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Continuous Operation Time for Electric Knife Sharpeners

We test electric sharpeners’ continuous sharpening time by letting them run for 25 minutes straight.

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This test is part of How We Test and Rate Electric Knife Sharpeners v1.0

Continuous operation time is the longest duration a machine can safely run without pausing or stopping. Sometimes, the continuous operation time (COT) is stated in the user’s manual, but not always.

Some top-notch sharpeners, such as the Work Sharp Ken Onion or the Chef’s Choice Trizor XV, can run for a whole hour without issues. Some others, the Narcissus being one example, have a safety mechanism that switches the unit off when it reaches a certain temperature — sometimes well before the advertised COT — and resumes working once the machine has cooled sufficiently. And then there are machines, such as the EdgeKeeper, that do not list a COT limit but die without warning when they get overheated.

The real COT of each machine can, as such, only be discovered via testing.

Why Continuous Operation Time Matters

Regardless of the mechanism and factory-stated time limit (if any), it’s always better for an electric sharpener to be able to run continuously for a long time. Many people buy these electric machines for their monthly knife maintenance, where they sharpen and hone their whole knife collection at once. Unsolicited pauses or stops are frustrating and can extend the sharpening time.

Continuous operation time makes up 20% of the Performance score.

How We Test Electric Sharpeners for Continuous Operation Time

We test COT by running a knife through the electric sharpener for 25 minutes. This is the time we estimate it should take to sharpen the five most popular kitchen knives (chef’s knife, cleaver, santoku, utility knife, paring knife) in one go.


Here’s a list of what we use to conduct the test.

  • Electric sharpener
  • 8-inch, 20-degree-bevel, stainless steel chef’s knife 
  • Clock app to record the time

The Test Procedure

We set a timer for 25 minutes and run a knife through the coarsest stage for the first 15-20 minutes, then 5 minutes on each of the remaining sharpening stages.

We turn off the sharpener briefly if that’s what is necessary when progressing between stages. For example, in the case of the WorkSharp Ken Onion, we must switch the machine off for a few seconds to change the belts. This is part of the sharpening process and we don’t deduct points for these pauses.

How We Rate Continuous Operation Time

Every 5 minutes that the machine can run without pausing or stopping gives it 2 points in the continuous operation time score.

An unplanned pause (usually due to the sharpening wheel getting stuck from excessive blade pressure) that lasts 5 seconds or less translates to a 2-point deduction.

A pause that lasts more than 5 seconds is considered a stop. The continuous operation time is the shortest duration the machine can work between pauses.

If a machine dies before 25 minutes elapse, it receives zero points in this test.

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