Butcher block is normally coated with lots of mineral oil over the years and that will rapidly clog sand paper. I usually pre-clean the butcher block with low odor mineral spirits trying to lift as much of the oil residue as possible. After that dries then I use a 4" belt sander with a moderately course (80) grit open coat paper and work with the grain. Be careful not to remove so much material that you can't match the edges where the sander won't reach. The course paper is being used mostly because it is clog resistent, not to grind off a lot of wood. If the sandpaper clogs, it will usually knock off by sanding a clean material briefly. I continue to sand going down to about a 150 paper, then finish sand with a palm sander at 200+ grit. You can find odorless mineral oil at the hardware store. It is a good counter preservative, or you can use a coating of lacquer or polyurethane if you don't plan to cut on the surface.