Thickness behind the edge

[XooMG]

For knives with very very thin blades, I prefer a tiny bit of meat immediately behind the edge:

(knife is Carter Muteki, thinned)

For thicker knives, I like having a pretty thin edge, as it is still pretty stable:

(knife is a Sakai Takayuki Shoshin Sakura, out of the box)

In both cases, I'm just a home user and don't beat up my edges at all.

 

[Kippington]

Haha there's so much going on in that last picture (grind angles/grits/layers) its like a picture of the Burj Khalifa!

But in all seriousness.. those are some very nice looking grinds you have there!

 

[rico]

+ 1

 

[nepastovus]

the first picture is Takeda classic gyutoh which had bad OOT bevels, no root veg could have been cut without tearing. the second picture is Fujiwara Teruyasu Nashiji, which looks way too thick but actually cuts way better than it looks.
and yes, Takeda that thin chips very easily and doesn't get used near as much as another

 

[labor of love]

the first picture is Takeda classic gyutoh which had bad OOT bevels, no root veg could have been cut without tearing. the second picture is Fujiwara Teruyasu Nashiji, which looks way too thick but actually cuts way better than it looks.
and yes, Takeda that thin chips very easily and doesn't get used near as much as another

Nice job on that Takeda.

 

[mhpr262]

Would anybody be willing to show how thinning is done properly on European/German knives that don't have a convex bladeface? I usually thin mine by putting the whole bladeface on the flat, supported part of my belt sander, but press down only on the part closest behind the edge. The part of the bladeface closest to the edge barely rests on the belt. So far the results (on three $10 stainless knives) have been quite good. grinding only on the flat supported part tends to leave a slightly uneven finish though, so I usually finish on the "slack" unsupported part (that is still under pretty high tension though) which leaves a very slightly convex bladeface.

would that be considerered proper technique by the pros out there?

 

[mhpr262]

The part of the bladeface closest to the edge barely rests on the belt

Sorry, of course I meant

The part of the bladeface closest to the SPINE barely rests on the belt

 

[rick alen]

You can take the thinning right to the spine and beyond, especially at the tip where a distill taper of 3"+ to a <.02" tip is highly desirable (except maybe in a rough pro kitchen where closer to .04" at the tip would be safer).

Taking a knife like the Vic rosewood, with completely flat sides and an already decently thin edge (.015"/.38mm), just .003 of convexing/per side [to bring the edge to .009"] makes a noticeable difference in food release. Not dramatic mind you, just noticeable. So in the case of flat sided knives, especially if you are going to be cutting potatoes, certainly take advantage of some or all of the convexing you can, on both sides.


Rick

 

[mhpr262]

So convex is actually helpful? That's good to know. I keep being surprised how much the knives are improved, and how mostly decent they look after having done the work, despite my being mediocre at best with my hands. Next in line are three F. Dick ProDynamic industrial kitchen workhorse knives that have a genuine "battle axe" geometry. I swear the bevel is 2mm wide .... in some places ...

I use a cheap a$$ $90 fixed speed stationary belt sander and a felt buffing wheel and it does have its limitations, but good belt sanders are $$$$$$ ....

 

[Ruso]

Little thinning on Hiromoto AS, before and after

 

[Benuser]

That's for sure no little thinning. Good work. I prefer proceeding by little steps and verify for steering and food release.

 

[rick alen]

That's for sure no little thinning. Good work. I prefer proceeding by little steps and verify for steering and food release.

Here I think it would be a good idea to use a jig to set in the bevel leading to the edge. A while ago I did some solid modeling of cross-section edge profiles and it seemed to me as I recall that 2deg/side was about right for a middle of the road gyuto, a laser would be 1.5deg or maybe less, and a wide-bevel gyuto as much as 3deg, probably not more. Looking at the Geshin Heiji, that got mention in the recent wide-bevel gyuto thread as an extreme example, it does appear to have about a 3deg lead in from the photo on the JKI site.


Rick

 

[Prize78]

How much does thinning affect the 'finish' of the edge? As surely, you have to 'scratch' the metal in order to remove some? I'm not confident in doing mine incase I scratch it up and it looks terrible?!

 

[XooMG]

How much does thinning affect the 'finish' of the edge? As surely, you have to 'scratch' the metal in order to remove some? I'm not confident in doing mine incase I scratch it up and it looks terrible?!

I'd bet that aside from major thinning work that requires massive amount of material removal, the biggest issue holding folks back from thinning their knives is messing up the finish. For less extreme thinning jobs, people will generally tell you most of the work is in refinishing.

 

[malexthekid]

I'd bet that aside from major thinning work that requires massive amount of material removal, the biggest issue holding folks back from thinning their knives is messing up the finish. For less extreme thinning jobs, people will generally tell you most of the work is in refinishing.

I think you hit the nail on the head. It is the reason I have not done any progressive thinning on my knives.

 

[rick alen]

C'mon, really? Seriously???? Are we talking about Safe Queens here or real working knives?


Rick

 

[Timthebeaver]

Agree, why anyone would ruin the geometry and compromise the performance of their knives for the sake of some scratches is beyond me - they are tools.

 

[Geo87]

Sandpaper... Problem solved.
Unless you have a clad knife and care About the contrast. Then you need stones that will bring out that contrast. There's really enough information on these forums for anyone to have a crack at thinning and get pretty good results

 

[Chuckles]

Not all thinning jobs need to be extreme. If you keep consistent angles there is no reason that you would need anything but stones to restore your finish. Here you see the hazy King 800 finish is where the 'major' part of the thinning occurred. The mirrorish finish toward the edge is still mostly above the cutting edge. Just that much above the edge would still be thinning and could help a knife quite a bit by 'knocking off the shoulders'. Setting up a convex knife like this with a faux shinogi and then a smaller thinning angle helps you know where the maitenance thinning should take place and where the big work is when the time comes. I don't think thinning has to be a scary major project everytime but it does need to be done on the small scale periodically to keep the knife performing.

 

[rico]

I'd bet that aside from major thinning work that requires massive amount of material removal, the biggest issue holding folks back from thinning their knives is messing up the finish. For less extreme thinning jobs, people will generally tell you most of the work is in refinishing.

I just thinned a Damascus AEB-L and I need to go back and polish to bring out the Damascus finish. The improved performance is well worth a few weeks of dull finish. What should give people pause is doing a crummy job of thinning of a good grind on an expensive knife !!! imho . . :O

 

[malexthekid]

This is sort of what has my hesitant to thin my knives.

The ones that I think I would do (or at least have some work to do to them that would then require thinning) are damascus. And I am hesitant to then having to re-etch them aftewards.

Maybe I should just bite the bullet and do it.

 

[gregg]

Your Akifusa is a bone-splitter at the moment. A $20 pair of verniers will tell you just how thick you are. .015"/.38mm is still thick enough for a work horse, I prefer >.010" for 99% of what I do.

Speaking of thinning cheap knives, I thinned some very soft stainless to about .008" and the other day I was cutting around some ribs with it, I didn't think I made much contact with bone but there appeared 2 sizeable dimples bent into the edge.


Rick

Just a quick question; where exactly on the edge are you getting the .38mm, (or .25mm) thickness from? eg., just behind the primary bevel, or higher up?

 

[bkdc]

Do the experts have any advice on doing some major thinning on a san-mai knife where the outer cladding is a VERY soft stainless steel? It is sooooo labor intensive as the metal does not want to abrade off no matter what stone or diamond plate I use.

 

[JBroida]

what knife?

 

[bkdc]

It's a Teruyasu Fujiwara Nashijii. I took it as my project knife and completely reground it on nothing but whetstones all the way up to the spine. It cuts well now, but wow.. I don't know how much total time was put into it. The cladding was soooo slow to work off even on the lowest grit stones or atoma plates. It was just so soft!

 

[JBroida]

It's a Teruyasu Fujiwara Nashijii. I took it as my project knife and completely reground it on nothing but whetstones all the way up to the spine. It cuts well now, but wow.. I don't know how much total time was put into it. The cladding was soooo slow to work off even on the lowest grit stones or atoma plates. It was just so soft!

yeah.. they are time consuming. I use my big wheel to thin, then refinish on the belt grinder and buffer. By hand, they take forever. Better than the diamond, the 220 grit stones work wonders on these kinds of steel.

 

[rick alen]

Just a quick question; where exactly on the edge are you getting the .38mm, (or .25mm) thickness from? eg., just behind the primary bevel, or higher up?

Just behind the primary. And the other point should have indicated <(less than) 0.010".


Rick

 

[CaremeFraiche]

Regarding Japanese knives, does anyone thin their knives in Japan?

 

[chinacats]

Regarding Japanese knives, does anyone thin their knives in Japan?

Only the people that like for the knife to cut well...

 

[Lizzardborn]

Regarding Japanese knives, does anyone thin their knives in Japan?

If you look at Jon's videos the thinning is built in into single bevel knives sharpening. You move the shinogi line up a bit, then sharpen the secondary bevel to the edge, then blend together the two.

So you are just removing the fatigued steel and moving the whole configuration up.