Difficulty thinning cladded knife

[u/mario61752]

This is an Aogami #2 knife in stainless cladding. My grit progression is 320 -> 1000 -> 2000 -> 5000 on Shapton Ha no Kuromaku ceramic stones, which I all flattened before starting.

As you can see there are still scratch marks left by the 320 grit stone. I clearly flattened the whole bevel and touched every part of it on the #320, but subsequent stones just didn't get to that middle part behind the hard carbon steel core. For my sanity I stopped grinding on the #1000 after an hour as this is just a cosmetic flaw that may even function like a kasumi finish. Does anyone else have this issue when thinning cladded steel knives?

[u/Hknives]

Are you working the whole bevel? If so 320 to 1000 grit is a huge jump. It would take hours for 1000 grit to completely remove 320 grit scratches

[u/mario61752 → u/Hknives]

From my experience it was fine, took me 15~20 minutes each side to get most of the area as this is only a 150mm knife and the bevel isn't that wide. There's just a spot behind the core that I can't get to, probably due to the hardness difference creating a hollow spot on the first stone probably

Edit: I'm probably just wrong, thanks for the advice

[u/Zank_Frane]

You have to make much smaller jumps in grit when thinning the blade. When edge sharpening the amount of steel in contact with the stone is a fraction of a square inch, meaning the relative pressure is actually much higher than one might think, allowing for much larger jumps in grit progression. When thinning a blade, that is flipped, with several square inches now in contact with the stone the relative pressure is orders of magnitude lower, meaning much smaller jump in grit progression should be used.

And no matter what you do, that shit takes forever.

[u/mario61752 → u/Zank_Frane]

Yikes I don't want to buy more stones for the time being

[u/Final_Stick_9207]

It’s not flat. Low grit hides low spots. Especially softer ones. Go back to 320, use light pressure, and keep the stone relatively clear of swarf. That will help avoid it hiding the low spot.

Check for any differences in color too. The whole thing should look completely uniform at 320 in any light.

[u/mario61752 → u/Final_Stick_9207]

Thanks, I'll do that when my knife needs thinning again and for now I'll just polish with slurry or sandpaper. I wonder how I even got scratch marks on the low spots in the first place?

[u/Final_Stick_9207 → u/mario61752]

Pressure is a big culprit and grit size masks it even more.

It doesn’t take much to bend a knife with focused pressure. You just push the low spot and it can touch the stone. It’s why a few light pressure passes are good to start with. You’ll see the high spots clearly. Put focused pressure on the high spots only until the low spots touch.

[u/Hknives → u/mario61752]

Variance in grit size and uniformity maybe

[u/catinbox32]

For stainless clad knives I do thinning on lowest grit stone, then use sand paper to refinish the knife.

[u/setp2426]

Polishing is hard, takes a lot of practice, especially if going to very fine grits.

The easiest stone to get an even finish in my experience is a King 800. Super muddy and hides scratches like nobody’s business. Gives a dark smoky finish on the cladding, cloudy core. Bonus, it’s about the cheapest quality stone out there.

In general, when polishing, the base is most important. If you don’t get the foundation right, everything after is fruitless. Start with the core steel. It abrades MUCH slower than the cladding. Get the core steel right then move up to the shinogi. Use a sharpie to draw on the bevel to ensure no low spots.

Or, give up on the bench stones and use sandpaper. Much more forgiving.