Knife blade thinning

Hi Guys,

It just occurred to me that even though I've been into knives for a long time I've never encountered a discussion of thinning the knife's blade before I got into kitchen knives. So is it the function of the geometry (convex) of kitchen knives, or is it that kitchen knives are used a lot more and so get sharpened much more? It seems that something like a "laser" would not have to be thinned as much or at all, especially if there was very little convex to the blade shape, food release would suffer, but that is a different topic. Do all geometries require thinning, how does S-grind or asymmetric compare to convex as far as thinning is concerned? Thanks.

All styles of kitchen knives will need thinning eventually IMHO. Field knives, pocket knives, etc
Are asked to perform different tasks that usually favor durability over cutting performance on soft materials.

You wouldn't thin a blade that was thin already all the way to the spine, since there would be very little to thin? Or would you still try to raise the sharpened/edge portion of the blade?

all geometry benefit from thinning, even a laser gets thicker toward the spine. Thinning a laser is simply blending the "shoulder" created by the primary edge

I'm no expert but I think that even "lasers" need thinning after a few sharpenings. It comes down to the difference between a thin blade and a blade which is thin behind the edge. I suspect that they'll be easier to thin (behind the edge) given that they are pretty thin (in the blade) to start with.

Thanks guys. That's what I was trying to figure out, so "blending" the shoulder is what needs to be done even on thin knives after some time.

Once again, I'm no expert but I think it depends on the knife. Easing the shoulders is probaly the simplest form of thinning and will realise some real improvements in cutting ability if a knife is too thick behind the edge. Probably reasonable to start with this and see how your knife performs.

Some knives have the thinning angle built in (I'm thinking wide bevel knives). Single bevel knives have thinning built in to the sharpening process.

It's worth looking at the JKI sharpening videos. Jon has a video or two on thinning.

Thanks. I am not ready to thin any knives just yet, my question was more theoretical. I've looked at many Jon's, excellent videos and will look for the thinning one. Thank you Nemo for answering my followup questions. I was thinking that thinning single bevel knives one would have to follow the bevel angle itself....

The way I see it, if you have any amount of taper from the spine to the primary bevel, then at some point, after X sharpenings, you should thin the knife above this primary bevel (assuming you want to keep the level of cutting performance).
Wide bevels and single bevels pretty much make it so restoring the geometry of the knife as the edge moves up incrementally closer to the spine is built into routine sharpening.
Some folks also thin along the entire blade face to have an overall slimmer knife, reduce wedging, etc.

Nemo said:

Once again, I'm no expert but I think it depends on the knife. Easing the shoulders is probaly the simplest form of thinning and will realise some real improvements in cutting ability if a knife is too thick behind the edge. Probably reasonable to start with this and see how your knife performs.

Some knives have the thinning angle built in (I'm thinking wide bevel knives). Single bevel knives have thinning built in to the sharpening process.

It's worth looking at the JKI sharpening videos. Jon has a video or two on thinning.

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Sorry I didn't explain it very well. Basically a laser is so thin that having the "built in thinning" of a wide bevel gyuto is almost impossible. And when you lay a laser down to thin the spine is incredibly close to touching the stone. So the thinning you should be doing from the start of your sharpening is basicly easing the shoulder since there is no guide as in a wide bevel or single bevel.

Oh so on wide bevel knives you sharpen the whole bevel every time, not creating a secondary bevel? Same as when sharpening puukkos? I don't have any wide bevel knives, so never thought of it.

Barmoley said:

Oh so on wide bevel knives you sharpen the whole bevel every time, not creating a secondary bevel? Same as when sharpening puukkos? I don't have any wide bevel knives, so never thought of it.

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There is a hair line primary bevel on wide bevel knives, and I would say yes it is good practice to thin every time you sharpen a knife, but it really depends on volume of use.

"All styles of kitchen knives will need thinning eventually IMHO"

I think something used eg mainly for rock-mincing stuff (especially stuff that is already small) can benefit from a thicker edge... and there are other cases where you might *want* some splitting action (otherwise there wouldn't be so much appreciation by some but not all people for Takeda-style grinds and edges )

LifeByA1000Cuts said:

"All styles of kitchen knives will need thinning eventually IMHO"

I think something used eg mainly for rock-mincing stuff (especially stuff that is already small) can benefit from a thicker edge... and there are other cases where you might *want* some splitting action (otherwise there wouldn't be so much appreciation by some but not all people for Takeda-style grinds and edges )

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The idea is that however thick the edge is, after repeated sharpening it's going to get even thicker. That's just how the geometry works. Unless you want your knife to get progressively thicker as it ages, you have to thin it occasionally. Thinning can either be about making a knife thinner or about keeping the same.

Well the thickening will more or less stop once the shoulders of your edge hit into an area where the blade face is near flat But that is indeed a cold chisel