MTConnect is becoming a widely accepted Internet communication standard for factory automation. It is being used for collecting and analyzing data of manufacturing machines and monitoring them over the Internet. This paper describes an implementation of MTConnect RESTful protocol for monitoring networked open-source RepRap based 3D printers in a Cyber Physical Manufacturing Cloud. The open source RepRap based 3D printers are gaining popularity over past few years because of cheaper price, easy-to-use and self-replicating features. The implementation includes establishing communication with the 3D printer, collecting and transmitting status data using MTConnect Adapter developed in a Raspberry Pi and publishing the data in a standard XML format via MTConnect Agent over the Internet. We also describe detailed design of appropriate MTConnect standard dataitems and discuss how to use them to implement probe, current and sample operations of MTConnect Internet communication protocol for factory automation. The performance of the implemented system is evaluated and the results demonstrate excellent feasibility of real-time manufacturing process monitoring of networked open-source 3D printers with MTConnect over the Internet in a Cyber Physical Manufacturing Cloud.