How do I convert a Part's Cframe and Angle back to a previous Cframe and Angle?

How do I convert a Part's Cframe and Angle back to a previous Cframe and Angle?

mini diagram:

Let's say the parts tilted - \ then it moves to this _ how do i convert it back to \

I'm using this to make Weld Animations.

I'm going to make a idle animation (where the character's arms are randomely moving)

and thena attack animation. That's the tough part, how do I make it look like a natural swing without the angling looking bad.