Several people have modified bench planers to beam walking planers. Not sure how long they will last/life. They will smooth the surface, but will not make a beam square. This winter I intend to buy the Woodmizer MP100 planer head. This is a heavy duty planer that runs on 2 rail sawmill tracks. This type of planer can be used to not only smooth the surface, but make it planar, and square faces on a beam.