OAUSA Net - 11/15/18 & 3/14/19 - Edged Implements I & II

[DaveK]

EDGED IMPLEMENTS

Back in November of last year, we did one of our favorite nets, Edged Implements. Our guest speaker was Daniel Humphries, and we learned, in addition to his impressive expertise with edged implement, that we just didn't have enough time to cover all the points on these important tools. Between the holidays, conflicting schedules, power outages and severe wind storms, we couldn't schedule the second half of this net - that is until now.

We are back, Daniel is ready, and we can't wait. What you see below is the original preview for this net, including all of the topics that we didn't cover in the first net. So here we go!!!!!!!!!!

Part of your essential outdoor gear should be edged implements (such as knives), whether in your vehicle, in your emergency supplies, your bug out bag, or what you always carry on your person. Edged implements go beyond just knives, however, and include hatchets, axes, shovels, machetes, saws, multi-tools, and even such things as chain saws. Although the net will primarily focus on knives, we will cover some others as well.

Our guest for this net will be Daniel Humphries, KI7NAI, who is an engineer with a great deal of knowledge on this subject. Post your questions or comments here and join us on the net.

[KI7NAI]

Hardness and toughness

Hardness refers to a material's ability to resist deformation, in the knife industry (as well as any other metal working industry) hardness is measured using a rockwell hardness tester, a special tool that uses a diamond tool of a specific geometry that is forced into the metal with a specific force, the depth of the resulting indentation determines the hardness. For knife blades hardness is typically expressed in HRC or Rockwell C. Normally cutlery falls in the range of 50-65HRC depending on the material and the intended use.


Ductility is a material's ability to deform under stress, a ductile material will bend before breaking. In knife blades ductility isn't necessarily desirable, but it's often referred to when comparing steels because ductility relates to toughness. Toughness is a combination of ductility and strength, it is normally measured with a Charpy notch test where a sample of a specified geometry is impacted with a specific weight dropped from a specific height and the energy absorbed in the impact is recorded as the toughness. For blades this is normally 20-85 Ft Lb depending on the material and the intended use.

Hardness and toughness are a tradeoff, harder materials have lower toughness and tougher materials have lower hardness. Compare a glass bottle to a plastic bottle, the glass bottle is very hard but will easily crack if impacted, the plastic bottle is very soft, but will resist impacts.



Ultimately hardness determines wear resistance, which is the ability to cut through abrasive things without dulling. Knife steels have been developed to maintain high toughness at high hardness.

[KI7NAI]

In the last 2 decades Powder Metals have grown popular, with improvements in manufacturing processes the cost has dropped considerably and superior alloys have been developed. At this point anybody who is a knife enthusiast most likely owns one or several knives with a powder metal blade.



The goal of powder metal is to provide a finer and more consistent grain structure. Because the metal is powdered and sintered the grain growth is limited by the physical boundary of the powder sphere. Highly alloyed steels can be produced with even distribution of small carbides, if the same alloy were produced with conventional manufacturing processes the carbide grains would grow together and become un-workable.


Powder metal has tangibly superior characteristics compared to traditional steels, it can be heat treated harder for better wear resistance without sacrificing toughness. Theoretically the fine grain structure of powder metals allows for sharper edges as the small carbides are less likely to tear out during sharpening. In the real world, your mileage may vary.

[KI7NAI]

Steel comparison

Metallurgy is a very complicated topic, comparing one steel to another can be very confusing. Reputable knife manufacturers will provide some guidelines for comparing one steel to another. Spyderco has a fairly comprehensive comparison tool on their website: https://www.spyderco.com/edge-u-cation/steel-chart/ this tool allows you to compare the percentages of certain elements within the alloy.

Steel composition chart.png (12.79 KiB) Viewed 753 times

Steel composition chart II.png (17.12 KiB) Viewed 751 times

Generally speaking the following assumptions can be made when comparing one steel to another
Carbon: The higher the carbon content the harder the steel can be heat treated
Chromium: Chromium increases toughness and wear resistance, as well as gives the steel stain resistant properties, steels with more than 13% chromium are considered stainless
Cobalt: Increases hardness and strength
Manganese: increases hardness, makes the steel more stable in quench, increases wear resistance and tensile strength
molybdenum: increases hardness and high temperature strength, improves machinability, improves corrosion resistance, is a carbide former
Nickel: increases ductility and toughness
Niobium: Is a grain refiner, carbide former, improves strength and toughness.
Nitrogen: Can replace carbon in steels, increases stain resistance
Phosphorous: Considered an impurity in steel, can cause brittleness
Silicon: Can increase toughness and hardness, helps to remove impurities from steel
Sulfur: Considered an impurity in steel, in small amounts can improve machinability
Tungsten: Forms carbides and promotes wear resistance
Vanadium: Helps control grain growth, increases toughness and strength



There are lots of blade steels to choose from, an incomplete list includes
1. A2
2. D2
3. O1
4. M4
5. W1
6. CPM 3v
7. 52100
8. 154CM
9. CPM 154
10. ATS-34
11. 420HC
12. 440C
13. CPM S30V
14. CPM S35VN
15. CPM S110V
16. CPM 20CV
17. CTS 204P
18. M390
19. Elmax
20. 12C27M
21. 13C26
22. 14C28N
23. 8Cr14MoV

I'll talk about my experiences with most of these. Please share your experiences with any of these steels or others I haven't listed.

[KI7NAI]

Excessively hard, wear resistant steels can be very difficult to sharpen with common honing stones. Most of the powder metals will require diamond hones to sharpen


Because of the difficulty sharpening high hardness steels great care should be taken to sharpen the blade with precise angles so you're only removing the minimal amount of material necessary. There are a number of sharpening systems, most of them are not inexpensive, Wicked edge, Edge Pro, Lansky, and others make sharpening systems for home sharpening with a very short learning curve.

Lansky


Wicked Edge


Edge Pro



A DIY version can be made inexpensively, this version uses automotive finishing sandpapers as an abrasive.


https://www.youtube.com/watch?v=Htow3lz_Z8M

[KI7NAI]

Crock sticks are a simple sharpening system using ceramic rods that are set at a specific angle, with a little practice these sharpening systems can provide very sharp edges


Crocksticks


The Spyderco Sharpmaker is another take on the crock sticks, it's a little more versatile for sharpening serrated blades, fish hooks and other unusual geometry.


Spyderco Sharpmaker


Natural stones and waterstones have been used for centuries, they are still very useful for sharpening most steels, but require considerably more skill. Stones are almost always used in a progression from coarse to fine regardless of the sharpening system used. Large bench stones, especially high quality Japanese waterstones can cost hundreds of dollars, much smaller stones are often used with sharpening systems, although the initial investment is high to pay for the sharpening mechanism, in the long run the cost savings of smaller stones or alternative abrasives makes the cost more comparable.

[KI7NAI]

Freehand sharpening

Sharpening freehand is a skill every knife enthusiast should strive to learn. I have found using a the sharpie trick has helped me to build muscle memory to sharpen more efficiently.
https://www.youtube.com/watch?v=mvl-Y5bZwtw

SHARPENIG PROGRESSION.jpg (343.35 KiB) Viewed 742 times

Regardless of the sharpening method used the progression from dull to sharp should always include forming a wire edge or burr, once the burr is formed the two bevels have completely intersected and the burr can be polished away. Certain steels are easier to form a wire edge on, some steels will develop a very pronounced burr, coarse grained, high hardness steels may need magnification to see the burr form.

[KI7NAI]

The work sharp electric sharpener is supposed to be user friendly


Work Sharp

A paper wheel is another option


Paper Wheel

Grinding wheels and other powered sharpeners require a lot of skill to use, it's easy to destroy a blade either by removing too much material or by overheating the blade when using powered equipment. Hand sharpening is recommended for anybody who isn't a professional.

[KI7NAI]

The two most common blade geometries are flat ground (or variations of a flat grind) and hollow ground. How the blade geometry is formed plays an important role in how much the blade cost and the materials used.

Flat grinding is used for most high end blades with powdered metal steels.
https://youtu.be/LSZ9F0MNi5o

Hollow grinding is a faster process that grinds both sides of the blade simultaneously. It's not very easy to see what's going on in this video but I'll discus in detail how the machine works during the net.
https://youtu.be/8S6p-IR6vy4

Blade Grinds.jpg (59.5 KiB) Viewed 336 times

Flat ground blades are very strong, there is a lot of material supporting the edge, as the blade cuts into the material it is gradually wedged apart. A hollow ground blade creates a very thin cutting edge, these blades can perform very well, but the hollow grind can very abruptly wedge into a material when making deep cuts.

Scandi grinds found on Mora knives is a variation of a flat grind, the full flat grind found on many spyderco knives is another variation of a flat grind. Chris Reeves uses a proprietary process to form a very shallow hollow grind, it's nearly a flat grind with a very slight concavity that cuts very well. Many of the traditional slip joint folders were originally manufactured with a flat grind, as factories grew and demand increased some of the more recent models have moved to hollow ground blades, especially brands like Schrade, Old Timer, Uncle Henry, that have gone out of business and the names and trademarks were bought by Chinese factories.

My favorite grind depends on the usage, for an everyday carry knife I like a hollow ground blade, I find they cut through thin materials like packing tape, envelopes and cardboard easily. For camping or other outdoor activities where I might be cutting into something with considerable force I like a flat ground blade. I'm not a huge fan of serrated blades because of the difficulty sharpening the serrations, that said when the serrations are sharp, they do cut extraordinarily well.

[KI7NAI]

handle materials

steel

Kershaw Leek with steel handle

titanium


Lionsteel SR1 with Titanium Handle


aluminum


Swiss Army Classic with Aluminum Handle

G10


Spyderco Tenacious with G10 handle


carbon fiber


Zero Tolerance 0770 with carbon fiber handle


Micarta

Esse Izula with aftermarket Micarta handle

FRN


Benchmade Griptillian with FRN handle


wood


Buck 110 with wood handle


bone


Case Peanut with bone handle