Unlike AutoCAD, to start any Model in Autodesk Inventor you will need to create a Project file. Inventor is a BIM software and it stores very sketch drawn, parts created, assembled part and host of other things in this project file. so create a project file to commence the model of a simple gear in inventor.

1. sketch a circle of diameter 50 with centre at the origin this will make your sketch rigid and also makes it easy to create plane at the centre if need be.
2. Finish sketch and extrude by 20.
inventor-gear-2

3. Create 2D sketch on the top surface of the extruded cylinder and draw another circle of diameter 8, this time the centre should on the circumference of the bigger circle as shown below.

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