This is a common pull through sharpener, many variants are made, some have carbide only and some like this one have carbide and then two crossed ceramic rods. This is one of the most basic ones as
A shot of the unit alongside a SALT from Spyderco :
The goal was simply to compare the sharpeness produced and the edge retention of the carbide slots only vs a hand honed edge. Cardboard was cut as a blunting medium and sharpness was measured by cutting light jute under 500 g of tension and measuring the length of edge required to make a slice - fairly simple.
A Pacific SALT from Spyderco in H1 was the knife used. Five runs were made and between each run the micro-bevel was completely removed with a 1000 grit waterstone. A micro-bevel was then applied with the ceramic slots so each run was basically a completely fresh edge. Each run was 155 cuts in total through the cardboard 30 lbs of force used with a draw cut through three inches of blade.
A short summary of each of the five runs :
It was obvious from the first run that this is not trivial or mindless to use as is often claimed in similar infomercials, i.e., just pull the knife though once and it is "razor sharp". If care is not paid during the honing then the results will be poor and inconsistent. However, with attention to detail a razor edge can be produced just on the carbide slots alone. A summary of the technique points which were found to be critical :
On the force, basically it should sound and feel like it is cutting. Too little force wall cause nothing to happen (it will just align like a smooth steel). Too much force and the edge will break apart. With very heavy force there is a loud scraping sound of metal on metal and the knife will also tend to catch and skip and not get a smooth pass on the carbide slots. Keeping the carbide blades clean is also very vital as if they get too covered in shavings from the edge then the shavings also mash into the edge and will also blunt it. Removing the burr is also critical, a simple draw through clean hardwood is fine but optimally just rotate the knife a little to the left and then right and cut the burr off with one pass each. The image on the right is a 50X magnification shot of the edge which shows just how badly the carbide can leave a burr.
This may sound overly complicated, however it only took five sharpening sessions to figure out how to use the sharpener. The main point is the "as seen on tv" method of just yanking the edge through a few times will produce a fairly low sharpness. It just takes a bit of care and focus to obtain a quality edge.
Back to the results, the averge of all five runs produces the following graph :
The y-axis is the normalized sharpness and the x-axis is the number of cuts, the sharpness starts at one at zero cuts and decreases to about 0.25 or 25% after the 155 slices each 30 cm long though 1/8" ridged cardboard. The average is the red data points, the fitted curve is the solid line and the green points are the first run (not how poorly it performs there) just for comparison.
Unfortunately the first trial has to end here because it took the full five trials to figure out how to properly use the sharpener which used up all 250 m of cardboard on hand, thus no edge retention comparison could be made. However at least information was gained on how to obtain a quality edge from the sharpener which at least on the surface is not by any means horrible in regards to quality or lifetime. As a final point, this sharpener removes a lot of metal, it literally peels off shavings from the edge which are are easily big enough to be visible. To the right is a picture of a piece of metal stripped off from the edge which is shot at just five times magnification.
The second comparison of the sharpener was an extended comparison of four knives used in the kitchen. Two of the knives were sharpened with the carbide slots and two knives were sharpened with a 600 grit DMT rod. The knives used were :
All of these knives had very thin and acute edges, ground between 5-10 degress per side so the edge retention being examined was on a micro-bevel with the carbide vs the DMT rod.
First trial, Willington Sword sharpened on carbide, the Japan and Stewart knife sharpened on a 600 grit DMT rod.
Second trial, again the Willington Sword sharpened on carbide, the Japan and Stewart knife sharpened on a 600 grit DMT rod.
Third trial, this time the Willington Sword blades were sharpened on the DMT rod and the Japan and Martha Stewart blade were sharpened on the carbide.
Forth trial,again the Willington Sword blades were sharpened on the DMT rod and the Japan and Martha Stewart blade were sharpened on the carbide.
Table summary :
|#1||#1||Carbide is sharper|
|#2||Carbide is sharper|
|#2||#1||Neither - Both Equal|
|#2||600 DMT is sharper|
|#3||#1||600 DMT is sharper|
|#2||600 DMT is sharper|
|#4||#1||Neither - Both Equal|
|#2||Carbide is sharper|
Kind of surprising, it was expected that the 600 DMT finish would clearly outclass the carbide edge. With further consideration, the edges were not not dulling from wear or light rolling as much as they are being damaged from contacts off of plates, pots, kitchen sink, etc. .
This sharpener was not expected to be significantly useful and in general these types of sharpeners are often pretty strongly degraded such as noted in the video on the right. However it was found that :
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|Last updated :||Sun, 18 Mar 2012 22:28:09 Newfoundland Daylight Time|
|Originally written:||11 / 28 / 2011|