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 Post subject: How do I know if my knife is sharp?
PostPosted: Wed Apr 25, 2012 1:51 am 
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Here's a thread devoted to tips and tricks you use to know if your knife is sharp or not.

This sounds simple, but can get very complicating when we start involving many different grits and techniques. Let's stick to the basics for now, and hopefully this thread develops into something more advanced. So, onto the basics.


How do you know if your knife still has a decent, "functioning" edge? The number one trick I like to use is the back of my fingernail. Your thumbnail is the best one to use. Gently place the knife's edge on your nail. If the knife edge sticks to your thumbnail, you know the edge is still functioning. You can still hone the edge back to razor sharp fairly easy. If the knife slides around your thumbnail, you know the edge is completely rounded beyond simple honing. At this point you need to break out your coarse stones and start building a slurry.

Just because a knife sticks to your fingernail doesn't mean that you have a great edge. You merely have a functioning edge. Ultimate sharpness is determined many other ways, but ultimately up the discretion of the user.

There is the "Murray Carter 3-finger method", which involves taking 3 fingers and spreading them over the length of the blade, then seeing if your fingers slide or not. This sounds very dangerous, but believe me, and Murray points this out, you will instinctively stop your fingers before they get cut, and placing 3 fingers down distributes the weight evenly, lessening the chance of a cut. When your 3 fingers stick you know you've "reached the edge" while sharpening. If your 3 fingers don't stick then you must go back down to a lower grit. This test will be a little more accurate than the fingernail test when you get towards the higher grits, but can be painful if you aren't very careful. :)

Another test is cutting a folded paper towel. This is great to use at lower grits to let you know you've reached the edge. Even a 120 grit edge will cut a folded paper towel on the cutting board, that is, if you've reached the edge. At this point you can move onto a finer grit.

I can go on, but let's let someone else jump in! :)



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Shaun Fernandez

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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Wed Apr 25, 2012 3:33 pm 
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When I first watch Murray Carter's three finger test it freaked me out. It is a subjective measure that requires the user to learn how to integrate what their fingers are perceiving. In my learning process I continued to used objective measures such as shaving arm hair in both directions, and push cutting a piece of paper from a fixed anchor point.
I think the three finger test is the most subject test of sharpness because if you do not train you perception correctly a 500 grit edge will feel sharper than a 1u edge simply because of the coarseness rather than the sharpness. However it has been my experience that the body can learn the difference and the three finger test can be one of the quickest measures on any knife at any time. :D
In contrast the anchored paper test is one of the most objective test I have found. Basically you take a piece of paper an make an anchor point. Then you attempt to push cut the paper by starting the furthest away from the anchor point, moving closer to the anchor until the knife cleanly push cuts. You can see it done in his video. http://youtu.be/6YexiF2PkcA
One test that I do for fun on most of my knives is the hair cut test. This is somewhat subjective because everyone's hair is different and you can create variance in the technique itself. Now with the edge facing up you take a single hair and move it into the edge. The edge should sever the hair. :shock:
Of course my left forearm is frequently devoid of hair in patches.


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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Wed Apr 25, 2012 10:18 pm 

Joined: Sun Apr 22, 2012 7:49 pm
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Can't really do the old finger test a lot as they are getting well used from knife work and stones. Normal push cut receipt paper is a nice little bench mark,as is the old arm hair shave, but when all is said and done you have to take it to food plain and simple. I don't care if it can shave the hair off a peach and leave the skin, if it can't blow through onions and such then back to the grinding stone. On a small side note. It should be mentioned that you don't need fifteen stones in order to get a piss-willy sharp edge. Hell, off of my natural 800 and 1k push cutting receipt paper isn't a problem at all. Take a house if you will. It's only as good as its foundation. Same as knife sharpening. If you do a bad job on the low grits and don't correct them and move past and finish it, you'll just end of having to go back and re-sharpen as you'll find that your edge well sucks for the most part. Sorry to get off topic a little, but personally speaking that is a good bench mark on how you know if your knife is sharp by seeing how good your foundation is. If that makes sense.


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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Thu Apr 26, 2012 6:38 am 
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I agree that the edge needs to be good at the 1k level. It will come back to haunt you if it's not!



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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Thu Apr 26, 2012 4:00 pm 

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Great useful info. I've been watching the videos on facebook with sharping techniques; but I doubt I have all the money to buy all those different kind of stone grits. Any suggestions would be great.


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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Thu Apr 26, 2012 5:08 pm 
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Thanks for the question ntaubs. We should start a separate topic for this question. What are some of the bare essentials? There are articles about this in the newsletter also. Please check back later today, I should have some info up for you.



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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Sat Apr 28, 2012 6:11 am 
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Honestly, just cutting up a lot of Bell Peppers. I find myself unconsciously adjusting my technique when cutting them in response to how the knife is performing.



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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Sat Apr 28, 2012 1:15 pm 

Joined: Sat Apr 28, 2012 12:44 pm
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Since invesring in water stones and better knives I have realized that you should sharpen a given blade depending on waht it's primary use will be. Being a self-taugh(with help from the 'Net)sharpener,waht \Iam saying is mostly experiental. I found that double-bevel knives used mostly for slicing need a little "tooth and bite" so I usually don't go past 3K with them. Those that I use mostly for veggie prep(chopping) I can take to 5K or even 8K. I did discover that a strop on newspaper makes a difference! Just my $.02USD.


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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Sat Apr 28, 2012 2:27 pm 
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Hey Redstickboy,

That is absolutely right, a blade should be as sharp as it needs to be for a given task. However, this is a long time debate between members of other forums. Some of us believe that a properly polished edge will last longer no matter what, while some believe you shouldn't go past 6,000 grit.

In hopes of preventing this side-topic from taking over this thread, we shall start another one.

What else do you guys use to test your knife's sharpness?



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 Post subject: Re: How do I know if my knife is sharp?
PostPosted: Wed May 02, 2012 1:11 am 

Joined: Tue May 01, 2012 9:37 pm
Posts: 365
Location: Pensacola, FL, USA
burkecutlery wrote:Honestly, just cutting up a lot of Bell Peppers. I find myself unconsciously adjusting my technique when cutting them in response to how the knife is performing.


The straight razor guys figured this out a while ago, that the the only meaningful test of your edge is to shave with it. Nothing else will do.

So the only meaningful test of the edge on a kitchen knife is to use it. All other tests can tell you something, but actual use of the knife will always be the only evaluation of the edge that you need.

I'll have to try cutting up bell peppers, Eamon. Thanks for suggesting it.

Rick


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