Page History

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http://www.yeggi.com/ - Yeggi is the google for 3D model databases. It searches all the others listed here.

https://www.ameede.net/ - Found a new one. It has sections for 3D Models and for CNC/Laser files.

https://grabcad.com/ - Nice engineering models, but not necessarily focused on printing. These you may have to modify in a CAD package before printing.

http://www.turbosquid.com/ - Turbo Squid. Last resort site. All models are paid and there is no way to sort by printable items. 

In case I missed some, here are some more.