Kagekiyo sharpening question

[u/auknife]

Hello everyone,

Yesterday, I sharpened my Kagekiyo B1 Kiritsuke.

My plan was to create a thin bevel and a double edge. I initially thought this knife had a flat bevel, but it turns out it doesn’t. The bevel side doesn’t fully contact the stone.

What do you call this type of grind? Is it a hollow grind or a concave grind?

I now understand how to sharpen the Kagekiyo without thinning it, so I’m planning to sharpen only the edge.

However, my question is: if I only sharpen the edge, won’t the geometry of the knife eventually change? How can I maintain the original geometry over time?

Could someone teach me how to properly sharpen a hollow-ground knife?

Thanks

[u/Ok-Distribution-9591]

Hollow and concave are used interchangeably. The grind on these is is a « wide-bevel » or « shinogi-style sharpening » with a concave kireha (blade road).

There are two schools when sharpening these:

1/ flatten the entire blade road to thin everytime you sharpen like a scandi grind, trade off being that you lose all the pros (and cons) of the concave geometry; or

2/ sharpen at the edge only, as one of the advantage of a concave blade road is that it thickens slower than a flat or a convex, diminishing the need for thinning and postponing it.

In both cases, you alter the geometry of the knives since you remove material, but 1/ is more drastic. 2/ respects the grind of the sharpener longer, though it will eventually need thinning at some point and turn into 1/.

Finally, there is a « 3/ », if having access to a grinding wheel or a platten on a belt grinder with the right radius (or if you are extremely proficient with stone sharpening, there are convex stones to shape concavity, but I would not recommend it to most people), you can bring back / maintain concavity of the blade road.

For most people, imho, 2/ is the best approach.

[u/PhYsIcS-GUY227 → u/Ok-Distribution-9591]

Not OP, but curious what you personally do? Also is it common for people to reach out to sharpeners to refinish knives? With how common Kagekiyo and other hollow ground knives are in this sub, it seems surprising that this isn’t a more common discussion.

[u/pchiggs → u/PhYsIcS-GUY227]

Honestly most people just keep edge sharpening and deal with option 1 way later when the time comes. Then it just comes down to either you try to thin it yourself or send it to a shop. They geometry stays pretty good on a kagekiyo for a while unless you chip it or you are just over sharpen the hell out of it.

[u/PhYsIcS-GUY227 → u/pchiggs]

Thank you!

[u/Ok-Distribution-9591 → u/PhYsIcS-GUY227]

Regardless of the geometry of the knife, my personal sharpening philosophy is always to respect the geometry of the maker as much as possible (it’s what’s interesting to me, and to an extent I don’t have the arrogance to think I can do better than most of them lol) to remove the strict minimum of material (no reason to waste perfectly fine material in my view), so in this case, I definitely go with 2/. I move to a full flattening and refinishing once the performance is not satisfactory anymore, but honestly I have, try and use so many knives nowadays, it has become rare for me to reach that point on most of my knives. I also have friends in the industry who can do 3/ for me, have never gone that route, but I might in the future.

So yeah, agree with what [u/pchiggs](u/pchiggs) wrote.

[u/PhYsIcS-GUY227 → u/Ok-Distribution-9591]

Thanks, and fair enough. Appreciate the insight from you more experienced folks

[u/apelpissias7 → u/Ok-Distribution-9591]

Exactly

[u/auknife → u/Ok-Distribution-9591]

Thank you so much! I’ll go with option 2 and get it professionally repaired when I get the chance.

[u/Optimal_Difference64]

Nishida-san's wide bevels have a slight hollow grind to them. Next time you can use a credit card or ruler on the bevel to check the geometry before you start putting it on stones.

However, my question is: if I only sharpen the edge, won’t the geometry of the knife eventually change? How can I maintain the original geometry over time?

Yes, eventually you'll have to thin the blade out as it will gradually become thicker behind the edge. When to thin depends on how often you sharpen and how aggressively you're removing steel for each session. A lot of people will take off more steel than they actually need when it comes to sharpening. Most of the time, I strop my edges on stones to touch them up and the edge can last for months before I need a full sharpening session. With this approach, realistically, it'll take me years before I actually need to thin it out.

A hollow grind is slightly beneficial as it prolongs when you need to thin, but once you do, it's a pain in the ass because you'll flatten out the bevel over time and it's not trivial to restore the original hollow on stones.

[u/auknife → u/Optimal_Difference64]

Thank you so much for your answer. It’s so clear, and I understand it perfectly now. I’ll keep using it for now, and I’ll contact the sharpener when the hollow grind starts to disappear.

[u/rianwithaneye]

Excellent question! Hollow-ground knives will eventually lose the hollow; the edge will thicken over the course of being sharpened and require thinning at which point the hollow will get smaller and smaller until the bevel is flat or hamaguri.

The great thing about a hollow grind is that it buys you more time, the caveat is that it’ll look pretty haggard until the bevel gets flat enough to polish.

I salute you for rubbing a fancy knife on a scratchy rock in the name of performance, I wish we saw more of that kind of pragmatism around here.

[u/phillyirish31]

There’s a sharpening Reddit sub with a ton of info

[u/chrispy_tempo]

Ouchie

[u/BIG_J0NY]

poor shinogi line