Quantifying Sharpness - Part Two
The Sharpest Edges With Measurable Results
Professional Knife Sharpening Service Is A Process Which Can Be Measured, Controlled, And Improved
Enter The BESS Sharpness Tester and Tester
I've gathered information from testing my knife sharpening protocol with the Edge On Up BESS sharpness tester. A few of the findings were a bit unnerving at first. The good news is that when you have a way to quantify and measure your work, you can control and improve your process! Here's what I came up with in a completely unscientific presentation on making the sharpest edges and
You all may remember that a while back, I wrote about the Edge On Up edge sharpness tester I purchased to measure the sharpness of sharpened edges(Quantifying sharpness) on my custom knives and for the Knife Sharpening Service. (If not, you can catch up HERE!) I was both curious to know if my edges were as sharp as I THOUGHT they were and frustrated because there was no way of knowing beyond slicing phonebook paper and shaving my arm hair.
While those tests provide "feedback" on the quality of edges, they don't offer a number or "quantify sharpness." Say an advantage shaves hair cleanly and push cuts phonebook paper with no slicing action; that's SHARP. But how much sharper than SHARP might it be? We want the sharpest edges we can reasonably get.
I like testing methods that give a reading of what is being tested. A micrometer will read ".0001-.0005", and a Rockwell hardness tester will read 62.5HRC. A "Knife Sharpness Scale" chart came with the Edge on Up knife sharpness tester(shown left) showing how some fairly well known edged tools measure up to each other. For instance, the sharpest edges measured on the chart are double edge razor blade, measured at 50 grams to cut the test media (1.76 oz). New utility razors come in between 150 and 200 grams, and new high end factory cutlery between 250 and 350 grams. Anything above that is considered "in need of maintenance", and I completely agree! So I decided to do some testing, of course.
I sharpened five knives for a customer according to my usual protocol. Since this was my first time seeing these kitchen blades, I thinned the edges at 13 degrees per side until a burr was raised on both sides. After buffing the burr away, I sharpened them on the Hapstone fixed angle sharpener at 16 DPS with bonded diamond stones at 80, 240, 400, 800, 1200, and 2000 grit. After the stones, the knives were stropped with hard-backed strops, leather loaded with fine white polishing paste, denim loaded with Flitz chrome polish, and finished on leather loaded with 1-micron diamond paste, ten strokes per side with each of the strops. Each of these blades was tested on the Edge On Up Knife Sharpness Tester in three places along the edge, and all measurements for the five knives were between 180 and 230 grams. They all slice and cut phonebook paper and shaved arm hair with a slight pull. Needless to say, I was disappointed! (But here is WHY we test and measure features! A guess is just a guess, not a fact!)
I returned to the Hapstone at 2000 grit, raised a burr on one of the knives only, and deburred it on the Hapstone with a 3000 grit sintered ceramic stone, no stropping. I tested 180 grams. Three light strokes on the denim/Flitz, and tested 170 grams. Three strokes on the 1-micron diamond/leather, 160 grams. I was easily shaving arm hair with no noticeable pull. Looking back, I'm confident I was overstropping the edges and rounding the apex. To test this, I resharpened all five blades at 2000 grit, followed by the 3000 grit ceramic, and three strokes each on the denim/Flitz and 1-micron leather. Retesting the edges found they all fell between 140 and 175 grams. Well, within the utility razor window on the BESS scale. These results were what I expected from my regular sharpening protocol, and had I not purchased this instrument, I may have never known what was causing the inferior (to me) edges! I believe that now that I have "the feel" of pressure on the strops, I can test every 5-10 knives to verify that I'm still on track.
I believe I could also sharpen blades into the 100-gram range with more testing and trial and error. I also know it would increase the expense of sharpening for customers, and that an edge keen wouldn't last long on a cutting board. That doesn't seem cost-effective for the customer, or a good use of my time. I'd love to hear your thoughts on this post, on knife sharpening in general, and what you think of this kind of post or page in particular. Get in touch if you like!
NOTE: I'm not trying to sell anyone a Knife Sharpness Tester. It's just that I know from many years as a machinist making EXTREMELY precise production parts, dimensions drift away from what is ideal. What you can't see with the naked eye must be measured with an acceptable degree of accuracy. And it just makes me feel better knowing!
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Thanks for reading,