Also see my Diamond Stone version of this rolling sharpener.

Most home knife sharpeners have you drag the blade across a sharp edge or small diameter grinding surface. While this works well initially, after repeated use, it'll start to form divots on the edge -- kind of like washboarding on a dirt road -- eventually turning your knife edge into a ragged mess. This rolling sharpener works more like a sharpening stone, where the flat surface keeps the edge flat and even.

Modeled after those pricey rolling diamond or ceramic sharpeners, this one uses 3"/75mm dia. discs of emery paper instead. You can buy adhesive backed discs, or you can simply cut out discs from standard sheets and apply them to ends of the sharpener with glue stick or double-sided tape. I use 320 grit emery paper on one end of the sharpener for rough sharpening and 600 grit on the other end for finishing.

The knife holder holds the blade at a fixed angle with three 12mm dia. x 3mm thick neodymium magnets. Sitting flat, it holds the blade at 15 degrees, but there is also an adjustment screw that will raise the angle by 2 degrees per rotation of the screw. Once you've got it set to the proper angle, roll the sharpener back & forth along the blade with light pressure, as shown in the animation. Just make sure that you are pressing the front edge of the holder firmly against your worksurface so that you are getting 3-point support from the front edge of the holder and the adjustable post in the back.

Assembly of the sharpener is simple: just screw the two rotating discs together through the center of the cylindrical body. I added wide rubber bands as tires to the crowned edge of the rollers for a smoother feel, but it'll also work without them. For the knife holder, you just need to superglue the three 12mm x 3mm magnets in place and then insert the angle adjuster screw. Oh, and if your plastic wants to squeak, just use a little light grease or oil on the shaft during assembly.

Here's a sharpening how-to video for one of those pricey commercial sharpeners: