Keywords: Animation, Maya, Rigging, Skin

This series of articles:

How to bind skin (combine skeleton and mesh)

Rigging (F3) -> select both the skeleton and mesh -> Skin -> Bind Skin.

How to separate skeleton and mesh:
Skin -> Unbind Skin.

Mesh must bind skin before painting skin weights.

Skinning Method 1: Paint Skin Weights Tool

Rigging (F3) -> Skin -> Paint Skin Weights.

You can check the weights with visualization after open painting tool: select mesh first in Outliner, then select the target joint in Paint Skin Weights Tool.

You can check Color Ramp to check weights more intuitively.

You can also switch state between Paint Skin Weights Tool and Transform Tool.

As the follows shown, the torso is severely twisted.

To sovle this problem, you can use painting brush.
Hold down key B and drag mouse left button to left or right to adjust brush size.

Check the Solid Brush, and hold down key Ctrl to erase the weights.

Check the Soft Brush, and check Smooth in Paint Operation, thus you can smooth the edge.

Even you tweak the weights carefully, and it looks right, but there are still flaws.

The auto skin binding is limited to rotate bone in simple scenario.

Skinning Method 2: Interactive Bind Skin

Skin -> Interactive Bind Skin.

Now you can tweak the collision sharp and transform for each joint.

The final effect for upper arm joint.

The effect is acceptable.

Skinning Method 3: Rigging in Unreal Engine asset

In UE5 rig, there’s no weight in upper arm joint, and there’s external bone named clavicle inserted between neck and upper arm.
And the weights is more light then auto bind skin.

The effect is perfect.

Tips: Make sure the bone at the shoulder joint don’t have any weight, and move the weights of the shoulder to the clavicle joint.

The structure of clavicle bone.

How to copy Skin Weights

To copy all smooth skin weights from one bound mesh to another

  1. Do one of the following:
    • Select the smooth skin polygonal mesh (or group of meshes) you want as the source skin, and then select the polygonal mesh (or group of meshes) you want as the destination skin.
    • Select the vertices you want as the source, then select the vertices you want as the target.
  2. Select Skin > Edit Smooth Skin > Copy Skin Weights.
  3. Do the following:
    • Set the Surface Association options appropriately based on the type of correlation you want to occur. For most situations, the default setting of Closest point on surface works best. If your characters differ widely in scale or proportion you may wish to use the UV space setting.
    • Set the Influence Association options appropriately based on what you believe will provide the best correlation between the joints. For most situations, the default setting of Closest joint works best. If the skeleton hierarchies in your scene are identical, the One to one setting can be useful.
  4. Do one of the following:
    • Click Copy to copy the smooth skin weights from the source skin to the destination skin.
    • Click Apply to copy the smooth skin weights from the source skin to the destination skin.
    • Click Close to close the options window without copying the skin weights.

Reference:
Copy smooth skin weights - Autodesk Maya Documents

How Do I Transfer Skin Weights? - antCGi (Recommended)
https://www.youtube.com/watch?v=BbKDxKKFh-U

Tools & Plugins

ngSkinTools is a skinning plugin for Autodesk Maya, introducing new concepts to character skinning such as layers, any-pose-mirroring, enhanced paint brushes, true smoothing, and more.
https://www.ngskintools.com/

Do not confine your children to your own learning, for they were born in another time. -Chinese Proverbs