Micro Bevel How To
- This topic has 24 replies, 9 voices, and was last updated 12/26/2015 at 4:28 pm by
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By the way, I have photos which show that even scalpels are made with a toothy edge. The packet I bought off Amazon is ground both sides with about 600 grit, and then polished only on one side to leave the toothy edge. This stands to reason as you need a toothy edge to bite into slippery tissue.
Completely irrelevant, but
Surgical scalpels should not have a toothy edge. It’s actually a big point of contention in the medical community with regards to obsidian scalpels, which have been proven in animal studies to drastically reduce healing time because under a microscope, a steel scalpel, no matter how sharp, will tear along the line of incision, whereas obsidian scalpels will actually cleave individual cells in half. Less damaged tissue, less inflammation, better healing. The reason we don’t have them in the operating theater yet us because of concerns that the obsidian blades can chip easily and leave slivers in the flesh. For biology slides, scalpels of glass are used for primary divisions and then slide cuts are made using diamond scalpels, which are prohibitively expensive but obviously very clean cuts at a cellular level. The idea is a bevel so fine that the friction line is so microscopic that it doesn’t even need a bite to sink through flesh. Also, flesh isn’t actually that slippery and incision points aren’t exactly trying to shave a tomato, all you want is clean cuts with a minimum of inflammation-causing tearing.
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Tom, here is one of the “articles” I was thinking about… good read if you have time.
Here is a straight razor I finished up recently. This picture is done at whatever the angle was (don’t remember – don’t measure on straight razors usually) and taken through 3um lapping films. Yes, I micro-bevel my straight razors because I CAN on the wicked edge 😀 And not only does it add strength, it gives the most consistent apex…. not that this apex was lacking lol.
And here is the same edge, w/ an increase of exactly 1 dps w/ the 1um lapping films, alternating, edge leading passes – no stropping yet.
I also recommend switching from edge trailing to edge leading if you want minimal burr/wire edge. I can’t remember where I saw Todd post this exactly (check out his blog!), but a few points that I have seen him say… 1. only a couple strokes with your highest grit stone (when micro-beveling) will lead to a wire edge until you do more and the micro-bevel both establishes and stabilizes. 2. edge leading will give you minimal burr removal but can lead to micro-chipping/irregularities.
keep in mind, todd is mainly dealing w/ straight razors and not knives (which are typically at much higher angles) but I think the research is still very important and relevent to this discussion =)
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As far as toothy vs polished for surgical scalpels…
I would say it depends on how the edge is sharpened. The thicknesses of the apexes being the same I personally believe the toothy edge would be much more effective but I do need to do some more comparisons when processing game.
From the Science of Sharp blog I posted above… This apex width is measured at 100 nm (nano-meters) and is finished, edge leading, on a DMT 325 plate (which would produce a toothy edge by definition)
Here’s an edge finished off of a 16k Shapton waterstone then stropped on loaded denim
Both have irregularities on a small enough scale, but I would think that the one w/ more but the finest apex width (without forming a wire edge) would peform the cleanest cut – but I may be wrong. I am not drawing any conclusions from my limited knowledge/research. As far as effectiveness goes I will be doing my own comparison in the near future when I process this next pig =)
Without getting too much further into it, you’re also looking at the crystalline structure of the elements evolved beyond the sharpening when it comes to the obsidian vs steel argument.
It’s basically the works of ultramicrotomy starting to bridge into surgery. The diamond knives of ultramicrotomy are used to create 2000 radial cross sections of a single hair, or 100 cross sections of a single red blood cell. That’s how fine we’re talking when it comes to the obsidian and diamond knives. The edges are not sharpened, they are made using fracture lines.
…..I have seen him say… 1. only a couple strokes with your highest grit stone (when micro-beveling) will lead to a wire edge until you do more and the micro-bevel both establishes and stabilizes.
This specifically refers to low angle primary (less than 10dps) where the apex will bend rather than abrade unless the micro-bevel angle is at least 5 dps higher. For example, micro-beveling a straight razor by adding tape gives inconsistent results because of this.
2. edge leading will give you minimal burr removal but can lead to micro-chipping/irregularities. …
Edge leading almost always prevents a burr on mid- to high-grit stones. Low grit results are quite variable, depending on the stone. The micro-chipping process is what removes the burr, so it is not a negative in this case.
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Josh, maybe I should better ask this question at the guy of Science of Sharp (sorry, forgot his name), but how can you exactly measure the width of an apex? I.e. where do you measure it. For example, if you do it at the exact top you might end up with a few molecules’ width. If you do it just half a millimeter lower, it will already be much thicker.
So how can the concept of apex width make sense without saying where you measure the width. (And this is even apart from measurement apparatus – unless you’ve got an electron microscope – and my hands simply not being exact enough to measure consistently at the same location for every knife.)
This is the reason that in my Japanese Kitchen knife Reviews blog I measure the edge thickness only at 5 mm above the edge. I simply cannot get it more exact.
Measuring the apex geometry (in 2 dimensions, ignoring “tooth” for now) requires two quantities. Edge width or more correctly the radius of curvature of the apex is what determines the pressure exerted by the blade on an object being parted and this is typically less than 100nm for any razor blade, utility blade or scalpel. Obviously this cannot be measured without an SEM. The second measurement must quantify the thickness behind the apex – this could be angle or the width at some distance behind the apex. If the bevel is not convex, these are directly related. The relevant distance from the apex will depend on the material being cut, for shaving I believe 3 microns behind is representative of the performance. For deeper cuts, the thickness further back is more relevant.
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Follow up on the ZT 0770
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