Questions on angles

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Rey HRH

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Oct 6, 2014
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I'm on the path of improving my sharpening skills and knowledge.

I've just read the following books: Sharpening Made Easy by Steve Bottorff, Knife Sharpening Made Easy by Stefan Steigerwald, and The Razor Edge Book of Sharpening by John Juranitch. I have two sharpening DVD's by Murray Carter which I haven't seen yet. Prior to all these, I went through some youtube videos. I've also read some of the threads here on sharpening.

My questions on angles are these:

1) Does everybody (majority) believe in having both the Secondary (or relief) edge and the Primary edge? I guess those who use convex edges don't believe in this?

2) If the primary bevel is 22 degrees, then the Secondary bevel needs to be smaller than this but by how much? And what about Japanese knives which is suppose to be 16 degrees, what should the secondary bevel be? I'm asking the second question in particular because I have Shun knives.

3) I think I understand why the secondary bevel needs to be smaller than the primary so that as the primary is cutting, the cut part won't rub against the secondary bevel (hence it's called the relief). But what if the secondary bevel is made to be as smooth (or refined) as the primary? Can the secondary angle be the same as the primary (meaning just one angle) if the surface is ultra refined?

Thanks for your help.
 
1. Steve Bottorff advocates a true microbevel. This means the first bevel you grind in is a normal sized bevel, something like 1/16 to 1/8" wide on a kitchen type blade. The next bevel is a microbevel, which is very, very narrow and is something like 1/32 to 1/64" wide. Juranich seems to advocate thinning the entire "back bevel" of the blade. That is, he wants you to grind on the *side* of the blade, up above where the cutting bevel is. Lots and lots of sharpeners do this because thinner blades perform better for cutting. My point here is that these authors are discussing two different things.

2. When microbeveling or just thinning out a blade, the difference between the two angles can be 3, 4, 5, or a few more degrees. Give or take. The exact numbers tend to not be that important. So a back bevel of 20 degrees and a microbevel of 15 degrees is just fine. For Japanese knives, Murray Carter will tell you to do essentially what Juranich says: Thin out the back bevel until it's "thin enough". Then raise up a bit and grind in the actually cutting bevel. A technique that some sharpeners use is to stack coins on the stone to use as a guide for the height of the spine while sharpening. When you raise up to grind the cutting bevel, you add one coin. So maybe 3 to 5 degrees difference.

3. I think this question is asking if you need two bevels. You don't. You just need some edge bevel that leads to the sharp edge (apex).


Brian.
 
I would not overthink the whole angle/primary/secondary bevel too much. From what I have experienced in kitchen knives and outdoor knives may not answer your question but the easiest way to increase performance is to keep any bevel as acute as possible and then change the actual cutting bevel (or micro bevel) to fit your needs. The beauty of a very thin ground full flat blade with "almost sharp" before the edge is that you can easily sharpen it with a few strokes, you don't have to follow a large bevel (which is also cosmetically nicer) etc. Maintenance is a breeze. If you think that the steel and the given applications don't support that thin main bevel, add a relief bevel to the full flat grind. So for instance, the full flats are likely somewhere at 5 dps, add a 10-12 dps relieve bevel to it and finish up with a thin 15-20 dos.

Nick Wheeler shows his approach here to thin out the knife enough to be a slicer but strong enough to resist failure. He full flat grinds the bevel, then adds a slightly more obtuse grind to almost sharp and add the cutting bevel after. At 5:28 he adds the more obtuse bevel to the grind, then blends it in. I think this explains pretty much everything:

http://www.youtube.com/watch?v=RhijW7L9Cm4&list=UUM3ezocAUFI1HtIi4V7SLmw
 
I thin out my kitchen knives (and pocket knives) as much as possible and then convex or microbevel the edge just a few feather pressure strokes.

If I don't microbevel, it is screaming sharp, but will roll quickly, but if microbeveled, I can go my 10 workday without touch ups.
 
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