HOW DO I ADD A JOINT TO A SKINNED MODEL WITHOUT LOSING MY WEIGHT VALUES?

When working on any project, be it for a game or visual effects studio, you can expect your rigs to be constantly evolving. As the project moves through its various stages, features are inevitably added, so the character rig then needs to be updated to account for these. This could be adding a single joint to aid deformation or extending a rig to add an accessory or body part, but if not done correctly, this could end up being more work than it needs to be.

The problem is, once you’ve spent days refining a character’s skin weights you don’t want to then add more joints to the skin cluster, something that can result in the weights being changed and sometimes lost.

It’s not all doom and gloom because there are steps you can take to preserve your weighting information. For example, you could export the weight values and

Because you locked the weights to preserve the rest of the model’s values, you may not be able to edit them. To unlock your new influence, simply click the small padlock icon, which will be yellow, next to the joint’s name in the Paint Skin Weights tool.

reimport them, but doing this with Maya’s native tools doesn’t always give you the same results, so you may need to go in and fix any problem areas.

The good news is that there is an easier way to add joints to your rigged model without touching your existing weights.

As you may already know, to add a joint to an existing skin cluster you first make sure the joint and model are selected and then use the Add Influence tool found in the Skin>edit Influences menu. By default, this will add the joint to the influence list,

but it will also replace the weight values, reverting them back to a default state, so you unfortunately lose all your hard work.

To avoid this happening, you can simply check the Lock Weights box and then set the Default Weight slider to zero. Now when applied, your joint will be added to the influence list but with zero weight values, plus all the existing weights will remain untouched.

You can now use the Paint Skin Weights tool to gradually add the influence of the new joint.

The thought of adding an influence to a completed rig can strike fear into the heart of any technical artist, but there is an easier way to do it