This surprised me. Thoughts?
https://youtu.be/u1mMoXjHWcQ?si=gAGpWFrQJulJnGBt
Ken
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.
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.
Quote from: Ken S on May 28, 2024, 04:55:10 AMThis 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...
Ceramic Dust.jpg
... 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.
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.
Quote from: tgbto on May 29, 2024, 02:01:08 PMThe 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.
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.
I wonder if it should be sharpened trailing edge instead into the grinding stone, as it doesn't create a burr.
Quote from: AlInAussieLand on June 05, 2024, 05:08:09 AMI 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?)
Quote from: cbwx34 on June 05, 2024, 02:54:50 PMQuote from: AlInAussieLand on June 05, 2024, 05:08:09 AMI 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.
Quote from: cbwx34 on June 05, 2024, 02:54:50 PMDon'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.
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.
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
Quote from: tgbto on June 06, 2024, 04:11:46 PMTL/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".
Quote from: AlInAussieLand on June 05, 2024, 10:37:40 PM...
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.
Quote from: Ken S on May 28, 2024, 04:55:10 AMThis surprised me. Thoughts?
https://youtu.be/u1mMoXjHWcQ?si=gAGpWFrQJulJnGBt
Ken
Only just found this. Don't worry, it surprised me too! Here's a bit more info.
I had a long discussion with the owner of the knife before he let me try. I set the SG to to about 960 grit (the fine setting) using the 320 grit diamond plate and started VERY gently as I was aware of the chipping issue. I was very surprised when I saw that the knife seemed to be accepting the grind so I continued ever so carefully and gingerly. I was using a super soft touch, expecting the knife to explode but nope. I was able to take a fairly chipped edge and turn it into a decent edge by treating it like a normal knife.
I didn't deburr as I couldn't detect a burr and it seemed to slice paper where as before it was tearing it and was useless as a fine slicer. It wasn't razor sharp though and he was happy to take it away vastly improved. The chips (damage) weren't large but there we very visible and numerous. I wish I'd take a video before I started but I really didn't expect it to work and just started grinding it as he was there watching. It was only after I had achieved a result that I knew I had to share it on YouTube. The edge as presented resembled a misused global edge if that makes sense.
I assure you all there was no trickery and my surprise (although slightly bombastic and cringey) was genuine. I caught some flack in the comments but I can assure you it worked. My advise, start with a smooth wheel and push down only just enough to maintain contacts on the wheel but yes, the SG wheel can "sharpen" ceramic knives. I love the SG wheel.
Quote from: tgbto on May 28, 2024, 11:13:57 AMA little info about the knife would help.
It was a Kyocera INNOVATIONblack® Knife similar to this although I don't remember a soft handle.
https://cutlery.kyocera.com/innovation-soft-grip-3-ceramic-paring-knife-black-z212-blade
Quote from: cbwx34 on June 06, 2024, 06:45:45 PMI 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 don't know much about the physical properties of SG and SB. But I haven't yet had to true the SB, and in its current state I would say the surface is more even than the surface of my (several-times-trued) SG. Ie the RMS of the indentations is smaller. So you are using a harder, smoother medium than the SG, and it is logical that the blade would chip less. If you are abrading rather than microchipping on a smaller scale remains to be seen, and will depend on the relative hardness of this ceramic and silicon carbide.
[Damn I messed up with the edits/post buttons]
Quote from: cbwx34 on June 06, 2024, 06:45:45 PMI 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 don't know much about the physical properties of SG and SB. But I haven't yet had to true the SB, and in its current state I would say the surface is more even than the surface of my (several-times-trued) SG. Ie the RMS height of the indentations is smaller. So you are using a harder, smoother medium than the SG, and it is logical that the blade would chip less. If you are abrading rather than microchipping on a smaller scale remains to be seen, and will depend on the relative hardness of this ceramic and silicon carbide.
Quote from: tgbto on May 29, 2024, 02:01:08 PMThe 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.
Today I dug out a 1200g CBN wheel and tried that. Noticeable difference in sharpness and edge smoothness, even vs. the SB wheel, and way better than the SG wheel. And the water was cloudy with very fine particles in the bottom. (Ignore the bigger "pieces" that's towel.)
Ceramic Dust 2.jpg
I'd say, from what you've posted, that this is actually the difference of abrading vs. microchipping the edge away? Certainly a different result.
QuoteToday I dug out a 1200g CBN wheel and tried that. Noticeable difference in sharpness and edge smoothness, even vs. the SB wheel, and way better than the SG wheel. And the water was cloudy with very fine particles in the bottom. (Ignore the bigger "pieces" that's towel.)
Interesting. Did you sharpen edge leading or trailing?
Quote from: 3D Anvil on June 13, 2024, 07:54:41 PMInteresting. Did you sharpen edge leading or trailing?
Edge leading.
Do you happen to remember what your edge angle was, CB? Outdoors55 from Youtube recently posted a video about sharpening ceramics on resin-bonded diamond stones. He had many unsuccessful attempts using various stones, but eventually concluded that the key was to use a more obtuse edge angle.
https://www.youtube.com/watch?v=FFEgg7OWsUk&t=508s
I found that curious, since my two Kyocera ceramic knives came with factory angles of 13 and 14 dps. I wonder how they sharpen them at the factory.... They measured at 100 and 110 BESS, which is waaay sharper than any factory edge I've gotten on a steel knife.
Quote from: 3D Anvil on July 15, 2024, 06:37:49 PMDo you happen to remember what your edge angle was, CB?
...
It was 20dps. (I think I tried 15dps on one of them a while back and I saw a lot of chipping.)
I believe this is an interesting read at
ScienceOfSharp (https://scienceofsharp.com/2018/02/24/ceramic-blades/).
It states that aluminum oxide abrasives are sufficient, however a much finer grit than the SG-250 is suggested.
Quote from: HaioPaio on July 15, 2024, 09:30:21 PMI believe this is an interesting read at
ScienceOfSharp (https://scienceofsharp.com/2018/02/24/ceramic-blades/).
It states that aluminum oxide abrasives are sufficient, however a much finer grit than the SG-250 is suggested.
Very interesting. It seems Kyocera has improved their sharpening process since that was posted in 2018. My examples easily push cut paper.
Quote from: HaioPaio on July 15, 2024, 09:30:21 PMI believe this is an interesting read at
ScienceOfSharp (https://scienceofsharp.com/2018/02/24/ceramic-blades/).
It states that aluminum oxide abrasives are sufficient, however a much finer grit than the SG-250 is suggested.
Nice find, this site really is a trove of useful information. In a pinch, it says that you have to use reasonably hard, but very fine material so you chip on a sub-micron scale. Which requires a blade made of material that can separate on a sub micron scale. Using a glass substrate makes for a hard, smooth support that ensures that the "angle of attack" of the hard particles wrt the blade remains constant and controlled.
It also confirms that the initial "sharpening" of the blade with the sg was probably more of a roughing-up of the shoulders of the apex, resulting in two fine hacksaws.
For me Paper Wheels used with diamond compounds completely solved the problem of sharpening ceramic knives to a very keen edge.
I only sharpen what i know to be good quality ceramic, and most ceramic edges i polish up to 6,0 micron diamond compound..
For an even keener edge i refine up to 1,0 micron diamond compound.
Some examples i did about 10 years ago:
https://www.youtube.com/watch?v=q4YGGHltloU
https://www.youtube.com/watch?v=dP6fNB_obN4
https://www.youtube.com/watch?v=dP6fNB_obN4
https://www.youtube.com/watch?v=hUkKfwGFogY
https://www.youtube.com/watch?v=RSkxPA9BK8E
Nice, Kwakster! I've never gotten along with paper wheels, personally, but your results speak for themselves.
Quote from: kwakster on July 16, 2024, 12:41:32 PMFor me Paper Wheels used with diamond compounds completely solved the problem of sharpening ceramic knives to a very keen edge.
I only sharpen what i know to be good quality ceramic, and most ceramic edges i polish up to 6,0 micron diamond compound..
For an even keener edge i refine up to 1,0 micron diamond compound.
Some examples i did about 10 years ago:
https://www.youtube.com/watch?v=q4YGGHltloU
https://www.youtube.com/watch?v=dP6fNB_obN4
https://www.youtube.com/watch?v=dP6fNB_obN4
https://www.youtube.com/watch?v=hUkKfwGFogY
https://www.youtube.com/watch?v=RSkxPA9BK8E
How prone to chipping are ceramic knives that are made very sharp with your method?
In general ceramic knives are still more chippy when compared to steel knives, but due to the much higher polishing process i have found the resulting edges to be less chippy when compared to factory sharpened ceramic knife edges.
They are also noticeably keener.
With ceramic knives polishing the edges to certain degrees greatly improves their edge retention, and an edge polished up to 1.0 micron diamond compound lasts longer than that same knife polished only to 6.0 micron, all else being equal.
The downside is of course that i need to do 2 more polishing steps (with 3.0 micron and 1.0 micron, all on dedicated Paper Wheels)
Through testing and feedback i have found 6.0 micron to be a good compromise between edge holding and time spent polishing.
Quote from: kwakster on July 16, 2024, 10:45:55 PM[...] due to the much higher polishing process i have found the resulting edges to be less chippy [...]
From a physical standpoint, "chippiness" will depend on intrinsic properties of the material used, and the thickness of said material.
So if the blade has a thinner apex, it will be more prone to chipping, not less. However, your particular sharpening process and methods may result in a geometry that will both be more resistant to chipping (so a thicker apex), but that might feel sharper as explained in the scienceofsharp article.
The intrinsic properties & the thickness of the ceramic material most certainly play important parts in useful edge life, but the degree of edge polishing also has proven to be very important yet often overlooked.
Scratches in a ceramic knife apex work as crack initiators, and when those scratches get smaller and smaller due to progressively finer polishing the apex becomes more resistant to chipping as well as keener.
The Forever white ceramic knife in the first two clips has an apex of ~25 degrees inclusive, and it could reverse whittle a chest hair, meaning from hair root to hair point, which is noticeably more difficult than from hair point to hair root.
There are also huge differences in ceramic knives from different manufacturers, and i have found many cheaper ones to be simply not worthy of resharpening.
The two best brands i've encountered so far are made by the Japanese companies Forever and Kyocera (in that order)
According to reports there seems to exist an ever higher quality ceramic knife material, which is made by Swiss company Rahven, but i have not been able to get my hands on one.
Not only does Rahven offer various kitchen knives under their own name, recently they also manufactured a so called "mule" model for Spyderco.
As a general comment, if you polish a scratch, you're essentially flattening the ridges, but the bottom of the scratch remains as it is. So there shouldn't be an impact on fissuration mechanisms.
That being said, I don't think these mesoscopic cavities are what drives the chippiness. As mentioned in the article :
Quotethe blade consistently separates along grain boundaries resulting in sub-micron roughness
.
The characteristic dimension of the grain boundaries is several orders of magnitude smaller than the typical dimension of your "scratches" (which aren't scratches as much as actual chips, really), so the local constraint is several orders of magnitude higher along those boundaries (as cavity size and constraint are inversely proportional).
It really is what happens on a sub-micron scale that matters for fracturation initiation, and it's not affected by polishing.
The thickness on the other hand plays a huge role in that it determines how far a fissure has to propagate before the material breaks.
Here's a link to the review on another forum of that Forever white ceramic knife i did years ago.
In it there are quite a few close-up pictures of the edge, among which several made with a USB-camera.
https://www.talkblade.info/viewtopic.php?f=2&t=24961&sid=db2731afeb2f0f27e9de84ee5ce1c77b
My invention of using fine diamond compounds together with certain types of oil on a naked Paper Wheel has been a game changer in sharpening ceramic knife edges, and a bit later also for steel knife edges.
When i explained my process on the Australian blade forum Vadim Kraichuck was one of the first knife sharpeners who adopted it.
Your edges look nice.
I was just commenting on this sentence :
Quote from: kwakster on July 17, 2024, 11:16:38 AMScratches in a ceramic knife apex work as crack initiators, and when those scratches get smaller and smaller due to progressively finer polishing the apex becomes more resistant to chipping as well as keener.
If anything having "smaller scratches" will increase the mechanical constraint due to local traction forces, so if this was the driving mechanism, the edge would be more prone to chipping.
But I think what's at play here is that higher RMS roughness along the edge results in areas where there is little material left at the apex, and these fragile areas will break off easily.
Back to the post of the OP, the SG is indeed much too coarse for it being any good on ceramic knives : it will tear off huge chips due not to the hardness of aluminium oxide, but to lateral stress on the blade at a scale corresponding to the rougness of the stone itself.
I can imagine that the SG, graded fine, could be a good place to start for grinding out larger chips. But from there I think it would best to move on to higher grits. I wonder if the Japanese Wheel would improve the SG result? After that 4000 grit finish, six, three, and one micron stropping could be the ticket. Or sharpening on 8000+ bench stones and then stropping.
Anyway, I'll have a go at it when the factory edge gets chippy enough (and it seems to chip quickly with my wife/chef behind the wheel).
Quote from: 3D Anvil on July 18, 2024, 05:08:52 PMBut from there I think it would best to move on to higher grits. I wonder if the Japanese Wheel would improve the SG result?
My .02: you'll shape the wheel long before you notice any significant difference in the finish of the ceramic blade.
As explained in the scienceofsharp article, you need a hard support with fine particles to sub-microchip the edge in a consistent fashion.
I think if I ever need to sharpen a ceramic knife, I will stick with the DF wheel.
Ken
Quote from: Ken S on July 22, 2024, 06:15:04 PMI think if I ever need to sharpen a ceramic knife, I will stick with the DF wheel.
Ken, based on the findings of the scienceofsharp article, the finer the grit the better, so you should probably go for the DE wheel.
Thanks, I will keepthatin mind.
Ken