When I sharpen a double bevel blade, 95% pop out in the 140 – 155 gf (PT50B) range without really jumping through any hoops. Most of the time, right about 150 gf.  Just a basic sharpening.  When I see 160 gf or greater, I always suspect that there is still burr.  When that happens, a little more deburring will almost get the blade back to expected sharpness.
 
I have no idea what’s up with that 150 reading.  For whatever reason, my method of sharpening/deburring just produces edges about that sharp very predictably.  If it’s much sharper than that I am surprised, and if it’s much duller I suspect burr.
 
It seems that it is common not only for me, but also for others, to generally end up right around 100 gf for single bevel edges.  I wonder if there is some similar, common sharpness that folks see for double bevel edges.
 
So, I’m curious – what sharpness do you guys usually end up with when sharpening double bevel edges?

I'm not asking how sharp you can get a blade.  I'm just curious as to if there is some common sharpness for double bevel edges that you guys see after a basic sharpening and deburring.

I was thinking about digital image microscopy and wondered what the resolution of the human eye is and how that compared to a 20mp digital camera image sensor.

   
 
Of course it’s nowhere near that simple because the human eye does not have pixels, but rather rods for low light and cones that are color sensitive which are not evenly distributed over the retinal area.  There are about 120 million rods and 6 – 7 million cones. Additionally, we don’t actually see individual pixels, but rather move our eyes around and assemble a more highly detailed mental image than simply the total of rods and cones.
 
I found this on the web: http://www.clarkvision.com/articles/eye-resolution.html   It is an interesting read.
 
“So the megapixel equivalent numbers below refer to the spatial detail in an image that would be required to show what the human eye could see when you view a scene. 90 degrees * 60 arc-minutes/degree * 1/0.3 * 90 * 60 * 1/0.3 = 324,000,000 pixels (324 megapixels). 120 * 120 * 60 * 60 / (0.3 * 0.3) = 576 megapixels.”
 
My little 5 mp digital microscopy really doesn’t cut it, and I think Apple has a ways to go before any of their iThings truly have a retina display.

I was down to only one sacrificial knife for testing and experimenting, so I went to the local Salvation Army store to see if they had anything interesting.  Occasionally I get lucky and find something nice, but this time not so much.   90% of the knives were worn out serrated pieces of that shiny stainless spring steel crap, whatever that stuff is.  I did find one 7” Santoku for $1.99 and a little 3.5” paring for $0.99.  The steel seemed to be the next step up from the shiny spring steel stuff, but nothing special at all.
 
I decided to sharpen them both with a new, unused 120 grit Cubitron II belt because I wanted to break in the belt.  When those belts are new they are extremely sharp and aggressive, but calm down to just right after break in.
 
The cheapo little paring knife couldn’t take such a coarse abrasive and the edge just crumbled away in chunks rather then getting sharp.  I didn’t really care, so I bailed and moved to the Santoku which was far more interesting. 
 
The Santoku had no problem with the coarse abrasive and formed a large, heavy duty burr.  I started deburring with light pressure, 45° angle strokes on the rough side of a leather belt.  It was easy to see the burr bending back and forth.  I did that for awhile.  Then a while longer.  The some more.  The burr just kept bending and bending and bending…
 
So then I started applying more pressure and counted 26 strokes on each side, plus some occasional strokes at almost 90° to the belt.  After that the burr seemed mostly gone, but under a good light I could still see a hint of burr.  I took 3 sharpness readings: 150, 155, 165.  So I deburred more.  A lot more.  Maybe another 20 on each side.  That kind of thing.  Then I took readings again: 140, 145, 150. 
 
Every so often I run across a blade like that.  Whatever that no-name steel is, it creates an extremely malleable burr that is highly resistant to deburing.  Far, far more difficult and time consuming than most knives.  Almost like the burr was made of gold.  The stuff just bends and bends and bends and bends and…  It’s almost flabbergasting.  How can such a thin little piece of steel be so resilient?   Had I not seen it before, I might have even been gobsmacked.
 
I guess it just goes to show that no two burrs are created equal.  It also shows the importance of carefully checking that the entire burr is removed as the effort required for complete burr removal is potentially highly variable from blade to blade.

I have to admit being in somewhat of a quandary as to how to test the MicroForge edge.  After a bit of head scratching, I decided to compare it to a smooth, polished edge because that is so commonly used.
 
I ground a blade, using 400, 600, 900 grit belts and finished with a 9 micron 3M Microfinishing Film belt.  Deburring was accomplished with the rough side of a leather belt.  Dividing the blade in thirds, three sharpness readings revealed 120, 130 and 125 gf.  Good enough.
 
The bevel was shiny, very reflective and smooth.  The blade performed as you would expect; shaved hair, effortlessly pushed cut paper and melted through tomato skin.  I was adjusting it under the microscope and realized that at some point I must have brushed the edge as I noticed evidence that I was suffering some minor epidermal leakage.  I’m always amazed at how easily that happens.
 
Here is an image of the bevel using side lighting to avoid reflection.  In other images that follow you will see the bevel is actually a mirror finish and difficult to photograph due to reflection.

   
 
Using moderately firm pressure and starting from the tip as per the included instructions, I pushed the first half of the blade through the MicroForge slot in the handle, leaving the other half of the knife untouched.  It passed through so smoothly and with so little tactile feedback my initial impression was that probably I had not used enough pressure and that not much had happened.  However, a quick look at the blade revealed I was laboring under a delusion.
 
Much to my surprise it had created a very fine, toothed edge that reminded me of a fine tooth, metal cutting hacksaw blade only with much smaller teeth.  “Micro” in MicroForge is apropos.  Closer examination reveals the hacksaw analogy is not exactly correct as it doesn’t create a row of teeth, but small depressions regularly spaced along the edge of the blade.  The ramifications of his distinction gained apparent significance during testing.
 
I had read a review that stated that drawing the blade over the edge of a piece of paper had a “zippy” feeling.  Well, I couldn’t resist, and sure enough it felt “zippy”.  I am at a loss for a better adjective.  It’s easier to imagine how it could feel “zippy” after checking out these images.
 
   
   

 
Here is a closer look at the edge fresh from the MicroForge.  The last image shows the edge against the open jaws of a Mitutoyo caliper open to 1.00 mm. Sorry about the blurry image.  Attempting to maintain focus and get it all within the FOV proved challenging.  Note how the steel is pushed up around the edges of the depressions.  I was surprised that simply pulling the blade over the little MicroForge roller can push steel around like that.  It appears to me that the depressions are not ground, but rather the steel is just pushed to either side.  Amazing.

   
   
 
I then took six sharpness readings within the MicroForged area of the blade; 165, 145, 175, 195, 230, 213.  Recall before the MicroForge the blade started at 120, 130 and 125 gf.  I took six readings because I didn’t know if the test media landed inside of the depressions or on the edge between depressions, so I thought more readings might be instructive.  I still don’t, so your guess is as good as mine.
 
Following the instructions, I then performed 10 light alternating strokes on the smooth sides of the ceramic rod.  The Ceramic rod is more abrasive than it feels, and this action appears to have reduced the raised, deformed bulges of steel around the edges of the depressions.  You can also observe the scratches in the bevel from the ceramic rod and some minor burr creation reflecting light on the edge that could account for the generally higher sharpness readings even if the test media was contacting the blade between the MicroForge depressions.

   
 
I then took six more readings of the MicroForge section; 185, 220, 290,330, 235,260.  The readings indicate using the ceramic rod slightly dulled the edge.
 
So, how did the blade perform?  To test that I sliced ripe but firm Moby Grape tomatoes and both the MicroForged section of the blade and the smooth part sliced effortlessly.  The only difference was that I could feel a very slight resistance as the Microforge section grabbed at the skin, while the smooth part of the blade just melted through.  The difference was very, very slight and even difficult to detect.  Suffice it to say that both sliced the tomatoes effortlessly and admirably. 
 
I thought this to be unremarkable as the blade was extremely sharp to begin with.  However, the MicroForged part tested as less sharp but it had the advantage of being “toothy”.  About the only thing I could derive from testing so far was the MicroForged blade seemed to cut about as well as the original edge. 
 
While not unexpected, it was a bit frustrating because the test had not demonstrated any significant differentiation between the MicroForged edge and the original edge.  Work Sharp states, “MicroForge technology creates a longer lasting, more durable edge…”  So, to test that claim I reduced a cardboard box to a pile of shredded smithereens.

     
 
After this abuse of the edge I took three sharpness readings of the smooth section of blade and three of the MicroForged section.  Smooth: 270, 240, 315.  MicroForge: 400, 440, 415.
 
Now here is the interesting part.  Even though the smooth section of blade tested as sharper, the MicroForged section seemed to slice tomatoes maybe ever so slightly better.  That said, I should emphasize the difference was not really remarkable.  Both sections of the blade were able to slice the tomatoes, both required a significant amount of slicing action to penetrate the skin, but it seemed the MicroForged edge performed, maybe, just ever so slightly better.  It was a close call however, and I had to do a lot of slicing to arrive at that conclusion.  Nonetheless I guess I’ll give the edge to the MicroForge.  Is there a pun here?
 
That really surprised me.  I had decided to use tomatoes for testing because I thought the toothy quality of the MicroForge blade would excel and perform much better tearing through the skin of a tomato than even a slightly rolled and dull smooth edge.  I wondered how the performance difference could be so diminutive and unremarkable. 
 
You may recall that earlier I stated, “Closer examination reveals the hacksaw analogy is not exactly correct as it doesn’t create a row of teeth, but rather small depressions regularly spaced along the edge of the blade.  The ramifications of this distinction gained apparent significance during testing.”  It was at this point I started wondering if the sections of blade between the MicroForge depressions affected how the blade performed significantly more than the MicroForge depressions did.  In other words, the depressions didn’t seem to have nearly as much influence on the performance of the edge as I would have expected.  I would have expected the MicroForge edge to have performed more like a conventional serrated blade, and as the blade dulled it would continue to cut significantly better than the smooth blade, but oddly, that was not what the tomato cutting was indicating.
 
The interior edges of the little depressions are more protected from dulling that the flat, exposed edge between them and should, in theory, remain sharper.  But how much influence does this have on cutting performance?  To test this and to save me from having to spend the afternoon obliterating cardboard boxes, I dragged the blade over 180 grit sandpaper 5 times as though I was trying to cut it into strips.  This efficiently and pretty evenly dulled the entire flat exposed areas of the blade and, in theory at least, should have impacted the interior of the depressions to a much lesser extent if at all.
 
Indeed, the sandpaper performed admirably.  I took three sharpness readings in the smooth area of the blade: 820, 1090, 950 gf.  For the MicroForged area, 950, 825, 975.  
 
Then I tried slicing more tomatoes.  As far as I could tell the entire blade cut equally poorly.  It was difficult to slice through the tomatoes without crushing them.  It took a lot of gentle slicing to penetrate the skin and every attempt to expedite the process resulted simply mashing the tomato rather than cutting it.  Here the smooth edge seemed to very slightly outperform the MicroForged edge.  That said, I should emphasize the difference was not really remarkable.  Both sections of the blade were able to slice the tomatoes, both required a significant amount of slicing action to penetrate the skin, but it seemed the smooth edge performed, maybe, just ever so slightly better.  I had to do a lot of slicing to arrive at that conclusion.  The difference was that close.  Sound familiar?  It is, except in this case I guess I’ll give the edge to the smooth edge.
 
Purely speculating, I am guessing that the areas of the blade between the MicroForge recesses are responsible for the majority of cutting performance of the blade.  Therefore, initial blade sharpness before applying the MicroForge is of paramount importance.  This seems reasonable considering that even after applying the MicoForge the majority of the edge is basically untouched.  I say basically untouched because both observation and sharpness readings seem to indicate that the roller also touched the part of the blade between the indentations and affected the sharpness of those areas.
 
Here is an image of the final smooth area of the blade.  You can see how the edge rolled into one, long, dull roll of steel.  I believe this continuous, contiguous rolling of smooth edges is illustrative of why smooth edges suffer general performance degradation more quickly than toothy edges which roll more unevenly. 

   

Here is the final image of the MicroForge edge.  The indentations are still there, but the area between is rolled, rounded and dull.  Surprising to me is that the depressions seemed to have little affect when slice cutting.

   
 
This was obviously a very limited and quick attempt to evaluate the MicroForge edge.  Is this a fair test of how a MicroForge edge would perform in real world use?  In some ways I think yes, in others no.  The part of the testing before the sandpaper seems reasonable, but running the blade over sandpaper is extreme and probably not representative of any type of reasonable real world use.  A far superior, more reasonable and informative test would be for someone like Mr. Max The Knife to get these edges into a commercial kitchen and evaluate the performance over a few weeks of daily use.  I am looking forward to other forum members impressions after putting the tool through its paces.
 
In closing, I am not going to offer any personal opinions or attempt to form any conclusions here other than to say that is what I did and observed.  Verily, your mileage may very well vary.
 
This was just one limited test and in no way extensive, comprehensive or conclusive.

-------------------------------
An addendum:
 
My apologies.  I forgot to include that after shredding the cardboard box I tried cutting some polypropylene baler twine.  The twine is formed from loosely twisted plastic fibers.  It’s a good test because a rolled smooth edge tends to just slide on the surface of the plastic.

   
 
Both the smooth and MicroForge edge were able to cut it with about the same amount of pressure required, but with a significant difference.  The smooth part of the blade, as expected, slid as it cut.   The MicroForged section of the blade didn’t slide on the twine at all.  The little depressions on the edge gripped the loose strands of plastic fiber and held fast as pressure was applied until the twine cleaved. 
 
As I mentioned, the pressure required to finish the cut was about the same, but the cutting action between the two was very different.  When pushing the MicroForge section of blade onto the twine, the blade just stopped.  Continued pressure then cut the twine.  The smooth part of the blade slid, but cut the twine as it was sliding.  Both cut the twine, but so differently it is difficult to compare the two.  One was very grabby, the other a smooth cut.
 
For cutting plastic baler twine, I can imagine that if the smooth part of the edge was any duller, the MicroForge edge may have outperformed the smooth edge.

My first exposure to Edge on Up testing and BESS was when Steve Bottorff very generously sent me a KN-100 with instructions to "use it until I got bored with it". Little did either of us know that after several years and two more EoU testers, I am still not bored with it. Sadly, in the marketplace, it seems to have been eclipsed by the quicker to use PT 50 models. They are very nice and quick to use, however, for accurate work, the KN-100 is still very comfortable and very accurate. The old standby still works as well as it ever did, and that was pretty damn good!

Ken

Thanks to Mr. Rupert I have the Work Sharp M3 Knife Sharpener here for testing.  When I have completed checking it out, I will send it to our esteemed moderator and bladesmith Mr. Mark for further evaluation.  A big thanks for your community minded generosity Mr. Rupert!
 
Before receiving the M3 and having only seen it in pictures, I was guessing that it would be a fairly cheap thing with a cheesy, light-weight plastic handle.  Suffice it to say, I was wrong.
 
It arrived professionally packaged and my first impression was that it was much heavier than I would have expected. 

   
   
   

Nothing about it evokes a feeling of cheap and flimsy at all.  The handle has weight and heft, and is big enough around for a firm grip even for larger hands.  The surface is non-slip knurled rubber, and feels very secure in the hand.  I’m sure that even wet slipping would not be a problem.

   
 
According to Work Sharp the ceramic rod is 12 micron, so around 1500 grit.  It feels very smooth to the touch.  That’s about the abrasiveness that I like in a ceramic rod used primarily for edge straightening maintenance rather than sharpening.  Two opposing sides of the rod are flat with ridges running the length of the rod and parallel to it.  The other two sides are rounded. 

   
 
Work Sharp states the diamond sharpening rod is 325 grit, and it feels sharp and pretty aggressive.  I have no doubt it can remove steel.  A nice touch is that a sturdy plastic sheath is included.

     
 
Both the ceramic and diamond rods have a metal end that when inserted into the handle slide over a steel post and are held firmly in place by a strong magnet.  Both fit the handle perfectly and there is no wobble.  I suspect this arrangement is very durable.
 
The business end of the handle contains the MicroForge engine.  It consists of a freewheeling, ~7 mm diameter ridged metal wheel set at about 45° from the handle.  The idea is that you hold the blade flat against the handle and with moderately firm pressure drag the blade through the MicroForge roller once.  The optimal amount of pressure required is not stated as far as I can discover.  Somewhere I read about the same amount of pressure required to cut a sweet potato, whatever that means.  I suspect that it may vary from blade to blade, and that with some experience the user develops a “feel” for it.  That type of thing.

   
 
At this point I cannot speak to the durability of the unit, or how long the MicroForge wheel will remain sharp enough to function adequately.  It would be nice if the wheel was user replaceable, but it does not appear to be so.   Maybe that is a non-issue.  If you look closely at the picture of the wheel, it appears that it is either quite coarsely ground or that it might be coated with abrasive.  It is difficult to tell.  Could it be diamond coated?  That would certainly enhance durability. 

   
 
That’s as far as I have gotten so far.  I’ll conclude this part of the review by saying that the M3 appears to be a very well considered, solid and quality tool.

In this post, http://bessex.com/forum/showthread.php?t...65#pid1265
 
I was talking about sharpening a single bevel chisel, and how easy it is to sharpen them to 100 gf sharpness.  I blurted, “I was surprised that it ended up @ 100 gf sharpness considering it is a 25° single bevel.  I would have thought that a more acute angle like a 15° dps knife would be easier to sharpen to 100 gf, but that was not the case.  The chisel sharpened to 100 gf without jumping through any hoops at all.”
 
Further in the thread, http://bessex.com/forum/showthread.php?t...78#pid1278
 
Mr. EOU stated, “To tell you the truth, we are very intrigued by the sharpness levels reported in single bevel edges. We do not doubt for a second that these edges are easily sharpened to that level because it is an edge commonly used in medical applications and we have seen reports of very similar successes before.”
 
I know that Mr. Ken routinely sharpens single side bevel chisels to 100 gf or sharper on the Tormek. 
 
I remember when I sharpened that chisel I thought the 100 gf sharpness without really trying was interesting, but for some reason didn’t give it further consideration.  But now I’m wondering if a single bevel edge can actually be sharper then a double bevel.  DE razor blades are double bevel.  Why not single bevel?
 
I know some knives are sharpened with one side bevel more acute than the other.  What is the reason for that?  If indeed a single side bevel can be sharper than an equal double side bevel, does it also follow that a 15° bevel on one side with a 20° bevel on the other sharper than a double bevel of equal angles simply because the bevels are not equal? 
 
I’m totally clueless!  Any ideas?

Almost all of the knives I sharpen are your basic kitchen and pocket knives.  No fine grain really hard super steel, just your basic blades.  As far as I can tell, most of these are in the RHC 56-59 range.
 
The interesting thing is that, almost always, they end up right about 150 gf sharpness.  It’s so predictable I hardly need to bother with a sharpness test.  I don’t do anything special, just throw some belt on the Kally, sharpen, deburr and that’s what happens. 
 
Even though they are all about the same hardness, it happens with different knives with steels of various names sharpened in the 15° - 20° bevel range.  Abrasive coarseness does not seem to be a factor as I see the same results using a 600 grit sic belt or a 120 grit Cubitron belt.  As long as the blade is well debured, they all seem to end up right about that sharp.
 
I have a friend that also sharpens using a Kally and he has noted the same thing.  While I have discussed sharpening with him, whatever exact method he uses is of his own invention.  I only mention it because I found the coincidence curious.
 
Mr. Mark recently posted, “Measuring initial sharpness of all three blades after the 140 Atoma showed I needed to be more careful and thorough about removing the burr. I was getting up to 230, and down to 150 on different parts of the blades. I tried two alternating passes per side +1-2*, and the apexes were clean and sharp. I could see the hint of microbevel with 10x, but they were way more uniform in the 150 range.”
 
There’s that magic 150 gf sharpness number again.  Sharpen, deburr, and… surprise!  ~150 gf.  Mr. Mark mentioned the blade was a 4" Wharncliffe.  I don’t know the exact model, but a quick Google search indicates RHC 57-59 on most of them.
 
Obviously with such a diminutive data set it would be foolish to even attempt to form any conclusions based upon it.  Nonetheless, I’ve seen that happen so many times with my own sharpening and seeing other folks with basically the same results has me wondering.
 
Foolish speculation has me wondering if steel blades within the RHC 56 – 59 sharpness range, sharpened without any special effort, tend to be about 150 gf sharpness and generally not much sharper.
 
If there is anything to that, and I’m not saying that there is, I wonder if it has something to do with the metallurgy of the blade. 
 
This could obviously be nothing more than utter blather, but I found it curious enough to bother to type all this stuff and post it.

If I got a tank of liquid nitrogen, could I get a blade cold enough to:
http://www.arrowcryogenics.com/cryogenic...-deburring


The Deflashing and Deburring Process
Using liquid nitrogen during our deflashing and deburring process, components are lowered to a temperature that allows the material to become brittle. Then, utilizing our cryogenic deflashing machines the flash and burrs are easily removed without altering the finish on the parts.
 
How cold would steel have to be to become brittle enough affect deburring?

How about dry ice?  How about just sticking it in the freezer?
 
Would the blade edge instantly warm too much the moment it was removed from the source of cold?

After looking around a bit, I guess storing liquid nitrogen is not exactly practical.  Dry ice a cheap though and apparently you can purchase various cryo freeze stuff in handy cans. 

This is probably a really silly post, but it got me wondering.

I've been wondering for a long time when we were going to start talking about edge retention, when I came upon the closed post by Mr Mike Brubacher at the top of this index page. It's definitely worth a re-read. There was/is/should be an intended mission here that we are totally overlooking. 

I know it's fun to see low numbers on a fresh edge, but that really isn't telling much of the story. It's just the fresh dawn of the edge, or even slightly before that. Like you're still kinda in the dark. You don't know how much you can cut.

Edge retention really is of much greater significance than initial sharpness, correct?