finding blade angle

[thedecline]

I have a japanese kitchen knife that needs a quick touch up. The problem is the blade is very thin and I can barely see the bevel so I have no idea what kind of angle it is. I want to keep it the same as the original since it cut like a dream but I don't know what that is. Any advice on figure out the angle and not just guessing what it should be based on the purpose of the knife?

 

[GatorFlash1]

Black magic marker used to put black on the existing bevel. Set sharpener to your best guess, say 10 degrees per bevel, 20 inclusive, and make a few passes. Examine the bevel and adjust the angle until you are removing the black. When you can remove it with a couple of passes you will know what your bevel angle is.

 

[bgentry]

^ GatorFlash1 has it right. Use your finest stone when doing this angle finding exercise so you don't put any scratches on the shoulder of the blade, if you go too low with your angle guesses.

You can also feel when the bevel is flat on the stone. I call this Secret #1 of sharpening. Lots more information here in The Seven Secrets Of Sharpening.

Brian.

 

[115Italian]

A lot of my kitchen knives are fully flat ground down to almost a zero grind with a micro bevel.

 

[thedecline]

^ GatorFlash1 has it right. Use your finest stone when doing this angle finding exercise so you don't put any scratches on the shoulder of the blade, if you go too low with your angle guesses.

You can also feel when the bevel is flat on the stone. I call this Secret #1 of sharpening. Lots more information here in The Seven Secrets Of Sharpening.

Brian.

The bevel is too small to be able to feel when its flat. At least for my senses. The marker trick didn't work too well either since its really hard to get it only on the bevel. When I say a small bevel I mean really small. Less than 1mm. I did the math to find what height to hold the blade off the stone to give me around 13 degrees and put it across 1000 grit a few times. Not enough to feel a bur but it wasn't noticeably hitting the shoulder. Finish with 6000 and its definitely sharper. I need a microscope

 

[bucketstove]

I have a japanese kitchen knife that needs a quick touch up. The problem is the blade is very thin and I can barely see the bevel so I have no idea what kind of angle it is. I want to keep it the same as the original since it cut like a dream but I don't know what that is. Any advice on figure out the angle and not just guessing what it should be based on the purpose of the knife?

It is completely dull, is the edge reflective?
Here is what you do, take a pen/highlighter/marker/plastic tube/dowel/fingernail,
optionally wrap newspaper once around , hold it smooth and flat,
hold this "pen" horizontally
hold the knife flat against it,
now slowly start sliding the blade forward toward the end of the "pen"
slowly keep raising the spine of the blade until it
digs into or bites into the pen/paper and then stop
thats your angle
now if you want to know the number of the angle
you could take a simple ruler and measure the height of the spine from horizontal
measure the width of the blade
and input those numbers into Triangle Calculator
For example 4 cm wide blade with spine height 2 cm has angle of ~26 (too high)

This is your angle in degrees per side for that one side, the other side might have a different angle

If your blade is really thick, or it isn't very wide ,
you can take a post it note, a sticky, or a piece of tape,
and tape it centered on the spine,
to make an extension, a long pointer, to compensate for the thickness,
so you can find the height measurement easier or more accurate
just remember the width measurement now includes the extension
the angle "triangle calculator" spits out should be more accurate

 

[Obsessed with Edges]

I have a japanese kitchen knife that needs a quick touch up. The problem is the blade is very thin and I can barely see the bevel so I have no idea what kind of angle it is. I want to keep it the same as the original since it cut like a dream but I don't know what that is. Any advice on figure out the angle and not just guessing what it should be based on the purpose of the knife?

That very thin blade geometry is what's making the biggest contribution to how it's cutting; I wouldn't worry too much about trying to match exactly the original edge angle. Chances are, if you keep your sharpening angle at or below 30° inclusive (15° per side), you shouldn't see much, if any degradation in cutting performance. Let the appearance of the original edge be your guide; if you make a sharpening pass or two at an angle that's a bit lower than the original, you'll see the width of the bevel widen a bit; conversely, if the newer bevel is even narrower, then you can assume you're hitting something more obtuse in your angle. Use a magnifier to closely examine it.


David

 

[Garvan]

I have a stick of red compound, and I use this to wax some copy paper, which I place on a flat counter. If you run the blade over the paper at a shallow angle, it will glide over the compound. As you pick up the angle you see it starting to shave off the high points of the compound. Too much angle and it digs in. Using this method it is easy to find the cutting angle.

With a thick blade I might find the angle using a fine stone, but with thin blades I am not sensitive enough.

Garvan

 

[samuraistuart]

David basically said what was running thru my head. If the edge is so thin that you're having trouble with the magic marker trick, and it's even hard to see the bevel, then the actual edge angle you choose isn't going to be much of a concern. The thin geometry of the blade is aiding your cut more than the edge angle. I would try a 10° per side edge and see how that holds up.