Sharpening HAP40

[chris206]

I recently bought the Kohetsu HAP40 Santoku and I'm loving it. But I'm feeling pretty intimidated by sharpening it. I've never attempted to sharpen anything close to this hardness. Could I get some advice on what angle I'll want? Also I'd be open to getting some stone recommendations.
I'm a home cook and mostly use this for veggie prep, 4-5x per week.

[cliff]

The best stones for Hap40 are vitrified or resin-bonded diamond stones. I haven't tried the ones Mark has, but they look to be a very good deal: see here for the 1K: https://www.chefknivestogo.com/dmddist10.html.

See here for 6K: https://www.chefknivestogo.com/dmddist60.html

Among traditional stones, Shapton Glass are good for special steels like Hap40.

[XexoX]

I've no advice on stones, but I did want to welcome you to the forum Mr. 206. The people here are most helpful.

[aporigine]

My Kohetsu Hap40 sharpens slowly but well on my Shapton Pro 1000 and my Chosera 400 and 3000. I have not tried the Cerax 5000 on it, but that handled ZDP which ime is a tougher test of a stone.

Either knife (my ZDP is a petty) will wear a King 6000 without losing any detectable metal.

As for angle, my gyuto came with a 10-90 edge. I hold about 15° on the 90 side and maybe 2 on the flat side … I treat it almost like a single bevel. Low-pressure strokes, far fewer than on the beveled side, with the blade laid near flat. “Sharpen the bevel and gently debur the flat on a fine stone” quite like a classic single-bevel blade e.g. a yanagi.

Unless you’re a power user, you won’t need to go to the stones often. The steel touches up very nicely on a strop (moo plus one-micron CBN).

[ex1580]

I have a couple of HAP40 petty knives and they sharpen fine on most modern stones. You don't need anything special just for them. Think of all of your knives and what sort of stone you want to use (natural feeling, nice feedback, etc) and go from there. If you are not sure then get a few different 1k stones and see what you think of them. I've used Shapton Glass, Cerax, Arashiyama, Kohetsu stones that are no longer on the site, Morihei Hishiboshi, Atoma, and some random odd others on my HAP40 knives. I have not used the DMD Diamond stones that recently came to the site. My only comment is that I found a 1k to 4k progression to work very well. Strop it after that on a loaded strop and they will be sharp for a looooong time.

Mine came with a pretty low angle, about 10-11 degrees per side I would say, and I stayed with that. If the bevel is not a 50/50 grind then polish the bigger one a little extra, but don't worry too much about this.

[Radar53]

Hi there Chris and welcome to the forum.

I agree with some of the advice offered above ~ in summary I would try to just match current angles but if you're looking to explore then an angle around the 10 degrees would be a start point. Also, most well recommended stones should "cope" with the HAP40 @ approx 65 HRC. Having said that HAP40 at those specs is going to take more work than say A-EBL @ 61 - 62 HRC. If it's just touch-ups then, not knowing what stones you have, I would say give them a try first. If you have yet to buy stones then I would err towards Shapton Glass or similar high performance ceramics with a reasonable progression.

The other thing is that at 65HRC it should take a finer finish grit, say 8 to 10k. I use 8k on mine.

HTH

[ex1580]

I would just like to follow up on my previous comment. I have heard multiple professional sharpeners claim that you need to use diamonds on PM steels like HAP40. There may be a lot of different reasons for this but I think it just boils down to efficiency. When I use stones for example I make sure they are clean and roughed up a bit so they release a lot of abrasive material. I would bet that a lot of stones start to struggle with wear resistant steels pretty quickly because they just aren't releasing enough abrasive fast enough and if it's your job to sharpen knife after knife all day it's less of a hassle to use diamonds. For a home user like me the pleasure of sharpening is more of a factor than raw speed. I like a synthetic stone that feels like a natural stone and this is not diamonds.

I had a pile of carrots to cut today so I used that as an excuse to sharpen my Kohetsu HAP40 Petty. For the sake of argument I used just diamonds and it came out great. I used my Atoma 600 and 1200 followed by bench strops loaded with 3, 1, and 0.5 micron diamond compound (I am not sure if I like the roo or moo more, they are both great, but I definitely prefer sprays to pastes). It took about 15 minutes and when done was as hair popping as ever while still being nice and toothy, really grabbing stuff. I find that diamond plates are very useful tools to own. I do a lot of odd little repairs with them in addition to maintaining stones and sharpening things. Go easy on the strops though, too much pressure may over convex the edge and make it feel dull again. Just my experience.

As a side note, I use this knife about every other day and probably wont need to sharpen it for another 6 months now. HAP40 has ridiculous edge retention.

[Jeff B]

You don't need diamonds to sharpen Hap40. Any quality sharpening stones can handle the job you just have to expect to spend a few extra minutes getting it done. Diamond stones/plates might be the most efficient way but are not necessary.

[ValeryD]

You don't need diamonds to sharpen Hap40. Any quality sharpening stones can handle the job you just have to expect to spend a few extra minutes getting it done. Diamond stones/plates might be the most efficient way but are not necessary.

Jeff,


According to: http://knifegrinders.com.au/SET/Sharpen ... Knives.pdf
"Vanadium 3% (Elmax) - CBN/diamond abrasives show high advantage over aluminium oxide, the
edge stays sharp by 4 times longer. In saying so we are talking in relative terms, and positive effect
of the CBN/diamond as such is not that much different from its neighbours of 2% and 4% vanadium
(as seen by absolute sharpness scores) – it is the aluminium oxide worsened edge retention that
makes the numbers so high.
Vanadium 4% (CPM20CV or M390) - CBN/diamond abrasives have moderate advantage over
aluminium oxide, clearly noticeable both in the initial period and prolonged life of the edge.
Vanadium 9.8% (Vanadis 10) - CBN/diamond abrasives have moderate to high advantage over
aluminium oxide, the working edge lasts 1.5 times longer.
3% vanadium is the threshold content, where sharpening with CBN/diamond becomes preferred
over common abrasives.
The following hardness graph shows why the common abrasives like aluminium oxide may weaken
steel matrix around the vanadium and alike wear-resistant carbides"(C)


So, Sam (ex1580) is correct telling that pros recommend diamonds for HAP40 sharpening.
HAP40 consists a bit higher than 3% of vanadium - just like Elmax steel.

This also valid for other supersteels with high percentage of carbids in their compositions.

Interesting reading about carbides in steels and sharpening with diamonds and ceramic stones.
https://scienceofsharp.com/2022/01/20/c ... -part-1-3/
https://scienceofsharp.com/2022/11/17/c ... -part-2-3/
https://scienceofsharp.com/2022/12/15/c ... -part-3-3/

More here: https://scienceofsharp.com/home/



Valery

[ex1580]

It is worth noting that Knife Grinders, like all sharpeners, looks at sharpening through their own lens. They primary sharpen knives for meat packing plants and they get their work done on Tormek grinders. They are well known for their "Proprietary 7-Carcasses Edge" (which I am very curious about if anyone knows more about this). The BESS sharpness tester they use tests how much force it takes to break a fine wire which is probably pretty accurate for cutting meat. How does this (or does this even) apply to vegetable slicing and/or chopping? I don't know, but I think the structure of vegetables tends to be a bit different. Please go cut a pile of apples before you tell me that I'm wrong. In addition, I don't use Tormek grinders so I am not sure how their data translates to bench stones and strops. I like to file this sort of information as "interesting" which I may or may not find useful in the future.

Todd over at Science of Sharp says in regard to S110V that in order to get a keen edge care needs to be taken to minimize carbide damage near the apex which leads to premature failure. But he has not yet posted the best sharpening method. I bet there will be diamonds but it will have to include something unexpected like a diamond plate followed by a strip of cereal box taped to a board. How big are the carbides in my knives anyway?

In other news, Steve Bottorff said in his book Sharpening Made Easy that natural stones and honing rods belong in museums (pg 44). Ha! I guess they weren't easy enough? He does agree on the use of "manufactured abrasives or industrial diamonds" for modern steels (pg 30, same book). This really generally agrees with everything recommended here in terms of using a quality stone.

Meanwhile, John Juranitch says in his book The Razor Edge Book of Sharpening that diamonds are best used "as a girl's best friend" (pg 20). But it was published in 1985 so...

I will continue to sharpen my HAP40 on whatever stone is convenient. But of my natural stones the only natural stones I would use on HAP40 is BBW and Coticule (because garnets).

[aporigine]

It is worth noting that Knife Grinders, like all sharpeners, looks at sharpening through their own lens. They primary sharpen knives for meat packing plants and they get their work done on Tormek grinders. They are well known for their "Proprietary 7-Carcasses Edge" (which I am very curious about if anyone knows more about this). The BESS sharpness tester they use tests how much force it takes to break a fine wire which is probably pretty accurate for cutting meat. How does this (or does this even) apply to vegetable slicing and/or chopping? I don't know, but I think the structure of vegetables tends to be a bit different. Please go cut a pile of apples before you tell me that I'm wrong. In addition, I don't use Tormek grinders so I am not sure how their data translates to bench stones and strops. I like to file this sort of information as "interesting" which I may or may not find useful in the future.

Todd over at Science of Sharp says in regard to S110V that in order to get a keen edge care needs to be taken to minimize carbide damage near the apex which leads to premature failure. But he has not yet posted the best sharpening method. I bet there will be diamonds but it will have to include something unexpected like a diamond plate followed by a strip of cereal box taped to a board. How big are the carbides in my knives anyway?

In other news, Steve Bottorff said in his book Sharpening Made Easy that natural stones and honing rods belong in museums (pg 44). Ha! I guess they weren't easy enough? He does agree on the use of "manufactured abrasives or industrial diamonds" for modern steels (pg 30, same book). This really generally agrees with everything recommended here in terms of using a quality stone.

Meanwhile, John Juranitch says in his book The Razor Edge Book of Sharpening that diamonds are best used "as a girl's best friend" (pg 20). But it was published in 1985 so...

I will continue to sharpen my HAP40 on whatever stone is convenient. But of my natural stones the only natural stones I would use on HAP40 is BBW and Coticule (because garnets).

Perhaps this reveals something about my internet habits, but BBW brings associations unrelated to cutlery.

[Jeff B]

You don't need diamonds to sharpen Hap40. Any quality sharpening stones can handle the job you just have to expect to spend a few extra minutes getting it done. Diamond stones/plates might be the most efficient way but are not necessary.

Jeff,


According to: http://knifegrinders.com.au/SET/Sharpen ... Knives.pdf
"Vanadium 3% (Elmax) - CBN/diamond abrasives show high advantage over aluminium oxide, the
edge stays sharp by 4 times longer. In saying so we are talking in relative terms, and positive effect
of the CBN/diamond as such is not that much different from its neighbours of 2% and 4% vanadium
(as seen by absolute sharpness scores) – it is the aluminium oxide worsened edge retention that
makes the numbers so high.
Vanadium 4% (CPM20CV or M390) - CBN/diamond abrasives have moderate advantage over
aluminium oxide, clearly noticeable both in the initial period and prolonged life of the edge.
Vanadium 9.8% (Vanadis 10) - CBN/diamond abrasives have moderate to high advantage over
aluminium oxide, the working edge lasts 1.5 times longer.
3% vanadium is the threshold content, where sharpening with CBN/diamond becomes preferred
over common abrasives.
The following hardness graph shows why the common abrasives like aluminium oxide may weaken
steel matrix around the vanadium and alike wear-resistant carbides"(C)


So, Sam (ex1580) is correct telling that pros recommend diamonds for HAP40 sharpening.
HAP40 consists a bit higher than 3% of vanadium - just like Elmax steel.

This also valid for other supersteels with high percentage of carbids in their compositions.

Interesting reading about carbides in steels and sharpening with diamonds and ceramic stones.
https://scienceofsharp.com/2022/01/20/c ... -part-1-3/
https://scienceofsharp.com/2022/11/17/c ... -part-2-3/
https://scienceofsharp.com/2022/12/15/c ... -part-3-3/

More here: https://scienceofsharp.com/home/



Valery

Hi Valery,

Some interesting reads. All I can tell you about is real world home user experience. In that capacity, Hap40 is not bad to sharpen on any decent quality stone and edge retention is still beyond excellent. As mentioned, pro sharpeners have their recommendations for whatever reasons but Hap40 can be acceptably sharpened without diamond stones/plates.

[ex1580]

Perhaps this reveals something about my internet habits, but BBW brings associations unrelated to cutlery.

Belgian Blue Whetstone

[trancher]

Perhaps this reveals something about my internet habits, but BBW brings associations unrelated to cutlery.

Belgian Blue Whetstone

Things not to go punching into google in public.

[XexoX]

Perhaps this reveals something about my internet habits, but BBW brings associations unrelated to cutlery.

Belgian Blue Whetstone

Things not to go punching into google in public.

Bath & Body Works or Build-a-Bear Workshop? I'm missing something here.
Although when I kept bees, searching for queen bees had some interesting results. Luckily, the IT people at work already knew I was strange and had told me I wasn't even on their radar for my web activity. I guess having the head of communications being escorted out of the building by state police because of his porn searching habits on state owned computers, trumped what I was doing.

[aporigine]

Belgian Blue Whetstone

Things not to go punching into google in public.

Bath & Body Works or Build-a-Bear Workshop? I'm missing something here.
Although when I kept bees, searching for queen bees had some interesting results. Luckily, the IT people at work already knew I was strange and had told me I wasn't even on their radar for my web activity. I guess having the head of communications being escorted out of the building by state police because of his porn searching habits on state owned computers, trumped what I was doing.

Big Beautiful Woman, a term used on “dating” sites to denote a woman considered overweight.
I did find a Netwit who suggested it’s instruction to a potential suitor to Bring Burgers With.

[Robstreperous]

FWIW.... and I'm responding to a comment much earlier in the thread.. I recently acquired some of the DMD diamond stones (1000/3000) to sharpen a CPM 20CV knife I own. They did a pretty nice job on it and I went ahead and ordered the 6000.

I'd have to imagine if they can take on CPM 20CV they wouldn't have much problem at all with HAP 40.

[taz575]

As someone who makes knives in CPM 20CV, S90V, Elmax and other high end steels, I have some experience in this arena. I just got an order for another 5, 18" x 2" wide Shechita in CPM 20CV.

After I make the blade, I rough in the initial bevel with a 120 grit ceramic belt on my belt sander. I often jump to a 220 grit belt afterwards and then deburr to make sure I am hitting the apex of the edge. I use a wet belt and go very slow to keep the heat down to a minimum when doing this. This is a hardest part! Once the apex is formed, it's cleaning it up. I agree diamonds would be fastest to get this stage done if you don't have access to a belt sander and coarser belts. Even a cheap 1x30 can accomplish this task, and they can be had for around $60-$80. KO Worksharps can handle this as well. Something to think about! Use little pressure, fresh belts and let them do the work and you won't overheat your edge. My theory is that the ceramics cut the carbides, and the other stones do some refining to the bevel, which may help reduce the "carbide damage" of using slower abrasives on the carbides?

Trust me, it really sucks to go through all of the stones and realize that you don't even have an apex on the edge! It looks sharp, feels sharp, but isn't sharp. If you go really coarse and the burr comes off easily, look at your edge to make sure the burr breaking off didn't flatten the edge out on you! Rough side bare leather works great for deburring, as does cork or felt. It's helps catch and pull the burr off.

Once I have the apex formed and deburred, I go to a Shapton Glass 320, Bester 1200 and Rika 5K. Other than the SG320 replacing my Latte 400 as my coarse stone, this has been my setup for 10+ years. I have sharpened a ton of steels and knives with this setup. Knives coming off of these stones are usually sticky sharp feeling on the edge if I strop on bare leather after the Rika 5K. I can typically slice paper towels horizontally with this edge. After the Rika 5K, I use my 14 micron and 3 Micron diamond compounds on leather strops and occasionally my 1 micron diamond spray on balsa strop. This refines the edge further and gives a slight convex to the apex while deburring and gives it more polish, but loses most of the tooth, which helps give that sticky sharp edge feeling.

I use the diamond strops to maintain for a while before going back to the stones. I can refresh an edge a few times with the strop before going back to the stones.

One of the big issues with wear resistant steel is muscle control and holding the angle. If you are using a slow stone, you are much more likely to be rolling the edge a lot and not keeping a consistent angle. This leads to a duller edge and taking longer. If you have good muscle control and can keep a consistent bevel, good stones work fine on these steels, but will amplify any flaws in your sharpening technique. Again, diamonds work better because they cut faster, so results are seen faster with less chance for muscle fatigue setting in to mess up/roll your edge. As you get to finer grits, again, the diamonds work faster with less chance for human error to kick in. It's easier to stay consistent for 10-15 strokes than for say 100 strokes!

So for routine sharpening, diamonds can help reduce the human error factor and cut quicker, but other stones do work on the steel, just slower.

Diamond strops are nice for finer grits and I am going to play with some coarser diamond compounds on strops as well soon! When I strop, I bring the edge angle to where the apex meets the leather and then drop the spine down closer to the leather a hair to make up for the give in the leather. Seems to help me clean up the edge itself, polish the actual bevel, but not roll over the edge too much and still keep a nice crispy edge. It's easy to over do it when stropping!

For thinning and chip repair, diamonds or a variable speed belt sander are your friend!


This article has pictures of various steels and their carbide size. Chromium carbides are much easier to sharpen than Vanadium carbides, too! Many carbides are in the 2-5 micron range if they are nice and fine. They can get much larger, but the higher end steels try to reduce carbide size as much as possible. Carbide tear out is another issue if they are larger and pop/rip out of the steel matrix, leaving jagged edges. Larger carbides mean that the edge generally won't be as fine and the steel in general is weaker, too.
https://knifesteelnerds.com/2019/05/26/ ... fe-steels/

[ex1580]

Excellent! Now I just need to find a spot to put a belt sander.

Other than the SG320 replacing my Latte 400 as my coarse stone, this has been my setup for 10+ years.

What caused you to switch from the Latte 400 to the SG320? I have both and they are both great. For me it comes down to time. If the Latte is soaked and ready I prefer it, but it takes a while to soak.

[taz575]

18" long S90v blades changes my mind! It stays flatter and is a bit faster. Latte 400 is still in my permasoak bucket and gets used occasionally on some steels, like more simple stuff.