Thinning without losing much height, also surface finishing

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gc0220

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Any good resources for the nuances of thinning knives of various grinds? My main concerns are practical and aesthetic. Obviously you need to be careful to maintain the blade profile but what about avoiding losing too much height on the knife? And how about surface finishing? I guess these kinds of things just takes years of hands on expertise to figure out. Is there a benefit to thinning on stones vs other methods? What are the nuances of the various methods and how they play with the different grinds? Like say a hollow grind, almost seems like this kind of grind is going to be thinner and also have decent food release, but how do you thin it out without wrecking it? You could carefully do it by hand with sandpaper, making sure not to hit one spot too much so the knife doesn't warp and whatnot? How can I thin out a knife without losing too much height from the blade? So I've already messed up at least one knife. I got a little Denka petty that came with what I think is probably a fatter grind, lower shinogi line. The knife performs really well probably cuz that steel just screams for whatever reason, idk why I guess super hard + fine grain will do that. On a sidenote though, is super blue actually even a decent steel? I mean it's apparently not very tough, obviously not very rust proof and yet it doesn't even have much abrasion resistance which I'm not sure what the right answer is there but I think the common logic is more is better, but is it? Seems like some balance of good enough but also easy to sharpen is what's ideal. I just don't know. Anyhow. I'd like to re-grind it, but I don't want to lose a bunch of height and I don't want to alter it's default aesthetics. Not sure how to do that, I guess I'd have to use something like an 80 grit to put deep scratches then go over the surface at a higher grit to remove all the scratches except the lingering remains of the deepest ones?
 

HumbleHomeCook

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Holy missing paragraphs. 😁

From my own experiences, the best thing I can personally tell you, is be prepared to alter (read as mess up) the looks of your knives when you start out. At least if you do some serious thinning. Others may disagree, but I think thinning and then polishing/restoring the looks crosses over into art or at the least significant practice and good gear.

Light thinning can work wonders though, even just softening the edge bevel shoulders can make quite a difference.

Starting out I wouldn't worry too much about losing a lot of height. Geometry is the number one priority here, especially if you're talking more heavy work.

The first few times I took the primary grind of knives to coarse stones I was shocked at how uneven they are. Be they hand or factory ground, kitchen or pocket knives, there's a ton of variation that your eye doesn't see until you disturb that finish. And once you do, it can be crushing. You can feel overwhelmed and discouraged. At least I did.

So for me, I split my approaches. First, I'm a function over form guy and I have some other issues that make aesthetics challenging but I decided right up front, than the only way I was gonna get better at the looks was to be willing to accept screwing them up. But, that doesn't have to mean ruining them. I have a couple knives where I'm just doing light work. Not a lot of pressure on the low grit stones and not going too low. These are good knives already that I'm just swirling my toes around in the thinning pool.

Then there's the, "screw it I'm all in knives". These are the knives that I just want to explore and push and see what I can get out of them performance wise and what I can learn. I have an Akifusa right now that looks like ten miles of bad road but runs like a race horse. I know that I'll never be able to fix the looks, I just won't have the patience for it but boy do I like using it.

You say you screwed up a knife. How so? Did you have a plan going in or just took the plunge (which is much like me)? Did you learn lessons?

If you're unsure, maybe a good approach to start is very light "thinning motions" on a higher grit stone. This can reveal the blade's story without causing too much trouble, either in metal removal or aesthetics.

Please understand, this all comes from a guy who is not good at thinning/re-profiling and still making the knife look good. I admire and at times are in awe of those who can pull this off, I'm just not there yet and not sure I ever will be.

Members like @ModRQC, @ethompson, @refcast, @Pie, @tostadas and so many others are much better sources.
 
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tostadas

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Thinning the knife should not result in any change in profile. You are essentially removing material from above the edge area. Only during sharpening should you really get too close to the edge itself.

You mentioned that you did some thinning. What are you using to thin with? What stone, sandpaper, or motorized equipment are you using. Thinning by hand is a very slow process for removing metal. And that's assuming you're using some very coarse stuff to begin with. On top of that, TF steel is ridiculously tough and hard to remove metal from. So unless you're using a belt grinder, or going super insane with ultra coarse stones, I suspect that maybe there was a lot of abrasion caused to the surface of the blade, but doubt there was significant "thinning" actually done.

I'm all for experimenting and just diving in head first. But I recommend at least having some sort of goal in mind, and a way to monitor your progress toward that goal. Digital calipers are very helpful here. You can get a decent one on amazon for less than $30.

If you're concerned about keeping original aesthetics, don't bother thinning. Removing steel necessitates affecting the aesthetics. So if this is important to you, also have a plan for refinishing the knife after you're done with the thinning process. In my experience, thinning makes up maybe 20% of the time spent on a knife (depending on how much you want to thin it), and refinishing will account for the remaining 80% or so.
 

Pie

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Hang on a second. Why are we thinning in the first place? I know denka aren’t exactly lasers, especially the ones with lower shinogi, but most applications of a petty don’t require it to be super thin. Is it just getting chubby from sharpening?

Either way that’s none of my business - thinning is difficult, and figuring out what you did, what you want to do, and whether you can even tell if you did it is a massive part. Make sure you have objective tests for progress. Otherwise efficiency falls off a cliff.

I don’t know, it’s a lot to explain, and there’s gotta be some solid threads on it. I’m not good enough to give many suggestions. One thing I can say is refinishing is madness unless you’re good at it. It’ll also be required after any steel removal from anywhere other than the edge. There’s a lot of ways to do it, and none of them are quick and easy.

Side answer: I like AS. Especially this AS. I never intend to let it sit dirty or push the limits of toughness. Denka steel is pretty damn good imo.

Oh yeah, and don’t get all the way to where you want on the coarsest stone. The next one up is going to take some as well. There is such thing as too thin.
 

ModRQC

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Any good resources for the nuances of thinning knives of various grinds? My main concerns are practical and aesthetic. Obviously you need to be careful to maintain the blade profile but what about avoiding losing too much height on the knife? And how about surface finishing? I guess these kinds of things just takes years of hands on expertise to figure out. Is there a benefit to thinning on stones vs other methods? What are the nuances of the various methods and how they play with the different grinds? Like say a hollow grind, almost seems like this kind of grind is going to be thinner and also have decent food release, but how do you thin it out without wrecking it? You could carefully do it by hand with sandpaper, making sure not to hit one spot too much so the knife doesn't warp and whatnot? How can I thin out a knife without losing too much height from the blade? So I've already messed up at least one knife. I got a little Denka petty that came with what I think is probably a fatter grind, lower shinogi line. The knife performs really well probably cuz that steel just screams for whatever reason, idk why I guess super hard + fine grain will do that. On a sidenote though, is super blue actually even a decent steel? I mean it's apparently not very tough, obviously not very rust proof and yet it doesn't even have much abrasion resistance which I'm not sure what the right answer is there but I think the common logic is more is better, but is it? Seems like some balance of good enough but also easy to sharpen is what's ideal. I just don't know. Anyhow. I'd like to re-grind it, but I don't want to lose a bunch of height and I don't want to alter it's default aesthetics. Not sure how to do that, I guess I'd have to use something like an 80 grit to put deep scratches then go over the surface at a higher grit to remove all the scratches except the lingering remains of the deepest ones?

Best to separate your questions into related groups, or even single entities for the most important ones, and start more focused posts. You have so much here and they're all crammed into a single paragraph. No one will answer them all because no one will care to sort them all out.

Aogami Super is alright, bordering excellent when from makers like TF. For all intents and purposes it's irrelevant to most of your questions - you said yourself, "as a sidenote". It's nothing so impressive on paper but still has an attractive set of properties for kitchen knives. Tough enough, a tad more corrosion resistance, a bit more wear resistance as compared with simpler carbons while still on the easier side of the sharpening curve. Makes it an interesting option, and makes for part of its fame, against the very widely used Shirogami and Aogami #2.

Now an interesting question would be: what's the knife you think you messed up and what is messed up exactly?

I like thinning on stones, but it's a personal notion that I cannot compare with all alternatives since I never used them. I did use sandpaper a long time ago, and I consider stones to be more polarized and effective towards my goals. Since I do all stone work on my kitchen countertop, I also like that stones don't get any steel/abrasive dust airborne.

It's not so difficult to get good enough to be serviceable to yourself. From there no big leap to get actually good enough to brag a bit around here with the rest of us. A bit more practice yet and you always know how to get just about exactly where you want. Some people will still be better than you - edit 1: or more aptly put, much more straightfoward and efficient to their goals and that's where experience plays the most - but really at that point you're pretty good yourself and can totally rely solely on yourself. It's a bit scary at first. Like the three first times are I guess the toughest moment where you're afraid of everything and always taken aback by every slight mistake or "surprise" along the way. Still long before the tenth time, if you got there, you know what you're doing quite alright, and you're enjoying yourself and surprising yourself while having seen enough not to be disturbed by anything much anymore.

Tostadas said it, refinishing is a bigger part of the equation, not only being indeed where you'll spend most time, but also HOW to refinish without having a negative impact with food. Like an easy place to get sucked in is refinishing to semi-mirror polishes with sandpaper because it's a straightforward, immediately rewarding process of turning dire scratches into looking nice again. IME it's also pretty much the worse place to get a knife to, with a pretty definite negative impact on both separation and release.

Edit 2: and to some extent you should not confound a refinishing process with a polishing one. Refinishing is mostly caring to the basics: refining a coarse scratch pattern a couple steps up is sufficient where performance matters most, a bit of hiding or blending can do wonders towards proper looks, and THAT doesn't take so much time. Beyond that, concerns shift towards esthetics entirely, and you need to set your expectations right because basically you can spend hours and hours into such projects, and results might not have a great correlation with performance at all anymore.
 
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Benuser

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In addition only: any sharpening at a lower angle than used for the very edge is thinning. If you want to make sure you don't touch the very edge, use a sharpie. Stop in time, when the paint is reduced to a hardly perceivable line. No way thinning should affect the blade's width. You may start by removing the shoulders, where bevel and face meet. Go on until you almost reached the very edge. By the way, touching up the edge is good practice after thinning. Don't expect the edge to remain exactly the same after all what happened just behind it, with all the pressure that was involved. Some burr formation may occur. A few strokes on your finest stone will do.
 

gc0220

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Hang on a second. Why are we thinning in the first place? I know denka aren’t exactly lasers, especially the ones with lower shinogi, but most applications of a petty don’t require it to be super thin. Is it just getting chubby from sharpening?

Either way that’s none of my business - thinning is difficult, and figuring out what you did, what you want to do, and whether you can even tell if you did it is a massive part. Make sure you have objective tests for progress. Otherwise efficiency falls off a cliff.

I don’t know, it’s a lot to explain, and there’s gotta be some solid threads on it. I’m not good enough to give many suggestions. One thing I can say is refinishing is madness unless you’re good at it. It’ll also be required after any steel removal from anywhere other than the edge. There’s a lot of ways to do it, and none of them are quick and easy.

Side answer: I like AS. Especially this AS. I never intend to let it sit dirty or push the limits of toughness. Denka steel is pretty damn good imo.

Oh yeah, and don’t get all the way to where you want on the coarsest stone. The next one up is going to take some as well. There is such thing as too thin.
I was curious and saw one was available for a decent price. When I compare it to other knives I have of a similar profile, 120 mm petty, both factory made production knives and lower end "artisan" knives, it's readily apparent how much fatter it is. I don't really know what I was expecting. But also seeing as this knife doesn't have any kind of special finishing I figured it probably wouldn't be too bad to give it a more generous grind. My main concerns are, surface finish. Which it seems like only experienced knife makers or metal workers are probably going to be able to give like good insight on that. The other concern which comes from experience is losing too much height in the process of thinning, though I might be jaded because my only experience was thinning a hollow ground knife, started out on stones, started off as a bunka and ended up as a cute little utility knife lol. It feels stupid enough to do that to a knife I overpaid for but could purchase again for $160, assuming it was available. It's another thing to do it to a tiny little wee knife that's listed for at least $400, if not more, if you can find it. It's currently listed for 562 USD on knifewear.
 

gc0220

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Here's some pictures I took of the knife earlier.

Just for some background, I ordered a 210 marb from them directly. It was supposed to be here a while ago, finally after a bunch of back and forth with Miho from customer service, after I expressed interest in maybe upgrading to the denka, or adding a denka in addition - locked in at the old price mind you - but I wanted a firm answer on what's happening with my order first, so I finally found out it's going to be another 6 months, at least. Anyway, I ordered this petty soon after I put in that order for the marb to have something to play with in the meantime, and I thought a denka petty would make a good set with the marb gyoto. The steel subjective the way it performed to me was impressive, which is why I bought it really, to play around and see. My girlfriends likes using this knife, it's cliche but she was like shocked the first time she cut with it. Sharpest thing ever. And I'm ofc a weirdo so I keep all my stuff hair whittling sharp but something about this knife, even with the fatty grinds just goes through ingredients like a laser. Anyhow. I got annoyed with Miho and found a 210 Denka that I ordered and should be here real soon. Not sure what I'm gonna do about the original order for the marb. Email them and cancel it? Or just wait 6 months and see if a knife actually shows up. It's annoying to deal with.
 

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gc0220

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Thinning the knife should not result in any change in profile. You are essentially removing material from above the edge area. Only during sharpening should you really get too close to the edge itself.

You mentioned that you did some thinning. What are you using to thin with? What stone, sandpaper, or motorized equipment are you using. Thinning by hand is a very slow process for removing metal. And that's assuming you're using some very coarse stuff to begin with. On top of that, TF steel is ridiculously tough and hard to remove metal from. So unless you're using a belt grinder, or going super insane with ultra coarse stones, I suspect that maybe there was a lot of abrasion caused to the surface of the blade, but doubt there was significant "thinning" actually done.

I'm all for experimenting and just diving in head first. But I recommend at least having some sort of goal in mind, and a way to monitor your progress toward that goal. Digital calipers are very helpful here. You can get a decent one on amazon for less than $30.

If you're concerned about keeping original aesthetics, don't bother thinning. Removing steel necessitates affecting the aesthetics. So if this is important to you, also have a plan for refinishing the knife after you're done with the thinning process. In my experience, thinning makes up maybe 20% of the time spent on a knife (depending on how much you want to thin it), and refinishing will account for the remaining 80% or so.
I have calipers. I have stones. I have sandpapers. All kinds of abrasives. I also have a bench grinders, belt grinders. The knife I'm talking about was definitely thinned. It's a whole new knife now, butchered but I've been working on my finishing to get it looking decent. I'd be too embarrassed to post it honestly. Its thin alright. It's so thin that it does the Murray Carter fingernail thing, if you know what I mean. It's a legit laser. I'm sure purchasing a knife with a grind like that would cost a lot more than the $180 I paid for this thing but yea, I still butchered a knife with a dude's signature on it, so it feels weird.
 

gc0220

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In addition only: any sharpening at a lower angle than used for the very edge is thinning. If you want to make sure you don't touch the very edge, use a sharpie. Stop in time, when the paint is reduced to a hardly perceivable line. No way thinning should affect the blade's width. You may start by removing the shoulders, where bevel and face meet. Go on until you almost reached the very edge. By the way, touching up the edge is good practice after thinning. Don't expect the edge to remain exactly the same after all what happened just behind it, with all the pressure that was involved. Some burr formation may occur. A few strokes on your finest stone will do.
I think the issue is the only knife I've tried to thin was hollow ground. So all I was hitting was the top of the shinogi and the cutting edge until it became a V grind. That's partly what I asked about. What's the right way to thin a hollow knife like that? Just use sandpaper by hand or something? Or maybe these knives can't be thinned, they're already quite thin and once you get past the hollow it's just game over. I don't know the answers.
 

M1k3

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If you lose height from thinning, you're holding it at to high of angle/fingers pushing to close to the edge or have gone to far.
 

Pie

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I think the issue is the only knife I've tried to thin was hollow ground. So all I was hitting was the top of the shinogi and the cutting edge until it became a V grind. That's partly what I asked about. What's the right way to thin a hollow knife like that? Just use sandpaper by hand or something? Or maybe these knives can't be thinned, they're already quite thin and once you get past the hollow it's just game over. I don't know the answers.
I see what you mean now.

Grinding to a V theoretically is thinning. It is… thinner in all areas of the bevel. Maintaining the hollow is a different story. Most people don’t (?). A convex has advantages over hollow grinds, but to each their own - if you want to thin and maintain the grind, I suppose some sort of domed surface wrapped in sandpaper. Or a slip stone. That’s *tough*. During Covid someone started a “grinding in concavity” thread. I apologize for not looking for it though.

I’m sorry I misunderstood your questions, hopefully this helps!
 
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