16 3D Printing Communities Online. Did I leave any out?
http://www.fulltimepassion.com/3d-printing-communities-online/
http://www.fulltimepassion.com/3d-printing-communities-online
We are the best!))
RepRap?
YouMagine
Ultimaker
reprap on freenode IRC; /r/Reprap on reddit, http://forums.reprap.org/, all of which are likely larger than most of the links you’ve got up there. LinkedIn communities are especially out of touch with the actual 3D printing community.
Thanks for sharing some of the other communities. Sorry I missed them. Will add them to the post ASAP. 