When adding your hair mesh to The Sims 4, you will need to assign bones in Blender to smooth the mesh and make sure the hair is weighted correctly. The following The Sims 4 tutorial is broken up into three sets of bone assignment for hair weight: head and spine2, breast bone, and clavicle bones.
For all three of these tutorials, you will need a final hair mesh already imported into Blender. We have a Blender tutorial if you need guidance for how to do so. The tutorial will also explain the purpose of the bones in Blender.
How to assign b_Head and b_Spine2 bones
Change into Weight Paint mode.
Step 1 : Create new vertex group and follow step by step in image below.
Please remember that the cyan line must be horizontal with the shoulders.
Step 2: Clone that vertext group.
Step 3: Invert that vertext group.
Step 4: Rename
To make it work in game, you must rename the mesh to what EA defines.
How to assign the breast bone
Now we will assign the following bones: b__CAS_L_Breast__ for the left and b__CAS_R_Breast__ for the right.
Step 1: Change into Wireframe mode (1 – 2).
Step 2: Add a new vertex group and change to left view (3 -4).
Step 3: Use Weight Gradient and draw a linear color like the picture (5 – 6 ).
I usually make it end at the shoulders. Remember changing to Weight Paint mode first.
Step 4: Now change to Edit Mode (7).
Step 5: Deselect all vertext first (8 – 9).
(Press A — you might need to press it a few times — and then PRESS B and select all vertex in the back by drawing a rectangle.
Step 6: Press remove in the right panel (10).
Please note that you are working the new vertex group that you added in the first step.
Step 7: Change to Weight Paint mode and front view (11).
You will get something like this:
Step 8: Duplicate the vertex group, just like you did for the head and spine bones.
Step 9: Change to Edit mode.
Deselect all vertex and then Select all vertex in the right and remove their weight data (13 – 14).
Step 10: Now change to Weight Paint mode to see the result and rename that bone.
Don’t forget the right one! Repeat all of these steps for the right breast bone.
Tada! You’re finished! Be sure to test how it looks in the game and keep editing it until you are satisfied.
How to assign the clavicle bones
For the last bit of bone assignment, we’re going to assign the clavicle bones: b_R_Clavicle_ and b_L_Clavicle_. This way, your custom hair mesh will move with the shoulders. It also helps the hair work smoothly with many animations and poses. You can see the difference in the before/after image below.
First, I want to show you the position of these bones. The b_L_Clavicle_ is on the right, and the b_R_Clavicle_ is on the left, so there is a small point you need to distinguish.
Let’s begin.
Step 1: Create two empty bones, b_R_Clavicle_ and b_L_Clavicle_. We will work with the b_L_Clavicle first.
Go to Weight Paint mode, and set the Curve as the image below.
Step 2: Select Weight Gradient and drag a line from two red points.
Step 3: Click on Level and type in a suitable number (it must be a negative number) to make the area smaller. I usually use -0.25 or -0.5.
Do the same for the b_R_Clavicle_. And that’s it.
Please note, however, that if you assign your hair mesh more than four bones, you should Limit Total to keep the number of assignment bones on a vertex under four, because the game only reads four bones per vertex.
Check out my hair meshes to see the differences:
Hope this weight assigning tutorial for The Sims 4 all helps with your future hair meshes!
