sharpening knives

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amuckart
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Re: sharpening knives

#76 Post by amuckart » Mon Jun 18, 2012 2:50 pm

Lisa,

In terms of the specific question you have to answer for your knifemaker, a 30 degree primary bevel should give you good performance. That will allow you to sharpen and hone with about a 31 degree angle at the edge.

To put that in context, the edge on a really good sharp kitchen knife is about 40 degrees.

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Re: sharpening knives

#77 Post by lancepryor » Mon Jun 18, 2012 8:13 pm

Lisa:

I am going to have to disagree a bit with Alastair. Really good Japanese knives are sometimes sharpened at a 20 degree, or even lower, angle. This is particularly true of single-bevel knives, such as those used for slicing fish for sushi, which may be as low as 10 degrees (10 degrees on the beveled side, 0 degrees --.i.e. flat -- on the back)

Double bevel Japanese knives are typically sharpened around 30 degrees, i.e. 15 degrees per side.

For skiving, I use a single-bevel (also called chisel ground) knife -- i.e. the blade is only ground on one side, with the other side remaining flat. For such a knife, you could definitely try something perhaps in the 20 degree range. The angle your knife can support is a function of the type of steel (alloy) used and the way it is hardened/tempered. The reason Japanese knives can be sharpened to such an acute angle is that the steel used is a different alloy from that used by the Europeans, and it is hardened to a substantially greater extent (Rockwell hardness of up to 62 or 63, vs the European knives being hardened more to the mid-50's). Also, the most acute Japanese blades are not meant to hit anything hard, such as bones. All things being equal, the more acute the angle, the lower the durability of the edge. But, you should be stropping very frequently, and even touching up the edge pretty often.

I will look at my favorite skiving knife in the next day or two and try to figure out the angle I have it sharpened at.

Lance

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Re: sharpening knives

#78 Post by amuckart » Mon Jun 18, 2012 9:29 pm

Lance,

You're right about the Japanese knives, I'll qualify my statement: the edge on a really good sharp western kitchen knife is about 40 degrees Image Sashimi knives are terrifying, and very high maintenance.

My experience so far with Japanese leatherworking knives having an iron back and a thin but very hard steel edge are that with the extremely shallow grind angles they chip if you look at them funny, but they are a lot more robust with a 30 degree (30 + 0 chisel grind) edge and still cut incredibly well.

I'm sure that's user error, and I need to find a Japanese expert to teach me how they use them and figure out what on earth they use as a cutting surface, because nothing I've tried stops the corners chipping.

Anyway, within reason you can grind the primary bevel as shallow as you like. In some ways a 20 degree primary bevel is better than a 30 degree one because your actual edge angle always has to be greater than the primary bevel angle.

That means if you go with a 20 degree primary bevel you've got the option of a 30 degree secondary bevel if you find a 21 degree edge chips or blunts too easily. It still won't be as robust as a 30 degree primary bevel though.

So, assuming a normal western type blade made of a chunk of tool or spring steel and hardened to around 58 rockwell, I'd still recommend a 30 degree primary bevel Image

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Re: sharpening knives

#79 Post by hidesmith » Tue Jun 19, 2012 6:01 am

Whenever I get a new knife (or a used one) that I intend to use, one of the first things I usually have to do is change the angle on them. Many people think that if it takes hair off one's arm, it doesn't need any sharpening, If it 'shaves', it's fine.

To start with, there is a big difference between taking hair off one's arm and shaving-sharp. Taking hair off one's arm is a good start, but shaving sharp requires very little pressure and the edge carries for the length of the blade.

I don't know what angle I use, my protractor is made by The Almighty and surgically planted in my head. It is fine for my purposes as well as many whose knives I've sharpened.

For regrinding knives, the best thing to remember is to keep a quench bucket close and use it every few seconds. If the edge gets hot, it will lose its temper and edge holding qualities. A rule of thumb I use is, if the metal gets too hot to touch, it's too hot. Quench sooner.

I also use and make single-edge 'chisel ground' skiving knives. Go to a junk shop and buy one-dollar kitchen knives that still have an edge. If you can reshape them without removing the temper (grind and quench often) you can come up with a pretty good set of knives.

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Re: sharpening knives

#80 Post by chuck_deats » Tue Jun 19, 2012 7:15 am

Not an expert, but skiving knives are pretty delicate use, usually flat on one side. Would suggest 15 deg. or less for the primary grind (width about 4 or 5 times the blade thickness), then a tiny secondary bevel on the edge of about 30 deg. The secondary bevel will change as you use it and find what works best.
Chuck

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Re: sharpening knives

#81 Post by lancepryor » Tue Jun 19, 2012 11:32 am

Lisa:

I endeavored to measure my skiving knife (a Tina knife) -- I estimated an edge angle of about 17 degrees. I would say chuck's advice is worth following. If the edge is too weak, you can always gradually increase the angle of the secondary/micro bevel, and over time the primary angle will increase as you sharpen the knife.

Let us know how it works out.

Lance

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Re: sharpening knives

#82 Post by russell_c_cook » Thu Jan 23, 2014 5:17 am

Hi all,

I have 3 oil-stones at home, a Coarse India (similar to I guess around sandpaper 60#), a Fine India (sandpaper 340#) and a Translucent Arkansas (very fine). I hope to use them for my Tina skiving knife.

My guess is that for my Tina skiving knife it'd be best to finish on the Trans Ark. Or does a skiving knife work better with a "toothier", less refined edge?

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Re: sharpening knives

#83 Post by dw » Thu Jan 23, 2014 5:47 am

Skiving is not "sawing," you need to sharpen to the finest edge you can get. I finish up with tripoli or some sort of buffing compound.
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Re: sharpening knives

#84 Post by das » Thu Jan 23, 2014 6:01 am

Russell,

I find any/all knives work best when honed to a razor edge on stones, then polished. Make a stropping stick about 3" wide, maybe 12" long and around 1/2" thick. Be sure the surfaces are all dead flat and level. On one side glue a 3" x 8" piece of 600 grit wet/dry emery paper (the black stuff), and on the other glue a 3" x 8" piece of smooth veg-tanned leather (5 oz?) flesh up. Rub the flesh leather surface with a stick of jewelers' rouge (iron oxide polishing compound) until it's dark reddish all over.

After you hone your edge to where you want it on your various stones, strop it on the 600 grit paper, then on the rouged leather until it's scary-sharp--this way your knife does all the work, not your muscles. In daily use usually touching the edge up on the 600 grit and rouge is enough. If you use the stones every time you sharpen, you wear away your knives faster. I might use a stone (lightly) once every few weeks only in constant use after I hone the "perfect" edge I like.

Delicate and accurate skiving demands the sharpest edge possible so you're not fighting the leather, nor the knife steering itself too shallow/deep because of a dull edge.

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Re: sharpening knives

#85 Post by russell_c_cook » Thu Jan 23, 2014 5:45 pm

Thanks guys, appreciate the detailed advice :)

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Re: sharpening knives

#86 Post by dw » Fri Jan 24, 2014 10:30 am

russell_c_cook wrote:Thanks guys, appreciate the detailed advice :)
Al said it really well. :goldstar: I was pressed for time but I second everything he said.
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Re: sharpening knives

#87 Post by Arttu » Thu Nov 17, 2016 1:20 pm

I've been struggling with sharpening knives, having to rely on disposable snap-off blades for most delicate work. I've tried sharpening rods, cheap stones, diamond files etc. but could never get a really fine "shaving edge". Last weekend I made myself a strop block with a piece of birch and some veg tan leather with a red polishing compound rubbed in it. I took my sharpest knife (a barely shaving one made from a handsaw blade) and stropped it for a minute or so. I tried it on my arm the way I had done it many times before and immediately cut trough the skin and fairly deep into my arm. It was somewhat bloody, a little painful and very embarrassing, but oh so rewarding. Now my knives are sharper than the disposable ones and skiving, for example, is far easier.

Again, goes to show that a little humility goes a long way and proven methods exist for a reason.

Enough rambling and on to a question, what do you use to fix the sanding paper/emery cloth to the wood? I assume it shouldn't be permanent like a contact adhesive, because sanding paper goes "dull" fairly fast. Rubber cement?

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Re: sharpening knives

#88 Post by amuckart » Thu Nov 17, 2016 1:32 pm

I use carpet tape to attach abrasives to flat surfaces. It's wide, incredibly strong, double sided sticky tape.

Contact adhesive works too, but carpet tape is easier and for sheet abrasives it's easier to peel and replace.

For anyone using edged tools I highly recommend getting a coply of Leonard Lee's Complete Book of Sharpening and spending some time reading Brent's Sharpening Pages at http://www3.telus.net/BrentBeach/Sharpen/.

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