USB microscropsy - Getting the best image quality

[Jan]

Grepper, I use Tormek terminology here, so the edge angle = the included bevel angle. You are correct, resharpening the Victorinox blade to 30° edge angle I brought it back to factory spec. I have measured it before and after the resharpening with my laser goniometer so I am sure about the angle with an accuracy of +/- 0.5°.

In this country they are quite common outdoor Swedish knives (e.g. Morakniv) with Scandi grind. I was surprised that they have only a 22.5° edge angle, the grind length is 6 mm. The heavy duty version comes with 26°. 

Do you sharpen blades with Scandi grind on Tormek?

Jan

[grepper]

I have never sharpened such a beast with a 6 mm bevel.  I'm surprised that an "outdoor" knife would have such a thin edge.  Generally they tend to go with a thicker bevel due to the abuse an "outdoor" is subjected to.

Herman, I hope that honing is more than cosmetic operation. Nevertheless in my understanding even below a scratch-free surface they are some groups of atoms in irregular positions as remnants of deep scratches. Those linear defects are called dislocations and are not visible on the surface.

Assuming that crystalline defects weaken the blade substructure and are caused by, and proportional to the depth of the scratch, then it would stand to reason that we should all spend forever sharpening with the finest abrasive possible from the start!

Nonetheless, a smooth cutting edge will of course be more durable than a "toothy" edge because there are not any laterally unsupported areas of the edge.  So, I think honing is indeed more than cosmetic as it removes burr and scratches at the edge. 

Jan uttered: "At this point it is important to note that crystalline defects are not always bad. Some of them were introduced intentionally to manipulate the steel mechanical properties."

It would indeed be remarkable if the intentionally introduced crystalline defects just happened to line up under scratched areas.  But, it could be magic steel, designed to respond with crystalline realignment under areas of stress to actually strengthen and support those areas.  But that could be detrimental because the hardened areas would result in uneven wear over time. 

Even in the presence of this most enlightening and erudite information, lacking any real alternatives, I guess I'll just blunder forth sharpening and honing like usual.  Except... I'll cringe a little whenever I feel the need to use a coarse grind. 

[grepper]

Jan-  You spiked my interest so I did a little reading on Mora knives.  I wondered why an "outdoor" type of knife would be sharpened to such an acute bevel angle.  I found this on the Morakniv website:

Knife blades made of hardenable stainless steel - 12C27 and 14C28N, hardened to HRC 56-58 - are found on knives with extreme strength and a long life. They also have a very high resistance to moisture, which otherwise can make the blades rust. Stainless steel stays sharp for much longer than carbon steel and is far less sensitive to rust.

I know how HRC 56-58 performs.  Nothing to really write home about, IMHO.  I mean, it's ok, but a super sharp edge won't make it through an evening of chopping kohlrabi, or dare I say carrots or possibly broccoli, or even potatoes for that matter without losing its super keenness.  I know you are probably wondering, how about horizontally slicing sashimi?  Ok.  That would probably be just fine.

Following links, I ended up on Blade Forums and folks said the best way to sharpen them is on a flat stone, which makes sense as a Scandi grind is by definition a flat grind.  There was discussion of the problem of edge roll when doing something like whittling hardwood, etc., which does not surprise me considering the HRC and the acuteness of the bevel angle.  People attempted alleviation of the edge roll problem by adding a secondary bevel. Then the purists chimed in and the discussion deteriorated into, well..., then that's not really a Scandi grind, bla, bla, bla. 

Anyway, they look like a fine knife and would no doubt cut very impressively, especially right out of the box or after a fresh sharpening, but as you say, such a blade would have limited edge retention, especially in an "outdoor" environment.  Amazon has them for $12.00 - $60.00 U.S. depending on model.

The reasoning behind choosing such an acute bevel angle for an "outdoor" knife, especially @ HRC 56-58, still eludes me.

[Jan]

Jan uttered: "At this point it is important to note that crystalline defects are not always bad. Some of them were introduced intentionally to manipulate the steel mechanical properties."

It would indeed be remarkable if the inteThentionally introduced crystalline defects just happened to line up under scratched areas.  But, it could be magic steel, designed to respond with crystalline realignment under areas of stress to actually strengthen and support those areas.  But that could be detrimental because the hardened areas would result in uneven wear over time. 

Even in the presence of this most enlightening and erudite information, lacking any real alternatives, I guess I'll just blunder forth sharpening and honing like usual.  Except... I'll cringe a little whenever I feel the need to use a coarse grind. 

Grepper, it is correct that you think critically about my posts here. My thoughts are partially recollections of my past experience I gained as a student working in a X-ray lab of a metallurgical department. I was measuring steel lattice constant, which is the distance between atoms of iron.

The statement: "At this point it is important to note that crystalline defects are not always bad. Some of them were introduced intentionally to manipulate the steel mechanical properties." is correct.

From physical point of view e.g. carbon atoms added to iron to make a steel are point defects of the lattice structure. Because the carbon atoms are almost two times smaller than the iron atoms, they fit into the open space between bulk atoms of the lattice. The effect of carbon content on the properties of steel is well known. 

Other crystal defects are linear and planar. Some of them can move within the material quite easily e.g. when bending the blade. Important is that dislocations determine the strength of the material.

Steel is a magic material for me!  Especially its magnetic properties are fascinating me from childhood.

Jan

[Jan]

A nice review "Morakniv – A Look at the Classics" you can find at http://tacticalreviews.co.uk/wp/?p=583

The reasoning behind choosing such an acute bevel angle for an "outdoor" knife, especially @ HRC 56-58, still eludes me.

The 22.5° edge angle of Morakniv knives is not so unusual. I have two craftsman's knives produced by Hultafors in Sweden. The Plumber´s knife shown in the attachment has a 20° edge angle! The blade is made from Japanese knife stainless steel, 2.5 mm thick, which was hardened to 57–59 HRC.

Jan

[Ken S]

I am a fan of Mora knives. I am not a knife collector; I just like Mora knives. They have the functional appearance of a woodsman's tool, not a fighting weapon. The design is clean; the materials simple and the machining well done.

Ken