Step 2: 3D Model Manipulation
After working with this a few times now I would really suggest doing your best to get a good quality 3D model out of 123D Catch, it is hard to shape the face correctly afterwards.
First we will use MeshMixer (I am using meshmixer 07 update 3) to clean up the model and smooth out any surfaces. This program is very easy to use. Hold the ALT key to change your view. Select the extra parts in the model with 's' and draw a loop around them. press x to delete. Once you have the extra stuff deleted we can smooth or modify the face. Check out the pictures below, they will walk through this process too.
Simply choose the smooth function and begin altering the model. You can alter the size and strength of the smoothing pad. Just play with it. I'm not a pro at this, I just messed around until it looked ok. I would suggest using the smoothing function minimally as too much made my face look fake.
You can also add or subtract material. Feel free to give yourself a nose job. The top of my head was messed up in my 3D model, it wasn't an issue since all I needed was the face. I simply leveled off the model in that region. The rest will get chopped off.
Finally, in meshmixer 07 update 3, there is an option for a plane cut. Move it around until just the part you want for the mask remains. The pictures below will make this step clear.
Now we have the 3D model for the mold. Export this as an .stl file so that we can generate the gcode for the CNC mill.
Here we are going to use 'Hexagon 2' which is available for free download from DAZ 3D. Similarly, we can select points and delete out the extra stuff.
Import the .obj file. You can rotate the model with the options at the bottom of the screen. Click on the model and then click on 'select points (F4)' you can now pick out the extra parts of the model and remove them. It is easier to change to the lasso tool (just below the 'auto select' button. Right click with the mouse to draw a lasso. press 'delete' to remove the points.
I deleted most everything but my face (and a little extra). I then added a box (3D primitives -> Cube) and moved it around (click on the cube and modify the properties on the right) until it chopped off the right amount of my face for the mask. The two parts were then added together with a surface Boolean addition (surface modeling -> Boolean operation). Select your object then select the Boolean operation. Now click on the cube. Give it a moment to work. A weird addition may be made, but look in the properties on the right, you'll see a bunch of circle and squares with different blue areas. This represents the different operation options. I chose the normal add function (all blue) so that it keeps everything.
This made a nice flat bottom surface. You can now delete the box parts, or leave them in depending upon your CNC application. Again, export as an .stl file.
Any other software (such as Blender or the Autodesk 123D apps) that allows you to manipulate 3D models will probably allow you to do this step as well.
In the next step we will convert the modified 3D model to gcode for CNC'ing.