GrabCAD, which operates a community for (and founded by) mechanical engineers, where they can share knowledge and collaborate on CAD models, projects and whatnot, has raised $4 million](http://www.crunchbase.com/company/grabcad) in Series A to add to its its $1.1 million seed round from back in June 2011.The Series A round was led by previous investor Matrix Partners; the firm’s David Skok will be taking a board seat. Other existing backers such as Atlas Venture also participated.