How to install

File > User Preferences > Add-Ons > install from file ... find file ... > click check-box

1. In blender, go to File > User Preferences. 
2. In the window that opens, click the Add-On tab. At the bottom of the add-on tab, click “install from file.”
3. Select the metaball_skinner.zip file that you downloaded, and then press enter to accept the selection. You do not need to unzip the file.
4. Search “metaball skinner” in the search bar of the add-on tab, or select the ‘user’ category. You should see the Metaball Skinner add-on. Make sure the small box is checked. This enables the add-on. 
5. To verify it is enabled, use the spacebar search in the 3D View to search ‘metaball skin.’ The metaball skin command should appear.

How to use

Run Command. 

There are two ways to access the ‘metaball skin’ command. Selected object must be a mesh, and in object mode.

1) Spacebar Search: Search ‘metaball skin’ in the View3D window using spacebar. Make sure that the active object is the mesh you want to skin, and that it is in Edit mode, otherwise the command will not appear. Hit enter, the command will run.

2) Button in Properties Window > Modifiers. The add-on created a new section in modifiers called "Metaball Skinning". There is a single button titled ‘metaball skin’ that will run the skinner. This button will appear below any modifiers already associated with the object. 

Adjust Parameters

Once you run the ‘metaball skin’ command, from the searchbar or the modifiers panel, you see a new metaball object forming the skeleton of the selected mesh. Woo! At the bottom of the View 3D > tool shelf there are two settings: Radius and Polygon Size. 

Radius - sets the radius of the metaball rods, in blender units. 

Metaballs are kinda funky and as a result the radius you set is not the exact radius of the rods! The true radius will be slightly smaller. This is related to the interaction between two variables: the stiffness setting for each rod and the threshold setting that acts on the entire metaball object. To get an exact radius: Select MetaSkinned, then go to Properties > Data > threshold. Set the threshold for the metaball object to .001. This will change the aeshetic of the object, removing bulges and making it sharper, more like booleaned rods than blobby metaballs.

Polygon Size - sets the size of the polygons that make up the surface. 

The smaller the size, the higher the resolution, and the slower blender will get. On the other hand, really large polygon size will make a chunky surface. An extremely large polygon size will make the metaball rods completely disappear. The size where the surface will look nice is relative to the radius of the metaball rods. 

Note: Once you change to edit mode, select a different object, or in anyway change the context of the application, the settings in the tool-shelf will disappear. This is similar to the behavior of the commands in the 'Add' menu, like 'add cone.'

Optional: 3D printing

A) Convert the metaball to a mesh (Alt C)

1. Select the "MetaSkinned" object. It is easy to find it in the Outliner window.
2. At the bottom of 3D View:  Object > Convert To > Mesh from Curve/Meta/Surf/Text. Or use Alt C.
3. The MetaSkinned object will now be renamed to something like MetaSkinned.001. You can verify it is a mesh be entering edit mode and seeing all the faces. The average edge length of the faces is going to be close to the polygon size you set.

B) Export STL

1. Go back to File > User Preferences > Add-Ons and search "STL"
2. Ensure that the "Import-Export STL files" add-on is checked.
3. With the new MetaSkinned.001 mesh selected, run the File > Export > Stl command.