Low Grit Stropping

Sadden

Sadden

Joined
Dec 19, 2011
Messages
795
So i have this mini Khukri. It was stored dry, but developed some rust on the blade. I was only planning on removing the rust. I wound up using some cbn on a cotton cloth to polish out the corrosion. Then realised that the knife would barely tear paper. Clearly not acceptable..

Now i dont sharpen convex grind normally, nor scandi grinds for that matter. So I dont have the sandpapers and things needed to handle a project such as this on hand. But i do have a pile of kangaroo leather strops and high quality compounds from Ken Schwartz.

So I set to extreme low grit stropping. Dropping all the way down to 45u to get both sides to meet. Then back up to 30u, 16u and 8u respectively. The knife now slices and push cuts well (especially given the convex grind and obtuse geometry).

Given the knifes POU (wall hanger), I saw little point in continuing. But this could be further refined to as fine as necessary.
I am pleased with the aesthetics and sharpness achieved.

Corrosion :(


45u CBN on rough side of kangaroo


8u CBN on smooth side of kangaroo
 
How much swarf do you get from the 45 micron strop? It doesn't look like very much in the picture. Do you clean it with every use?
 
ToddS said:
How much swarf do you get from the 45 micron strop? It doesn't look like very much in the picture. Do you clean it with every use?
Click to expand...

Its not a strop i use regularly. Its definitely darkened significantly for being used so little. But that happens even with 0.025u poly diamond from ken. I originally tried starting at 16u CBN and applied 3 drops of fresh compound to that strop and went to town for about an hour. But couldnt get the edges to meet. That strop is black now and needs cleaned. I only spent 5 or 10 minutes on the 45u strop so its not as dirty.

I bought some leather cleaner and conditioner specifically for untreated leather that I use on my Kangaroo strops.
 
Sadden said:
Its not a strop i use regularly. Its definitely darkened significantly for being used so little. But that happens even with 0.025u poly diamond from ken. I originally tried starting at 16u CBN and applied 3 drops of fresh compound to that strop and went to town for about an hour. But couldnt get the edges to meet. That strop is black now and needs cleaned. I only spent 5 or 10 minutes on the 45u strop so its not as dirty.

I bought some leather cleaner and conditioner specifically for untreated leather that I use on my Kangaroo strops.
Click to expand...

Are you saying that you stropped 1 hr on the 16u CBN?

Could you make a guess at the rate metal is removed on the 45 and 16 micron strops compared with comparable grit stones (320, 1k) based on the swarf production?
 
ToddS said:
Are you saying that you stropped 1 hr on the 16u CBN?

Could you make a guess at the rate metal is removed on the 45 and 16 micron strops compared with comparable grit stones (320, 1k) based on the swarf production?
Click to expand...

Yeah I spent about an hour on it initially, taking my time and learning. But it wasn't coarse enough to get both sides to meet so i wound up dropping down to 45u. Things happened rather quickly there. Then i went through a progression 45u, 30u, 16u, 8u.

Its fast when you use the right one (the knife was rougher than I initially guessed), but gentler than comparable stones. Its extremely fast on a powered system, such as a WSKS, WSKO, 1x30 or 2x72...
 
Sadden said:
Yeah I spent about an hour on it initially, taking my time and learning. But it wasn't coarse enough to get both sides to meet so i wound up dropping down to 45u. Things happened rather quickly there. Then i went through a progression 45u, 30u, 16u, 8u.

Its fast when you use the right one (the knife was rougher than I initially guessed), but gentler than comparable stones. Its extremely fast on a powered system, such as a WSKS, WSKO, 1x30 or 2x72...
Click to expand...

I haven't tried anything larger than 15 micron, after seeing that these larger grits have no effect on denim or paper

https://scienceofsharp.wordpress.com/2016/05/29/the-pasted-strop-part-4/

but I have wondered if they could become bedded sufficiently on leather to actually cut. I did try one kangaroo strop with 15 micron diamond and it didn't seem to do anything, and didn't pursue it further as I was getting low on kangaroo tail strips.
 
I'll go as high as 20-25 micron, this is the level of most black "emery" compounds that I have checked. On a hard enough backing they can be used to sharpen in fairly quick order, esp on less robust steels. I once sharpened one of my mother in law's vintage Sabatiers on black compound applied to paper over a Washboard - it took about ten-fifteen minutes from butter knife dull.

If the edge needs more than a 20 micron reconditioning I'll reach for some wet/dry or back to the stones.

One can also apply the compound with a drop of oil to a scuffed board - works very well if a bit messy.

https://www.youtube.com/watch?v=1nxmn-aJwQY
 
ToddS said:
I haven't tried anything larger than 15 micron, after seeing that these larger grits have no effect on denim or paper

https://scienceofsharp.wordpress.com/2016/05/29/the-pasted-strop-part-4/

but I have wondered if they could become bedded sufficiently on leather to actually cut. I did try one kangaroo strop with 15 micron diamond and it didn't seem to do anything, and didn't pursue it further as I was getting low on kangaroo tail strips.
Click to expand...

Todd,

I've messed around with Ken Schwartz's CBM emulsions on leather, including the 16u, 30u, 45u and 80u. The major thing I discovered is that coarse particulate abrasives used on leather for stropping leave a much finer apex finish than their particle size would suggest because the particles become partially embedded in the substrate and the pliability of the substrate precludes them from cutting to their full potential scratch depth.

Now, when I say "finer effective grit" I should clarify that I estimate grit ratings based on the balance between pushcutting sharpness and slicing aggression the apex displays. Judged by that criteria, I found the 8u on highly pliable leather left an apex finish akin to a ~10,000-13,000 JIS waterstone, the 16u left an apex finish akin to a ~8,000 JIS waterstone, and the 30u left an apex finish akin to a ~4,000 JIS waterstone or Spyderco M or DMT EEF.

I made a video about it a while ago where I show the level of pushcutting sharpness obtained off a 16u CBN on leather strop:

[video=youtube;tUCWs6KD_do]http://www.youtube.com/watch?v=tUCWs6KD_do[/video]

I actually eventually ended up switching to mainly using the 30u CBN on leather strop as I wanted a little more slicing aggression, and I could still easily do crossgrain pushcuts on newsprint at 90 degrees off the 30u CBN on leather. I have a gyuto in my kitchen in super blue steel that I've been keeping touched up between uses for some time with my 30u CBN strop.
 
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