The Honing Progression

Following the bevel set on the Chosera 1k, the razor was honed on Shapton glass stones; 2k, 4k, 8k and 16k.   At each step in the progression, SEM imaging was performed.

The side-view images, at 5000x magnification are shown below.  As expected, scratch depth and width decrease with each step.   Although the Shapton 2k is rated 7.35μm grit and the 16k is rated 0.92 μm, the observed scratch depth is much shallower, less than one tenth the grit size.

CHO_1K_P

Chosera 1k

Shap2k_P

Shapton Glass 2k

SH4k_5kx

Shapton Glass 4k

Shap8k_P

Shapton Glass 8k

Shap16k_P

Shapton Glass 16k

The above side-view images provide little insight into the edge geometry or keenness.  Edge view images, taken at an inclined angle to provide perspective, allow direct assessment of the apex width. The edge width (or width of the apex)  decreases with increasing hone grit rating.

edge-on view images after Chosera 1k

edge-on view image after Chosera 1k, showing an apex width in the range of 0.7 microns.

Shap2k_E

Edge-on view images after Shapton 2k, showing an apex width in the range of 0.4 microns.

Shap4k_E

Edge-on view images after Shapton 4k, showing an apex width in the range of 0.3 microns.

Shap8k_E

Edge-on view images after Shapton 8k, showing a apex width in the range of 0.15 microns.

Shap16k_E

Edge-on view images after Shapton16k, showing an apex width in the range of 0.1 microns.

Cross-section images for the progression are shown below.

CHO_1K_X_measured

Cross-sectioned edge-on view images after the Chosera 1k.  Sharpness: 1.4 microns width at 3 microns from the edge.

Shap2k_x

Cross-sectioned edge-on view images after the Shapton 2k.  Sharpness: 1.2 microns width at 3 microns from the edge.

Shap4k_X

Cross-sectioned edge-on view images after the Shapton 4k.  Sharpness: 1.05 microns width at 3 microns from the edge.

No significant change in the bevel angle or width at 3 microns occurs after the 4k level.  No measurable difference is observed between the 4k and 16k level, other than a reduction in the apex width, observed in the edge-on views (above).

Shap16k_X

Cross-sectioned edge-on view images after the Shapton 16k.  Sharpness 1.05 microns width at 3 microns from the edge.

The convexity near the apex is removed by the 4k level, and the measured geometry is unchanged with higher grits beyond the 4k. Beyond the 4k level, the bevel polish is refined and the edge width is reduced from about 0.3 microns to about 0.1 microns.

Sharpness is achieved during the bevel setting stage up to 4k grit.  Beyond the 4k grit, Keenness improves, but Sharpness is not improved further.

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16 responses to “The Honing Progression

  1. This is interesting because it basically shows what Cliff Stamp and Tom Blodgett have said, that a coarser edge will typically have longer edge retention because the apex width is increased vs a higher polished edge. Thanks for posting this!

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  2. Pingback: Coarse apexed vs. Fine apexed edge | Razor Edge Knives

  3. Probably the most surprising result here is that the improvement beyond the 4k level is so visually underwhelming. At the same time, a dramatic improvement in performance, as measured by shave-testing, is typically observed over the same 4k-8k-16k refinement levels. The simplest explanation is that there is a keenness threshold required for comfortable shaving; an edge width in the range of 100nm.

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  4. On the previous article on bevel set, it was clear the diamond plate was more keen but less sharp than the Chosera. So you know if the progression here would change depending on which stone you used to bevel set?

    Would the micro convexity stick around thru to the 16K or would you end up in the same place regardless of which stone you used as a bevel setter?

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  5. Thank you for these awesome pictures. I have a blog and I sharpen knives by hand professionally. I have for years struggled with the “1k edge has better edge retention than a 5k edge” theory. The science was beyond me. However the photos support that. I know Tom so I’ll email him as well. Thanks again. Very Respectfully
    Peter Nowlan, Nova Scotia.

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    • In some peoples’ head-movie, seeing the truth with images is less reliable than their own qualitative experience (understandable), and in some cases, less reliable than information that somebody else with a high post count on a shave forum told them. It’s like telling somebody that their religion is wrong because “science”.

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      • It’s been my experience that many people will believe the first answer to their question and then not consider any other answer no matter how persuasive the arguments that the first answer was wrong.
        I would argue that a successful scientist doesn’t believe anything absolutely. A healthy skepticism of both old and new ideas is essential to being open-minded.
        Internet forums, on the other hand, are full of people who only skeptical of things that are inconsistent with their existing beliefs.

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  6. I would argue that ANY truly intelligent person doesn’t believe anything absolutely. I think ALL human knowledge is subject to revision with further (heretofore unknown) pertinent information. I for one truly enjoy reading this blog, and hope that there are many more installments to come.

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    • I see no reason to hold conclusions in my head, I’m happy to hold a probability function. There is an x percent chance that “a,” a y percent chance that “b,” and z percent chance that “c”…with as many letters as you like and of course “i” might be some horribly messy combination of a,c…& j.

      I guess we agree that those people who 1) encounter a doubt, 2) guess at the answer, and then in the next second 3) forget that there was ever any doubt…have, an unintelligent habit.

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