# Concave grinds



## Badgertooth (Jan 25, 2017)

What's the best way to maintain a concave grind without a water wheel? Or is it a gradual flattening out on stones until it's not a convex edge over time.


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## Nemo (Jan 25, 2017)

Great question. I'd also like the opinion of some expert sharpeners about this.


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## tsuriru (Jan 25, 2017)

Badgertooth said:


> What's the best way to maintain a concave grind without a water wheel? Or is it a gradual flattening out on stones until it's not a *convex* edge over time.



Im going to assume that the word "convex" is a slip of the tongue. 

As for your question, in my opinion, will be very difficult to maintain convexity of a blade using a flat stone. Impossible in fact. The only way I can think of maintaining a concavity using hand tools rather than a wheel, would be to stretch sand paper over a convex (cushion shaped) block of wood, laying the blade flat on your work surface, and using a top-to-bottom brushing motion make your way from the heel towards the tip and back. However, this may prove to be a very long process as compared to using a wheel. :2cents:​


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## Badgertooth (Jan 25, 2017)

Yup sorry, slip of the tongue. That does sound like a long process. I think I'll just hit it till it's flat, makes polishing easier too once it's at that point


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## RDalman (Jan 25, 2017)

I would guess most concave grinds are made with the maker intending the user to flatten it out over time. Atleast that's the case for me. I think the optimal way maintain the grind I do is to treat it like a short widebevel, that will get bigger over time as you move the shinogi up.


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## fatboylim (Jan 25, 2017)

Finger-stones perhaps. Also a slip stone might be the right shape. These are used mainly for cerated bread knives.


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## foody518 (Jan 25, 2017)

Which knife/knives?


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## milkbaby (Jan 25, 2017)

I thought most hollow ground edge bevels were meant to be easily sharpened with less or no need for thinning?


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## labor of love (Jan 25, 2017)

milkbaby said:


> I thought most hollow ground edge bevels were meant to be easily sharpened with less or no need for thinning?



That's been my experience.


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## Unstoppabo (Jan 25, 2017)

Unless im trying to preserve original geometry, I try to hit the first 5mm only when thinning, which kinda keeps things concave/hollow and try for geometry that looks like a shouldered rifle round. Using a well chamfered stone, I thin just a few mm against the side of the stone, using fingers on bottom of knife to guide depth evenly. On something really fat behind the edge, I start on diamond plate and basically grind back to get down to core 5-7mm up from the edge.


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## labor of love (Jan 25, 2017)

Unstoppabo said:


> Unless im trying to preserve original geometry, I try to hit the first 5mm only when thinning, which kinda keeps things concave/hollow and try for geometry that looks like a shouldered rifle round. Using a well chamfered stone, I thin just a few mm against the side of the stone, using fingers on bottom of knife to guide depth evenly. On something really fat behind the edge, I start on diamond plate and basically grind back to get down to core 5-7mm up from the edge.


Right. The concave grinds I've used are ground so high up the blade anyway all that seems necessary to maintain good performance is just thinning behind the edge.


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## Badgertooth (Jan 25, 2017)

foody518 said:


> Which knife/knives?



Well herein lies the rub. It's a Konosuke Fujiyama that I laid flat to polish not realising it was concave. In so doing I realised that with a bit of work I could get clouds in the cladding but only at the top of the shinogi.

Can you see the dark band between the edge and the top of the bevel. I would love those to be billowy clouds one day. Better get grinding


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## foody518 (Jan 25, 2017)

Can't imagine (or, hoping not to) that there is an expectation for the end user to maintain concavity. Go get em clouds


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## Benuser (Jan 25, 2017)

S-shaped?


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## Ruso (Jan 25, 2017)

Badgertooth said:


> Well herein lies the rub. It's a Konosuke Fujiyama that I laid flat to polish not realising it was concave. In so doing I realised that with a bit of work I could get clouds in the cladding but only at the top of the shinogi.
> 
> Can you see the dark band between the edge and the top of the bevel. I would love those to be billowy clouds one day. Better get grinding



How do you like your Fujiyama? I was eye-balling it for few years now.


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## Badgertooth (Jan 25, 2017)

It's a never-sell knife. It's the Togo reigou knife and I have no other Fujiyama to compare it to. What I can say is, blade forward weight balance, thin behind the edge and the best steel I have ever sharpened. Very good through most ingredients except the densest tallest stuff that a lot of knives would struggle even more with. Kurogaki (quince) handle is also my favourite. Slightly more pronounced oval with 8 facets, rather than perfectly even sides and a smaller handle.


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## Badgertooth (Jan 25, 2017)

Benuser said:


> S-shaped?



In a way, yes. Think a rhombus (as I think the apex of the shinogi is wider than the spine of the blade) then the bottom of the rhombus has a slight bulge like an S grind where there is a secondary bevel


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## Ruso (Jan 25, 2017)

sorry to deviate the thread once again, is it white or blue Fujiyama?


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## Badgertooth (Jan 25, 2017)

Ruso said:


> sorry to deviate the thread once again, is it white or blue Fujiyama?



Neither. 

It is Togo Reigou steel. Though it's not real Togo reigou steel, it's from a billet of old Swedish steel that the smith and sharpener said is a lot like Togo reigou


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## tgfencer (Jan 27, 2017)

Interesting read fellas. Beautiful knife, you always seem to have interesting things stashed away Otto.


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## panda (Jan 27, 2017)

I like concavity above shinogi but not below it. They cut weird and you can't really tweak it to your liking.
I've.read that togo steel is like AS but sharpens like shirogami. It's probably more in between but I've always wanted.to try it, that and tamahagane.


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## Jacob_x (Jan 29, 2017)

Looks the same as my fuji blue #2 grind. I don't think it's intentional to keep the concavity, more a result of the finishing done on a wheel? It does mean the first time you hit the wide bevel you end up with a funny contrast, where you hit the edge and top of shinogi, but nothing in between, and there doesn't really seem much to do about it bar waiting until ground flat, or maybe hitting it with fingerstones.
It's a fairly aesthetic, shallow wide bevel on the blue#2, and has been commented on in other threads as not being a 'true' wide bevel as in a heiji for example, so I wonder if maybe one can do the following... refinish the whole blade homogeneously, sharpen as normal (not 'flat' on the wide bevel), and when necessary thin where the top of the shinogi lay before... ?


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