Coticule love... show off your rock
- Thread starter Drybonz
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Been working on this myself. I think the paper towels over there are made different. I can cut a million tiny curly long hairs from a piece of paper and still not do the paper towel. Although the type of blade does make a difference too.
Same here, you could be right
I send you a couple of rolls guys... will improve your sharpening game no end
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Really though drop cutting kitchen towel isn't necessarily something you should be chasing in kitchen knife sharpening anyway. A really good low grit edge will cut food better than a really good high grit edge. If you can cut normal paper in twirly patterns easily - that's about as good a test as you're going to get for a knife edge in practical terms.
With knives you're looking for almost the opposite kind of 'sharp' that you want in a razor. It's fun to be able to get seriously good, toothy edges that'll also wing through kitchen roll, but it's far from necessary, and it can sometimes be detrimental.
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I've probably posted this video before, but here it is again. If you watch it carefully this is probably one of the best instructional sharpening videos I've done, it's a shame I wasn't talking to explain it at the time.
After maybe 35 seconds of sharpening (50s mark in the vid) I pause, before which my strokes have all been back and forth, and I've raised/flipped a burr on both sides of the knife. Everything else after that I'm effectively deburring, with full length edge leading strokes at gradually lighter pressure. And I'm touching the edge with my fingertips after pretty much every pass to assess the state of the burr, as well as the thumbnail test to check the level of refinement. Stropping is just on a bit of newspaper and my sleeve.
[Coti was heavily dished when I got it so I flattened into a 'V' shape, which is why I'm only using half of the stone]
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Oli I can shave nicely with those Roselli blade edges I got (one off the coticule and one off the Charnley Forest stone) and they still won't cut the paper towel. I think that maybe due to the thickness of those blades and the angle of them though. Either that or we really do have different towels here. They shave paper like crazy. I get a bit better with the towels on the Japanese knife, but even the I Wilson Sheffield you sent me with your edge won't cut my paper towels like that.I send you a couple of rolls guys... will improve your sharpening game no end
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Really though drop cutting kitchen towel isn't necessarily something you should be chasing in kitchen knife sharpening anyway. A really good low grit edge will cut food better than a really good high grit edge. If you can cut normal paper in twirly patterns easily - that's about as good a test as you're going to get for a knife edge in practical terms.
With knives you're looking for almost the opposite kind of 'sharp' that you want in a razor. It's fun to be able to get seriously good, toothy edges that'll also wing through kitchen roll, but it's far from necessary, and it can sometimes be detrimental.
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I've probably posted this video before, but here it is again. If you watch it carefully this is probably one of the best instructional sharpening videos I've done, it's a shame I wasn't talking to explain it at the time.
After maybe 35 seconds of sharpening (50s mark in the vid) I pause, before which my strokes have all been back and forth, and I've raised/flipped a burr on both sides of the knife. Everything else after that I'm effectively deburring, with full length edge leading strokes at gradually lighter pressure. And I'm touching the edge with my fingertips after pretty much every pass to assess the state of the burr, as well as the thumbnail test to check the level of refinement. Stropping is just on a bit of newspaper and my sleeve.
[Coti was heavily dished when I got it so I flattened into a 'V' shape, which is why I'm only using half of the stone]
This is exactly it. Thickness 'behind the edge', which is related to but not entirely to do with the edge/sharpening angle, is pretty much the most important factor in a cutting something like kitchen roll. And some blades simply aren't meant to do that kind of 'sharpness'. The geometry of the Roselli and I Wilson are simply designed for other kinds of sharp.
This is a simple analogy and I've used it before but... take a standard kitchen knife and a razor, which do you think is 'sharper'? Then try shaving with them. The razor cuts your beard very well as it's meant to, the kitchen knife does not, so clearly the razor is sharper. But the knife cuts your face to shreds whereas the razor doesn't, so perhaps the knife is sharper...
There are loads of different ways to test sharpness, and cutting kitchen roll isn't actually a particularly useful one, I just do it to show off in videos. And note when I do - I'm almost always using a Japanese knife from a Hitachi carbon steel, or at least a knife that's got that kind of grind, because they're designed to get that kind of sharpness.
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If anyone really wants to understand about how different factors affect types of sharpness in knives: practice sharpening a kitchen knife until it can cut a hanging hair. Not HHT5 but 3 to 4 (which is easily beyond sharp enough to cut kitchen roll). Even if you're a very good sharpener this will probably take you weeks, not hours or days, especially if you limit yourself to the kind of finishing grit you might normally use for a knife, say 3k.
HHT on a knife is a bad kind of sharp, it's far too refined to be of much use in a kitchen. But the act of practicing until can do it will improve your technique a lot, and give you a huge amount of understanding about things like; thinness, deburinng and refinement.*
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I used that Kippington which cut the toilet paper above in the evening to cut a load of ripe tomatoes my sister had harvested about a week ago. By the end it wasn't very good; the edge was too refined and the teeth didn't hold up on the board. That coti is definitely more of a razor stone I think.
* Credit to @captaincaed who suggested the 'getting HHT with a kitchen knife' experiment on KKF a year or two ago. I think everybody who took part agreed it massively improved their sharpening game.
I can get a knife to HHT but not to cut toilet paper. Go figure. Here’s a vid of a Takeda popping hairs from 3 years ago. I shaved one swipe on my right cheek with this edge. It cut the hair fairly easily but left a red spot on my face for a week. Won’t be doing that again.
It is only in recent times that I understood the concept of different types of sharpness. Until then I would always try to make knives as close to razors as possible. This worked well if I was trying to make videos of knife shaving, drop cutting tomatoes, push cutting fruit, etc. but those edges don’t hold up in the kitchen.
I still rely too much on shaving arm hair as a test for knives, in the same way as a lot of sr honers use the hht. But that is a vague guide, and does not really tell the whole story.
I still rely too much on shaving arm hair as a test for knives, in the same way as a lot of sr honers use the hht. But that is a vague guide, and does not really tell the whole story.
Impressive! If it's doing that and is completely properly deburred then it should cut kitchen roll quite easily.
Kitchen roll (in fact any kind of paper test) is most useful for checking for the existence of a wire edge. Any kind of burr or wire edge will not do well on it. The feedback when cutting 'S' shapes in normal paper will also give a clear indication.
If I use kitchen roll when testing an edge (and not showing off for a video
) it's for that.(My absolute top favourite thing for kitchen knives, which I would advise anyone to calibrate, is the thumbnail test. When you have a feel for it - it gives an extremely accurate assessment of an edge.)
I will be following this thread with some interest now.
In my mind there are two aspects of sharp that I care about. The first way to think about sharp is what is the radius at the very Apex. A very small radius will produce a good shaving edge. A very small radius may or may not produce a good night edge.
But A knife edge can be too smooth. It can have a very small radius but slide across things like tomato skins. It Will easily cut onions or cucumbers or something with some substance behind it. But it still may not cut a sheet of paper towel, I think you all are calling it kitchen roll?
In order to cleanly cut paper towel, the second thing I want is teeth at the edge. A lot of times you can easily get that with lower Grint Sharpening somewhere in the 1000 to 4000 range. there are some stones that will give you nice teeth with more polish. Honestly I haven’t really mastered that style of sharpening yet. but if you want a really nice kitchen edge, focus on getting those teeth. Those teeth often come from finishing with an edge leading stroke, lightly, into the stone. to maximize teeth, don’t strop on anything after the stone. If the edge can cleanly cut paper towel without snagging, after you do a couple rock chop motions on your cutting board, that means you probably have a good toothy edge, and no significant burr to speak of.
In my mind there are two aspects of sharp that I care about. The first way to think about sharp is what is the radius at the very Apex. A very small radius will produce a good shaving edge. A very small radius may or may not produce a good night edge.
But A knife edge can be too smooth. It can have a very small radius but slide across things like tomato skins. It Will easily cut onions or cucumbers or something with some substance behind it. But it still may not cut a sheet of paper towel, I think you all are calling it kitchen roll?
In order to cleanly cut paper towel, the second thing I want is teeth at the edge. A lot of times you can easily get that with lower Grint Sharpening somewhere in the 1000 to 4000 range. there are some stones that will give you nice teeth with more polish. Honestly I haven’t really mastered that style of sharpening yet. but if you want a really nice kitchen edge, focus on getting those teeth. Those teeth often come from finishing with an edge leading stroke, lightly, into the stone. to maximize teeth, don’t strop on anything after the stone. If the edge can cleanly cut paper towel without snagging, after you do a couple rock chop motions on your cutting board, that means you probably have a good toothy edge, and no significant burr to speak of.
In addition to the thumbnail test, a fun trick you can use to scare your friends is to see if the edge will catch on the hair on your head. Just rest it against the hair on the backside of your head, behind the crown, and if it catches immediately, and you’re probably good to go.
These differences you are referring to is the reason i edc 3 different knives, all finished on different stones, all for different applications. Usually a jnat, medium charnley, then coticule or ark. The day I learned how to take advantage of those different finishes from different natural stones is the day I truly BEGAN to understand sharp and the science behind it. It's probably the same day I fully developed H.A.D. but I want my son to have these stones and understand why each one is for a different job(and at 8 yo, he does). Some of these rare stones will be nearly extinct in the market and that's ONLY if the knowledge of them, their tricks, and *the art* is passed on and preserved. Knowledge is a powerful thing and a lot of the things I've learned about razors here has completely changed the way I do half of the things that earns me a living and it's helped me immensely preserve what's left of the use of my hands because I've never been smart enough to know when to quit. I've had broken teeth over it before to be honest.
I do this with my beard hair on my has line in sure it looks like I'm going to cut my throat. If I can get a good hht with a knife off of root in beard hair they're usually about where I want them. Next test is if I can like of my hair line on my neck easily. Those hairs are extremely fine and hard to shave off with a knife.
Yeah those Scandi grinds cut very differently than a razor or thin Japanese blade. They are great for outdoors and even Kitchen work though. They are great for shaving razor thin sections off off items such as meat, veggies or wood.
Just a heads up for you guys. The team is currently working on adding a dedicated knife section to the forum, so soon we will have a location to discuss all this good stuff, so it can be found again, instead of being buried in random threads.
Keep an eye out!
Keep an eye out!
This is a very good and important point here too. Everything about cutting anything is about how friction works...
The reason that normal paper is easier to cut than paper towel is because it is harder. That statement seems counterintuitive doesn't it? But actually by far the greatest impact it has in this scenario is that it means the Normal force exerted upward against your knife is far lower when cutting paper towel.
F = uN. The Frictional force between two objects (F) is the coefficient of friction (u) multiplied by the Normal force (N).
If you decrease the Normal force exerted upward against your knife then you need to increase the coefficient of friction between the knife and paper in order to be able to cut it. Ergo: While you do need your edge to be fine, you also need it to be toothy.
(Which is probably why we've ended up talking about all this on the coticule thread!)
Getting back on topic here are some gratuitous pics of the two 7x2s I found recently in the UK...
The coticules themselves are a similar colour but apart from that they're a little different; one is almost all yellow with a gradual transition to a very thin layer of BBW, the other is half n half with a sharply defined, wavy border. I'm going to try them side by side later, as to the touch they actually feel more similar than I remember.
The interesting thing here is that although one is marginally longer than the other, they've clearly been cut in the same way, to the same specs. And I assume were originally sold by the same UK distributor, someone like AB Salmen, or perhaps a Sheffield cutler or toolmaker who also sold stones like WM Marples...
Or is this size and cut a common thing for old cotis? Anybody else got one like this?
The coticules themselves are a similar colour but apart from that they're a little different; one is almost all yellow with a gradual transition to a very thin layer of BBW, the other is half n half with a sharply defined, wavy border. I'm going to try them side by side later, as to the touch they actually feel more similar than I remember.
The interesting thing here is that although one is marginally longer than the other, they've clearly been cut in the same way, to the same specs. And I assume were originally sold by the same UK distributor, someone like AB Salmen, or perhaps a Sheffield cutler or toolmaker who also sold stones like WM Marples...
Or is this size and cut a common thing for old cotis? Anybody else got one like this?
Oh and a random q. that someone asked me on KKF... if you go on the AC website and buy a coti - are they backed with slate or BBW currently?
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