BESS range

[Ken S]

I am pleased to be a part of this exciting and useful new forum!

When I make BESS tests, I typically get some variation in the readings. I attribute this to some parts of the edge being sharper than others. For a typical kitchen knife sharpened with reasonable care, how much of a range might one expect to find in the BESS readings?

Ken

[grepper]

I'm curious; how much variation are you getting? Is the variation about the same with all the edges you sharpen?

[grepper]

Maybe a month ago I sharpened a 3.5” paring knife and it’s been sitting unused in a knife block since that time.  When I sharpened it I remember that it got pretty sharp, but that was a month ago and I don’t remember the exact number.  I really hadn’t given it any special consideration when I sharpened it because it’s just a kitchen paring knife, and I don’t eat that may pears anyway.  It was just a dull knife sitting around so I sharpened it.  You know, no big deal.  So, even though I might risk exposing my sloppy sharpening habits, I thought this might be a good blade to check for consistency along the edge.  

I took three measurments, near the handle, middle of the blade and just where the blade starts to curve toward the tip.  I got; 265, 245, 240.  This surprised me because I thought I remembered getting it sharper than that.  So I gave it a few strops on my blue jeans along the top of my thigh, and measured again. This time; 165, 160, 160 which is more like what I had remembered getting what I first sharpened it.  

I was surprised again, but this time because it was so consistent.  Would I have seen the same consistency over an 8” chef’s knife?  I doubt it.  I think I got lucky on that blade.  I would have been happy with a 10g variation.

It would be interesting for more folks to post what they are seeing on their knives.  That would give us some real world data to help in forming an idea of what is reasonable to expect for consistency.

[grepper]

I was speaking with Mike from Edge On UP on a different matter, and brought up the question of what you would generally see in edge consistency.  Now, he’s done more edge testing that I will probably ever do, and he said that +/- 10 grams would really be doing pretty good but is attainable, and that it’s more common to see +/- 20 grams.  He also mentioned, and it totally makes sense to me, that a highly polished edge will have less variation then a more “toothy” edge.

Wow, I guess I really lucked out with my paring knife, eh?
 
I suppose one thing to consider with kitchen knives and other general purpose blades, is that for all intents and purposes, it’s going to be difficult if not impossible to even notice even a +/- 20g variation whilst chopping up your evening’s broccoli and onions.  From a sharpener’s point of view the numbers may be helpful in improving sharpening methods, but have less significance in real world use.  That said, I would think if you are seeing much more than that, the blade might need a bit more work or maybe there is some residual burr, etc.

[Ankerson]

It's going to come down to sharpening talent and being consistent, also what one uses to sharpen with.

I have gotten as little as + or - 1 point testing with the KN100, usually - or - 5 on a good day,  but I use the Edge Pro and have my method down pretty well by now.

But + or - 20 is generally good.

The KN100 is extremely accurate.

[EOU]

Jim is an absolute expert with a KN100 and an excellent example of the accuracy that can be "wrung out" of this instrument in practiced and experienced hands. As Jim says +/- 20 is an excellent result for most sharpeners. This would mean that the total variation in apex width along the apex of the edge was something on the order of 40nm - an incredibly small differential but still achievable by many sharpeners. Variations in measurements along the edge will be both a function of the skill of the sharpener and the roughness or "tooth" of the edge.

[Soxx]

Let me add my .015 worth to this thought. I can promise that after 2.5 years of testing that BESS Test media will not be the weak link in any edge sharpness test results. Instrumentation error provides a very small source of error.  Operator error/inconsistency provides a greater source of error.  It would be incorrect  to characterize edge reading inconsistencies as "error" though. If the question is "what is the sharpness of this edge at this very finite point then BESS test media used in conjunction with BESS certified instrumentation will provide that answer very accurately. Inconsistent answers throughout the length of an edge are "information" concerning that edge and not error or repeatibility issues. Mike Brubacher with Edge On Up provided  a very excellent analogy, in my opinion, on this subject when he asked "what is the temperature of your home?" It could be 70F in the rear of the house and 80F up front. You could likely find and measure a blend or  average of those two temperatures somewhere in between but that would be less information and not better information.

[grepper]

I think another way of saying what Mr. Soxx just said is; if you measure varying sharpness over the length of the blade, you can with high confidence assume it’s because the blade is not evenly sharp.
 
Then it’s just a matter of understanding why.  Still some burr?  Not evenly sharpened?  Didn’t get all the way to the edge in some places? 
 
What’s cool is that now there is instrumentation that can actually measure that variation.  Now not only can we measure variation, but because we know it exists, can go about fixing it.  I agree that more information is a good thing.

[Bobbo]

Near the point and near the handle are the two toughest part of the knife blade to get sharp for me. It's not a problem to correct it but it just seems that is the way it is pretty consistently. The reason I have discovered is because I pretty consistently do not seem to raise a good burr at those points. I definitely can distinguish between a toothy and a polished edge with my edge tester with the variation in readings. I can also see a very direct correlation between finer and coarser grits in my edge readings. I imagine that this is probably stating the obvious for you guys but for a new learner its really exciting and an eye opener.

[Bobbo]

While I am on the forum today I am going to respond to my own post with new observations. I definitely do see more variation in edge sharpness readings after using coarse grits compared to finer grits. Interestingly enough though, having refined and improved my burr removal techniques though, I see very similar sharpness levels. I just don't see those low numbers as often along the length of a given and coarsely ground edge. I guess that's the "tooth" in a "toothy edge". 

I'm going to order a 1" Kalamazoo and I don't think that I will even bother ordering belts that are more than 240 grit. This is a great forum guys!