My Santoku won't cut a tomato!

I have a Tanaka 7" (165) Santoku, blue steel #2, that I've owned for about 5 months. I keep it very sharp, and touched it up just the other day on a Naniwa 8000 stone. It slices easily through telephone book paper. In spite of this it has difficulty cutting through tomato skin. I've been growing tomatoes this summer and they have much thicker skins than a typical store-bought tomato, but still, they're tomatoes. For comparison I've tried my Togiharu 240 gyuto and my Shun 210 gyuto, and they both work fine. I was thinking that maybe because the gyutos have a more curved edge that they put more pressure on the tomato during a forward slice, and thus cut more easily, but I also tried my very straight Zakuri sujihiki, which floated through the tomato with no difficulty. All of these knives have been sharpened by me and last touched up on the aforementioned 8000.
I am a novice, having only been sharpening for about 5 months, so it would not surprise me if I'm missing something. My question is, does the santoku just suck? Is it the wrong knife for the job? Could it possibly be too sharp, i.e. not enough friction on the edge to saw through the skin? I don't think it's too dull, but maybe? Is it too light? Is there something wrong with my cutting technique? All of the above?
Thanks in advance for your suggestions.
Chris

Probably too sharp. Try a few stropping type strokes on a 4000 or even 2000 and see if that helps.

Shun, Zakuri both sound a fair bit thicker at the edge than a Tanaka, but I could be wrong.

Do you have lower grit stones? I am assuming you do, so it may be wise to drop down to 4k and establish a clean flat edge with minimal pressure (thinner the edge, lighter the pressure), do a deburring, clean the edge with a few strokes on 4k, then test on tomato before returning to 8k. Go as light as possible on the 8...if you see swarf, it's cutting and you needn't bear down more. Don't spend much time on 8k if the bevel is thin and focus more on edge-leading than edge trailing.

No need take a Santoku to 8K it can make the edge slippery on tomato skin. Diced cases of tomato's for Lomi Salmon thin carbon gyuto 1K toothy edge works well.

Considering the stone you are using, your edge is too smooth. Either use a lower grit stone for a more aggressive edge, or a stone that leaves an edge with more bite.

i dont think the 8k is quite yet in a range of skidding over the edge... i'm gonna say its some kind of technique issue, but its hard to asses without a picture of the knife (especially a closeup of the edge) and/or a video of you sharpening said knives.

the tanaka is much thinner than your other knives, you are rolling the edge over.

Thanks guys for your input. I will try stropping with my 3k and if that doesn't help I will perhaps send a video to John of my sharpening/cutting.
I'll post a follow up!

I would give it a good sharpening on a relatively coarse stone, starting far behind the edge, and use finer stones only for light stropping and deburring. Think sharpening at 400, strop and deburr at 800 and 3000, deburr only at 8k.

Could be too low of a micro bevel or the bevel could be rounded. I think Benuser's suggestion to start back at 400 is a good one.

I find I need to revisit rough stones on knives that will dull quickly because the bevel may be too rounded. The temptation with fine stones is to cheat by raising the bevel…this works initially but eventually causes a 'sharp' edge that won't cut.

I think my problem was a rounded edge, as several of you pointed out. I was probably applying too much pressure, especially on my edge following strokes. I've since worked the knife on my 1k and my 3k stones, applying very light pressure, but slightly more on the edge forward strokes, I then did a few passes on the 8k using almost no pressure. Now it slices easily through my thick-skinned tomatoes.
Thanks again KKF, you guys were really helpful!

Pressure is only helpful at a very low angle with a coarse stone, if you want to reach the very edge. Otherwise you better keep a light touch.

JBroida said:

i dont think the 8k is quite yet in a range of skidding over the edge... i'm gonna say its some kind of technique issue, but its hard to asses without a picture of the knife (especially a closeup of the edge) and/or a video of you sharpening said knives.

Click to expand...

Not that Jon needs a cosign, nor am I in a position to really give him one, but I'll note my experiences here...

I used to find my 4/5k stone was "too sharp" a finish for cutting tomatos when I started out sharpening, but as I have become better and better I find slippage basically a non issue.

I've found the concept of "too sharp" to be a bit puzzling, but given my limited skill it's not a problem I will likely have anytime soon.

I can draw cut a tomato with a blade finished with a Nakayama asagi….so I agree that 'too sharp' is not an accurate description of why the blade is not cutting.

If you revisit your edges with finish stones a lot you will have a tendency to raise the edge to get a burr and at some point the angle is simply too steep to make an easy cut.

If it is thin enough behind the edge this shouldn't be a problem. My soft vintage carbons cut like crazy despite of the large inclusive angle or fat microbevel

I also found this to be true "too sharp" not to good for thick skinned vegetables. I take it that is why we don't have disposable razor blades that we use in our kitchen. Sure cuts paper good. Easiest way to detect a bur i found is to fell the edge of the blade with your three middle fingers and reflection of light against the edge of the blade. And use a loupe until you get an idea of what a mico burr feels like with and without a burr. Once you know what it feels like its hard to forget.

I use my nails and verify with the finest cigarette paper

Benuser said:

If it is thin enough behind the edge this shouldn't be a problem. My soft vintage carbons cut like crazy despite of the large inclusive angle or fat microbevel

Click to expand...

Another possibility is that the burr was not completely removed.

Can someone please explain too sharp? This is a topic we discuss on razor sharpening a lot on FB and other forums and the consensus is that it isn't a 'thing'.

I also finish my knives, for fun, to stupid sharpness with japanese naturals and have never experienced a nicely done edge even from my hardest and finest stones that won't cut a tomato.

I do not quite understand the use of the term either but my guess is that it refers to a slippery edge?

It should be taken as too sharp for the task at hand. To paraphrase Dave Martell's example, you don't sharpen then hone a pocketknife like a razor and expect to cut through a seatbelt. The edge is inappropriate to the use.

I think a fresh edge that is as sharp and keen as possible will always cut well once.

It's described as "running" - I think I saw the explanation in one of Jon's posts. When the blade is so sharp it does not have a bite. It will "run" across the face of a tomato or other product rather than cutting into them.

Don't know if there is a similar phenomena applicable to razors.

daveb said:

It's described as "running" - I think I saw the explanation in one of Jon's posts. When the blade is so sharp it does not have a bite. It will "run" across the face of a tomato or other product rather than cutting into them.

Don't know if there is a similar phenomena applicable to razors.

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Dave, thanks for the comment. It's hard to say with razors as we never cut stuff other than hair with them. One of the hard hitters on the forum, a gentleman with years of experience and an incredibly talented straight razor restorer actually uses cherry tomatoes to test his bevel at the 1k level. He's the only one I know of that cuts food with them :cookoo:

I'm going to do some testing when I get home from deployment and do some different natural stone finishes just for the purpose of trying to experience this phenomenon.

Eamon Burke did a video (I can' seem to find it right now) that explained a running edge perfectly.

Here you go
[video=youtube;lqsbO1w8rXE]https://www.youtube.com/watch?v=lqsbO1w8rXE&ab_channel=burkecutlery[/video]

cclin said:

Here you go

Click to expand...

Exactly, thanks Charles!

It seems that stropping with diamond spray on a substrate like balsa can help add some tooth to a polished edge. Jon's natural awasedo also does a nice job of combining a polished yet toothy edge and I think his latest "artificial natural" stone which I haven't tried yet will probably work similarly

Don't stay too long with the finer stones and you won't have to re-establish some bite, or am I simplistic?