It would be great if Inventor had a pierce constraint, like in Solidworks. Many people say that using project and a coincident constraint is the same, but that's only partially true. The pierce constraint is really telling your sketch geometry to connect to the intersection point of your sketch plane and your target geometry (that you would project). The problem with a simple projection is that it doesn't give you an intersection point, only a piece of geometry with end points (see picture "projected geometry.png"). The current work around is to first create a construction point by clicking on your sketch plane and your target geometry ("construction point.png") and then connect your sketch geometry to that point ("connected to construction point.png"). See the attached pictures. The pierce constraint would eliminate the need for the construction point and for any geometry projection.