How low is it practical to go in microns for stropping?

[North Arm Knives]

All of my carry knives have edges between 15-18 degrees. I feel this is a good compromise between cutting ability and edge stability. Kitchen knives are 20 degrees but the blades are already thin and are too soft to support much thinner. I did notice that polishing them down to .5 micron last time increased the time to needing sharpening from 1 week to about two. Previously they were being finished on an 8k stone at 3 microns.

Is that 15-18 degrees inclusive, or per side?

 

[mainaman]

That 0.35-0.45 micron measurement is an unfortunate bit of misinformation...

Got any proof other than one sentence negation of a scientific article? If so show it, you know SEM images, measurements etc.

 

[ToddS]

I've measured approximately 20 different brands of razor blades and the average edge width is about 100nm.

 

[yepimonfire]

I've measured approximately 20 different brands of razor blades and the average edge width is about 100nm.

So you're that science of sharp guy! Love that site. What do you mean by edge polish but not keenness improves? Does the edge get any thinner? Does it actually impart better cutting ability even in a minute sense below .1? I know between .5 I actually did notice an improvement in the ease at which it sliced through paper and other things, like fileting slices of bread cleanly.

 

[mainaman]

I do not see real measurement here, I am use you got some pics that have the actual distance on the image?

 

[mainaman]

So you're that science of sharp guy! Love that site. What do you mean by edge polish but not keenness improves? Does the edge get any thinner? Does it actually impart better cutting ability even in a minute sense below .1? I know between .5 I actually did notice an improvement in the ease at which it sliced through paper and other things, like fileting slices of bread cleanly.

Ask him how he gets red slurry from an Asagi stone, that will be an interesting explanation

 

[yepimonfire]

I do not see real measurement here, I am use you got some pics that have the actual distance on the image?

On his site there's cross sectional measurements. Even knife edges reach .1 microns (100nm iirc)

 

[mainaman]

On his site there's cross sectional measurements. Even knife edges reach .1 microns (100nm iirc)

How does a cross section with general triangular shape tell you anything about radius of curvature of one of the angles (the apex of the edge)?
An SEM has an option to measure distances on the image in real time from point 1 to point 2. That can be used to show actual distance between two points on opposite side of the apex just under it. Then one can say that the edge has dimensions smaller than the measured distance. It will be even better to measure the radius of curvature of the very edge, but that may not going to be so easy. For what is worth the images taken could be showing burr on those razor blades.

I think the answer to your OP question lies in the size of the carbides that are present in the steel of your knife, how they pack the steel matrix and how they get abraded during sharpening.
Maybe someone that knows those things will explain better.

 

[yepimonfire]

Makes sense. Fine grain steels like most carbon and Aus 8a will reach insane levels of sharpness most other steels aren't capable of. Anybody know where we can find grain size?

 

[ToddS]

I do not see real measurement here, I am use you got some pics that have the actual distance on the image?

Measurement of the edge width or radius of curvature of the apex is not trivial, particularly at and below 0.1 micron (100nm).

The images above are at 10,000x magnification relative to a Polaroid standard. In my expert and professional opinion, the edge width cannot be measured reliably at such a low magnification and that is why I do not put measurement bars on those images - there is a micron bar on the images which provides adequate scale information if you wish to measure yourself. My measurements/assessments are typically made while imaging at 50,000x to 100,000x (relative to Polaroid) and viewing full screen on a 30 inch professional monitor with contrast optimized for viewing micrographs - so screen magnification exceeding 500,000x meaning 0.1 micron (100nm) is 5cm or more on the screen.

 

[ToddS]

Ask him how he gets red slurry from an Asagi stone, that will be an interesting explanation

That stone was a given to me by Alex Gilmore and the attribution of Nakayama Asagi is his. If you need further provenance of the stone, I would suggest you contact him directly.

I agree that the iron-oxide-rich dots on the stone appear more brown than red when wet; however, I have no idea what your are referring to with your "red slurry" jibe.

 

[Obsessed with Edges]

I do not see real measurement here, I am use you got some pics that have the actual distance on the image?

Look at the lower right of each image frame, in the black 'bar' of technical info below each image. At the right-most side of that black bar, there's a 'scale' with a line of a given length, and the numerical value in microns (µm) represented by that length, like the 'scale of miles' on a map. In the most recent images he's posted, he references that line as 1µm in length. Compare that length to the apex width seen in the frame (they do look pretty thin, by comparison).

(You could use a dial caliper against your screen, to 'measure' the apparent width of the apex and compare that to another caliper measurement of the scale referenced in the image, to get an idea of the fractional relationship between the two measurements.)


David

 

[ToddS]

So you're that science of sharp guy! Love that site. What do you mean by edge polish but not keenness improves? Does the edge get any thinner? Does it actually impart better cutting ability even in a minute sense below .1? I know between .5 I actually did notice an improvement in the ease at which it sliced through paper and other things, like fileting slices of bread cleanly.

My preliminary experience is that 0.25 micron diamond yields the ultimate keenness and that 0.1 micron (on the same substrate) will begin to round the bevel rather than improving keenness further. This is absolutely dependent on the choice of substrate, so I would not generalize. The polish of the bevel certainly improves between 0.25 and 0.1 micron.

What I would suggest is to go from an 8k stone directly to 0.25 micron diamond and then experiment with the addition of 0.1 micron stropping.

 

[yepimonfire]

So more then likely going lower is counter productive?

 

[ToddS]

So more then likely going lower is counter productive?

Not at all, it will depend on how you use your knife.

As an example, stropping a razor on my 0.25 micron diamond on latigo will produce a foil edge. Stropping on 0.1 micron CBN on another latigo strop will remove the foil very efficiently while very slightly rounding the edge. Returning to the 0.25 micron strop will improve the keenness without producing another foil.

Also, it may be that the slightly less keen edge from the 0.1 micron strop lasts longer.

Again, there are too many things going on to generalize, you need to experiment for yourself. I will say that the appropriate grit to follow an 8k stone is 0.25 micron - skip the 2, 1 and 0.5.

 

[Sadden]

Interesting topic.

Practicality is where you meet the point of diminishing returns... I have one of two bottles at 0.015u. The problem is that producing that kind of an edge is a huge investment in time (one I don't have the time to make right now) , but under an SEM yes there is a difference. How much is perceivable , well there is a perceivable difference between 0.050u and 0.025u , so 0.015 u should be even better yet. One of these days I will have to sit down and go there.

The other thought is what are you using the knife for. I wouldn't use a 1.2million grit edge for skinning a boar (30k is great though!) but its fun to EDC , and shave with.

30k with a few licks at 0.25u and sometimes 0.1u is my go to edge nowadays.

For those wondering I use Polycrystalline Diamond on Nanocloth.

 

[yepimonfire]

Not at all, it will depend on how you use your knife.

As an example, stropping a razor on my 0.25 micron diamond on latigo will produce a foil edge. Stropping on 0.1 micron CBN on another latigo strop will remove the foil very efficiently while very slightly rounding the edge. Returning to the 0.25 micron strop will improve the keenness without producing another foil.

Also, it may be that the slightly less keen edge from the 0.1 micron strop lasts longer.

Again, there are too many things going on to generalize, you need to experiment for yourself. I will say that the appropriate grit to follow an 8k stone is 0.25 micron - skip the 2, 1 and 0.5.

why would it round it?

 

[yepimonfire]

Interesting topic.

Practicality is where you meet the point of diminishing returns... I have one of two bottles at 0.015u. The problem is that producing that kind of an edge is a huge investment in time (one I don't have the time to make right now) , but under an SEM yes there is a difference. How much is perceivable , well there is a perceivable difference between 0.050u and 0.025u , so 0.015 u should be even better yet. One of these days I will have to sit down and go there.

The other thought is what are you using the knife for. I wouldn't use a 1.2million grit edge for skinning a boar (30k is great though!) but its fun to EDC , and shave with.

30k with a few licks at 0.25u and sometimes 0.1u is my go to edge nowadays.

For those wondering I use Polycrystalline Diamond on Nanocloth.

For edc purposes, sometimes cutting abrasive materials. And then kitchen use.

 

[Sadden]

Meh , get really good lower grit edges. Work on burr removal etc etc. What do you have leading into all of this. 0.025u will require a minimum 0.05u , 0.1u , 0.25u , 0.5u/30k shapton , 1u/15k , 2u/8k progression. Otherwise its a waste. and you probably wouldn't be able to perceive a difference. Substrate is also important. Nanocloth and Roo are ideal (on a hard backing) , hanging strops and soft leathers are not good.

Nice to see you Todd , what have you been up to?

 

[Sadden]

How does a cross section with general triangular shape tell you anything about radius of curvature of one of the angles (the apex of the edge)?
An SEM has an option to measure distances on the image in real time from point 1 to point 2. That can be used to show actual distance between two points on opposite side of the apex just under it. Then one can say that the edge has dimensions smaller than the measured distance. It will be even better to measure the radius of curvature of the very edge, but that may not going to be so easy. For what is worth the images taken could be showing burr on those razor blades.

I think the answer to your OP question lies in the size of the carbides that are present in the steel of your knife, how they pack the steel matrix and how they get abraded during sharpening.
Maybe someone that knows those things will explain better.

Using basic abrasives carbide size will limit how refined you can go. Once the abrasive reaches the same particle size as the carbide then you will no longer be able to effectively sharpen the knife. So lets say you are using waterstones on a steel that has vanadium carbides with an average carbide size of 2u. Once you reach around an 8k ish stone , you wont be able to further refine the knife effectively.

Switch to diamonds/CBN , or enhance the waterstones with a spritz/drop of some , and the problem is immediately solved.