When animating using any decent rig, there are typically tweak bones which allow deformation of parts of a mesh independent of that of the main bones. Example: let's say you're using FK to pose a spine. If you want to adjust something at a point further down in the chain, then because it's FK it then disrupts bones towards the end of the spine and you would need to manually re-adjust them. In this scenario it's convenient to use a tweak bone instead, which completely isolates that one area of the spine, so you can make little adjustments where you need them. Rigify creates tweak bones automatically.
My question is how to go about creating a tweak bone from scratch without using rigify? I currently have a rough method where I'll duplicate a vertex group and create a new bone for it which is parented to the original spine bone, and while that does work fine, I wonder if there's a better or more efficient way to do it. Duplicating vertex groups makes it problematic to go back in later though to edit weights if I want to keep auto-normalize on, I find myself having to delete the new vertex group, edit my weights, and then re-duplicate it again.
When I try to break it down in my head, what I almost want is a way to have a bone reference another bone's vertex group somehow, but maybe I'm completely off. I've fiddled around with constraints but haven't figured anything out. If anyone has any ideas how to do it, or if you know any tutorials then it would be much appreciated! :^)
