How to improve the edge on my well used Kohetsu

[ChefKnivesToGo]

I purchased a Kohetsu Aogami Super back in 2017 and has been my workhorse since. I used to be able to sharpen on whetstones back to a razor, but recently I can’t seem to get anywhere with it.

I’ve attached a few photos. Have I lost the primary bevel? Is the knife at the end of useful life? Any tips to bring it back? Should I just send it in?

Thanks so much, I’ve bought pretty much all my knives from you over the years.

C.

[jmcnelly85]

I don’t think knives have a limited timeframe of utility; however, if it has been sharpened numerous times and are getting substandard results, there’s a good chance the thinness behind the edge has been sharpened up high enough into the grind. Thinning behind the bevel can improve performance; I should say the job can be a bigger one than it sounds like depending on what you are sharpening with.

One thing that l strikes me as odd is a thick edge still should be able to get sharp. Try focusing on your coarsest stone and see if some heavy lifting can establish a new bevel.

[Jeff B]

Just needs a good thinning to bring it back to life. Many more years left in that knife. I usually do a little thinning with each sharpening, only takes a couple minutes. That keeps the knife near peak performance and prolongs the need for a major thinning later if ever.

[Radar53]

Two great replies above. If you used to able to keep it sharp and now can't, something has changed. Presumably you're using the same techniques, stones etc. If it were me (and I lived in the USA), I think that I would send it back to Mark to be resurrected and then begin sharpening again, focussing on technique. If the new edge starts to degrade or you're having trouble keeping up with Mark's good work, then come back here & someone will be able to help you work through it. The trick is not to leave it too late, as it's easier to revive an edge (and technique) if you catch it early.

Best of luck

[stevem627]

All it needs to be back where you can sharpen it well is a good thinning.

Find someplace you are comfortable with and get it thinned and then…proceed as you did in the past.

[ChefKnivesToGo]

All good responses and I agree that the knife most likely needs thinning. It’s easy enough to do but takes some time. You need to use a coarse stone and make sure you’re angle is lower that the edge angle (I tend to do it around 5 degrees on each side). For my home knives I thin for a few minutes before I sharpen.

Good luck and let us know how it turns out.

[ex1580]

You are all wrong. The knife is toast and should be sent to me for proper disposal.

Seriously though, that was a lot of good responses really fast. When I read the first post I thought "it probably just needs a good full sharpening starting with some thinning" then I scrolled down and you all had it covered. Buch of seasoned pros here!

[Jeff B]

You can see how close the cladding has gotten to the edge of the knife. Thinning the knife behind the edge will move the cladding line back and expose more core steel and bring that knife back to excellent performance.

[Mowgface]

You can see how close the cladding has gotten to the edge of the knife. Thinning the knife behind the edge will move the cladding line back and expose more core steel and bring that knife back to excellent performance.

This.

I bought my AS used and plenty thickened up. The cladding looked similar to yours. Pictured below Heavily thinned. (then used for months)

Most of the work done on a 220, followed up by a 2K I think.

[taz575]

Yeah, a good thinning will get it working again! It's probably sharp edge wise, but doesn't feel sharp in use due to the extra thickness behind the edge.

I am lucky enough to have a variable speed belt sander, so thinning is a breeze!

I even thinned out my Magancut gyuto a bit more to see how far I can push it after getting a nicer handle installed

mcc handle.jpg (26.48 KiB) Viewed 387 times

[Kerneldrop]

...I even thinned out my Magancut gyuto a bit more to see how far I can push it after getting a nicer handle installed

Dang, that looks great!
Do you thin on the contact wheel, platen, or in a slack area?
Can you thin with a bench grinder, or is that too much convex? I guess that would be sorta S-grind like?

[taz575]

I use a soft platen face of leather or felt to thin and convex. Others use the slack portion of the belt, usually just before or after a wheel where there is the most tension on the belt.

A bench grinder would be hard to thin with even if the stone was just trued and the blade would be more likely to bounce. A contact wheel would give a hollow grind, but not like the original hollow grinds. If you go along the wheel, you can really ripple the blade road due to the small surface contact area.

[Kerneldrop]

I didn't think about the blade bouncing....you're right, there's no way to precisely control that.

[jmcnelly85]

Based off my limited bench grinder experience with axes and mauls, I wouldn’t want to put a nice thin edge near it, too much can happen too fast

[Kerneldrop]

Based off my limited bench grinder experience with axes and mauls, I wouldn’t want to put a nice thin edge near it, too much can happen too fast

3500 rpm get a kicking don't they.
I have some MDF wheels on my bench grinder that I sharpen pocket knives and cheaper kitchen knives on... it takes 1 minute to sharpen and 1 minute to mess up. Sometimes I'll miss judge the angle and get a bounce. I only do edge trailing on the grinder.

[taz575]

I slow my 2x72 way down when thinning, especially when I get to finer belts. The soft cladding also tends to grab more on the belts vs the harder steel, so I gotta play with the speeds to find a speed it will grind the soft and hard steel well and not grab as much. When I start going up in grits and getting down to super thin, I reverse the belt direction and slow down and run the belts wetted with a sponge. This keeps the edge cool, the dust down and I can see what I am doing a lot better. You gotta be super careful thinning with powered equipment because you can mess up the blade or yourself VERY quickly!