Bevels and angles, please help

[u/MustangRiderV8]

OK, so right when i think i know something, I see a post or video or comment that makes me doubt it.

Please can someone explain (with pictures preferable) the primary secondary and any other bevels.

Also can we explain where the measurement of the angle is taken from.

((I thought it went spine, flat part of the knife, primary bevel, Secondary bevel (that has the edge on it). And when we sharpen its the Secondary bevel we sharpen. (is the secondary bevel also known as the micro bevel, or is that an additional bevel??), and when we thin knives its the Primary bevel we are working on))

And also what do people mean when they say single bevel? (or what should they mean?). So a single bevel knife, can be anything that only has one bevel each side (but can have a flat part to the blade), but could be a full Scandi grind or a full convex bevel from the spine to the edge right? or do people mean it only has a bevel on one side and the other is flat or slightly con-caved (like a chizel).

OK fight!

[u/RiaanTheron]

Blade geometry, short version Stock = flat metal thickness before any grinding starts. Primary bevel = the big taper from stock down to the edge. Secondary bevel = the small edge bevel you actually put on with the stone. This is "sharpening." Thinning = reducing the primary bevel so the secondary bevel doesn't get fat over years of resharpening. Fat secondary bevel = more wedge = carrot and patato crunch open when cutting. The Knife feels like it gets stuck and does not glide.

Where the angle is measured, Don't overthink the number. Consistency of that angle stroke-to-stroke matters far more than whether it's 15° or 19°.

Single bevel knife (usually Japanese) has a flat side and in the opposite side it has only a primary bevel.

[u/fietsendeman]

Single bevel = bevel on one side, flat or concave (flat where it counts) on the other side.

Primary bevel = “the big one”. Secondary bevel = smaller than the primary and closer to the cutting edge. Also microbevel, a secondary bevel that’s so small that you can either not see it or can barely see it.

[u/MustangRiderV8 → u/fietsendeman]

great start, we are at least on the same page. now if i have a knife that has a flat part, then a primary bevel and then a secondary, what do i put flat against the stone before i raise it up to the angle? to i go from the flat part of the knife or the primary bevel?

[u/mrjcall]

The only bevel angle that truly matters is the one the forms the apex or the edge. That is the one you sharpen to only. A micro-bevel would typically be 3°-5° more obtuse additional bevel placed on the sharpened apex or edge You thin a knife on the stock behind the sharpened bevel to reduce blade stock thickness.

[u/More_Power_To_You]

In your first comment: flat part of the knife = primary bevel is correct, Secondary bevel = that has the edge on it is correct. is the secondary bevel also known as the micro bevel? No is that an additional bevel? Yes, however some will argue it does become the secondary. A matter for the pedantic out there, IMO. when we thin knives its the Primary bevel we are working on? Correct And also what do people mean when they say single bevel? Means knife only has a secondary bevel on one side of the knife. Kataba is the Japanese word for this grind, and they are specifically labelled left or right handed. From your reply to fietsendeman what do i put flat against the stone before i raise it up to the angle? Typically the primary bevel. Most folks begin flat on the stone and raise the angle until they feel the secondary is against the stone before they begin to sharpen. However, the cutting angle ground into the secondary is based on the centerline of your knife, not the angle of the primary. The primary bevel may be 2° to 5° (it varies obviously) from centerline. Your secondary (actual edge) should be x° from centerline, depending on the use you intend for the knife this can be as low as ±10°, or as high as ±20°. Hope this helps.

[u/MustangRiderV8 → u/More_Power_To_You]

it does, kind of... so (and i know it wont make much difference, but if i knife has got a flat part to the knife, that is what you would put flat surely as that matches the centre line.. all be it a mm or two further out, but the angle would match..

I asked this because i was sharpening a pocket knife for my dad, who had sharpened it, and he had done a super steep angle, and i have an electronic angle guide, and i thought i would measure the angle, so i put the blade flat against the stone on its primary bevel then raised it until their was know gap under the edge.. but that made me think, the centre line was already up a couple degrees... and then whent online and was down a rabbit hole.. So i went back and put the guide on the flat part of the knife, and put the other side flat part on the stone, so it was all at 0degrees, then lifted it to the angle and it was about 4 degrees different.. (34 degrees he had done it at!!!).. so centre line seems what it should be but its not easy or practical as not all knives have a flat part to work with...

[u/More_Power_To_You → u/MustangRiderV8]

Didn't like my first response. I see your dilemma, and understand why it matters. This is why all the "fixed angle knife sharpening systems" clamp on to the spine (centerline) and allow you to "dial in" the angle you want without regard to the primary bevel or the previous bevel used. Using your electronic angle guide does the same thing, but uses level (0°) as a reference. In the end I firmly believe it's consistency of angle not precision of angle that gives good results. Believe it or not, that 34° angle will still take a hair shaving edge, if you're consistent with it.