Need to make something flat and smooth? This Bridge Planer will get smooth, even results on pieces too wide to fit through your normal planer. This router bridge is a simple design and Matthew Cremona goes through a great overview of how it works and how to make your own if you happen to have a board that needs to be uniformly flattened. Take a look at his video and file it under "when I need this I'll be able to do it".
A few things to keep in mind -
1. Keep the workpiece secured to the surface to maintain control
2. The workpiece will only be as flat as the surface it's on. Make sure the surface is completely free of small pieces of sawdust or errant specks.
3. The router shouldn't be in contact with the wood when started up. It can spin the wood or the tool out of control.