I just learned something...

[Wooden Spring]

OK, this may come as a "no, DUH!" to some of you seasoned bowyers, but I still feel like a dumb @$$ every time I start one of these things, so any time I learn something it's pretty cool.

OK, I was starting a hickory backed jatoba bow that was 1-1/4" wide, parallel for 6" and then tapers to 1/2" nocks for a planned 45# @ 28".

Here's the lesson... For thickness, I tapered from 9/16" to 1/2" for the parallel width, and then had a consistent thickness of 1/2" for the length of the tapered width section. By doing this, I inadvertently created a hinge right where the parallel width meets the tapered width...

Lesson: If ANY portion of the bow has parallel width, then the ENTIRE length of the bow must be tapered, NOT just the portion that is parallel. Otherwise, if ONLY the parallel width section is tapered, you create a hinge. And  PRETTY NASTY one too.

Oh, well, may it rest in pieces......

[burn em up chuck]

    i remember that one, doesn't it feel great, hope you have many many more

                                                              chuck

[Crogacht]

As someone new to this who would not have realised this fact until I messed a bow up, THANK YOU 

[Badger]

 Yep spring, you just used some "tiller logic". Jatoba is bad about chrysaling, not horrible but touchy, you might try keeping it paralell for 2/3 of the limb.

[RyanY]

I thickness taper my limbs like that all the time and never have a problem. 

[mikekeswick]

Yes chances are you just made it too abrupt a change. Your original thinking was right.
As for pyramid width tapers you quite often need some thickness taper to a pyramid. Mainly because you rarely have the perfect triangle eg. width at base and also the nock isn't zero width.

[Pappy]

I don't do backed bows but with self bows I never check the limb taper,I cut them
the same thickness all the way and let the wood and tiller tell where I need wood taken off.[maybe in the fad area from handle to limb] I assume it has some taper but have never measured it. 
  Pappy

[Wooden Spring]

Yep spring, you just used some "tiller logic". Jatoba is bad about chrysaling, not horrible but touchy, you might try keeping it paralell for 2/3 of the limb.

You've said that before, that jatoba is bad about chrysalling, but I have yet to see it. It's actually one of my favorite woods. I've chysalled red oak before, and that peruvian walnut that I had just crumbled under the stress...   Under what conditions did your jatoba bow chrysal? Was it design, or something else?

[Badger]

      It chrysaled on me making r/d bows with about 2" reflex and stiff outer limbs. None of the hill style bows I made chrysaled. I won't use it for r/d anymore. It really is a good performing wood. I think if you are really careful it won't chrysal. I tend to crowd my tillers mid limb and if a wood has a tendency to chysal I get it.

[Jim Davis]

Steve, I think you agree that any wood will chrysal if it is bent in a radius that is too much for the thickness. It's harder to keep that from  happening with bows that combine different thickness needs, like Molegabet (spelling?), RD and recurves. It's far easier to make the thickness correct  for  the radius with a pyramid design. That's why I always take the easier path and make all my bows that design.

As for the original poster, I can't attribute his disastrous hinge to the change of side taper as much as a possible local weakness  of the wood or having continued the thickness taper beyond the transition point...maybe...

Jim

[Badger]

  I agree Jim, a hinge is a hinge, I don't believe in pre cutting thicknesses beyond just roughing something out. I have heard of most all woods chrysaling on these forums. I have a few woods that just seem more prone and I don't fool with them anymore.

[Wooden Spring]

Steve, I think you agree that any wood will chrysal if it is bent in a radius that is too much for the thickness. It's harder to keep that from  happening with bows that combine different thickness needs, like Molegabet (spelling?), RD and recurves. It's far easier to make the thickness correct  for  the radius with a pyramid design. That's why I always take the easier path and make all my bows that design.

As for the original poster, I can't attribute his disastrous hinge to the change of side taper as much as a possible local weakness  of the wood or having continued the thickness taper beyond the transition point...maybe...

Jim

I'm pretty sure it hinged because I didn't carry the thickness taper out beyond the point of transition between the parallel width and tapered width.
Oh, trust me, what I did was kinda dumb now that I think about it. But if we learn from our mistakes, then nothing we do is useless, right?

[okie64]

I thickness taper my limbs like that all the time and never have a problem. 
[/quote
  X2 what Ryan said.
 Are you sure you didnt get a thin spot in that area? Some guys are meticulous about their thickness taper and others dont even pay attention to it, they just remove wood till the bend looks good. I used to use thickness taper religiously but after messing up a few good staves i quit doing that. Now I usually just scribe a pencil line on the sides of the limbs from 5/8" at the fades to 9/16" midlimb and then 9/16" at the tips and tiller it out from there.  Once your eyes are better trained for tillering you will learn to spot hinges and weak spots very early in the draw and avoid those issues altogether.

[Crogacht]

  X2 what Ryan said.
 Are you sure you didnt get a thin spot in that area? Some guys are meticulous about their thickness taper and others dont even pay attention to it, they just remove wood till the bend looks good. I used to use thickness taper religiously but after messing up a few good staves i quit doing that. Now I usually just scribe a pencil line on the sides of the limbs from 5/8" at the fades to 9/16" midlimb and then 9/16" at the tips and tiller it out from there.  Once your eyes are better trained for tillering you will learn to spot hinges and weak spots very early in the draw and avoid those issues altogether.

Seems like getting the bend right comes first in the equation. If the tiller is perfect then the thickness taper HAS to be perfect. Otherwise there would be hinges and flat spots.

I think the important part is understanding how width and thickness relate to each other and affect tiller, much past that I think you just need to have a shape in mind and tiller it to that as best you can, the taper will be whatever it will be.

So profound from someone with no bow yet  ... probably nonsense, but I like to speculate in between trips to the shed to make fancy firewood 

[RyanR]

I don't do backed bows but with self bows I never check the limb taper,I cut them
the same thickness all the way and let the wood and tiller tell where I need wood taken off.[maybe in the fad area from handle to limb] I assume it has some taper but have never measured it. 
  Pappy

+1