Using a drill press, a hand drill and a stack of 5/16″ washers. It went pretty easily. I marked the bolt in the extruder body with a sharpie with bearings and washers in place. I chucked up the bolt and used an abrasive stone to make a 3mm radius recess at the marked location. I took off the drill press belt to allow the chuck to spin easier then chucked up the bolt with washers up to where I marked the bolt and held the tap chucked in the handrill at 90 deg. The washers kept the tap from wandering much down the shaft. A few minutes gets the hobbs to a deep enough cut.
see my video: http://www.youtube.com/watch?v=jSmhUWTSlZE