First lets get straight what making Bio Diesel (BD) means.
There are sites that claim to make BD by adding some secret chemical plus gasoline and/or other ingredients to vegetable oil. That is NOT Bio Diesel.
Bio Diesel is produced by a transesterification process in which the vegetable oil molecule is torn apart producing 1 molecule of glycerol and 3 molecules of BD. While there is more than one way to accomplish transesterification the most common is the base (NaOH or KOH) alcohol (MeOH or EtOH) reaction in some kind (and there are several) of reactor vessel.

The site below will provide you with a good education in how to make BD and give you plans for an Appleseed processor (reactor).

Welcome - Collaborative Biodiesel Tutorial Website