Swedish wood carving knife

[Jan]

Recently I bought for my grandchildren small Swedish wood carving knife. The length of the blade is 2.4" and blade thickness is slightly more than 0.1". The blade is made of laminated carbon steel, the core hardness should be between 58 to 60 HRC. If we use the results of Rockwell hardness study we can say that steel with 60 HRC is by 10% harder than 58 HRC steel.

The measured included angle of the Scandi grind is 29°.

BESS score is between 150 and 160.

Based on my measurements and calculations the thickness of the core of the blade is circa 0.06".

The Morakniv carving knife is not expensive (USD 25), but quality woodworking tool with premium-quality carbon knife steel.

Jan

   

   

[Mike Brubacher]

I see several interesting things in this post Jan. The knife is perfect. I attended a rural grade school grades 1-8 and the curriculum was a little different than today. In addition to the standard school art fare I learned hand sewing, knitting and in my 7th & 8th grade years, wood carving. Can't say that i was terribly proficient at any of them but it was good experience. I think that the wash cloth that I knitted began at about 12 inches wide and finished at 14 and today, I don't imagine that they'd let a kid spread his own butter if it involved a knife. Seeing your wood carving knife makes me want to take it up again. 

When you say "core" HRC I assume you mean exactly what you say but are you actually distinguishing hardness levels between the core metal of the blade and the surface? If so, then A; what leads you to believe that the two are different and B; how did you arrive at an estimation of the core hardness? If I've misunderstood your intent here then pardon me.

I've seen your optical knife angle instrument before but studied the picture a bit more this time. It's quite ingenuous. Reminds me of the HRC question we just took on in that I've seen this question asked a thousand times as well. The difference being that everybody has a suggestion for determining grind angle but none are even remotely as elegant or accurate as your solution. I realize that the mechanics here are key. Have you ever attempted an edge with a secondary bevel? If so, do you get two sets of reflections or just one? Next question, is the reflected laser line width indicative of the behind the edge measurement/sharpening angle and if so, is this readily apparent? This last question is with regard to thicker metal sharpened at more acute angle = wider bevel. Of course the limiting factor here might be the original width of the projected laser line.

As usual, great stuff Jan!

[Ken S]

Jan,

Although I am not a knife collector, I really like Morakniv. With good quality and functional design, Morakniv seems the perfect knives for both young and not so young users.

I am pleased you are passing along your love of using tools to your grandchildren.

Keep up the good grandparenting!

Ken

[Jan]

Mike and Ken, thanks for your kind responses.
 
During my youth we also had workshop works in the school and even agricultural works on the school ground. Our Ministry of Education considers to reintroduce it again.

What concerns "core" hardness. The manufacturer declares that: "The core of the blade is made of high carbon steel surrounded by a softer alloyed steel layer.”. Based on this sentence I deduced that the HRC 58-60 has to be the core hardness, because it is too high for the surrounding softer steel.

When I have inspected the bevel grind in detail, I saw a line/curve running parallel with the edge, some 0.12"above the cutting edge. I have assumed that it was caused by laminated character of the steel and not a remnant of grinding. Because I have measured the included angle, it was not difficult to calculate the thickness of the core of the blade (0.06")**. I plan to ask the manufacturer if I am correct.

     

The attached picture shows how the laser beam splits at the edge. If the bevel reflects laser light well you can see without difficulties also reflections on the secondary bevel or tapering blade. Reflections on a narrow microbevel are usually weak, difficult to photograph, but detectable in a low ambient light also.

   

   

Mike, you are correct, the incident laser beam has to be wide enough to illuminate both, the primary and secondary bevel. Not well focused laser beam is typical for inexpensive laser modules and in this situation we can use this inaccuracy for our goals.   The correct solution is to use some optical collimator, than you will not be limited by the blade thickness.

After some time you learn to understand the laser reflection images of the blade. For example, if the blade that has a convex grind (often hardly visible by the necked eye), you will get a bunch of weak reflected laser lines. The angles corresponding to the onset and the ending of this bunch carry info about curvature of the convex grind. Something similar is true for hollow grinded bevel also.

       

Jan

**P.S.: Japanese Suminagashi Takefu steel used for swords and for hunting knives is laminated steel with 23 layers. Middle layer thickness is also 0.06".

[Mike Brubacher]

Thanks Jan for the lesson and explanation. Very interesting. I can see where the system might get more difficult to use if most of the light is scattered as opposed to reflected. Of course that effect would be determined by the surface finish of the bevel as you point out. I wonder if there wouldn't be a very thin and shiny "sticky back" metal film (foil) available that might aid the process. Just wrap a strip over the edge and convert light scattering surfaces to reflective. We used to use this very same material for RF shielding but it was copper. Zinc or aluminum might do the job. I think that the foil we used is two thousandths of an inch thick (.002"), and comes on a paper backing. Just peel the metal foil off the backing and stick the foil where you wish. The adhesive back used here is conductive, not that it makes any difference in this application. Here's a picture of our copper foil.

   

Just looked at the picture and to tell you the truth this stuff is pretty shiny. You can see the partial reflected image of me shooting the picture.

[Jan]

Yes, Mike, it is a perfect idea to use thin metallic foil.  

Gold leafs may be as thin as 1/250,000 of an inch. Such a gold leaf is transparent.

Jan

[Ken S]

Morakniv sells a carving kit with this knife, a sheath, and a rough cut pine block for carving a traditional Swedish dale horse. If you go to tormek.com and to the Tormek friends videos, you will find an enjoyable video explaining the carved horses. The kit seems a delightful introduction to woodcarving.

Ken

Ps the kit can be ordered online for about $33 US.

[Bud]

It's winter now and I'm looking for things to do. I'm going to give this woodcarving thing a go Ken. I'm worried about my lack of artistic ability so hope that somehow the wood will forgive me.

[Mark Reich]

My favorite wood for carving is diamond willow. It's very forgiving, because the "diamonds" in the willow make it sort of like a "connect the dots" picture instead of a blank piece of paper.

[Bud]

Thanks for the tip Mark.