A 1-in. Belt Sander is a Versatile Sharpening Tool
Most carpenters know that a belt sander can produce a reasonably acceptable edge on a dull chisel. And knife-makers and professional sharpeners often use special belt grinders to shape and sharpen blades. You can get many of the benefits of a professional belt grinder for a fraction of the cost with a 1 x 30-in. benchtop belt sander. The one shown is the Grizzly 1-Inch Belt Sander, available from amazon.com for less than $100. Buy 180- and 240-grit belts and you'll be set for serious knife sharpening. Plus, you can use the belt sander to grind other tools like axes and chisels, and to sand small woodworking projects.
For really dull knives, start with a 180-grit belt and finish with a 240-grit belt. Practice on an inexpensive knife until you get the feel of holding the knife at the correct angle as you move it across the belt. Try to maintain the angle that's on your knife. This is usually about 20 degrees. For a razor-sharp edge, buy a leather belt along with honing compound and mount it on your sander for the final sharpening step.