Testing the sharpness of a knife after sharpening

[Ken98660]

Here, to the best of my knowledge, are the three (3) most commonly used methods of testing a knife for sharpness after sharpening:

Slicing a piece of paper

Shaving the hair on your arm

Placing the newly sharpened edge of your knife against your thumbnail and seeing whether or not it "bites."

The paper cutting method is counterproductive imo because it has a tendency to dull the edge, and although I'm quite fond of the arm-shaving method (as it strikes me as being a fairly reliable method of testing a knife for sharpness) if you happen to be sharpening knives for a living like most of the folks in this forum then it won't take very long before you finally run out of body hair altogether.

Isn't there a better method of testing a knife for sharpness, preferably a method that doesn't involve a large cash expenditure ?

[cbwx34]

...
Slicing a piece of paper
...
The paper cutting method is counterproductive imo because it has a tendency to dull the edge
...

Took me a while to learn this, but you shouldn't see a noticeable dulling making a slice or two thru paper, to test the edge.  If you do, you're not properly deburring the edge.

So, the paper is telling you something...

[micha]

Hi Ken,

I think the paper slicing test ist quite valuable, and running the whole length of a freshly sharpened edge through a piece of paper tells a lot about the quality. The thinner the paper, the better.
Hence an old phonebook or warehouse catalog is always next to my workbench. Performing a slow cut over the whole length of the knife will also reveal breakouts or remaining micro-nicks, burr etc.

One single test cut will IMHO not cause the edge to dull notably - if it would, I'd consider getting better knives (Any physical test will cause more or less dullness, btw.)The thumbnail test is also valid, but may also be replaced by trying to cut into a bent sheet of paper. 

I'd add "Inspection with a good magnifying glass or pocket microscope" to the list. 


Other methods have the drawbacks you mentioned.
Mike

[Ken98660]

I've been reading in the comment sections of various YouTube videos that there's something called a "jeweler's loupe" which may (or may not) be useful in the realm of knife sharpening. I may even be inclined to get one of these providing that it has a noticeable advantage over a cheap illuminated magnifying glass.

[Ken S]

Ken,

I highly recommend the recent online class with Stig Reitan to you. Here is a link:

https://youtu.be/8uLMWXqobRM

I have had the pleasure of knowing Stig for eight years. Whenever Stig is demonstrating for Tormek anywhere In Ohio, I try to spend the day observing him. He is a real deal Tormek knife sharpening expert. He is also very practical.
We can all learn a lot from Stig.

Any use or sharpening testing will cause slight dulling of a knife edge. Even unwrapping a brand new double edge razor blade exposing it to the atmosphere will cause a slight deterioration of the BESS reading (a commonly used measure of sharpness). The real question is at what point does this very gradual loss of sharpness become a real world problem?

Ken (S)

[Ken98660]

Thanks Ken. I'm going to watch that video. Peace.

[RickKrung]

I've been reading in the comment sections of various YouTube videos that there's something called a "jeweler's loupe" which may (or may not) be useful in the realm of knife sharpening. I may even be inclined to get one of these providing that it has a noticeable advantage over a cheap illuminated magnifying glass.

Magnification of some sort can be extremely valuable.  I have found the usual "jeweler's loupe" to not be that useful, primarily due to its usual low magnification.  I've tried quite a few different hand lenses/scopes and some USB microscopes/cameras.  The absolute best magnifying tool I've found is the Kingmas 60X unit.  Can be a little getting used to how to use it, but by far better than anything else I've used. 

Rick

[cbwx34]

...
The absolute best magnifying tool I've found is the Kingmas 60X unit.  Can be a little getting used to how to use it, but by far better than anything else I've used. 

Rick

Kingmas 60X

(You had it as an email address).

Ken,

I highly recommend the recent online class with Stig Reitan to you. Here is a link:

https://youtu.be/8uLMWXqobRM
...

I think their video on honing might be more appropriate for this thread...

https://youtu.be/40AoJ8UBprI?t=675

[Ken S]

Perhaps so, CB. We are allowed to watch more than one online class, even all of them. 

Ken

[John_B]

$6.99 for KINGMAS Mini 60x Microscope; could not pass that one up.

I find slowly slicing a page from a telephone book is an excellent indicator of a well sharpened edge. Knife must be pretty sharp to cut this thin paper and you can easily feel any irregularities in the blade. BESS is good but only for one spot on blade. I am just as happy using Vadim's sharpness equivalency chart. For the knives I do for customers they fall into the BESS 100-150 range based on chart. This is significantly better than most out of the box knives.

Cardboard is abrasive and will dull an edge. Slicing thin paper should not be any worse than real cutting tasks a knife faces daily.

http://knifegrinders.com.au/Manuals/Sharpness_Chart.pdf

[cbwx34]

Perhaps so, CB. We are allowed to watch more than one online class, even all of them. 

Ken

In that case, perhaps a link to their main video page is in order...

https://www.youtube.com/TormekSharpening/videos

[Ken98660]

I find slowly slicing a page from a telephone book is an excellent indicator of a well sharpened edge. Knife must be pretty sharp to cut this thin paper and you can easily feel any irregularities in the blade. BESS is good but only for one spot on blade. I am just as happy using Vadim's sharpness equivalency chart. For the knives I do for customers they fall into the BESS 100-150 range based on chart. This is significantly better than most out of the box knives.

Cardboard is abrasive and will dull an edge. Slicing thin paper should not be any worse than real cutting tasks a knife faces daily.

http://knifegrinders.com.au/Manuals/Sharpness_Chart.pdf

I'm not sure that it's even possible to get ahold of a telephone book in the current day and age. Newspaper on the other hand could be the thinnest type of paper that's easy enough to procure in the digital age, but as for the suitability of using newspaper as a means of testing the sharpness of a knife's edge, about the only thing that I can say to that is .... ??

[micha]

As mentioned above, printed catalogs from your office or tools supplier are almost as good as phone books. There's no lack of those so far.
And their paper is more suitable for checking sharpness than that of newspapers.

[John_B]

Periodically I get a couple of add books left at my door. The paper in these is extremely thin. I have far more than I will ever need as one page suffices for several knives. In addition to sharpness it is easy to feel any imperfections that you might miss without magnification.

I was a bit shocked to see that the Kingmas 60X was only $6.99 on Amazon. Mine is on its way.

[micha]

FWIW, over here in Europe it's also sold under a different name: KIMILAR Mini 60X LED, at the horrendous price of 8.99€
for example: https://www.amazon.de/gp/product/B00X5LTKI4/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1&pldnSite=1