Pull cut vs push cut difference

[Pie]

Ngl I’m not ashamed of spending my lunch break watching potatoes being cut.

I wholeheartedly agree with “teeth” being less of a factor in reality, but more just in my head as it could theoretically have an impact that supports my experiences.

the discussion among those who know what they’re taking about is much appreciated guys

 

[Jovidah]

Are 'teeth' even an actual physical thing? I understand that it's brought up in discussions to describe the feel an edge gives, but I don't recall ever actually seeing any on for example really high manigification pictures of edges, or them being discussed by certified steel nerds.

 

[Bico Doce]

Are 'teeth' even an actual physical thing? I understand that it's brought up in discussions to describe the feel an edge gives, but I don't recall ever actually seeing any on for example really high manigification pictures of edges, or them being discussed by certified steel nerds.

Here’s an article with some pretty good shots of “teeth” and how they change as you progress to higher grits while sharpening

https://scienceofsharp.com/2014/04/16/the-honing-progression/

 

[ian]

Are 'teeth' even an actual physical thing? I understand that it's brought up in discussions to describe the feel an edge gives, but I don't recall ever actually seeing any on for example really high manigification pictures of edges, or them being discussed by certified steel nerds.

By teeth we typically just mean irregularities in the apex geometry. “More toothy” means higher hills and lower valleys. They aren’t regular little things like on a saw.

 

[Pie]

Here’s an article with some pretty good shots of “teeth” and how they change as you progress to higher grits while sharpening

https://scienceofsharp.com/2014/04/16/the-honing-progression/

It’s been a while since i took a look at that article, I’m glad that it makes a hell of a lot more sense to me now.

“Too big of a jump” really shows how high grit honing, hybrid edge business works. The height irregularities really get smoothed out, but as the honing progression article shows, there is limited keenness gains past 4K. I kind of wish dude was a knife guy instead of razors, as some info is less applicable in our cases.

 

[Bico Doce]

It’s been a while since i took a look at that article, I’m glad that it makes a hell of a lot more sense to me now.

“Too big of a jump” really shows how high grit honing, hybrid edge business works. The height irregularities really get smoothed out, but as the honing progression article shows, there is limited keenness gains past 4K. I kind of wish dude was a knife guy instead of razors, as some info is less applicable in our cases.

I had a hard time understanding what was happening with grit progression until I saw the photos - “toothy” was a complete mystery to me!

 

[M1k3]

Just to add some confusion. Toothiness can also be from exposed/unabraded carbides.

 

[M1k3]

Just to add some confusion. Toothiness can also be from exposed/unabraded carbides.

https://scienceofsharp.com/2021/09/14/carbides-in-k390/

 

[ian]

Just to add some confusion. Toothiness can also be from exposed/unabraded carbides.

I guess this is still just a hill, but a hill that’s formed for a specific reason?

 

[Delat]

https://scienceofsharp.com/2021/09/14/carbides-in-k390/

Interesting and slightly confused that the SP320 abraded the vanadium carbides. I thought aluminum oxide wasn’t tough enough to abrade vanadium carbides? Or did I misinterpret something?

Thanks for sharing that article - it was a very interesting read.

 

[Bico Doce]

Interesting and slightly confused that the SP320 abraded the vanadium carbides. I thought aluminum oxide wasn’t tough enough to abrade vanadium carbides? Or did I misinterpret something?

Thanks for sharing that article - it was a very interesting read.

I think that it takes a lot of aluminum oxide to wear down the vanadium carbides so it is not practical in use

 

[stringer]

Interesting and slightly confused that the SP320 abraded the vanadium carbides. I thought aluminum oxide wasn’t tough enough to abrade vanadium carbides? Or did I misinterpret something?

Thanks for sharing that article - it was a very interesting read.

I didn't read the article. But according to Larrin aluminum oxide can work fine at coarse grits because the grit is larger than the carbides. So even if it can't abrade them it can cut them out of the surrounding steel matrix. At finer grits the alox becomes less and less effective and you must go to diamonds or CBN.

 

[HumbleHomeCook]

Interesting and slightly confused that the SP320 abraded the vanadium carbides. I thought aluminum oxide wasn’t tough enough to abrade vanadium carbides? Or did I misinterpret something?

Thanks for sharing that article - it was a very interesting read.

Basically it's what @stringer said. The carbides are just coming out with the softer matrix at the lower grits so the abrasive doesn't need to grind them. Above about 600 (I believe ANSI) grit, then the carbides and abrasive sizes stat to align and they do need to grind on them. So, that's why diamond/CBN is preferred at the higher grits as they can abrade the carbides and matrix and maintain a keener edge.

If you hunt around the Science of Sharp, Todd has SEM images of it: Index

Another thing to remember is the wear on our ceramic stones at higher grits if used on high alloy steels.

 

[Barmoley]

You guys should read the article since it says otherwise. The whole point of the article is to say that the "scooping" by low grid stones doesn't seem to happen in practice or at least the mechanism is different.

 

[Delat]

There’s comparative photos in the article that illustrate the point and piqued my curiousity. Diamond abrasives are fracturing the carbides (fractures are visible just below the surface). softer abrasives are scooping around the carbides, but the photo of the SP320 shows the carbides cleanly sheared off at the surface.

For reference, here’s the diamond stone with the fractured carbides (the darker spots).

Here’s the SP320 with the cleanly sheared carbides.

Here’s the Arkansas with exposed carbides.

 

[stringer]

There’s comparative photos in the article that illustrate the point and piqued my curiousity. Diamond abrasives are fracturing the carbides (fractures are visible just below the surface). softer abrasives are scooping around the carbides, but the photo of the SP320 shows the carbides cleanly sheared off at the surface.

For reference, here’s the diamond stone with the fractured carbides (the darker spots).
View attachment 153591

Here’s the SP320 with the cleanly sheared carbides.
View attachment 153592

Here’s the Arkansas with exposed carbides.
View attachment 153593

Which is what Larrin says. At coarser grits the substrate and carbides get sheared out together.


"However, if the abrasive size is larger than the carbide size then the abrasive is able to pull out the steel and the carbides together so that the carbide hardness isn’t as important. Abrasive wear tests of S90V and D2 showed superior wear resistance of D2 [7] even though the S90V has a large amount of hard vanadium carbide because D2 has very large carbides."


........

"So grinding and sharpening with coarse grits are generally effective with vanadium-alloyed powder metallurgy steels even if the abrasive is softer. At finer grits the hardness of the carbide becomes more important and polishing vanadium-containing steels can be challenging because aluminum oxide is too soft. Silicon carbide has a similar hardness to those hard carbides but is not clearly harder, and in general silicon carbide is not as good at cutting steel as aluminum oxide. CBN and diamond are significantly harder than any of the carbides so they are generally better at least in terms of grinding and polishing high wear resistance steels with hard carbides."

 

[Barmoley]

The linked article seems to say the mechanism is somewhat different.

From the article:
Contrary to popular belief, coarse stones do not cut deep enough to “scoop out” 1-2 micron diameter carbides in these very hard steels. Instead, the mechanism appears to be that the carbides are abraded/worn in place, flattening and thinning them until they are thin enough to shatter and be removed along with the metal swarf.

My conclusion:
The bottom line is that CBN and diamonds are best for hi wear steels, which we impericly knew. At low grid any abrasive seems to work regardless of the mechanism.

 

[stringer]

The linked article seems to say the mechanism is somewhat different.

From the article:
Contrary to popular belief, coarse stones do not cut deep enough to “scoop out” 1-2 micron diameter carbides in these very hard steels. Instead, the mechanism appears to be that the carbides are abraded/worn in place, flattening and thinning them until they are thin enough to shatter and be removed along with the metal swarf.

My conclusion:
The bottom line is that CBN and diamonds are best for hi wear steels, which we impericly knew. At low grid any abrasive seems to work regardless of the mechanism.

I agree that the terminology may not match up with the mechanism. And I agree with everything you are saying here. Coarse stones still work. Finer conventional stones (1000+) don't do much. I always think SOS pictures are wonderful but I often find his analysis to be overgeneralizing.

 

[ian]

I always think SOS pictures are wonderful but I often find his analysis to be overgeneralizing.

 

[Barmoley]

I agree that the terminology may not match up with the mechanism. And I agree with everything you are saying here. Coarse stones still work. Finer conventional stones (1000+) don't do much. I always think SOS pictures are wonderful but I often find his analysis to be overgeneralizing.

Yeah, he acknowledged it himself in the article that his analysis might be overgeneralized. In the end the presise mechanism doesn't really matter for the end user. Low grid stones still work as does sand paper or belts or whatever. Medium to high grid is where you run into issues with conventional stones and steels with lots of hard carbides. I also found it interesting where he speculates that even though conventional abrasives might eventually get the edge sharp because of prolonged bending back and forth of the burr the edge might be weakend and become more brittle and chippy. I don't know if this is what happens, but it sounds like it could. I am just happy we have Larrin's work as well as this resource to have better understanding of what might be going on in reality. We know so much more now than even 5 years ago.

For myself I've determined that with high wear steels and my sharpening skill level, diamond stones make a huge difference in the quality of the edge. Now, when I hear people say that there is no difference in real world applications between high wear steels and low wear steels I always think it is due to them not using the "correct" abrasive.

Of course there are some people whose sharpening skill level seem to transend all this and they seem to be able to get anything sharp with any regular abrasive. I am very, very far from such skill level so I cheat with diamonds.