My first thinning

[bobo990]

So... After a couple of years of home use and abuse i tuink it is time to thin my most used knife. I think it is a wide bevel.

I lay it flat on the bevel on a shapton pro1000 (and later on a 200 diamond) ad start goong up and down...

Fingers are close to thr edge...

Somehow the main bevel road it looks concave... The stone touches on the top and bottom parts. While the middle patina stays there... What ammi doing wrong? Is this supposed to happens and it will go away with the thinning?

Any useful hints/suggestions?

Cheers

 

[Bico Doce]

Unless a knife is finished on stones it will have low and high spots or even a concave/hollow grind

 

[Matt Jacobs]

Im no expert in thinning but that is pretty common. When I have had this with one of my knives I dont worry about it. Keep thinning until you are happy with performance. Go back over the bevel with sandpaper to even the finish and remove the patina. Put a final edge and go back to using it. Over time you can get rid of it but if you try to tackle that in one shot you will more than likely mess the grind up.

 

[Stevem627]

I agree with the posts before me here. A lot of knives have a concave bevel since they use a wheel to sharpen them. Your knife looks pretty good for now, so just do the aforementioned sandpaper on the area you can’t get done on stones and it should turn out great.

 

[bobo990]

Thanks for reassuring me guys.

I will keep happly using it.

But in the future, i might consider thinning it a bit everytime i sharpen it (maybe... I am lazy after all) that way it shuld keep ita grind more consistently....

What wpudl ypu do? Is it a bad idea?

Thanks.

 

[Matt Jacobs]

Its a very viable way to keep your knife performing its best. Murray Carter has a bunch of videos on it. I personally don't do that because I like my knives to look Purdy and don't want to refinish every time I sharpen. I may dedicate one to that method though for top tier performance and see what I think.

 

[Stevem627]

If you use a knife a lot, you should do thinning pretty often or else it will be time consuming when you HAVE to do it. The concave grinds make it easy to get a decent cutting edge bevel sharp fast, but you are delaying the inevitable thinning.

 

[deltaplex]

So... After a couple of years of home use and abuse i tuink it is time to thin my most used knife. I think it is a wide bevel.

I lay it flat on the bevel on a shapton pro1000 (and later on a 200 diamond) ad start goong up and down...

Fingers are close to thr edge...

Somehow the main bevel road it looks concave... The stone touches on the top and bottom parts. While the middle patina stays there... What ammi doing wrong? Is this supposed to happens and it will go away with the thinning?

Any useful hints/suggestions?

Cheers

Isn't that a Shindo? Those are VERY concave and VERY thinly ground on the primary bevel. So much so that when I was contemplating converting mine from a concave grind to an asymmetrical convex grind, the height loss combined with more or less wiping out the shoulder at the shinogi and the concave geometry of the hira coming into that same shinogi made it not worth attempting.

This is a very rudimentary drawing highlighting the high areas on the LH side (in RED) and the low (concave) areas (in YELLOW):

To work this knife to the point that you'll be able to touch all of the area in the convex section below the shinogi, you'll have to completely grind away the "shoulder" at the shinogi, at which point it's a completely different knife, geometrically. Starting from a concave wide bevel with a concave hira and ending up with a flat or convex ground laser with the primary bevel starting significantly higher up the hira than it does today. You can sharpen the knife A LOT when it's ground like Shindo-san does before the geometry becomes thick enough to warrant thinning, mine varies between ~.35mm and ~.50mm thickness 5mm above the cutting edge, and when I have taken a full 3-4mm off the height from sharpening alone, I would start thinking about adding thinning the primary bevel as part of sharpening the cutting edge.

 

[bobo990]

Its a very viable way to keep your knife performing its best. Murray Carter has a bunch of videos on it. I personally don't do that because I like my knives to look Purdy and don't want to refinish every time I sharpen. I may dedicate one to that method though for top tier performance and see what I think.

What do you mean "dont want to refinish the every time i sharpen?"

 

[bobo990]

Isn't that a Shindo? Those are VERY concave and VERY thinly ground on the primary bevel. So much so that when I was contemplating converting mine fr...

than it does today. You can sharpen the knife A LOT when it's ground like Shindo-san does before the geometry becomes thick enough to warrant thinning, mine varies between ~.35mm and ~.50mm thickness 5mm above the cutting edge, and when I have taken a full 3-4mm off the height from sharpening alone, I would start thinking about adding thinning the primary bevel as part of sharpening the cutting edge.

You have a good eye indeed.

It feels very concave.

It has been a couple years of home duty so not an accessive amount of work, but it is my only gyuto, it is my first nice knife and my most used one, so id say that recived at least 10-15 sharpenings.

It came from the shop with a wiked zero edge whose performances (but not its durability) i have been chasing since.

Thr shaprning bevel was i d say a couple of millimeters wide ( i dont have a micrometer to measure the width bte)

 

[deltaplex]

I'm not trying to pile on here or anything, but I'd personally get the edge profile adjusted before I did anything else (again a quick mark up to give a general idea):

 

[deltaplex]

You have a good eye indeed.

It feels very concave.

It has been a couple years of home duty so not an accessive amount of work, but it is my only gyuto, it is my first nice knife and my most used one, so id say that recived at least 10-15 sharpenings.

It came from the shop with a wiked zero edge whose performances (but not its durability) i have been chasing since.

Thr shaprning bevel was i d say a couple of millimeters wide ( i dont have a micrometer to measure the width bte)

My Shindo doesn't get up into the 1mm material thickness range on the bevel until about 10mm above the cutting edge. To get this kind of grind back to the ~0.1mm thickness range 1mm above the cutting edge, you either will be losing some material thickness at the shinogi, or you're setting the knife at an angle low enough that you have to keep the majority of the blade off the stone. In essence, you're only touching the ~1-2mm above the cutting edge on a flat stone, or you're doing the work on a convex stone.

 

[Nemo]

Your knife definitely has a concave wide bevel and you seem to be in the right ballpark as to how you have thinned it.

As for refinishing: When you thin, your thinning stone leaves scratches in the knife's finish. If you used a coarse stone, these are often coarser scratches than you want on your knife. So you need to remove them with scratches from a finer stone, finer sandpaper or even a progression (depending on the finish you want).

If you are aiming for optimal food release, a finish in the 1k to 3k region seems to be the sweet spot in my experience.

So if you thinned with a 400 stone, you may want to refine that finish by moving to a 1k (and maybe beyond) stone.

OTOH, if you do a little maintenance thinning when you sharpen, you can get away with doing it with a 1k stone, so are already pretty close to your target grit, so refinishing may be easier (or even not necessary if your knife is a wide bevel and your target grit is 1k).

My most usual approach is to touch up on a fine stone until I can't create a burr with fewer than 10 or 20 strokes. The edge will then need the attention of a medium (1k ish) stone and I take the opportunity to do a little maintenance thinning while using the medium stone.

Wide bevel knives are often ok with this finish. Other knives might need a short sandpaper progression to neaten them up. 5 to 10 mins work. Unless you have a Damascus or mirror or semi mirror finish. These need much more refinishing work. To the extent where I'm discouraged from using them because they won't get thinned as often so won't stay at peak performance.

 

[Nemo]

It's worth mentioning that changing a knife's profile needs a lot more work than thinning and will require re establishing the grind. It's also pretty easy to stuff it up.

 

[bobo990]

I'm not trying to pile on here or anything, but I'd personally get the edge profile adjusted before I did anything else (again a quick mark up to give a general idea):
View attachment 338744

no offense taken at piling, if anything i am thankful that you took some time to help me.

but i am not sure what you exaclty mean with this picture... i don't think i changed that much the profile that i need to correct for it... what are you looking at the image? what cues are leading you? what am i missing?

 

[bobo990]

My Shindo doesn't get up into the 1mm material thickness range on the bevel until about 10mm above the cutting edge. To get this kind of grind back to the ~0.1mm thickness range 1mm above the cutting edge, you either will be losing some material thickness at the shinogi, or you're setting the knife at an angle low enough that you have to keep the majority of the blade off the stone. In essence, you're only touching the ~1-2mm above the cutting edge on a flat stone, or you're doing the work on a convex stone.

sorry, english is not my first language, so i might have not explained myself correctly.

the sharpening bevel was 1mm wide viewed from the side of the knife, i am not at 1mm in thickness where i sharpen.

 

[deltaplex]

no offense taken at piling, if anything i am thankful that you took some time to help me.

but i am not sure what you exaclty mean with this picture... i don't think i changed that much the profile that i need to correct for it... what are you looking at the image? what cues are leading you? what am i missing?

It looks like you have under-sharpened the heel over the time that you have been using and maintaining this knife:

The area under the red line is (crudely) showing the approximate amount that I would remove from the back 1/3 of the edge profile to bring it back to where it was when it was new.

 

[Delat]

It looks like you have under-sharpened the heel over the time that you have been using and maintaining this knife:
View attachment 338989
The area under the red line is (crudely) showing the approximate amount that I would remove from the back 1/3 of the edge profile to bring it back to where it was when it was new.

That might be some weirdness from rotating the pic. The original image looks ok to me.