sharpening knives

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Re: sharpening knives

#76 Post by amuckart »

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 »

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.

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Re: sharpening knives

#78 Post by amuckart »

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 »

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 »

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.
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Re: sharpening knives

#81 Post by lancepryor »

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.

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Re: sharpening knives

#82 Post by russell_c_cook »

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 »

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 »

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 »

Thanks guys, appreciate the detailed advice :)
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Re: sharpening knives

#86 Post by dw »

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 »

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 »

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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Re: sharpening knives

#89 Post by anakim »

I believe I may be using an inappropriate knife. I am not sure at this point if it is my poor sharpening skills, or the wrong knife (or both).
But perhaps the biggest problem is that it is curved across the width - I am sure this very useful if you know what you're doing and if you have it curved in the right direction for your hand. Unfortunately when I ordered it over the phone I just asked for them to send me a Tina knife and they did. Can anyone enlighten me what this is for (the convex/concaveness), and whether it is for left or right hand? I am right handed. I'm using this knife for everything. When I'm holding it in my right hand, the blade is convex (across width) on the side facing me, and concave on the other side. I am stubbornly trying to sharpen it on flat surfaces (even though this is probably the wrong thing to do) because with my level of sharpening skill I do not want to deal with curved and rounded anything. I was going to post a photo but will have to figure out how to do that later.
It appears if I understand the discussion on here, that they do have a completely flat knife - flat across the blade, which I should probably get.
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Re: sharpening knives

#90 Post by dw »

Well, if I understand your description correctly, that's a Tina 270. At one point in time, they were designated "L" and "R" but AFAIK, no more.

IIRC, assuming that the point is on the left side of the knife, the knife you have is a left handed 270.

All that is significant only relative to to how you use the knife. If you are skiving with a 270L, on a flat surface, such as a pane of glass, drawing the knife towards you with the left hand is the way it was intended to be used.

I skive on a rounded surface and I push skive. So that 270L would be fine for me. If I wanted to pull skive on a flat surface, I would want a knife that was the mirror image of your--a 270R, if I have the nomenclature correct.

As for the concavities, I am near-as-nevermind certain that this is an attempt to 'hollow grind' the knife. On such knives I also use a flat stone to sharpen but I don't sharpen from the convex side...no, I lie--I sharpen from the convex side but only to remove the burr created from sharpening the concave side.

Thing about sharpening is that, for most people, sharpening from both sides tends to 'round off' the edge and eventually you have to reconfigure the angle and the edge to achieve decent and long lasting sharpness. Stropping has the same effect except on a more subtle level.

Sharpening from just one edge...esp. against a known surface tends to produce a sharper knife.

Naturally, working the burr from one side to the other and then honing to remove and refine the edge, is the key no matter how you do it, no matter what kind of edge. If you're not thinning the metal at the edge to the point where a burr will roll over to the other side...und so weiter, pete and repeat...you're not going to get a sharp edge. Or at least not one that will last or remain sharp for very long.

And lastly, being right handed, if I wanted a knife that I could use everywhere (sic), I would want the 270R--I could pull skive on a flat surface and trim outsoles etc., with my right hand. I'd still want a 270L for push skiving over a dome shaped surface, but I can, in extremis, use a 270R to push skive if I really had to.

Again, your mileage may vary ...and yes a flat blade is easier to understand, and perhaps a bit more versatile.
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Re: sharpening knives

#91 Post by anakim »

Thank you for your quick and thorough reply!
It's much appreciated.
Well, that solves that - I had better get another knife. The odd thing is that it says "211/15" on it, but the numbers do not matter as you have described which way it should go. I guess it stands to reason that the concave side should be facing up, away from the leather.
I have been struggling with it for quite some time now, so I've forgotten, but it's possible I put a bevel on the side that didn't have one, thinking, "I'll fix this! No one will know but me" and now I have to admit I tried to bevel the side that was supposed to be flat.

I do get a bead and move it from side to side, gradually decreasing in grit size, being extremely careful to lay the knife as flat as possible against the stone so as to sharpen exactly up to the edge but not round the bevel. I get it "very" sharp (enough to skive more or less okay), though this needs improvement as I am not at the shaving point yet, and do not get it "very" sharp consistently. But I can more or less do this part, kind of. It is the shaping of the blade that is the hard part - it always wants to go wonky - but I think now that I understand, it's probably partly due to trying to sharpen the convex side, and the rest o the problem is likely my technique of bracing my arm against my body when doing this.
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Re: sharpening knives

#92 Post by anakim »

Maybe I should give push skiving a try. I did try once, and occasionally when things don't seem to be working well I flip the knife and do that but only on thicker veg tan. Pushing seems less manageable with chrome tanned upper leather. Perhaps that is due to not having it razor sharp. And re-reading your reply, I do remember seeing you talk about pushing on a curved surface elsewhere, which makes sense. Do you use push skiving exclusively or in certain circumstances?
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Re: sharpening knives

#93 Post by dw »

Sounds like you're on the right track for sharpening.

I push skive (almost always) on a round surface...a cider jug inset into your bench will work. This creates a configuration where two convex surfaces are meeting--the under-surface of the blade and the flesh surface of the leather stretched over the side of the jug. Doing it this way creates a great deal of control simply because it narrows the surface area being cut at any moment, and it allows the scraps and crumbs to slide down the side of the jug and out of the working area.

Some leathers, esp. chrome, are simply very hard to skive, often because residual chrome salts are left resident in the leather. A good way to deal with this is to wet the flesh side of the area about to be skived (along the edge of a seam-line, for instance). Allow the leather to dry enough that there is no standing moisture and then try to skive again. I suspect you will be amazed.

Finally, a comment on your edges---one of the reasons sharpening from only one edge results in a sharper edge is that, if you use the knife correctly, and the sharpened side is away from the work, the edge will tend to 'bite' into the leather a little more aggressively. The bevel on the edge of the knife 'digs in.' You can see this same effect on woodworking tools--planes and chisels. Sharpening the knife the way you have, you must 'angle' the blade more to get a bite and often it feels alarmingly too high, as who should say. More, when the blade is sharpened and used correctly, the part of the knife edge that is not actually cutting can hold the rest of the leather flat...thus preventing the leather from 'rucking' up. This last bit is hard to describe or even imagine but when you get your knives sharpened right...whether push or pull skiving...you will notice the effect.

Hope this helps.

PS I've never heard nor seen a 211/15 but change is the only constant in the world :oldnwise: . It sounds like you visualized my 270s just fine and that the 270 and 211 are near-as-nevermind the same.
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Re: sharpening knives

#94 Post by anakim »

Thanks again DW. I'm amazed at your detailed descriptions of the nitty gritty of how it works with a one sided blade and a rounded surface. This is helping to sell me on the idea of pushing. I at least will try it. That seems like an ingenious way to do it with a cider jug. I am aware that it will dig in with only one side sharpened, which is exactly why I wanted an equal bevel on both sides. A blade that will dig in scares me (seems too hard to control). But I do understand it is a matter of practice and getting used to something different. Thanks for the idea about wetting the leather. I will try that too. I do know what you mean by the leather "rucking up", I think - I would say it puckers, though maybe that is something else perhaps due to a dull blade, stretching the leather.
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Re: sharpening knives

#95 Post by dw »

Puckering is a synonym for 'rucking up', according to some sources. Although I kind of narrow it down to the little pipes and wrinkles that form in the leather ahead of the edge of a knife whether clicking or skiving. In my experience, for instance, even if the blade is scary sharp, if the edge is too perpendicular to the leather it will ruck up...esp. with thin leathers like kangaroo. I'm sure you've seen some variation of this, yourself.
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Re: sharpening knives

#96 Post by jlboykin »

I've been wondering for a while, regarding single beveled shoemaker knives, the reasons people choose to bevel either the front side or the back side the blade. Front side referring to the side visible when cutting or skiving, and back side referring to the side touching the surface of the material.
knives_1.jpg
FRONT
knives_3.jpg
BACK
knives_2.jpg
I've tried both ways. With a front bevel there seems to be less of an undercutting "buffer zone" when cutting insoles or bottom work, as the edge of the blade is flush against the surface. And, with skiving the knife needs to be held at a slightly more shallow angle, making less room for your fingers.

With a "back side bevel" there is less of a likelihood to undercut, as the edge is slightly pitched away from the material. And, with skiving the pitch of the bevels means the knife can be held at a steeper angle giving a little more room for your fingers.

Earlier in my experience I was in preference for a back side bevel, because of its less likelihood to undercut and more room for my fingers when skiving. But, as i've gained more experience I've noticed that it is harder to predict the direction of the cut exactly because the edge doesn't directly follow the shaft of the blade. This leads to more time cutting the material down to the desired shape.

So, I am still feeling it out, but I am currently at the at the understanding that it is more favorable to use a front side bevel when cutting and a back side bevel when skiving.

But, I was wondering if you guys know the reasons for beveling one side or the other. Maybe even historical or traditional reasons.
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Re: sharpening knives

#97 Post by dw »

@jlboykin Of course, a lot of it is what you're comfortable with, what you've gotten used to, whether you're left-handed or right-handed, and how readily you can make the 'micro adjustments' in the angle at which you hold the knife. The last bit is one of the critical skills necessary for using a knife, IMO (second only to sharpening).

As I mentioned above, if I were pull skiving...as so many shoemakers do, I'd use the front beveled knife all the time. But for many of the reasons you mentioned...if I were right handed (which I am) and pull skiving...I would never use the 'back' beveled knife for skiving.

YMMV

I doubt there is an historic or Traditional reason...perhaps @das will correct me.... I suspect that it's just down to personal preference.
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Re: sharpening knives

#98 Post by jlboykin »

Thanks dw. I think I agree with you, I'm gonna try a front bevel from now on.

Just so you know rather than working alone like I have been doing previously for a number of years I have recently I've joined a team of shoemakers in Italy so I am happy to learn from them.

In fact, using a front side bevel will make me the odd one out in my crew, as all of the shoemakers I work with use back side beveled knives. And, a side note, I cant help but recall that all of the French shoemakers I've seen in images used back side beveled blades, not sure why. But, many English shoemakers I have seen use front side beveled blades.

There's a particular craftsman at the shop who is a stark traditionalist with strong opinions who has been heavily schooled in the French way of making shoes. He uses all back side bevels of coarse. He probably will have his opinions but many of these older craftsman think the way they were taught is the only correct way to do it.
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Re: sharpening knives

#99 Post by dw »

FWIW, I suspect that it is no accident that Japanese Shoemaking knives (descended from the same traditions that gave rise to the Samauri sword) are all sharpened on one side. And that every photo I've ever seen of them in use shows the bevel towards the user.
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Re: sharpening knives

#100 Post by jlboykin »

I changed my bevel to the other side with my Berg and Tina knife. I definitely prefer the bevel on the visible side, both for cutting and skiving, the action is a lot more predicable.
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