Create a new composition in the final size and frame rate you want your scene to use. We’ve gone for 720p at 25fps here – five seconds long. Now drag your different compositions onto the timeline to bring them in. For each, check the 3D switch and Collapse Transformations switch. This allows After Effects to treat them as if all the layers inside the compositions were in your main composition, but without the mess of hundreds of layers.
We need to arrange our different elements so that they sit in the right place relative to one other. Using the top, front, left, right and custom views arrange the different elements together so that the bookPageGround object sits directly on top of the bookCoverBack object. Do the same for the front cover and the bookPageSky element, and cap it off with the spine. This can be fiddly too, and you’ll need to rotate objects and alter the spine orientation to get it to work.
Once you’ve got everything aligned, parent the bookPageSky to the bookCoverFront layer. Next parent the bookCoverFront Layer to the bookSpine layer. Select the bookSpine layer and use the Pan Behind tool to move the anchor point from the centre of the layer to the edge where it meets the bookCoverBack layer. This will be the point of rotation, so it’s important to get it in the right place.
Create a keyframe for rotation on the bookSpine layer as shown above then move 1 second down the timeline. Rotate the layer by 90º so the bookSpine layer (and the bookFront and bookPageSky layers) sit at right angles to the back cover and bookPageGround layers. You’ll notice the pages don’t meet, but we’ll hide this with a nice camera move.