To effectively change which bone influences a vertex group in Blender, you'll essentially be reassigning the weights of the vertices within that group to a different bone. Here's how you can do it:
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Enter Weight Paint Mode: Select the mesh object you want to modify and switch to Weight Paint Mode. You can do this by selecting "Weight Paint" from the mode dropdown menu in the 3D Viewport's header.
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Enable Bone Selection: In the 3D Viewport's header, make sure the "Bone Selection" option is enabled. This allows you to directly select bones to display their corresponding vertex group weights. This is crucial, otherwise you'll be painting on the active vertex group rather than changing it.
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Select the Target Bone: Select the bone whose vertex group you want to view or modify. Use Alt + Left Mouse Button (LMB) to select the bone directly in the viewport. If that doesn't work, especially with complex rigs, try Shift + Ctrl + LMB to cycle through bones at that location. This action activates the vertex group that corresponds to the selected bone, displaying the current weights on the mesh.
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Weight Painting (Optional): If you just want to view the influence of a specific bone, you're done at this stage. If you need to modify the influence, Blender is now in Weight Paint mode for that particular bone's vertex group. You can now use the various weight paint tools (Brush, Gradient, etc.) to adjust the weights as needed. For example:
- Reduce a vertex's weight for the current bone by painting with a lower weight value or using the "Subtract" brush.
- Completely remove vertices from the current bone's influence by painting with a weight of 0.
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Alternative: Manually Assign Weights: If you prefer a more controlled approach, you can use the following method:
- Object Mode & Vertex Groups: Switch to Object Mode, select your mesh, and navigate to the "Object Data Properties" tab (the green triangle icon) in the Properties panel.
- Vertex Groups Panel: In the "Vertex Groups" panel, you'll see a list of all vertex groups for that mesh.
- Select Vertices: In Edit Mode, select the vertices you wish to reassign.
- Choose Target Vertex Group: In the "Vertex Groups" panel, select the new vertex group (corresponding to the bone you want to associate these vertices with).
- Assign Weight: Set the "Weight" value to the desired influence (usually 1 for full influence), and click "Assign." This adds the selected vertices to the newly targeted vertex group.
- Remove from Old Group (Optional): If you want to remove the vertices from their previous vertex group, select that vertex group in the "Vertex Groups" panel, ensure the same vertices are still selected in Edit Mode, set the "Weight" to 1, and click "Remove."
In summary, changing the vertex group bone involves selecting the correct bone in Weight Paint Mode (or using the manual method), then using Blender's weight painting or manual assignment tools to adjust which vertices are influenced by that bone.
