I needed to model a working involute gear to be used in a close up shot for a project I am working on. It proved it be a little more time consuming than I first envisioned. Anyways I managed to complete it and have uploaded some screenshots showing the topology flow and a video of the gears meshing. I found the trick with this was to model up one spoke of the gear and make sure that the topology flowed around the outside edge. I then duplicated and rotated the spoke to create the rest of the gear resulting in an edgeloop that ran along the entire edge of the gear without any triangles or poles on the exterior faces. This meant that all the beveling and extruding went off well resulting in a model with all quads and 100% planar faces.