Edge Geometry Discussion

[me2]

This is an extension of some discussion from the Why Are Burrs So Malleable thread here:

http://www.bessex.com/forum/showthread.php?tid=104

Thanks Mr. Me2. I just keep on learning. Don't know if you can tell from the picture but I've got more than a 1/32 with this knife. I suppose that's because its probably a thicker knife than yours. To me, Japanese sushi knives are supposed to be super sharp small little thin things. My knife is none of the above. But that's okay with me because it worked just great on some venison tenderloin last night.

Don't mean to bug you but I've seen others talking about this behind the edge before too. So what's the meaning of this? If it's thin or thick behind the edge what difference does it make? I suppose that if I sharpened this knife at a smaller angle that the behind the edge would increase because this knife gets gradually thicker going toward the spine.

Thinner behind the edge cuts easier, thicker behind the edge is stronger.  The trick is to find where it's just thick enough to not get damaged, thus as thin as possible for maximum cutting ability.  Of course as a buyer, normally all you can do is make it thicker via sharpening.  Finding that balance is tricky for general purpose knives, but can be quite beneficial for specific use blades.

Yes, you are correct regarding lowering the sharpening angle meaning increased behind the edge thickness on the same knife.  Thus for a complete picture, you need to know the sharpening angle and the behind the edge thickness (BTET).  My Japanese kitchen knives are sharpened at 12 degrees per side, and a BTET of less than 0.01".  They were thinner when new.

[Bud]

Thank you for your time Mr. Me2. I'm going to measure when I get to the shop tomorrow. I'm going to say that my knife is going to be thicker than yours.

[me2]

The 2 Japanese knives I have are exceptionally thin, though I've heard of thinner. The thinnest I've seen in hunting knives was a David Boye folder. It cut far better than the Buck knife I had at the time. I didn't measure it, but it was substantially thinner. The thinnest in recent memory was my Cold Steel Lite Hunter. It was 0.01" when I got it, and was 0.015" or so after rebeveling to 12 degrees per side (dps). Most are that thick with a 20 degree or greater bevel angle. I like the simplicity of the single bevel angle on the Puuko style knives, but, since I don't do much wood carving, I don't see much benefit. They are supposed to excel at shaping wood. The couple I've had I don't remember using for that. Just as a point of clarification, the thickness at the top of the edge for these style blades is the same as the spine thickness.

[scott.livesey]

I like Joe Calton's method where he lists thickness at the edge, 1/4"/6mm up, 1/2"/12mm up and spine. I have made several that are 0.05 at the edge, 0.015 at 1/4", 0.025 at 1/2" and 0.06" at the spine. Primary bevel is about 3*, secondary bevel is 7.5*, microbevel about 10*. the steel is O1 at Rc 62-63. I scribed lines on the upper jaw of my calipers so I measure in the same place every time. the knives cut very well, but I only use them for boneless proteins and "soft" fruits and veg.
My small cleaver is 2 1/2" tall, 1/8" at the spine, with a 7.5* bevel, a sabre or scandi grind.
I use 7.5* because I found some 7.5* angle blocks at the office that I incorporated into a grinding jig.

[grepper]

Wow!  That’s a very acute bevel angle for a cleaver.  I would think that while it would cleave very well, it would dull quickly.  I would expect at least 10° per side for a cleaver if not less acute than that.  That said, I’m no cleaver sharpening expert and that’s just from what I’ve gleaned from research.  I don’t own a cleaver.

I find it interesting that you would go to the trouble of a primary, secondary and micro bevel on a blade that’s going to whack, chop, hack and bash away at stuff.  Like I mentioned, I don’t own a cleaver so maybe you are using it more like a knife than a hacking and whacking type of tool.  Maybe that works considering how hard the steel is.

That’s really hard steel for your general cleaver.  What brand/model is it?

FWIW, a handy way to type a degree ° character is to turn on the num-lock on the keyboard, hold down the ALT key and type 0176 on the number keypad.  Using the numbers on the top row of keys won’t work.  I’m using Windows, I don’t know if Apple is the same.

[Ken S]

I recently sharpened my favorite Chinese cleaver for the first time with my Tormek.(This cleaver is designed for vegetable slicing and is of thinner construction than a meat cleaver designed to be in contact with bones.) I carelessly set the bevel angle for my usual fifteen degrees, without verifying the factory bevel. I found out that the knife had more acute bevels. The next time I sharpen it, I will use somewhere in the ten to twelve degree range.

Ken

[scott.livesey]

this cleaver is what I use for a chef's knife. basic 1084 steel at Rc61-62. it is mostly used for boneless protein and vegetables. I do use it to remove fish heads and tails, didn't notice any damage or loss of sharpness.

[grepper]

I suspected that you are using it more like a knife than for whacking and hacking apart chickens or something.

Did you make the cleaver?

[scott.livesey]

Yes, i made the cleaver and all the other knives i use in my kitchen; and the cutting boards and magnetic knife rack. I do have a WW2 vintage Foster Bros. cleaver, but it is more for show. almost all the meat sold here is boneless.

[Bud]

Do you have some pictures of your stuff Scott? Would love to see them if possible. I need inspiration to keep me going while waiting for kiln parts.