in the corner of shame until last week when I put a belly lam on it. I thought it would make a good tillering exercise. It's only an inch wide. I've been having trouble getting it to bend(it's flipping) but I thought it was just string alignment. I've been doing minor heating the correct that. haven't trid it today.

   I think you will need to get more bend in the inner limb, as much as you can get. I also think it is too narrow but the profile you have is doable.

Offline DC

  • Member
  • Posts: 10,396
Re: Bow design and development
« Reply #145 on: November 09, 2018, 11:27:57 am »
I knew it was too narrow. Not much I can do about that. Would making it a bendy handle help or hurt. I think I remember reading something here that bendy handles aren't good for stability. Might be dreaming. I just thought it would be fun to test myself. It can always go back in the corner ;D

Offline Badger

  • Member
  • Posts: 8,119
Re: Bow design and development
« Reply #146 on: November 09, 2018, 11:40:12 am »
   I would lower the draw weight to 35#, I don't think that profile would suit a bend handle very well.

Offline DC

  • Member
  • Posts: 10,396
Re: Bow design and development
« Reply #147 on: November 09, 2018, 12:00:21 pm »
Will do. Sorry about sidetracking the thread.

Offline Bayou Ben

  • Member
  • Posts: 661
Re: Bow design and development
« Reply #148 on: November 09, 2018, 12:25:14 pm »
Will do. Sorry about sidetracking the thread.
It's your thread....sidetrack away...

Looks awsome Ben what target draw weight are you shooting for ?

Anything over 50# I'll be happy with.  Going to see how set is going further out in the tiller before deciding for sure though.

Offline Halfbow

  • Member
  • Posts: 133
Re: Bow design and development
« Reply #149 on: November 09, 2018, 02:02:20 pm »
DC, I'm pretty sure this thread got a bit sidetracked a long time ago. XD That may be partially my fault. Sorry for that.



But because I'm afraid I was being confusing earlier, let me clarify what I was saying.

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." Recurve may not have been the word I was looking for. I meant any concavity of the back/convexity of the belly at brace. In other words, the profile bending away from the direction the material is being pulled. I feel like there should be a word for this!

To illustrate:



So Ben, your bow (at the low brace in this pic) is an example of the sort of profile I was talking about being less stable originally, and this is what I meant by being in line with the string.

Looking at a different profile, bows with recurved tips will usually show both convex and concave sections of the back, like so:



And bows with a kink/siyahs/whatever have the concave sections too, whether working or not. All kinds of weird things are possible:



But all these bows have at least one area where the back is concave at brace. I'm suggesting that this concavity makes flips much more likely in reflexed bows. It decreases string angle at the ends, and gives initial twist more leverage to twist more, in a sense.

As opposed to:



There is no area of that back that is concave, every part of the limb is going in the direction that it's being pulled. And nowhere is the limb close to running along the string. Given reasonably wide limbs, I'd expect this bow to be in negligible danger of flipping, no matter how much tension the string is under. It's hard to picture these limbs twisting in a way necessary to flip.

I wanted to use "recurve" to describe this concept, but I guess that implies that it's near the tips and curvy. I think it would be useful if we had a general word for concavity of the back at brace. Anyone with me?
« Last Edit: November 09, 2018, 02:24:17 pm by Halfbow »