We put all the sharpeners through their paces, using each machine to sharpen the blades of brand-new copies of our favorite chef's knife that we’d dulled by dragging them over a whetstone, repeating the dulling-and-resharpening test a total of four times. We assigned one copy of the knife to each machine throughout testing. To evaluate the results after each sharpening, we sliced through sheets of copy paper, our standard sharpness test; used an industrial sharpness-testing machine that assigned a numerical score to the sharpness; and finally circled back to the real world by slicing ripe, juicy tomatoes. 

To see if the machines could handle chef’s knives made with different designs, metal composition, and blade hardness, we also dulled and sharpened a single copy of a Japanese carbon-steel knife that we recommend, the Misono Swedish Carbon Steel Gyutou, 8.2". And to see whether the sharpeners could repair damage, we used a tool to drill small notches in all the Victorinox blades to simulate chips you can get on your knife when cutting very hard or frozen food. Throughout testing, we evaluated how easy the sharpeners were to operate, as well as how much time and effort we had to devote to bring our knives back to razor-sharp condition. We also noted whether the machines kept our countertops clean of metal dust and whether the knives’ blades or handles were damaged by the sharpeners.

Electric sharpeners operate by rotating an abrasive sharpening material as you pass a blade along it to grind metal from the edge of the knife. Typically, the rotating sharpening material is set inside the body of the machine for your protection, and you pass the knife through one or more V-shaped slots that help you control the angle of the blade as it touches the abrasive. The sharpeners in our lineup contained diamond, Sapphirite (a synthetic ceramic), or other ceramic-based abrasives in the form of disks or belts. They offered one of two sharpening methods: either you pass the knife through a series of slots in stages containing a range from coarse to fine abrasives, or you put it through a single stage while the machine varies the speed of the rotating abrasive. Both methods are designed to regrind and then polish a knife’s edge.

We judged the sharpeners on a few key factors. First and foremost, if they couldn’t make a dull blade truly sharp again, any other features really didn’t matter. Three of the machines never restored the razor sharpness of the brand-new blades—no matter how long or carefully we used them. Four other models did have that capability.

That said, consistency was a problem with one of the four. The Work Sharp Culinary E5 was undoubtedly the most compact, easiest, and fastest to use—we simply pushed a button to start an automatic 90-second cycle and then drew the blade repeatedly through a single pair of left and right slots—but the outcome wasn’t always optimal. We often discovered a rough spot along part of the edge during our paper-slicing test. These uneven results may have been due to the design of the slots: Since they’re wide, they didn’t help control the blade angle; instead, we had to remember to consistently lean the blade away from the rotating abrasive and toward a leather-lined outer wall, and the direction in which we had to lean the blade was different depending on the slot we were using. We usually had to run the sharpening cycle more than once to get a uniformly sharp blade. We preferred models that gave us dependable sharpening that was consistent from blade heel to tip, every time. For the same reasons, this model did a less-than-stellar job sharpening our carbon-steel blade. We also discovered after testing that this sharpener had cut into our favorite chef’s knife’s handle where it joins the blade, leaving it rough and damaged, though this might be avoidable if you are aware of this potential and are very careful.

Work Sharp Knife & Tool Sharpener Ken Onion Edition presented the opposite situation: It was by far the most effective sharpener in our lineup, providing the utmost control and flexibility, but because its rotating abrasive belt is exposed, it was daunting to use and it made a mess of our work area, spraying metal filings and grit everywhere. It belongs on a tool bench rather than the kitchen counter. That said, if you’re up for handling a semi-industrial tool and have a pair of protective goggles handy, this is your sharpener, and it’s capable of dazzling results. The package included five abrasive belts in a range of professional-grade materials and coarseness levels and a lot of information about how to use them to sharpen everything from kitchen blades to shears, hunting knives, and tools. You can set the edge angle from 15 to 30 degrees and precisely adjust the speed of the sharpener. One final note: With its exposed belt, this sharpener literally chewed off the front edge of our Victorinox knife’s Fibrox handle before we had time to adjust it.

Our journey ultimately led us back to our previous winner, the Chef’sChoice Trizor 15XV Knife Sharpener. Once again, this three-stage machine was the most dependable and consistent sharpener of the lineup and the clearest in its instructions. The steps to achieving a sharp edge are detailed in the manual, and we recommend following them each time you sharpen, since they showed us precisely what to look for at each step before proceeding to the next.

When we followed the steps, we got an impressively razor-sharp, polished, and uniformly sharpened edge on even the dullest knife in about 2 minutes. It quickly removed all traces of the notch we cut to damage the blade, and it did a swift and superlative job restoring the carbon-steel knife’s edge, too. The narrow, spring-loaded slots made it simple to maintain the correct knife angle. The first two slots, one coarse and one medium, contain diamond abrasives that allowed us to easily power through the sharpening process, with each stage creating a slightly different-angled bevel on the cutting edge. The third slot contains a “stropping” disk made of a proprietary flexible plastic material with ultrafine diamond abrasives. Traditionally, strops for blades are made of leather, and their role is to remove burrs and polish cutting edges, leaving them extra-smooth and sharp. Any metal grit created by sharpening was collected neatly in a magnetic holding bin that was easy to empty (though it would take many months to fill with normal use). This sharpener can also be used to maintain other knives in your kitchen, including paring and boning knives, single-bevel traditional Japanese-style knives, steak knives, and even serrated blades (in this case, using only the stropping disk in stage three).

This model shares some of its characteristics with a slightly less expensive version, the Chef’sChoice 315XV Knife Sharpener, which gave us almost equally good results in about the same time frame, so we’ve named it our Best Buy. Like the Trizor, this model also can sharpen a variety of kitchen blades, not just chef’s knives. Where the two models differ is in the number of sharpening stages—the Trizor has three, the model 315XV machine has two (the medium-abrasive and stropping disks). Since one less bevel provides less blade support, the two-beveled blade edge created by the less-expensive model may require a bit more frequent sharpening over time. However, how often you need to resharpen can also depend on the hardness of your cutting board, what you are cutting, and how you use your knife, so it’s difficult to say whether having two or three bevels makes a perceptible difference. We did come to the conclusion that the Trizor put a slightly more smooth, razor-sharp edge on knives, particularly the carbon-steel blade, but either model will help you sharpen quickly and get right back to successful cooking.