These devices do not use electric motors. They can be cheap, easy to use, last for years and produce very sharp edges. In short, they are ideal for home use.

How Slot Devices Work

Slot devices use overlapping steel (or ceramic) rods (or rings) to form a fixed V-shaped angle.

  • This V-shaped angle is embedded in a plastic slot that guides the knife.
  • Pulling the knife through the slot scrapes the edge of the knife against the V-shaped angle, sharpening the knife.

Because the sharpening angle is fixed by the device, the user does not need to hold the knife at a special angle. Instead, the knife is held horizontally, the edge pointing straight down. This makes it easy to use, almost fool-proof.

Steel Ring Sharpeners

  • These use two to eight interlocking steel rings to form a V (see photo below).
  • Rotating the rings will cause a different part of the edge of the ring to be used to sharpen the knife. This distributes the wear on the steel rings so these sharpeners can last for decades.
  • The steel rings are harder than the knife’s steel, but not that much harder. Therefore this kind of sharpener is good for touching-up (honing) well-maintained knives but not for sharpening very blunt knives (it can take thousands of strokes to sharpen a blunt knife).

Characteristics of a good steel ring sharpener:

  • Rings should be tightly packed together with little side movement (“play”).
  • Edge of the rings should be smooth.
  • Bottom of the sharpener should be open, exposing the rings and allowing them to be easily wiped clean.

Ceramic Rod Sharpeners

  • Two small ceramic rods (either cylindrical or flat) are fixed in a V shape in the slot to form an angle (see photo below).
  • Ceramic is much harder than any steel knife. A blunt knife can typically be sharpened with less than a hundred strokes. After which less than ten strokes every few weeks will keep the knife sharp.
  • These are simple and can be cheap. Effective sharpeners costing only a few dollars can be found.
  • Though all the wear of sharpening is concentrated at the tip of the V, ceramic is so hard that these sharpeners can last for years.

Ceramic Ring Sharpeners

  • These are like the steel ring sharpeners, only ceramic rings are used instead.
  • They are just as fast as the ceramic rod sharpeners, and can last as long as the steel ring sharpeners (if the rings are rotated by hand before each use, to even out the wear).
  • They are normally the most expensive of all the slot devices.

Beware of Deep Slots

  • Slots that are too deep can block some parts of the knife edge from reaching the sharpening element (because the knife handle can’t get through the slot).
  • This will not be a problem for big knifes (because the knife handle is far away from the slot), but can cause problems for small blades – the knife edge nearest the handle can’t be sharpened.

Slot Device Usage

  • Knives should be pulled through the slot, not pushed.
  • Gentle pressure is best. Pressing down too hard can damage the sharpener.
  • The sharpener should be held firmly with one hand.
  • Care should be taken to control the knife at the end of each sharpening stroke. As the tip of the knife exits the slot, the sudden release of the knife from the device can cause the knife to slip and cut the table.