https://sims4studio.com/thread/1792/tutorial-splitting-blender-remove-bottom

Introduction

This mini tutorial will show how to fix the shadow that sometime appears at the bottom of skirts and tops. It is caused when we remove the double vertices of our mesh. The game needs to know if the point of conjunction between two faces has to be smooth or defined. The shadow is caused by a "smooth angle". Thanks to that shadow everything looks round but we need a hard edge sometime.

What you will need

:

Sim 4 Studio

Blender 2.70

I will use an EA skirt as example but as you can understand this method works for any CAS mesh. I will try to show you the difference between a smooth edge and a hard edge. To do so I will not work on a small part of the bottom.

This picture shows what we usually get when we use Remove doubles on the whole mesh. Everything is smooth but a shadow appeared at the bottom of the skirt.

Step one:

In Edit mode select the edge that you want to be hard. I usually use Edge selection mode to speed up the process.

Note: The red square underline a point I did not select. I will not split the edges in that spot so you will be able to see the difference once we are done.

Step 2:

Once the edge is selected. Click on Mesh tab then Edge. A new list will appear and click on Edge split. The shortcut for the Edge window is Ctrl+E.

Step 3:

Now that the edge is split you can save and import it back. This is how it will look in game.