Golden Rules

No scaling.

This rule can be broken later but when you start, make sure you never introduce any scaling. This includes any negative scaling as a result of mirroring tools.

The direction of all bones should be the x-axis.

Another way of saying this: all bones should have an x-axis that points towards its children.

This is assuming you have an XYZ order of rotation. If not, make sure it’s the first rotation in your order of rotation.

This maintains the ability to animate a roll on your bones/joints without completely destroying your animation.

Align your bones so that the Z rotation is the first thing you animate.

This is assuming you have an XYZ order of rotation. If not, make sure it’s the last rotation in your order of rotation.

The Z-axis is the safest axis to rotate on, because it affects the other two axis rotations.

Minimize the need to use Y rotations.

This is assuming you have an XYZ order of rotation. If not, make sure it’s the second rotation in your order of rotation.

This is where gimbal lock can happen and ruin your day. Follow these alignments to reduce having to “Fix Euler” or to re-order your rotations.

The translation, rotation, and scale values of any object are always dependent on its parent.

If a child is exactly in the same place as its parent, its values are always zero.

Another way to look at this is that your object’s coordinates describe how different it is from its parent.

This isn’t only limited to objects since vertices and their coordinates (or any other component) are technically children of the object-transform they are attached to.

When mirroring bones, if we flip each axis direction we get a mirrored behaviour and interchangeable animation.

When mirroring joints, we should follow all the rules established for bone alignment but include per axis flipping to maintain the behaviour of mirroring. Not only does this preserve the right-hand rule, but it also allows for animation to be fully swappable to either side.