Thinning...?

[ModRQC]

@ian — When you say that some people thin with every sharpening, I’m assuming they’re doing it with higher-grit stones, not pulling out the 220 grit or belt sander every time?

It’s rather a question of steel. Starting higher grit with stainless, stainless clad, high alloy monosteel, will take forever even with just maintenance thinning on a stone not coarse enough. Semi-Ss, low alloys, carbon monosteels or iron clad, starting too low grit may result in removing too much towards what is needed.

Then of how: if I work towards a flat bevel, I start with a more agressive grit and a harder stone, when convexing, I prefer to buy time using a softer stone in between coarse and med. Any stone too fast and/or hard can all too easily create faceting when convexing.

Learning to balance needs out (experience will tell) is even more important than just a grit number. Then finding the stones that allow you to do your best work out of any circumstances is the graal.

 

[kpham12]

Yeah. My favorite for thinning was my shapton 120. Now I use my manticore. talk about removing material. It's a 60 grit, silicon carbide waterstone. Now most of the time I spend is just polishing it back up.

How are the scratches from thinning on the Manticore? Do you think they could be removed with a Shapton Pro 220?

 

[Blank Blades.]

How are the scratches from thinning on the Manticore? Do you think they could be removed with a Shapton Pro 220?

I've never used the 220 so I couldn't say. They would definitely be removed by the 120 though. I use a coarse norton idia to get rid of the scratches most of the time, because it's the next coarsest thing I have.

 

[kpham12]

I've never used the 220 so I couldn't say. They would definitely be removed by the 120 though. I use a coarse norton idia to get rid of the scratches most of the time, because it's the next coarsest thing I have.

Thanks, might try that. I’ve been looking into getting a manticore for some heavy lifting thinning, but 60 grit sounded real low.

 

[Blank Blades.]

Thanks, might try that. I’ve been looking into getting a manticore for some heavy lifting thinning, but 60 grit sounded real low.

It definitely is real low. Just make sure you have a normal low grit stone to take the scratches out. An atoma 140 could work too. I can say for sure my king 300 and cerax 320 are just a bit too fine to get the scratches out in a timely manner.

 

[VICTOR J CREAZZI]

Thanks, might try that. I’ve been looking into getting a manticore for some heavy lifting thinning, but 60 grit sounded real low.

I just ordered a Manticore and the scythe stone of the same abrasive.

 

[HumbleHomeCook]

The Manticore is a beast.

Be aware, you may need to dress the surface to get it working right. Mine was so compacted it seemed almost slick. Some heavy scratching (read grinding down) of some screws and then re-profiling a thick Buck knife got it performing well.

 

[VICTOR J CREAZZI]

What kind of belt sander are you guys using? What advantage would one gain by using a $500 2x72 vs the $50 Harbor Freight one if they are only breaking it out every once and awhile?

I have a 2 x72, but I would think that anything with speed control could be useful. I like to get down around 900 SFM when working close to the thin sections, especially at the tip

 

[Benuser]

It’s rather a question of steel. Starting higher grit with stainless, stainless clad, high alloy monosteel, will take forever even with just maintenance thinning on a stone not coarse enough. Semi-Ss, low alloys, carbon monosteels or iron clad, starting too low grit may result in removing too much towards what is needed.

Then of how: if I work towards a flat bevel, I start with a more agressive grit and a harder stone, when convexing, I prefer to buy time using a softer stone in between coarse and med. Any stone too fast and/or hard can all too easily create faceting when convexing.

Learning to balance needs out (experience will tell) is even more important than just a grit number. Then finding the stones that allow you to do your best work out of any circumstances is the graal.

In my l experience, you may very well use say a SG220 for thinning behind the edge with the least abrasion resistant carbon, without the risk of facetting, and obtain an nice convex bevel, in line with the face. And if facetting were to occur, I guess it's easily remediated within a few strokes. Just as simple as easing shoulders.
That being said said, I don't use much pressure and like to create a bit of mud. And essential with the SG's: keep them wet.

 

[Benuser]

I should have added that I had thinning as a part of a full sharpening in mind.

 

[ModRQC]

In my l experience, you may very well use say a SG220 for thinning behind the edge with the least abrasion resistant carbon, without the risk of facetting, and obtain an nice convex bevel, in line with the face. And if facetting were to occur, I guess it's easily remediated within a few strokes. Just as simple as easing shoulders.
That being said said, I don't use much pressure and like to create a bit of mud. And essential with the SG's: keep them wet.

Yes I can convex with a coarse/hard alright. Then again, with experience. This is the gist of the subject: from the OP standpoint and more broadly general approach. Excessive pressure being a common occurrence with beginners and all that. I just like to widen the scope in which one can look at thinning vs what job there is actually to do.

 

[ModRQC]

I should have added that I had thinning as a part of a full sharpening in mind.

In this spirit, I probably should have mentioned that I had a polishing progression in mind, and convexing not just behind the edge but a whole bevel although the latter doesn’t change anything to what you said. Just for sakes of clarification.

Edit: and obviously, a full polishing prog is also way to avoid faceting as it would tend to correct as you go. But the general idea is: softer/muddier works best for at once polishing and convexing, and going very coarse not needed if the convex is already installed.

And bla bla bla... working on stones is such a personal thing and ongoing philosophy for me still. 1 year ago I had barely sharpened my first knife; thinking in terms of preferences of stones for the job is pretty much a 2021 thing for me.

 

[whirlwynds]

What kind of belt sander are you guys using? What advantage would one gain by using a $500 2x72 vs the $50 Harbor Freight one if they are only breaking it out every once and awhile? Sanding by hand, I would be afraid I'd cut myself and/or really mess up the edge? I feel as if I'd have more control once I got my timing down with a belt sander and it would take a fraction of time.

A few things.

the Harbor Freight runs at 3450rpm which puts its speed way to high for most anything except hogging of steel for reprofiling. I know people do sharpen on these, but for fine knives i would not recommend it. the high speed can generate major heat and potentially ruin your blade. the 1" platten and contact patch make holding the correct angle challenging as well as having consistent contact across the blade. you're better off going with a stone and controlling the rate of abrasion. also if you touch that belt at that speed it will make quick work of your fingers as well, way more than one errant pass on sandpaper or a stone.

a 2x72 with speed control means you can run it in the right pocket for the speed of the activity and also have better angular control of the knife and target the spots for removal. it's really no different from a stone, but the belt moves instead of your arms and it happens about 10x faster.

to put it in perspective, if you have a 12" stone, one pass is 1 surface foot. let's say you can do 2 passes per second. that's 120 surface feet per minute. a low speed 2x72 will run at about 900sfpm, so about 7.5x faster than you can grind by hand. the harbor freight will run at approx 3600sfpm so about 30x faster.

 

[branwell]

What kind of belt sander are you guys using? What advantage would one gain by using a $500 2x72 vs the $50 Harbor Freight one if they are only breaking it out every once and awhile? Sanding by hand, I would be afraid I'd cut myself and/or really mess up the edge? I feel as if I'd have more control once I got my timing down with a belt sander and it would take a fraction of time.

KMG 2x72. You can thin even the most hard case knives in a few minutes but.......

Assuming you are working to a zero grind or almost a zero grind, you really need a 2x72 with a variable speed control and fresh belts. Its doesn't take much to friction heat edges above their tempering temperature and soften the edge. A misting system or water dripper really helps here.

The $50 HF grinders don't come with VFD's and I've not seen a good solution to this. Without speed control....

If you have a bunch of spare change sitting about or have a way of making it pay for itself, a 2x72 is a great thing to have.

 

[iandustries]

tbh I keep telling myself I'll thin a bit during ever sharpening session, but end up ignoring it until it becomes a problem.

how do u know when its become a problem? I‘ve never thinned a knife before …

 

[Bigbbaillie]

how do u know when its become a problem? I‘ve never thinned a knife before …

Really it's just preference for whenever you think your knife isn't cutting well anymore. You would probably notice it wedging in harder foods like carrots, if you hear a cracking sound when you cut a carrot, large or big, your knife could probably use at least a little bit of thinning. Most knives will probably give you some cracking, but a knife very thin behind the edge will just cut straight through with minimal cracking. Not every knife needs to pass this really, but it's an easy test.

If you don't know what wedging is, it's when the steel behind the edge gets thick enough that it gets stuck in the produce above the edge, preventing your knife from cutting. Just imagine if you were trying to cut something with a sharpened doorstop (weird I know) but on a much smaller scale.

 

[adam92]

When I do thinning maintain with my R2 Takamura, I start with SG500, only behind the edge, when I do heavy thinning I start with SG220, I think harder stone is better, as not easily gouge.
I usually stop at SP2k, sometimes SG4K. depand on what I gonna cut on that day.

 

[Blank Blades.]

I actually read in another thread that past a certain point, it’s hard to thin adequately without power tools to speed things up. I’ll see if I can get hold of a 220 grit stone, though. But won’t that scratch up the blade path terribly? Or do you go through the whole grit progression when you thin, same as for sharpening, before you refinish with sandpaper?

That is the whole reason you see the people here obsessed with jnats. Check the kasumi thread.

Polishing a blade back up for me is a big part of the thinning process. I probably worry more about it than I should. It's sort of a skill that you build over time. I try to make my knives look as good as I can, just to see if I can do it.

 

[stringer]

how do u know when its become a problem? I‘ve never thinned a knife before …

In a professional setting with randoms grabbing your knives, maybe 15 or 20 seconds. If you buy a gem from a god and you baby it you may never need to thin a knife ever.

 

[happy_c]

That is the whole reason you see the people here obsessed with jnats. Check the kasumi thread.

Polishing a blade back up for me is a big part of the thinning process. I probably worry more about it than I should. It's sort of a skill that you build over time. I try to make my knives look as good as I can, just to see if I can do it.

I saw in Jon’s thinning video that thinning may cause food to stick to the blade more. Why is that? Is it blade geometry or polishing out the scratches or … ?

 

[big_adventure]

I saw in Jon’s thinning video that thinning may cause food to stick to the blade more. Why is that? Is it blade geometry or polishing out the scratches or … ?

It's both and more.

If you take a full convex grind, then thin it at a flat, unique angle, you could wind up with an absolutely flat surface. Flat, smooth surfaces are more likely to stick.

The surface also matters to an extent: a hairline or rough kasumi surface may stick less than a polished surface.

It's a combination. I have a couple of knives that stick more than I'd expect given finish and geometry, and a couple that stick less than I'd expect given the same criteria.

Basically, test it out! I've changed finishes on some of my own knives, basically operating under the idea that, with the exception of removing ku finishes, I can probably correct any change that I don't like. I smooth-sanded a damascus finish, then just re-etched it with hydroclorique acid. A mirror finish can be returned to kasumi with a litle work.

 

[iandustries]

In a professional setting with randoms grabbing your knives, maybe 15 or 20 seconds. If you buy a gem from a god and you baby it you may never need to thin a knife ever.

Thank you, this makes sense. I m in the camp of buying knives from God and babying them so hopefully, I wont NEED to thin a knife, but would do it as an experiment for fun like I did giving my Takamura Santoku a mirror polish

 

[Grayswandir]

Really it's just preference for whenever you think your knife isn't cutting well anymore. You would probably notice it wedging in harder foods like carrots, if you hear a cracking sound when you cut a carrot, large or big, your knife could probably use at least a little bit of thinning. Most knives will probably give you some cracking, but a knife very thin behind the edge will just cut straight through with minimal cracking. Not every knife needs to pass this really, but it's an easy test.

If you don't know what wedging is, it's when the steel behind the edge gets thick enough that it gets stuck in the produce above the edge, preventing your knife from cutting. Just imagine if you were trying to cut something with a sharpened doorstop (weird I know) but on a much smaller scale.

Wouldn't anything around 1.5mm (at the spine) be fine and not cause this problem? I'm thinking 1.5mm where the blade meets the ferrule/bolster, after that the blade gets thinner as you travel down (distally) towards the point. I guess it depends on the product your cutting and how thick it is. If it's thicker then the heel of your knife, then I would expect the thinner the knife, the better, within reason?

I recall reading something recently (within the past month or two) about people polishing (and sanding) their knives to a mirror finish, apparently to help stop food from sticking to the blade. Someone said that a mirror finish actually makes the problem worse because it acts as a suction cup. By polishing away the tiny imperfections in the surface, there's no longer any way for air to get caught between the food and the blade, so the highly polished blade acts like a suction cup to whatever you're cutting. I don't know if this is really true or not, it just something I remember reading. Apparently there were a lot of people polishing the heck out of their Japanese knives to get that mirror finish, not only for aesthetic reasons, but to reduce food from sticking to their knives.

I know this is different then thinning, but I thought I'd bring it up as it is related to some degree.

 

[Bigbbaillie]

Wouldn't anything around 1.5mm (at the spine) be fine and not cause this problem? I'm thinking 1.5mm where the blade meets the ferrule/bolster, after that the blade gets thinner as you travel down (distally) towards the point. I guess it depends on the product your cutting and how thick it is. If it's thicker then the heel of your knife, then I would expect the thinner the knife, the better, within reason?

I recall reading something recently (within the past month or two) about people polishing (and sanding) their knives to a mirror finish, apparently to help stop food from sticking to the blade. Someone said that a mirror finish actually makes the problem worse because it acts as a suction cup. By polishing away the tiny imperfections in the surface, there's no longer any way for air to get caught between the food and the blade, so the highly polished blade acts like a suction cup to whatever you're cutting. I don't know if this is really true or not, it just something I remember reading. Apparently there were a lot of people polishing the heck out of their Japanese knives to get that mirror finish, not only for aesthetic reasons, but to reduce food from sticking to their knives.

I know this is different then thinning, but I thought I'd bring it up as it is related to some degree.

Spine thickness isn't really what you are looking for, it's more of the thickness directly behind the edge. If you have a sharp edge but it's .5mm right behind the primary bevel, your knife will still cut poorly and need thinning. So regardless of how thin spine is, if your edge is too thick >1cm behind edge you will probably feel the need to thin.
Low grit finish will cause friction which will be noticeable while cutting but its definitely not like you need a mirror finish to reduce stiction. I usually only sand to 600-1200 grit and feel like that is totally fine.

 

[Grayswandir]

That makes sense, I just remember hearing Murry Carter talking about thinning what he calls the secondary bevel on his knives (it seems like most of the knife industry calls the cutting edge the secondary bevel, I find that a bit odd, since it's the bevel that cuts things, go figure).

I'm not sure if it was preventive maintenance, something you do over time, so as the knife's cutting edge slowly loses steel over time, the geometry between the primary and secondary bevels stay the same, or if it was done to aid in cutting? He talks about both things, so I guess both is the correct answer. He always says a thin knife slices better, but he was putting more emphasis on the secondary bevel in his knife sharpening videos in regards to thinning. You're talking about the the steel directly above the cutting edge, which is now something I'll keep in mind.

I just bought a 250mm Gyuto (Shirogami #1), and it's pretty thin above the edge. It slices really well, and I guess that's the reason why (what you said).

Funny enough, I used some 2000 or 3000 sand paper to remove a little orange rust that appeared after making some sushi. Totally not on purpose, between the Kurouchi finish and the hamon, I accidentally created a semi-mirrored finish, so I decided to sand the entire length of the knife between those two points just so everything looked uniform. Shirogami #1 truly does take a wicked edge, it seems sharper then my Aogami Kiritsuke. It's already kissed me twice (I really need to pay more attention while handling these Japanese knives), nothing serious or anything, but I felt it. They're so light, it's easy to forget you have a dangerous tool in your hand!

 

[stringer]

Wouldn't anything around 1.5mm (at the spine) be fine and not cause this problem? I'm thinking 1.5mm where the blade meets the ferrule/bolster, after that the blade gets thinner as you travel down (distally) towards the point. I guess it depends on the product your cutting and how thick it is. If it's thicker then the heel of your knife, then I would expect the thinner the knife, the better, within reason?

I recall reading something recently (within the past month or two) about people polishing (and sanding) their knives to a mirror finish, apparently to help stop food from sticking to the blade. Someone said that a mirror finish actually makes the problem worse because it acts as a suction cup. By polishing away the tiny imperfections in the surface, there's no longer any way for air to get caught between the food and the blade, so the highly polished blade acts like a suction cup to whatever you're cutting. I don't know if this is really true or not, it just something I remember reading. Apparently there were a lot of people polishing the heck out of their Japanese knives to get that mirror finish, not only for aesthetic reasons, but to reduce food from sticking to their knives.

I know this is different then thinning, but I thought I'd bring it up as it is related to some degree.

Very thin spined knives don't allow for as much convexity. Less convexity means more sticking. They are also less comfortable to hold if you are chopping all day. Nothing smarts like a split knife callous.

This is why we look for ways to make knives that are beefier where you need to hold it but still thin behind the edge

Geometry and surface finish are separate questions. After you alter the geometry with coarse stones then you have to decide what kind of surface finish you desire.

That makes sense, I just remember hearing Murry Carter talking about thinning what he calls the secondary bevel on his knives (it seems like most of the knife industry calls the cutting edge the secondary bevel, I find that a bit odd, since it's the bevel that cuts things, go figure).

I'm not sure if it was preventive maintenance, something you do over time, so as the knife's cutting edge slowly loses steel over time, the geometry between the primary and secondary bevels stay the same, or if it was done to aid in cutting? He talks about both things, so I guess both is the correct answer. He always says a thin knife slices better, but he was putting more emphasis on the secondary bevel in his knife sharpening videos in regards to thinning. You're talking about the the steel directly above the cutting edge, which is now something I'll keep in mind.

I just bought a 250mm Gyuto (Shirogami #1), and it's pretty thin above the edge. It slices really well, and I guess that's the reason why (what you said).

Funny enough, I used some 2000 or 3000 sand paper to remove a little orange rust that appeared after making some sushi. Totally not on purpose, between the Kurouchi finish and the hamon, I accidentally created a semi-mirrored finish, so I decided to sand the entire length of the knife between those two points just so everything looked uniform. Shirogami #1 truly does take a wicked edge, it seems sharper then my Aogami Kiritsuke. It's already kissed me twice (I really need to pay more attention while handling these Japanese knives), nothing serious or anything, but I felt it. They're so light, it's easy to forget you have a dangerous tool in your hand!

If you want to see the knife's convex grind check it out by looking at the reflections on an angle off of some horizontal light sources like window blinds. I bet that your gyuto is ground more similar to the style we are describing than to a flat grind. It's all about balancing competing conflicting qualities and that balance is different for everyone.

An axe has great food release but is by definition a wedge monster.

A flat ground laser has very little cutting resistance on food. But the spine also has great cutting power on your skin. A split knife callous can really ruin your day. And flat ground knives are prone to stickiness and stiction.

A typical asymmetric Japanese grind allows you to have convexity on one side for food release and strength, but a relief bevel on the other side to keep it thin behind the edge, reduce wedging, and increase stiction resistance.

 

[Grayswandir]

A flat ground laser has very little cutting resistance on food. But the spine also has great cutting power on your skin.

I take it you mean how using the knife all day (in regards to an uncomfortable spine), even the spine can wind up hurting you (bad ergonomics) because of the repetition involved, or am I misunderstanding you?

I'll have to take a few snaps of my Gyuto and see what you think. It looks like it's a flat grind, but to be honest, I haven't really given it a good, studious look up to this point. I haven't even owned the knife for a full month yet. I haven't had any problems with food sticking to the blade, but then I haven't really cut a lot of foods that tend to stick, like starchy potatoes, or even squash (which tends to be wet). So far I'm enjoying the knife. I'd really like to crush some garlic with the wide portion of the blade, but I've heard it might not be the best idea with white steel. The blade is pretty beefy, but I guess I'll think on it some more before I attempt it. If worse comes to worse, I can use the back end of the handle to crush garlic cloves, it works, just not quite as well as the widest point of the blade.

 

[stringer]

There's no issue whacking garlic with any knife. Just make sure you are hitting with the part of the knife on the spine half instead of the edge half.

Here's what I mean by using horizontal light to look at the grind

 

[stringer]

Here's one that's ground this way deliberately exaggerated my me on a very thick spined knife.

Here's the convex side

And here's the relief bevel side. You can see the difference

On some knives the relief side is even concave.
I talked about that here

 

[Grayswandir]

Yeah, I'd make sure to thump the garlic on the side closer to the spine. I'll check out your video, thanks.