Howdy,
A Joint’s Z axis must be aligned to the next joint down in the chain (its child joint) before applying IK to the joint chain. This is what the Align tool does.
The reason for this is because of the internal rotation order of Cinema 4D, which makes the Z axis the perfect twist axis. Animating an object’s rotation around the Z axis gives you stable interpolation between keys. If you’ve ever tried to animate an object rotating around any other axis than the Z axis, while the object is not originally oriented to the world 0,0,0, then you’ve probably experienced wobbly rotation interpolation between the keys.
If you’re not familiar with my rigging tutorials, you can check them out here:
https://www.c4dportal.com/forum/showthread.php?t=4374
The tutorials are based on using my rigging plugins, but there are a lot of explanations of why things are done a certain way which can be applied, no matter what tools are used or what software application is used.
Adios,
Cactus Dan
Cinema 4D R10 XL Bundle, BodyPaint, Dynamics
http://www.cactus3d.com
http://www.cactus3d.com/Plugins.html