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EDGE RETENTION/ROLLING PART II
Good stuff Mr. Knife Grinders. I sort of like this "working edge" thing that you speak of. I like it because I think that's the sort of edge most people end up using most of the time. It seems like from all the things we have seen with the SET results or Mr. Grepper cutting carrots or just letting the knife sit out overnight that an extremely sharp edge lasts a very short period of time. A sharp edge seems to last about two weeks in my kitchen and then I start noticing that things just aren't falling apart as easily as they used to. Two weeks after that I start thinking about sharpening my knives. That's about the time my wife starts complaining so maybe a month later I finally get around to a mass sharpening event. I always test before I sharpen just because I'm curious. They'll range anywhere from 350 to 650. Then back to 170 or so after sharpening and the cycle begins again. My carry knife edge is a different story. It might be OK from anywhere between an hour and three months depending on how it get's abused. 

I used to have a Sharp Pad in the kitchen and it definitely stretched the life of the edge but we both got lazy and it ended up in a drawer. Now it sits in my shop and I use it there sometimes for burr removal or just dinking around experimenting. There isn't much doubt in my mind that there is a place for a steel or a strop with knives that are being used daily. I think that everyone, including me, are just to lazy to use them. If you have a Kally or other good sharpening method it's just too easy to sharpen again. Who cares if you're wearing your knife away quicker than need be? A brand new Victoranox is only $30.00 or so.
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Excellent observations Mr. Bud.  I agree.  Probably 99% of kitchen knives are used in some state of “working edge” and I suspect most of those continue to be used long after “working” is really not the proper word to describe what’s left of the edge.  I’ve been given chef’s knives to sharpen that were actually in use, but would require a good smack on the spine with a mallet to cleave a carrot!

Your last paragraph takes words right from my mouth,

I used to have a Sharp Pad in the kitchen and it definitely stretched the life of the edge but we both got lazy and it ended up in a drawer. Now it sits in my shop and I use it there sometimes for burr removal or just dinking around experimenting. There isn't much doubt in my mind that there is a place for a steel or a strop with knives that are being used daily. I think that everyone, including me, are just to lazy to use them. If you have a Kally or other good sharpening method it's just too easy to sharpen again. Who cares if you're wearing your knife away quicker than need be? A brand new Victoranox is only $30.00 or so.

It’s funny.  I know I should strop and maintain my edges but I don’t because I'm too lazy.  I have a Sharp Pad and it resides in my shop for deburring and dinking around with.   I have a Kally, actually enjoy sharpening and can do it so quickly I’m just too lazy to bother straightening edges.  I guess I really don’t care if my knives wear more quickly than necessary considering I can usually find a blade at Salvation Army for only a few dollars, and a new Victorinox is only $30.00 or so.

We’re lucky.  We know how to sharpen.  Most folks don’t, and getting knives sharpened is at the least inconvenient so they simply don’t and continue to use the knife until it’s unusable.  The solution is then to declare the knife used up, throw it in the ever growing too good to throw away but too dull to use knife box and purchase a new one.  I guess that’s one way to go and works for a lot of folks.  After all, a brand new Victorinox is only $30.00 or so.
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Steel hardness is related to its compressive yield strength which tells us the stress at which steel begins to deform plastically. 

A2 steel hardened to 62 HRC has compressive yield strength some 320 ksi while the same steel hardened to 54 HRC has compressive yield strength only some 250 ksi.

The middle part of the graph posted by KG may be interpreted in the following way:
   
For the blade hardened to 62 HRC the stress generated by the SET roller is probably slightly below the compressive yield strength, while for the blade hardened to 54 HRC the stress generated by the SET roller is probably slightly above the compressive yield strength and so some fraction of the deformation remains permanent. This permanent edge deformation cumulates and causes the observed sharpness decrease for 54 HRC blade.

Jan


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Well noted Jan, thank you.
Even though a tool steel, the A2 at 54 HRC deforms similar to what we've seen in mainstream kitchen knives, while at 62 HRC just won't transit from the elastic to plastic deformation - we could see how resilient the HRC62 is by its sharpness returning to better scores as we kept rolling the edge.
http://knifeGrinders.com.au
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