Sharpening HAP40

[ex1580]

18" long S90v blades changes my mind!

That'll do it! Clear your schedule and grab some snickers bars, that's going to take a while, haha.

When I have a knife to sharpen that is a more simple steel I often look into the bin of stones I don't normally use for something fun.

[taz575]

Yeah, grinding them was bad, too. One 5" x 2" wide s90v Shechita in 1/8" stock was about 5-6 hours of grinding after heat treat. I bought more s90v and did 80% of the grinding pre HT for the 18" ones I did and it still took like 8 hours to grind 2 of the 18" ones!

[atang]

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?

Disclaimer: I wrote this before reading the science of sharp articles. I have since read them and has slightly changed my perspective of edge retention with the vanadium steels. Although the more narrow subject of simply ‘can it sharpen’ has remained the same. As I feel my observations somewhat mirror what the articles have shown. Thank you so much for posting those Valery!!

I would agree with this as the 2 most important points are addressed here. Minimizing carbide damage near the apex & asking how big are these carbides? I don’t own any AO stones as they are inferior to the other types mentioned in this thread. Diamond vs AO is obvious which one is better. But will ceramic still get the job done?

I will establish a bevel with the Atoma 140 followed by the Atoma 1200. The Latte 400 handles HAP 40 with ease and have had acceptable results finishing on ceramic stones at 2k - 4k.
Diamonds are fantastic. I would expect a Tormek with a diamond wheel produce very exceptional results. What about the standard wheel? Would the carbide still fall out even on a tormek?

If there’s nothing wrong with the heat treatment the HAP 40 it should sharpen without issue. If you need to take the kitchen knife to 8k or higher, look to strops loaded with diamond compound. If say, a 3k edge would suffice, I am willing to bet diamonds are not entirely necessary to create an edge able to capitalize on the characteristics of HAP 40. A “perfect” edge? No. Will there be an unacceptable loss of carbide due to fall out? I don’t think so.

When sharpening by hand, is the angle being held more or less consistent than the metal matrix and/or the micron size of the stone being used? I would assume hand sharpening is the less consistent factor. IME HAP 40 with a very precise edge on ceramic will go farther than a mediocre edge off diamonds.

This is of course we are to presume the OP is hand sharpening and not using a tormek. Great thread! Thank you

[taz575]

One thing to remember is Science of Sharp is geared towards razors and shaving. These edges are often much thinner bte than our kitchen knives and the razors wouldnt survive what we put kitchen knives through. Carbide fall out is more of a concern with less material at the edge and will cause a rougher shave. Food will not notice it and the kitchen knife edges are thicker and can support the carbides more. They have excellent info on sharpening, but just remember kitchen knives are different than straight razors!

[FisherMAn1298]

I sharpen my HAP40 blades on either Naniwa diamond stones or SG, Nubatama and Morihei Hishiboshi 9k, which has natural stone powder added to it, giving you an extra toothy bite along with a great polish. This is some very interesting reading but I generally just fall in line behind taz575, even buying a used belt sander from him ! You the man TAZ!! Let's also not forget the late,great Ken Schwartz who taught me so much!!

[FisherMAn1298]

I have the Morihei 9k with natural stone powder added and I love it!! Gives a great polish as well as an added bite to your edge. You will love it! The 4k isn't bad either.

[ex1580]

I have the Morihei 9k with natural stone powder added and I love it!! Gives a great polish as well as an added bite to your edge. You will love it! The 4k isn't bad either.

I second that. I have the 1k as well but don't see a ton of difference between it and an Arashiyama except the price (stick with the Arashiyama). The 4k and 9k are real stand out stones though that I love to use.

[FisherMAn1298]

I also have the 1k Sam, I like to stay with the same kind of stone through the lower grit progressions.

[ared715]

Great advice wow. I would add my personal experience to the mix for what it worth......

I owned a kohetsu hap40 for years and I made a few mistakes at first.....

1. I was finishing at 8k or a fine jnat at the edge felt washed out..... didn't get the type of edge retention necessary for the steel characteristics.

2. The burr is a bit more tenacious than other steels so the removing of it is a process. I had to learn to do more stropping type, edge trailing strokes after sharpening on my 4k-6kish finisher/natural and really work the burr until it was removed as much as possible.....

Only after I learned these things the hard way (as usual) did I get the results that justified using the hap40 and what's its meant to do.

Just some personal experience, take it for what it's worth.....

Good luck!