How is sharpness measured on blade

On a fillet or skinning knife, it should be able to cut very quickly without having to saw through the meat. If you really want to get down to fine-tuned levels of sharpness there are a few more tests you can use. My personal favorite is to take a piece of paper and hold it vertically. If you try to cut it with a dull knife, the paper will crumple beneath the knife. A sharp knife will cut it cleanly when use a slicing motion to cut through the paper. A razor sharp knife can cut the paper cleanly by just pressing down on the edge of paper without any slicing at all.

Another test is to shave the hair on your arms. While we recommend caution using this method, it can be very useful. The test utilises the constant cut depth method in which the blade is pushed normally without longitudinal travel into the test media The cutting force is recorded as a measure of the sharpness, which means the lower the force the sharper the blade.

The test media is either 8 mm square or with a 3 mm wide side bead silicon rubber which is bent around a 20 mm former and the cut is made into the outer periphery of this bend.

This causes the rubber to open up the cut as the blade penetrates, thereby reducing the point of contact of rubber and blade to the tip of the edge only.

As the blade contacts the rubber the force increases to a maximum at which cutting starts to take place after which this cutting force falls to lower level.

It is this maximum force that is used as the sharpness related figure. Although the above curve is not visually produced by the standard instrument the maximum cutting force is numerically recorded, however it is visible with the computer interface option. For needles and other sharp pointed blades an optional alternative feed unit can be fitted using a polyurethane membrane as the test media, which is pulled taught, the point of the needle then penetrating through it. A similar force curve is generated and the instrument again displays this peak force as a measurement of sharpness.

This test system has been proved by extensive trials to be able to accurately evaluate blade sharpening techniques and edge coatings, providing an essential tool for blade quality control and research and development such as heat treatments, sharpening and coating technology. Where should the edge be observed? What is the effect of variability in edge radius?

Edge roughness. Some edges have changes in height; does that affect sharpness? The edge has high roughness; the edge does not reach a uniform point [6]. Edge finish and friction. In some cases it is possible to have a poorer finish but still a small edge radius, or a high finish with a large edge radius. How does that impact the edge sharpness? The top edge has a rough finish while the bottom edge has a fine finish [6]. Edge coatings are relatively rare in knives but are sometimes present on razor blades.

Therefore despite the seeming simplicity of defining sharpness with edge radius or width it is not necessarily a perfect definition. Also I prefer to define sharpness by an actual measure of cutting rather than leaving it to geometrical definitions. Otherwise it may not be known what variables actually improve cutting behavior. Experiments comparing the radius of the edge and the force required to initiate a cut show a very strong correlation [7]:.

From those graphs it is clear that the edge radius is the most important factor for cut initiation, with perhaps a small secondary effect of edge angle. While the above graph shows sharpness vs edge radius with relatively dull knives, the correlation works with sharper edges as well [4]:.

When it comes to making complete cuts the effect of edge angle is very strong. A test was performed with beet topping using knives with either single bevel asymmetric or double bevel symmetric with a range of edge angles [8]:. The cutting force required for cutting through the beets increased with increasing edge angle.

Interestingly, double bevel edges cut with less force at the same angle as the single bevel edges. So despite the similar sharpness edge radius , the force required is much greater to cut through the beets with a more obtuse edge. So while the sharpness is reduced over the course of the test the CATRA machine itself is measuring the change in overall cutting ability and this property is reduced throughout the test through changes in sharpness.

When comparing different edge angles, however, a more obtuse edge cuts less cardstock because of its reduced cutting ability even if its sharpness, or edge radius, is superior to the more acute edge. This reduction in cutting ability with more obtuse edges has been repeated on carrots and potatoes with single bevel knives as well [9][10]:.

Sharpness does not have the same effect with cutting all materials. Some are more difficult to initiate a cut and some are more difficult to cut through either due to friction or from the energy required to propagate the cut through the material.

The graphs below show the cutting force vs displacement for a sharp edge black along with a dull edge grey with different foods [7]:. On one extreme is the pumpkin flesh where there is almost no difference in behavior between the sharp and dull edge.

The pumpkin fractured easily and therefore the displacement to begin a cut was small. On the other end of the spectrum is asparagus and ham where because they are soft materials which easily deform, sharpness is a significant factor for allowing it to be cut.

The friction that resists cutting is much higher with cheese and ham than asparagus which is why the force to cut continues to increase to a greater extent with those foods.

CATRA is perhaps best known for their edge retention tester, but they also produce a sharpness tester. The sharpness tester uses a rubber test media and the blade is pressed slowly into the rubber until a small drop in load is measured indicating that the cut has been initiated [11]:.

Because the thread is thin and the cut propagates easily then the test measures the force required for initiation of the cut. Their sharpness test is also reported to correlate strongly with edge width [14]. Most of the tests referenced above other than the CATRA edge retention test uses a push cut rather than a slicing cut. A great comparable standard for sharpness and one of the few ways to quantify sharpness. The BESS value is the maximum weight you need to push your knife through a certified test medium.

The sharper the knife, the less weight you need. A lower score is therefore sharper than a higher score. Because all tests are carried out with the same test medium you can easily compare the results. Because a number doesn't say a lot without context a table was set up to make sure you can see how the score relates to the total scale. From the BESS you need to cut through the test medium with an unsharpened knife, to the 0-score: ultimate sharpness. Granted: there are few knives that come close to the 0 BESS.

A double-sided razor is approximately 50 BESS, to give you a better idea. With the BESS everyone can test the sharpness of a knife. The Edge-On-Up test tools are relatively affordable. Therefore, you no longer need half a laboratory to end up with reliable results.

As long as everyone uses the certified equipment and the certified test medium. As such you measure the sharpness of your knife like every other user in the world. Comparing results is, as such, easy! BESS also provides clarity. Abstract terms like 'razor-sharp' or 'incredibly sharp' are replaced by a value. But also 'pretty blunt' suddenly has a value that can be compared to other values.