"Thinning behind the edge"?

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Salty dog

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A phrase I've been hearing a lot lately. To be honest I'm confused?

It may seem like an obvious question but could someone explain it to me?
 
Laying the knife flat on the stone and thinning the steel behind what is making the initial cut. The idea is to prevent the steel behind the edge from getting progressively thicker so you have both an acute secondary and primary edge.

sharpen4.jpg
 
I confess I am/was a bit confused as well because I think people use the term for two different activities, no?

Namely,

(1)Literally thinning behind the edge for example when one lowers the angle, sharpens, and then raises the angle a wee bit and puts on a microbevel with the final stone?

and

(2)Thinning up the surface of the blade, keeping the knife really really flat against the stone (<10 degrees??) for example and grinds away up to the shinogi line or even grinds away at the whole width of the blade to change the geometry of the knife.

Or am I missing something??
 
Neither....

3) Laying the kitchen knife flat, literally flat on the stone, like, 0 degrees.
 
6vsciQB.jpg

This is a picture of a mizuno I once had while it was in the thinning stages. You can thin behind the edge at any angle you're comfortable with really the lower you go the thinner your edge will be. I don't usually lay the entire blade "flat" but rather thin at around 2 degrees or so. Just a c-hair off the stone with the spine. Changes the geometry a touch but leaves a bit of convexity that I like.
 
I confess I am/was a bit confused as well because I think people use the term for two different activities, no?

Namely,

(1)Literally thinning behind the edge for example when one lowers the angle, sharpens, and then raises the angle a wee bit and puts on a microbevel with the final stone?

and

(2)Thinning up the surface of the blade, keeping the knife really really flat against the stone (<10 degrees??) for example and grinds away up to the shinogi line or even grinds away at the whole width of the blade to change the geometry of the knife.

Or am I missing something??

Either can be thinning behind the edge, depending on the knife design and your intended purpose.
 
I guess saying "behind the edge" is redundant if you are thinning the knife. The whole knife is behind the edge. Where else are you going to thin it?
 
You know that is a very good insight. Ergo shouldn't we say: thinning a knife for effecting the geometry whereas thinning behind the edge should mean just affecting the actual edge as in my example of low angle + applying microbevel??
 
For me it means wearing away the steel at an angle somewhere around 4 degrees
 
I have been tweaking my sharpening routine for some time, because i'm still a beginner (1.5 years now almost daily). I feel most satisfied with the current approach:
Thin the bottom 1/4" of my gyuto once a week, symmetrically on a 400 grit stone.
Keep up the edge through the week on a 4k stone at a much higher angle, creating a 1mm bevel, symmetrically again.
pull through a cork and strop on newsprint laid on the 4k stone (too lazy to buy a proper strop kit).

when i wasn't thinning behind the edge, my knife cut like crap.
when i sharpened it asymmetrically, it cut like crap (steering).
when i didn't apply the small bevel at the edge, it got destroyed on the board (and was miserable to sharpen and touch up).

the way i see it, the poly boards most of us have to use at work will destroy and edge at some point during the day, at which point you are left more with the function of the knife's geometry. a slightly dull edge and thin knife will still perform admirably if you don't get a chance to touch it up.

plus, making a 'shinogi' line on your gyuto is fun.
 
I'm still a firm believer that many are too quick to remove a bunch of metal. Why thin and sharpen so frequently? Does ones knife really need a full progression starting all the way down to low grit full thinning every week? I like to try and do as little metal removal as possible, increasing my knifes longevity. I do agree that some knives need a bit of tuning, and thinning is all part of upkeep; that being said, I only resort to a full progression when my actual bevel has deteriorated, which takes a ton of abuse to achieve. Usually touch ups will get me through for a very, very long time.
 
+1
I'm still a firm believer that many are too quick to remove a bunch of metal. Why thin and sharpen so frequently? Does ones knife really need a full progression starting all the way down to low grit full thinning every week? I like to try and do as little metal removal as possible, increasing my knifes longevity. I do agree that some knives need a bit of tuning, and thinning is all part of upkeep; that being said, I only resort to a full progression when my actual bevel has deteriorated, which takes a ton of abuse to achieve. Usually touch ups will get me through for a very, very long time.
 
I'm still a firm believer that many are too quick to remove a bunch of metal. Why thin and sharpen so frequently? Does ones knife really need a full progression starting all the way down to low grit full thinning every week? I like to try and do as little metal removal as possible, increasing my knifes longevity. I do agree that some knives need a bit of tuning, and thinning is all part of upkeep; that being said, I only resort to a full progression when my actual bevel has deteriorated, which takes a ton of abuse to achieve. Usually touch ups will get me through for a very, very long time.
+2
I haven't had to actually go through the full progression on my knives for months. Once they're set up how I like em touch ups on finishing stones, usually my little nakayama that I keep with me at work, keep my edges alive and kicking for a loooong time.
 
Just a c-hair off the stone with the spine. Changes the geometry a touch but leaves a bit of convexity that I like.

i love that you used that "measurement". i rarely hear this outside of the kitchen. haha
 
I'm still a firm believer that many are too quick to remove a bunch of metal. Why thin and sharpen so frequently? Does ones knife really need a full progression starting all the way down to low grit full thinning every week? I like to try and do as little metal removal as possible, increasing my knifes longevity. I do agree that some knives need a bit of tuning, and thinning is all part of upkeep; that being said, I only resort to a full progression when my actual bevel has deteriorated, which takes a ton of abuse to achieve. Usually touch ups will get me through for a very, very long time.
Totally agree!! I've seen many thinned knives with mess up blade geometry.
 
I don't know guys.... It really could be ok depending on how he sharpens... I have knives I've thinned at least once a week and they are still around after almost 8 years. Just because you're thinning doesn't mean you have to be removing a ton of metal... It could be just a bit each time... Just enough to keep the knife right where you want it geometry-wise
 
Is there something particular you look for when you can say that you've remove enough metal when thinning? Is there going to be a burr too?
 
i just eyeball it... a large part of being good at sharpening is having experience using the knives (or getting great feedback from someone who uses them), so you know what will work for a particular steel, HT, intended use, etc. Thinning doesnt always have to create a burr (and in many cases doesnt), but it is possible to thin so much as to create a burr. It just depends on what you are trying to do and how thin you want to go.
 
Is there something particular you look for when you can say that you've remove enough metal when thinning? Is there going to be a burr too?

i alway thin for a few minutes then cut something to test, and then thin some more...until it feels right.
 
Assuming you are not screwing up the geometry by thinning, how does repeated thinning reduce the life of the knife? Rarely ever are you hitting the edge while thinning, the knife isn't going to get shorter. It will get shorter from sharpening, but not thinning. It will get just get skinnier. When you go on a diet, you lose weight, you don't get shorter.
 
Assuming you are not screwing up the geometry by thinning, how does repeated thinning reduce the life of the knife?

It'll make it more flexible surely? If you're used to a knife with no flex, once is starts to happen it could limit the tasks you use it for and once it starts flexing unless you reduce the height of the blade, it's only gonna get worse
 
It'll make it more flexible surely? If you're used to a knife with no flex, once is starts to happen it could limit the tasks you use it for and once it starts flexing unless you reduce the height of the blade, it's only gonna get worse

That depends on the grind of the rest of the knife really. On a knife with a convex/blended diamond cross section, what you do to the edge isn't really going to be relevant for a good, long time....probably not till long after you've turned the thing into a filet knife. The same for an 'I' type grind like a Takeda. Even if you eventually make it a 'T' grind, that T is going to still provide the majority of the stiffness.

Mostly the knives that would be affected are truly even flat grinds.
 

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