Sharpening knives: Which degree is best?

golok

golok

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Oct 20, 2000
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I hear of people saying 30 degree angle for sharpening is good. Others say 40 degrees. Then somewhere out in the back, another whispers 25 degrees.

Actually, I am slightly confused by these three different degrees of separation. How does one tell what degree is best for a blade edge and how do you know whether you are getting the right degree?
 
depends on the use the steel would be put to. generally, blades meant for chopping (as opposed to slicing n dicing) have more obtuse angles, like 40 degrees. Slicers can be sharpened at 30 degrees or even 20 degrees. However, at such acute angles, certain steels may chip or roll upon impact. I think Cliff Stamp recommends lowering edge bevel angles to as low as the steel can get, even to 10-15 degrees included.

If you're looking at optimising sharpness, the other factors to consider besides the edge bevel angle are the grit of the edge finish, the thickness of the edge and the type of blade grind.
 
The optimal angle is the lowest one which has the necessary level of durability. For light use knives there really is no limit, you can hone right back into the primary grind ~3-5 degrees per side, which is fine for ropes, cardboard, foods etc. . As the demands on the knife increase (chopping), the angle needs to be more obtuse to withstand the increased impacts, but again the same principle holds, keep it at the minimum which will prevent damage and thus maximize the cutting ability.

-Cliff
 
Personally, I think an engineering degree is best. A philosophy degree is too obtuse for general chores. A liberal arts degree may offer all around utility, but then its never just right for the task at hand is it?
 
I agree, it has to be easy toresharpen for you. So take a look, the way you are grinding. There is something like human touch. At least i nearly always grind the way i hold the knife for cutting.

Another question might be, how thin a belly may be for general use. Surely thicker han the kitchen knives, but how thin minimum? I ask it myself since i hold one of the BM 5000A, which came with a primary bevel, around .02" thick.
 
It also comes down to the environment that the knife will be used in. Boners and slicers used in meatworks can have virtually no angle at all as they work in a 'sterile' environment but take those knives out into the field and you will soon damage the edge as they come in contact with grit etc.
 
The first kind of confusion is whether people are talking about "sharpening angle" which is how far you tip your blade off of the plane of the hone when shapening or "edge angle" which is the included angle between the surfaces of your edge. The included angle is 2x the sharpening angle. When people refer to sharpening to 30 or 40 degrees they are usually talking about the edge (included) angle. When people talk about sharpening to 25 degrees I tend to think that they are talking about sharpening angle. This is a common angle for cheap commercial knives.

I tend to go with Cliff. I thin blades down to the lowest angle that I think is up to the task. I go to stronger alloys for more edge strength rather than to higher angles. Higher angles reduce cutting efficiency so I try to avoid them. I will tolerate edge damage in an emergency to get higher performance in normal use. My primary sharpening angle is in the 10 to 15 degree range. I finish with a few strokes at 17 to 25 degrees depending on how hard I figure to use the blade. If I need something tougher than that I look of a carbon steel hatchet or cleaver.
 
I always sharpen to the inverse angle to the secondary convex grind, unless using for boating.

For boating, I use an angle equal to the complimentary angle opposite the primary grind multiplied to a power of three.

(Note: Today has been a difficult day and accordingly the above makes me feel better.):rolleyes:
 
Of course the grind of the knife will also determine the angles used -Flat vs Hollow vs sabre (or scandanavian) all have their own pecularities. One grind I use on butcher knives is the triple grind:-

Primary grind - 5 degrees

Secondary grind - 10-12 degrees

Final grind - 15 -17 degrees

I find this extends the life of the knife esp. with boners which will end up toothpicks if sharpened too steep and too often.
 
I use the Lansky system a lot, and generally try to use the 20% angle whenever possible, and only go higher if edge durability becomes an issue. I like my knives thin and sharp. I primarily slice and dice with mine.
 
I agree with Mr. Stump , a liberal arts degree is the jack of all degrees and master of none :) .
 
I learned a lot of my sharpening lessons lately from Cliff and Joe T... I drop my edges as low as I can humanly get them without getting damage after each use.

kitchen and yard use knives get about 35-40 inclusive, work knives(rope, cardboard, fabric) get 30deg.

I have my EDC beater(spyderco ss dragonfly), which sees use and some abuse(including light prying with the spine) on everything the 2" blade will handle has the edge thinned down so that my sandpaper is right on the flats. 2.5mm spine and 1" at max, 1/8" at same from tip... so you can figure out how thin that is. The double grind on the edge is about 2-3 deg above that(just enough that the paper doesn't contact the blade.
The current edge on it, I did July 31st, and haven't touched the edge since. It was a series of sharpenings on this blade to see how sharp I could get, over the last year and some.

Some, like my FB03 lum tanto(4.5mm spine, 7/8" belly, hollow grind starting at 1/2") I just sharpen as thin as it lets me, not even measuring. I set it down on 1200 grit paper and just lift that 2-3deg clearance so I'm not hitting the shouler on the grind. I use it about 2-3 weeks and it needs a strop. get about 2 weeks and then the 1200grit paper again.

Learned from Joe T. that the edge angle is dependant upon the steel used. ATS-55 and VG-10 will take and hold a thinner edge than Aus steels.
 
OwenM :

I'd rather have an angle that's easy for me to match when touching up or resharpening, as a matter of convenience, and let blade geometry, and edge thickness (as opposed to angle) be the determining factor in cutting ability--edit: and durability.
Click to expand...

There are indeed other factors besides edge angle which influence cutting ability, edge thickness is next, then the nature of the primary grind. However all of these are far secondary to edge angle, which can in fact be so large on some cutting it ignores the others completely.

Puukkos for example have horrible edge thickness usually, ten times as great as most other knives, yet still cut very well because the edge angle is acute, ~10 degrees per side. The stock thickness is also small, but that only comes into play on really deep cuts (thick cardboard) for a lot of cutting, it is also ignored though for some it can be critical.

For ease of resharpening, use a secondary edge bevel. It has little to no effect on cutting ability and also greatly increases edge durability. The secondary edge bevel can be set with a jig or v-rod to make sharpening trivial. The primary edge angle can be done freehand and very sloppy with no effect on functionality.

Of course for the other geometrical factors, edge thickness and nature of the primary grind, the same principle follows, the minimial amount of steel which has the necessary level of durability.

-Cliff
 
Originally posted by Cliff Stamp
For ease of resharpening, use a secondary edge bevel.
Click to expand...
Sorry, that's what I was referring to, a secondary bevel on top of a lower angle edge, just left that part out...
 
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