ceramic knives with the S G

[Ken S]

This surprised me. Thoughts?

https://youtu.be/u1mMoXjHWcQ?si=gAGpWFrQJulJnGBt

Ken

[John Hancock Sr]

Baz is great. Love his vids. He is across town from me.

This surprises me as well. Nice to know though. Thinking about it, it will depend on the ceramic and its hardness. No doubt like steel, they will vary in hardness depending on composition.

[tgbto]

A little info about the knife would help.

The edge looks kinda shiny which is odd for a ceramic blade, but I lack details and might be completely mistaken.

Also, my experience with those hard blades is that they will chip on a very tiny scale instead of being sharpened. So it might be that tiny shocks against the SG might somehow grind the edge, but again, that edge looks very refined to me. I am yet so see that kind of polishing even on a stock ceramic knife.

On the other hand, I have a supposedly "tungsten carbide" knife, that I can sharpen on the SG because it actually consists in microscopic tungsten carbides embedded in a soft matrix. The matrix gets abraded, not the carbides. Maybe some ceramic knives are made in a similar fashion.

[cbwx34]

This surprised me. Thoughts?

https://youtu.be/u1mMoXjHWcQ?si=gAGpWFrQJulJnGBt

Ken

I'll give it a little credibility...

I have a cheap KitchenAid ceramic knife, so I gave it a shot.  I graded the stone fine, wiped out the trough, then put in some fresh water.  After a dozen or so passes per side, I checked the water...

You cannot view this attachment.

... and there was a little improvement in sharpness, although nothing spectacular.  (The only way I've seen a real improvement in sharpness on a similar knife was with a diamond belt on a Worksharp.) Thinking about it, I probably should try a bit of honing... even though a burr isn't created, it might help refine the edge.

As mentioned above, I'm sure quality plays a part.

[tgbto]

The particles seem quite coarse. So it looks more like the edge is somehow getting microchipped away. It would be interesting if you could somehow get a microscope shot of the edge and the particles.

[cbwx34]

The particles seem quite coarse. So it looks more like the edge is somehow getting microchipped away. It would be interesting if you could somehow get a microscope shot of the edge and the particles.

Can't really do microscope pics... mainly just wanted to show the wheel does abrade away ceramic.  (In reality, doesn't the wheel also "microchip" steel to an extent?  You're left with a similar "dust" in the water.)  I can tell you that running a fingernail down the edge is pretty smooth.

[tgbto]

Common steel does not get microchipped like ceramics do, in the same way that hitting a plastic bottle with a stone will not have the same result as with a glass bottle. Sure, you might end up with breaking the bottle in the end in both cases, but through different deformation/fracturation mechanisms. Which will also result in quite different particle sizes.

And to be fair some very hard steels tend to microchip too, but they're not the common lot of knife steels.

I think steel particles found in the trough after grinding on a fine-graded SG will be at least one order of magnitude smaller than what you're showing.

[AlInAussieLand]

I wonder if it should be sharpened trailing edge instead into the grinding stone, as it doesn't create a burr.

[cbwx34]

I wonder if it should be sharpened trailing edge instead into the grinding stone, as it doesn't create a burr.

This made sense, so I tried it this a.m., but got an unexpected result.  Sharpening edge trailing left the edge rough with little chips all along the edge (not visible, but I could feel running a fingernail down the edge, and cutting thru ad paper.)  I went back to edge leading and it cleaned it up.

Don't know why, maybe someone can explain?  Wasn't expecting that.    (Or maybe a fluke?)

[AlInAussieLand]

I wonder if it should be sharpened trailing edge instead into the grinding stone, as it doesn't create a burr.

This made sense, so I tried it this a.m., but got an unexpected result.  Sharpening edge trailing left the edge rough with little chips all along the edge (not visible, but I could feel running a fingernail down the edge, and cutting thru ad paper.)  I went back to edge leading and it cleaned it up.

Don't know why, maybe someone can explain?  Wasn't expecting that.    (Or maybe a fluke?)

Thanks for testing and letting us know.
I have a very expensive Boker Ceramic/Titanium folding knife that I need to get sharp again. I tried with my Edge Pro Professional and their diamond stone multiple times over the years and had less then satisfactory results. Any other stone had zero effect on it.
I will have to get a bit more experience with my T8 before trying it on that knife.

[John Hancock Sr]

Don't know why, maybe someone can explain?

My thought would be that on trailing edge the grit is dragging out over the edge and could cause the trailing grit to chip out the edge slightly. Leading edge the grit would leave the knife away from the edge thus not tending to chip out the edge. The effect would be small but noticeable I would have thought, as you have found.

[tgbto]

TL/DR : it's normal, and don't try sharpening your expensive knife with a SG even graded fine.

Don't know if that's what you mean, but those are two very different fracturation modes : tensile stress and compressive stress (hopefully those are the english terms, and to be precise there is also the notion of shearing). A given material can be fairly resistant to one and not the other.

If that given ceramic (or cement or whatever that knife is actually made of) exhibits the same kind of behavior as - say - concrete, it will be quite resistant to compressive stress (so you can stomp on it or try to crush it). But it will not resist to tensile stress, so you can't pull on it or bend it without breaking it. If you sharpen edge-leading, you will be more in  the compressive domain, if you sharpen edge-trailing you will be more in the tensile domain. 

The wheel substrate doesn't need to be too hard to chip the blade, it just need to be able to transfer energy to the blade. You can break a diamond chip with a screwdriver, or your precious ceramic knife on the edge of a hard plastic cutting board, if you hit sideways hard enough.

Steel usually has a very different behavior (and sharpening steel is an abrasion phenomenon, not a fracturation phenomenon). Brittle steel can be susceptible to chipping, as many of us know, but sharpening brittle steel still isn't the same as microchipping it.

The behavior experienced by @cbwx is consistent with a material that is less resistant to tension as it is to compression, but this is still a fracturation phenomenon. The chips we see, even though smaller in the edge-leading case, are still evidence of fracturation. You're doing something more akin to making a knife out of silex (the stoneage way) than out of steel. I would not call that sharpening unless done with a very hard, very fine (diamond ?) substrate, that will abrade the material instead of chipping it however microscopically. A rough, hard substrate may lead to fracturation instead of abrasion. That can be computed given the rotation speed of the wheel, applied pressure, angle, maximum particle size and a few physical constants describing the blade material.

[Ken S]

I do not own or sharpen any ceramic knives. My first inclination, no disrespect intended to the video presenter, would be to follow the advice of the Tormek expert staff.

Ken

[cbwx34]

TL/DR : it's normal, and don't try sharpening your expensive knife with a SG even graded fine.

Don't know if that's what you mean, but those are two very different fracturation modes : tensile stress and compressive stress (hopefully those are the english terms, and to be precise there is also the notion of shearing). A given material can be fairly resistant to one and not the other.

If that given ceramic (or cement or whatever that knife is actually made of) exhibits the same kind of behavior as - say - concrete, it will be quite resistant to compressive stress (so you can stomp on it or try to crush it). But it will not resist to tensile stress, so you can't pull on it or bend it without breaking it. If you sharpen edge-leading, you will be more in  the compressive domain, if you sharpen edge-trailing you will be more in the tensile domain. 

The wheel substrate doesn't need to be too hard to chip the blade, it just need to be able to transfer energy to the blade. You can break a diamond chip with a screwdriver, or your precious ceramic knife on the edge of a hard plastic cutting board, if you hit sideways hard enough.

Steel usually has a very different behavior (and sharpening steel is an abrasion phenomenon, not a fracturation phenomenon). Brittle steel can be susceptible to chipping, as many of us know, but sharpening brittle steel still isn't the same as microchipping it.

The behavior experienced by @cbwx is consistent with a material that is less resistant to tension as it is to compression, but this is still a fracturation phenomenon. The chips we see, even though smaller in the edge-leading case, are still evidence of fracturation. You're doing something more akin to making a knife out of silex (the stoneage way) than out of steel. I would not call that sharpening unless done with a very hard, very fine (diamond ?) substrate, that will abrade the material instead of chipping it however microscopically. A rough, hard substrate may lead to fracturation instead of abrasion. That can be computed given the rotation speed of the wheel, applied pressure, angle, maximum particle size and a few physical constants describing the blade material.

Thanks that is interesting.

I sharpened the same knife this a.m. on a SB stone (edge leading)... and while I didn't spend a lot of time on it, I'm pretty sure I got a better edge... at least slicing thru some ad paper.

I do agree that the SG probably isn't the best route, unless your goal is "better than it was".

[cbwx34]

...
I have a very expensive Boker Ceramic/Titanium folding knife that I need to get sharp again. I tried with my Edge Pro Professional and their diamond stone multiple times over the years and had less then satisfactory results. Any other stone had zero effect on it.
I will have to get a bit more experience with my T8 before trying it on that knife.

I recall Clay from Wicked Edge sharpening the same model knife (I think), if I recall correctly, he said the only way he got it sharp was diamond pastes on a hard stropping medium.  Even a fine diamond stone would chip away the edge.