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.

I ran the speed on the Dremel at 3-4 which seemed to work fine for me.

Here is before: And after:
Here are some more joints:

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.