Maintaining/sharpening Kohetsu HAP40

[metamorpheus]

I'm still pretty new to sharpening and have mainly practiced 50/50 bevels on cheaper western blades like Mercer and the Cozzini knives my work uses. On Monday I got the Kohetsu HAP40 210mm gyuto and need some advice about sharpening/maintaining it. I do cook for a living, but the hospitals mgmt won't let us bring our own knives, so this is for home use.

I currently have a Norton combo bench stone (oil), a Mercer 1000/3000 grit combo water stone, and a 5000 grit Naniwa super stone. I have done some reading on the subject and see that Shapton Glass or the Kohetsu 800 & 2000 grit stones are recommend to cleanly remove the carbide. I do plan to get the Kohetsu stones in a month or so.

My questions are:
1.Would it be advisable to use the 5000 grit stone once a week or so to maintain my blade in place of using a steel?
2.Will the knife perform well with this level of polish or would a rougher toothy edge be better?
3.How would you recommend sharpening the uneven bevel?
4.What is the advantage of having an uneven bevel vs doing 10-12 dps with a 15dps micro?
5.If my initial 5000 grit touch ups create a secondary bevel rather than refine the primary, will this make a full sharpening more difficult later? If so what approach needs to be taken to reset a bevel that has a secondary?

[Radar53]

Hi there metamorpheus & welcome to the forum. Interesting questions. I have the Kohetsu HAP40 210 gyuto as well and mine came pretty sharp out of the box and like you as a home user, I don't think that I first sharpened it for close on a year.

1) Please don't use a steel on this knife and at first I would simply strop it on your 5k Naniwa SS. It should hold it's edge for ages
2) I enjoy sharpening and when I did sharpen it I took it to 10k and it was mega sharp and has held that edge for another 12 months, without touch ups.
3) It's probably a 70 / 30 bevel, but you can just ignore that and gradually move it to being a 50 / 50 bevel over a number of sharpenings. Alternatively you can sharpen roughly 7 strokes on one side to 3 on the other should you want to.
4) This is a really hard super steel and it can handle really acute edges. I have used 8 dps for the bevel with a micro of 10 dps with no problems.
5) Unless your knife is not sharp OOTB just 3 or 4 edge trailing strokes with light pressure & your 5k should keep it sharp for a long time. Use the Sharpie trick to find the angle of the bevel and simply work at that angle until you are ready to do a full sharpening at your own angles. (Having said that there are many sharpeners on the forum who like to do a full re-sharpen when they first get their knives, and others like me who like to work with the factory edge for a while, assuming it's pretty sharp to start with.

Just as a last comment, if you are relatively new to freehand sharpening, you might want to get pretty comfortable by practicing on beater knives until you are confident about your results.

[Altadan]

+1 on all that Radar said.

[metamorpheus]

Hi there metamorpheus & welcome to the forum. Interesting questions. I have the Kohetsu HAP40 210 gyuto as well and mine came pretty sharp out of the box and like you as a home user, I don't think that I first sharpened it for close on a year.

1) Please don't use a steel on this knife and at first I would simply strop it on your 5k Naniwa SS. It should hold it's edge for ages
2) I enjoy sharpening and when I did sharpen it I took it to 10k and it was mega sharp and has held that edge for another 12 months, without touch ups.
3) It's probably a 70 / 30 bevel, but you can just ignore that and gradually move it to being a 50 / 50 bevel over a number of sharpenings. Alternatively you can sharpen roughly 7 strokes on one side to 3 on the other should you want to.
4) This is a really hard super steel and it can handle really acute edges. I have used 8 dps for the bevel with a micro of 10 dps with no problems.
5) Unless your knife is not sharp OOTB just 3 or 4 edge trailing strokes with light pressure & your 5k should keep it sharp for a long time. Use the Sharpie trick to find the angle of the bevel and simply work at that angle until you are ready to do a full sharpening at your own angles. (Having said that there are many sharpeners on the forum who like to do a full re-sharpen when they first get their knives, and others like me who like to work with the factory edge for a while, assuming it's pretty sharp to start with.

Just as a last comment, if you are relatively new to freehand sharpening, you might want to get pretty comfortable by practicing on beater knives until you are confident about your results.

Thanks for the advice. The emphasis on edge trailing strokes made me read more and I have improved my sharpening technique. My Kohetsu is sharp OOTB, but nothing spectacular. I'm not quite satisfied with the stock edge, but that's ok. I didn't buy this knife thinking it would be samurai sharp OOTB. I bought it because I wanted something that would hold close to a 10 degree primary bevel without having to do a full sharpening once a week or more for home use.

I'm feeling confident enough to sharpen the Kohetsu once I get those stones. I got the cheap western cozzini bros knife I use at work razor sharp. Dropped right through tomatoes and bell peppers with the weight of the blade and the slightest pinch grip push cut. That's how sharp I want my Kohetsu to be

I''ll be ordering the Kohetsu 800 and 2000 grit with the 4 pc stropping set. Im thinking I'll use the Kohetsu 800 using the scrubbing technique and ending with edge trailing strokes, same for the 2000, I'll do edge trailing strokes only on the Naniwa 5000, strop with the 1 micron paste on balsa, and strop on bovine leather to finish.

[Bensbites]

I am pretty sure there is a set of Kohestu stones in the classifieds.

[Chefcallari]

So.... Yea.... Welcome to the forum!

So everyone here is well aware of my love affair with my Kohetsu HAP40 240mm gyuto.
I am a pro as well but i do use my kohetsu at work........ A lot.

Now i have choseras, Kohetsu, and shapton glass stones. All will cut that steel. However.... Dun dun dun!
Ive been doing alot of experimentation. I sharpen steels and test them for fun...(i know.. It's weird)

I would recommend adding a diamond stone to your line up.
Preferably in a low grit
The whole "carbide tear out" argument got me going about 6 months ago and ive been chasing it.
While not having the feed back and fun of water stones.. Diamond cuts Every thing.... Period lol
Ive noticed the last 2 sharpenings ive done with diamond on my HAP40 edge has lasted significantly longer (yea i know right)

My theory is that the diamond cuts the vanadium, tungsten and molybdenum carbides deeper and more evenly leaving a coarser, more even edge.
Then, when the edge breaks down it basically "micro micro chips" instead of just blunting...keeping the cutting aggression high and an edge that cuts forever(it seems that way)

Just my 2 cents.
Ive sharpened my kohetsu alot of ways over the last year and a DMT extra coarse/Kohetsu 2k/ 1 micron diamond paste on wood (checking often until the edge gets where i want it) has given me an.edge that is polished enough to.drop through an onion but with enough bite to ghost tomatoes.
And most importantly it STAYS that way for basically forever! I can slice paper 2 weeks later after banging it against polly boards for 14 hours a day.

[Radar53]

+1 to Chefcallari on the use of diamonds on HAP40. I'm just a home cook so I don't put my HAP40 gyuto 210 through anything like the same rigors as he does every day.

Forumites seem to be split on the carbides thing and I am open minded on the issue, but have chosen to err on the conservative side thus using diamonds. I use 3M diamond tapes and sharpen this knife on my EdgePro for absolutely precise edges. I've said it in previous posts that I think it would be great to sharpen two identical HAP40 knives one using diamonds and the other using say Shapton Glass and then look at the resulting edges under a scanning electron microscope. Being an engineer I tend to be evidence based and with carbides that you can't see, something like SEM will give a definitive answer. Anyone able to help out here with one of sharpening's greatest mysteries (certainly to me)

Anyways, in sharpening my knife, I went through the following 3M progression of 1500, 2500, 5k & 10k grits taking great care, grinding precise bevels with a main bevel at a true 8º & a micro bevel of a true 10º and man it is crazy sharp. Drops through fruit & veges like they're just not there & being a home cook, I haven't noticed any deterioration in the edge.

[metamorpheus]

So.... Yea.... Welcome to the forum!

So everyone here is well aware of my love affair with my Kohetsu HAP40 240mm gyuto.
I am a pro as well but i do use my kohetsu at work........ A lot.

Now i have choseras, Kohetsu, and shapton glass stones. All will cut that steel. However.... Dun dun dun!
Ive been doing alot of experimentation. I sharpen steels and test them for fun...(i know.. It's weird)

I would recommend adding a diamond stone to your line up.
Preferably in a low grit
The whole "carbide tear out" argument got me going about 6 months ago and ive been chasing it.
While not having the feed back and fun of water stones.. Diamond cuts Every thing.... Period lol
Ive noticed the last 2 sharpenings ive done with diamond on my HAP40 edge has lasted significantly longer (yea i know right)

My theory is that the diamond cuts the vanadium, tungsten and molybdenum carbides deeper and more evenly leaving a coarser, more even edge.
Then, when the edge breaks down it basically "micro micro chips" instead of just blunting...keeping the cutting aggression high and an edge that cuts forever(it seems that way)

Just my 2 cents.
Ive sharpened my kohetsu alot of ways over the last year and a DMT extra coarse/Kohetsu 2k/ 1 micron diamond paste on wood (checking often until the edge gets where i want it) has given me an.edge that is polished enough to.drop through an onion but with enough bite to ghost tomatoes.
And most importantly it STAYS that way for basically forever! I can slice paper 2 weeks later after banging it against polly boards for 14 hours a day.

Well timed reply! I wanted to order tonight and before seeing this I was wondering if getting both kohetsu stones was really necessary. Was considering doing 800 to 5k instead, but I'll take your advice on the DMT extra. I'll be getting the DMT extra, the Kohetsu 2000, and the 3x8 stropping set. Excited to sharpen my first J knife. Between getting sharpening supplies piece wise and using cheap western knives to learn with, there have been some frustrating moments. It did give me a taste for how good things could be though. Part of my practice was on a gouged out rotating tri oil stone at work that doesn't lock. Only the coarsest stone doesn't start turning on me with the slightest lateral pressure. I was taking it to the smallest counter, wedging a glove box against the wall and one of the turning knobs, and pressing the other knob against my abdomen to keep it steady..ish . They said we couldn't bring our own knives, but never said anything about stones so I just started bringing my own stones and hiding the knife I sharpen with a blade guard I bought.
I've caught the edge chasing bug too, so I don't think sharpening & testing steels for fun is weird. It's can be a zen experience and almost puts me in a trance- like only me, my stone, and my knife exist for a while. Prep is so much more fun with a sharp knife too.

[metamorpheus]

+1 to Chefcallari on the use of diamonds on HAP40. I'm just a home cook so I don't put my HAP40 gyuto 210 through anything like the same rigors as he does every day.

Forumites seem to be split on the carbides thing and I am open minded on the issue, but have chosen to err on the conservative side thus using diamonds. I use 3M diamond tapes and sharpen this knife on my EdgePro for absolutely precise edges. I've said it in previous posts that I think it would be great to sharpen two identical HAP40 knives one using diamonds and the other using say Shapton Glass and then look at the resulting edges under a scanning electron microscope. Being an engineer I tend to be evidence based and with carbides that you can't see, something like SEM will give a definitive answer. Anyone able to help out here with one of sharpening's greatest mysteries (certainly to me)

Anyways, in sharpening my knife, I went through the following 3M progression of 1500, 2500, 5k & 10k grits taking great care, grinding precise bevels with a main bevel at a true 8º & a micro bevel of a true 10º and man it is crazy sharp. Drops through fruit & veges like they're just not there & being a home cook, I haven't noticed any deterioration in the edge.

I was a science student myself, but liked organic chemistry a lot more than physics & math. I would also like to see this testing done. If it turned out that diamond wasn't necessary, oh well, it would still be useful for sharpening any cpm s35vn or cpm s90v folders I may want down the road.

[Chefcallari]

+1 to Chefcallari on the use of diamonds on HAP40. I'm just a home cook so I don't put my HAP40 gyuto 210 through anything like the same rigors as he does every day.

Forumites seem to be split on the carbides thing and I am open minded on the issue, but have chosen to err on the conservative side thus using diamonds. I use 3M diamond tapes and sharpen this knife on my EdgePro for absolutely precise edges. I've said it in previous posts that I think it would be great to sharpen two identical HAP40 knives one using diamonds and the other using say Shapton Glass and then look at the resulting edges under a scanning electron microscope. Being an engineer I tend to be evidence based and with carbides that you can't see, something like SEM will give a definitive answer. Anyone able to help out here with one of sharpening's greatest mysteries (certainly to me)

Anyways, in sharpening my knife, I went through the following 3M progression of 1500, 2500, 5k & 10k grits taking great care, grinding precise bevels with a main bevel at a true 8º & a micro bevel of a true 10º and man it is crazy sharp. Drops through fruit & veges like they're just not there & being a home cook, I haven't noticed any deterioration in the edge.

I was a science student myself, but liked organic chemistry a lot more than physics & math. I would also like to see this testing done. If it turned out that diamond wasn't necessary, oh well, it would still be useful for sharpening any cpm s35vn or cpm s90v folders I may want down the road.

So... Yea.... My sharpening addiction has taken me into the world of folders too lol
Dont get me wrong... I use my folders at work a dozen times a day.... But i have no NEED to own 13 of them lol

S35vn, s90v those high carbide steels NEED diamonds... Not just for the carbide cutting... Just shear time!
While i dont own s90v or s35vn... I do own s30v and s110v.... And shapton glass and even choseras struggle a little... S110v makes my chosera 400 feel like a 8k stone! Fucking glass!

And just grabbed some Maxamet! Now that is a steel that needs diamonds!
Edge retention is just absurd though!

[Chefcallari]

So.... Yea.... Welcome to the forum!

So everyone here is well aware of my love affair with my Kohetsu HAP40 240mm gyuto.
I am a pro as well but i do use my kohetsu at work........ A lot.

Now i have choseras, Kohetsu, and shapton glass stones. All will cut that steel. However.... Dun dun dun!
Ive been doing alot of experimentation. I sharpen steels and test them for fun...(i know.. It's weird)

I would recommend adding a diamond stone to your line up.
Preferably in a low grit
The whole "carbide tear out" argument got me going about 6 months ago and ive been chasing it.
While not having the feed back and fun of water stones.. Diamond cuts Every thing.... Period lol
Ive noticed the last 2 sharpenings ive done with diamond on my HAP40 edge has lasted significantly longer (yea i know right)

My theory is that the diamond cuts the vanadium, tungsten and molybdenum carbides deeper and more evenly leaving a coarser, more even edge.
Then, when the edge breaks down it basically "micro micro chips" instead of just blunting...keeping the cutting aggression high and an edge that cuts forever(it seems that way)

Just my 2 cents.
Ive sharpened my kohetsu alot of ways over the last year and a DMT extra coarse/Kohetsu 2k/ 1 micron diamond paste on wood (checking often until the edge gets where i want it) has given me an.edge that is polished enough to.drop through an onion but with enough bite to ghost tomatoes.
And most importantly it STAYS that way for basically forever! I can slice paper 2 weeks later after banging it against polly boards for 14 hours a day.

Well timed reply! I wanted to order tonight and before seeing this I was wondering if getting both kohetsu stones was really necessary. Was considering doing 800 to 5k instead, but I'll take your advice on the DMT extra. I'll be getting the DMT extra, the Kohetsu 2000, and the 3x8 stropping set. Excited to sharpen my first J knife. Between getting sharpening supplies piece wise and using cheap western knives to learn with, there have been some frustrating moments. It did give me a taste for how good things could be though. Part of my practice was on a gouged out rotating tri oil stone at work that doesn't lock. Only the coarsest stone doesn't start turning on me with the slightest lateral pressure. I was taking it to the smallest counter, wedging a glove box against the wall and one of the turning knobs, and pressing the other knob against my abdomen to keep it steady..ish . They said we couldn't bring our own knives, but never said anything about stones so I just started bringing my own stones and hiding the knife I sharpen with a blade guard I bought.
I've caught the edge chasing bug too, so I don't think sharpening & testing steels for fun is weird. It's can be a zen experience and almost puts me in a trance- like only me, my stone, and my knife exist for a while. Prep is so much more fun with a sharp knife too.

Glad i was on time! Lol

In the future try other stones as well. Just for your own knowledge.

For shits i tried a Belgian blue natrual stone i grabbed on a trade on my HAP40...... Horrible horrible edge.
Took me 30 min to just get a burr lol then i couldnt get it off on the stone lol
I went to work and after like a dozen onions the edge was shot... Looked at the edge under light..
Chop city lol... It was the burr... Just mangled lol


Have fun trying different finishes

[matchplay18]

I just wanted to weigh in. I like what Chefcallari has to say. I have been using Hap-40 for awhile. And for sure you will want to keep it sharp. I have used all types of stones on the Hap-40 some are very time consuming. I decided to try the diamond stones. Wow it made short work of the Hap-40. Something I have experienced, most likely your knife is sharp just needs a touch up. Stay around 1200 or 2200 to start you will be surprised how fast it will cut. If you start around 300 or 600 you will have to do a lot of stropping to get the grind out of the edge. Once mine is sharp a little maintenance from time to time on a Shapton Pro glass 16000 works great. Also most diamond plates go up to 2200. Give this a try on the powered steel Eversharp Diamond plates lifetime warranty go from 300 600 1200 2200 4000 8000 3x8 plates . I have the 300 600 900 1200 2200 4000 8000 I was told they are useless after 2200 but on some of these super steels I find they work great.

[lsboogy]

I have the thick shapton stones (I think they call them "Pro") - and I have two HAP40 Kohetsus (210 and 270) - a well soaked stone will sharpen the knives really well - I usually stop at 8K, but I have run the big one at 16K - the steel takes an edge that will drop through food and holds it. Take your time and use some good stones - I only sharpen my main knife (the 210) once a year, but strop it every few weeks on balsa with some 0.5 micron paste. Holds an edge as long as any steel I have used, and will take an edge on par with white #1

[metamorpheus]

Thank you for the advice Chefcallari! That DMT XXC was a bitch to work with the first time around. There was no using light pressure or the blade wouldn't move. Had to trail stroke first. On my first go at it I think I rounded my edge stropping on the 2k Kohetsu. Still dont have the singular fluid strop motion down quite right.  Cut some onions and Dikon yesterday and wasn't happy.

I started over with some lighter pressure applied mostly on the trailing stroke with the DMT XXC, very briefly took it to the 1k side of the combo, spent some time with the Kohetsu 2k, used the Naniwa SS 5k, ran it through the felt block, stropped it on balsa with the 1 micron paste section wise, and then stropped it on bovine leather....

This knife is a monster now. Highly polished edge, but the deep diamond scratch pattern going up the bevel makes it like a micro serrated blade. It quietly creeps through veg with crisp clean edges on the cut. I cut mostly raw beef shank and it made this sound like a tiny zipper. Could feel the teeth biting through that beef like a shark attack as I pushed through. Very clean edges on the beef too, no visible tearing.

 I'm blown away by how how well this thing cuts now and how it behaved with veggies vs meat. It's quiet and graceful with veg, but loud and agressive for meat. I've never used a knife this sharp or had one that seemed so versatile. There's a local artist in Seattle, that goes by the name of Dozfy, and he's been making custom octopus sayas. I want to get a shark saya from him now.

[lsboogy]

Try using just good whetstones to sharpen it with next time - my hap40 knives are shiny under a microscope, and still look great in the SEM at work. An 8K edge on these knives is great - goes through fish and lamb like butter, and still has enough bite for tomatoes and peppers (skinned veg). But I'm guessing you will only strop the thing for the rest of the year - all that's required with mine and I use it on a daily basis

[Chefcallari]

Thank you for the advice Chefcallari! That DMT XXC was a bitch to work with the first time around. There was no using light pressure or the blade wouldn't move. Had to trail stroke first. On my first go at it I think I rounded my edge stropping on the 2k Kohetsu. Still dont have the singular fluid strop motion down quite right.  Cut some onions and Dikon yesterday and wasn't happy.

I started over with some lighter pressure applied mostly on the trailing stroke with the DMT XXC, very briefly took it to the 1k side of the combo, spent some time with the Kohetsu 2k, used the Naniwa SS 5k, ran it through the felt block, stropped it on balsa with the 1 micron paste section wise, and then stropped it on bovine leather....

This knife is a monster now. Highly polished edge, but the deep diamond scratch pattern going up the bevel makes it like a micro serrated blade. It quietly creeps through veg with crisp clean edges on the cut. I cut mostly raw beef shank and it made this sound like a tiny zipper. Could feel the teeth biting through that beef like a shark attack as I pushed through. Very clean edges on the beef too, no visible tearing.

 I'm blown away by how how well this thing cuts now and how it behaved with veggies vs meat. It's quiet and graceful with veg, but loud and agressive for meat. I've never used a knife this sharp or had one that seemed so versatile. There's a local artist in Seattle, that goes by the name of Dozfy, and he's been making custom octopus sayas. I want to get a shark saya from him now.

Hey!

Glad i could help.
Like i said, the DMT plates have a break in period and are SUPER rough when you first get them. I use mine as a flattening stone and that helped break them in.

What made me super happy was that you weren't happy with the first attempt.... But you went back at it and tried until you were satisfied!

Its half the fun for me!
And again like i said ... This combo works great for ME at work, but always try new stuff! As you can see by all the posts from other sharpeners... There's many ways!