Sharpening Question.

K

kaphil

Joined
Nov 15, 2016
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5
Hi all.

When people talk about specific angles: 20 degree for example.

Say you have a knife with a Sabre grind.

Im assuming its 20 degrees in relation to the flat bit of the blade, before the the angle change. (Hope that question makes sense)

So having the spine verticle and tilting the knife 20 degree from that angle?

Same with a full flat grind, not going from the angle of the grind but from having the spine verticle?

Thank you =)
 
Sorry I was rather busy earlier. So if you have your knife vertical the angle we are talking about is the primary bevel. Which is normally referred in either degrees per side (20 dps) or inclusive 40 degrees. Your secondary bevel angle will be dictated by your grind. Hopefully a real knife maker will chime in here to further assist with more indepth and accurate information.
 
Blindmouse showed it well in his drawing.

The main flat area is the primary bevel. It is can be referred to as The Bevel, The Primary Bevel, The primary angle, The Flats, or the Main Bevel. It is the plane from the spine to the edge. On a saber/sabre grind there is usually no taper to the area between the spine and the ridge line. The two flats on a saber grind are simply referred to as the upper bevel and the lower bevel. The primary angle is the lower bevel.

The angle of the primary bevel is a factor of the thickness of the spine and the width of the blade. It does not matter what it is, and you can't change it.
As an example - for a hunting blade that is 1.5" wide and .125" thick at the spine, the main bevel angle is 4.75° For a really fat bowie that is .25" thick and has a 2.5" wide blade the primary bevel is 5.75°. For as thin fillet knife that is .07" thick and 1" wide, the bevels are 4°.

The angle of the edge, or secondary bevel, is what you choose to fit the use of the knife when sharpening.
It can be confusing because different people describe it differently. Some state the angle as the whole and refer to it as inclusive, meaning both sides. Others refer to it as degrees per side ... DPS. They measure the angle between the blade and the sharpening stone/belt on each side. This is helpful if you use a jig or mechanical sharpening system.
Technically, the inclusive angle is the correct way to list the edge angle.

Regardless of what you call them, just remember that it is nearly impossible to have a main bevel (the flats) more than 7 degrees.
The practical secondary (edge angle) is usually between 10° and 30° for most knives, with angles as obtuse as 50° for heavy chopping tools like breakdown cleavers.
 
Last edited:
JoeBusic said:
To simplify. Primary bevel is in the shaping of the knife and the secondary is sharpening angle
Click to expand...

I think in the Eastern countries like Japan, they refer to the bevels the opposite. Cutting edge is primary, the grind of the blade being secondary.
 
Stuart Davenport Knives said:
I think in the Eastern countries like Japan, they refer to the bevels the opposite. Cutting edge is primary, the grind of the blade being secondary.
Click to expand...
Hmm, that's a thinker. Interesting. Didn't really dive into it tho I'm in jap arts a long time. I lack culture.
Usually they have just one bevel and sharpening is really a form of cheating to get by easily. After a lot of sharpening, they rebevel it all to sharp. What was seen in history as convex grind is in fact sharpened away flat grind. Of course western way creeped into their ways so there are mixtures. It becomes easier to ask someone for a picture what they want as explanations today easily lead to miscommunication.
 
I had put that in my post but took it out so as to not muddy the waters. Yes, the easturn cultures value the edge so it is the primary angle or bevel.

Every surface on a Japanese blade has a different name. On a different style blade, the name may be different. There are hira, shobu, zukuri, and many other names for the flat sections (some are not flat but curved)

In very general and simple terms:
The upper bevel surface on a standard shinogi-tsukuri Japanese sword grind (roughly equivalent to a saber grind) is the Shinogi-ji
The lower bevel surface is the ha-ji. (You don't even want to start talking about hira-niku)
The ridge line or place where the two bevels meet is the shinogi.
The actual edge area is the ha. The primary bevel is the ha angle (actually a radius). The secondary angle is the ha-ji. The shinogi-ji angle is the mune bevel angle.
If the blade does not have a shinogi it is what we Westerners call a full-flat grind. This is called hira-zukuri (zukuri can also be spelled tsukuri).


Something that many Westerners don't know or understand is that most modern Japanese swords you see are not the traditional swords in thickness and edge shape. The old swords had lots of niku and a fairly large edge angle shaped in a radius (apple-seed-grind). These had robust edges that could take heavy hits without significant damage.
The newer style swords you see today for cutting matts and silk ribbons are called trick-cutting swords by some folks. Thery have very little niku and very low angle edges. They cut soft things very easily, but take damage easily if they hit a hard object.
 
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