Awhile ago I say this article on Hackaday http://hackaday.com/2014/12/30/3d-printing-technique-friction-welding/ on how to quickly and easily use friction welding on 3D prints.
I recently printed out a model of the Hubble Space Telescope to honor 25 years in space. http://nasa3d.arc.nasa.gov/detail/HST
The print was in several pieces and it need some assembly.
The technique is quite simple. Put a piece of filament into a Dremel and push it into a joint. You will need a smaller collet as the default one is too big. I happened to have one from a set I purchased years ago. Insert the filament with about 3/8″ sticking out. Don’t worry if its not exactly straight it will fix itself with a little pressure.
It works great it is quite easy and it seems to form a great bond. Be ready to stop the Dremel and pull more filament out especially when you are filling a big joint.