Bess to Grit Ratio

[Mark Reich]

I'll skip to the end of the story to say what made me think of a "Bess to Grit Ratio". I tested a 140 grit Atoma edge this evening with lows in the Sixties! Average of 5 tests was 76, low of 69, but I was getting lower numbers as I got closer to the heel. I had to measure it. I could not believe it was consistently tree topping arm hair.

When I hit 69, it dawned on me that I was approaching a 1:2 ratio. Average Bess of 60 with a 120 grit finish would actually be 1:2. 

I've been sharpening some EDC knives with a well used, still working perfectly, Atoma 140 for a few weeks or more. This is in direct relation to Mr. Grepper's quest for Mega-Tooth edges... Which may have sorta originated from Mr. Max's experience with commercial cutlery. 

I'm not sure, but it happens to fall in line with the fact that I've been pushing the limits of coarser CBN and poly-diamond compounds, on linen or leather belts, for... over 3 years, actually. I remember what I had worked up for the Sturgis Rally event three years ago, 30 and 80 micron CBN on linen belts. 

Just had time to say... Yay Tooth! 

[grepper]

Very cool, Mr. Mark!
 
I’m curious- How have you been finding the general usefulness of nice toothy edges compared to polished edges?  My personal experience is that they cut more stuff without riding on the surface like even a slightly used polished edge tends to.  And the toothy edges keep cutting better longer.
 
I got fed up with polished edges.  They work great right off the sharpener, but so very soon start that frustrating riding on the surface of stuff starts when the edge of the blade rolls even just slightly.  I proved it to myself last year during tomato season with some over ripe tomatoes with rotten gushy centers and tough smooth skin.  I tested many bowls of tomatoes that were decomposing on the ground.  A little disgusting, but a great test.  That started my quest for a better general purpose edge.
 
I like the idea of BESS = grit/2.   Hmmm… Sharpen with a 20 grit stone?  I found it interesting when you mentioned using a pretty coarse CBN grit on linen in some previous post.  That was the first time I head heard of someone going toothy with compound.  It made sense to me!
 
60 gf BESS is very impressive!  I mean, that’s really sharp!   I’ve never achieved that, but then I don’t carefully hand sharpen like you do.  I just use the Kally.  That said, if I ever got a 60 gf reading, I’d be suspicious that I was dealing with a wire edge.  Not saying that’s what’s happening for you, but with the way I sharpen I would be a tad bit suspicious and have to check it out under the scope.
 
I’ve got to agree!  + 1 for Yay tooth!  Please keep us informed of your experiments.

[grepper]

Mr. Mark,  When you refer to a 60 gf reading, are you using a KN-100?  If so, are you taking into consideration the 50 g  piston weight (BESS A scale)?  I have a PT50B which uses the BESS C scale.  adding 50 g to the 60 gf reading you mention would be 110 gf (BESS C scale) sharpness reading which would seem more in the range that I'm used to seeing. 

In other words, is the 60 gf reading just the weight of the material you are adding to the piston of the KN-100?

[Mark Reich]

I'll have to try to be brief, Mr. Grepper. I'm sorry, I'm having trouble keeping up with you. I'm producing some mighty fine cutlery though!

I use a stock KN100, and I only measure the weight added to the piston. I didn't know there was a different way. I've actually gotten down to single digits, but I know you are right, stones and hones do make an enormous difference. Probably all the difference there is between us. If I had one suggestion it would be to get an Atoma.

Now that I'm becoming used to finishing on the Atoma 140, I'm actually pretty surprised by how quickly mega-tooth loses it's initial bite. It doesn't get worthless slippery like a polished edge, but I'm seeing a pretty quick drop off, and that's with the best carbon steels, like M4 and my 52100, and one of the newest, best stainless steels, S35VN. 

I think most others would say that's to be expected. Over the centuries that people have been sharpening with stones, it's always been fairly accepted that refinement leads to longevity. I think we've gone WAY too far in that direction, and quit looking at the practicality of coarse stones. 

IMHO, there is a sweet spot somewhere around 400-1000 grit. It could go down as far as about 150 grit, and up to 2000 grit, mainly depending on the steel. For the most part, softer stainless will benefit from coarse grit, while carbon tool steel is strong enough to hold a keener edge. 

The thing I'm most wary of with coarse grit is how much metal I remove per sharpening. Especially on a belt, and especially with soft stainless. I can grind a butcher knife down to a paring knife pretty quickly at 120 grit. 400 grit is a huge difference. At least you can't watch your blade disappear before your eyes.

All in all, I will be happy to keep working in the 140-350 grit range. I'm not done by any means. I just received a couple really nice water stones in 150 and 325 grit, but I can already tell the 150 will have a tough time keeping up with the Atoma. The 325 grit stone is pretty awesome though. Nubatama stones are becoming my standard equipment, along with Atomas. I have entire sets of Choseras and Shaptons, but 400 and 500 grits are my coarsest, and I've been ok with that until recently. 

I know what I was thinking when I was talking about the ratio of refinement to BESS scores, but I don't think it's as simple as dividing the score by the grit or whatever. We could probably figure something out though, because low scores with low grits are significant. IMHO, 60 grit is just too coarse for anything I've tested so far.

The next question will relate to edge retention. I think I can guarantee there will be a difference between carbon and stainless steels, but it will take some work to quantify it.

I really like cutting rope for edge testing. The cheap 1/2" manila or hemp rope is perfect. Paired with a BESS machine, you can measure initial sharpness, make 100 cuts, and remeasure. That should be a good way to figure edge retention at different grits. I'm certainly interested in seeing some numbers. 

I'll also be revisiting coarse CBN and diamond compounds during the Sturgis Rally in a couple weeks. I can hardly wait to try my new, souped up Viel!