fixing one bone while stretching others

Please see the attached files. I have a cylinder and 6 bones for it. I linked bones with path and apply Volume preservation option. I want to deform the cylinder in such a way: I select the one bone and “somehow” says to blender that it have to stretch only it while keeping other bones the fixed size as they have before stretching. After such deformation my cylinder have to look something like sandglass. i.e. it have to be only one narrow region, associated with this bone, while other regions have to be the normal size.

Does anyone know how to do this ? Or maybe I need to use another tool, not Armature ??
Thanks.

Attachments



not sure if i understood you correctly, but as far as i know, you wish to be able to deform the sylinder with something else, in your case a string of bones.

i think i got a solution for you:


by using a path, im able to deform it however i want to, also as an hourglass as you said as an example.

setup:
add a cylinder (or whatever object you wish to deform)
make sure the origin is at the bottom of the sphere (http://gyazo.com/56daf9a6c7b02c09aac710748366a20c)
add a nurb path (Add > Curve > Path)

select the cylinger, and add a Curve Modifier
in the Curve Modifier, select the Nurb Path

now select the Path, and go into edit mode. you should now be able to play with the path, and it will manipulate the cylinder.
also, to make the sphere thicker or thinner, you wont be able to simply “scale” the polygons in the nurb path, you will have to “shrink” them. do this by clicking Alt + S in edit mode.

hope this helps.

How about this spline IK tutorial: