This will aim the X axis of the joint to point towards the next child joint below it in the chain. This will allow me to have the proper spin or twist axis to this joint. As well, if you wanted a different axis to be aimed, you can change which axis will be oriented in the options (Fig.07).
When we look at it now, this is a much better alignment. I can also bend it in just one axis now to bend the elbow. But perhaps this isn’t quite lined up with the crook of the elbow; in this case, if I want to spin it some to line it up better, I can rotate it on its X axis (we just rotate X now at this point, because it’s the one axis we’ve aligned so far) until the Y axis feels like it’s in the proper spot to bend the elbow. This part I just eyeballed to get right (Fig.08).
It’s a slight nudge but it’ll make all the difference in how my elbow bends and, when it does, if the hand ends up over the shoulder or not. To test it out, I go back into Object mode and bend the arm to see if it lines up (Fig.09).
And that’s what I want to see. I’m bending in only the one axis, Rotate Y and it lines up over the shoulder, like the bones should.
The elbow is just one example. I’d do this on the knee too, but any other joint as well. The spine here is another good example. In the Orient command, it tries to pick an axis to aim up. Well, if you build your spin in an s-curve, up depends which side the curve is on (Fig.10).
We are orienting our LRAs because we want our rigs to be logical to work with. For example, if I grab any joint in the spine, I probably want something like a positive number rotation to rotate the rig forward and a negative number rotation to be backwards. (It doesn’t match which goes forward and which goes backwards. Just that it’s consistent from joint to joint.) Let’s look what happens right now if I select each joint in my spine right now and rotate it +50 degrees (Fig.11).