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TOPIC: Sharpness testing

Sharpness testing 2 months 3 weeks ago #17361

  • LeoBarr
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Apart from the 3 finger test which is good it is good to test further.
I read on another forum a very sensible remark - you would not test a saw on paper so the best test of a blade is on the medium that it is going to be used for .
Often in the past I tested for sharpness on paper but then one day I tried to cut some processed ham in the form of a plastic sausage I add the knife failed it did cut through the plastic after a couple of goes but not first go .
I find now I look to see if there are any reflective spots on the edge then I check the blade with three fingers more than likely alternating between looking and three fingers and then test on the medium that it will be used on .
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Re:Sharpness testing 2 months 3 weeks ago #17364

  • razoredgeknives
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Great point Leo! I normally test arm hair shaving ability (on both sides) and then I like to test on old rags or a piece of twine to check for toothiness. Now, I pretty much know what a 600x edge will perform like so I don't always do this, but it is a nice gauge if you are messing around with different grits!
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Sharpness testing 2 months 3 weeks ago #17366

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LeoBarr wrote:
Apart from the 3 finger test which is good it is good to test further.
I read on another forum a very sensible remark - you would not test a saw on paper so the best test of a blade is on the medium that it is going to be used for .
Often in the past I tested for sharpness on paper but then one day I tried to cut some processed ham in the form of a plastic sausage I add the knife failed it did cut through the plastic after a couple of goes but not first go .
I find now I look to see if there are any reflective spots on the edge then I check the blade with three fingers more than likely alternating between looking and three fingers and then test on the medium that it will be used on .

Totally agree...

Up to and including cutting the material the blade is designed for, I try nearly everything .... haven't built my own hanging sharpness tester.... I've dissected a laser pointer; well on my way to making my own GONIOMETER!

I slide a cork under little more than its own weight over the length of the edge to see if it "grabs" the same along the length of the blade. I slide a paper towel down the length to see if the edge picks up fibers. I slide a cotton patch down the length for the same reason.

I'm not so good with the three finger test while the knife is still in the vice.

In Eugene a few weeks ago at the knife show, I bought a small bunch of stuff from Bob Nash and Oldawan. He gifted me with one of those pen/stylus sharpness tester. (Thanks, again, for everything, Bob.)

Not the end-all and be-all but it adds another test! It helped me find why a knife stopped slice cutting at a certain point -- a micro-chip I could neither see nor feel any other way. Got it.

If my fingernails were longer they might serve the same purpose.

I also chase the magic marker until I remove that last little micro-dot of blue at the tip or the heel until I'm satisfied it's no longer there.

About something else someone once told me, "If there's a doubt; there is no doubt." It applies, for me, to sharpness testing. After any and all tests, if there's any doubt in my own mind and I'm not happy; then it's not done.

I'll stop... there's so much more.
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"Things work out best for those who make the best out of the way things work out."

"My goal is to be a good, practical knife sharpener. My dream is to polish molecules."
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Sharpness testing 2 months 3 weeks ago #17370

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The cork the, paper towel and first I have heard of it the pen/stylus testers for micro chips left over .

"any grinding of the secondary edge will make your blade cut better. Keep in mind that while the Primary edge initiates a cut, it is the geometry of the Secondary edge that allows the blade to be pushed 'through' that which you are cutting. The more acute the secondary edge, the easier it is to cut through things. Ultimate cutting performance from any given blade relies on the complex relationship between these two edges" , Murray Carter.

Just thought I would pass on these words of wisdom from the Master.
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Re:Sharpness testing 2 months 3 weeks ago #17376

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I use paper to make sure I got a clean edge. If its not it will grab the paper and I know I need more.
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Sharpness testing 2 months 2 weeks ago #17379

  • tcmeyer
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Leo:

Shortly after getting my WE system, trying to cut through a plastic sausage casing was the first eye-opener for me that my polished edges weren't the be-all and end-all. If your edge bevels are wide enough and polished enough, they'll float right over a slippery substrate. Their "buoyancy" can/will keep the edge from biting into the plastic. Hence the need for a more toothy, more narrow edge.

Convex or multi-bevel profiles serve to reduce the width of the edge's shoulders, approximating a more acutely-angled edge.

Thank you for the continuing education.
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Sharpness testing 2 months 2 weeks ago #17381

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LeoBarr wrote:
The cork the, paper towel and first I have heard of it the pen/stylus testers for micro chips left over .

The pen/stylus edge tester: www.oldawan.com/sharpen/edge-tester/
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Gib

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"Things work out best for those who make the best out of the way things work out."

"My goal is to be a good, practical knife sharpener. My dream is to polish molecules."
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