In the past, we covered forge welding as it relates to Damascus steel here. But forge welding can be used to stick hot steel together in lots of different ways. San Mai is a Japanese technique now in widespread use in Japanese style and non-Japanese style knives. It translates to “three layers.”
Gimme the Steel Sammich, Extra Flux, Hold the Fries
San Mai steel is three layers forge welded together. The two outer layers are of the same type and often referred to as the jacket (bread) and the middle layer is referred to as the core (meat). Like Damascus steel, I make San Mai by MIG welding the layers together at the corners (this layered bar is called a billet) and welding a steel bar to the billet for ease of handling without tongs during the forging and forge welding process. Unlike Damascus, San Mai is not folded.
The manrikigusari, or 10,000 powers chain, also called the ryofundogusari, or double weighted chain, is yet another obscure Japanese weapon. The story about its origins that I like best is that the samurai who guarded Edo castle were forbidden from spilling blood, and so they set aside their usual weapons in favor of this unusual but effective weapon. The same story tells us that this is a modification of the kusarigama, or sickle and chain, with the sickle removed to create a weapon with no blade. I’m not certain I buy that because the kusarigama is Okinawan, and the samurai were not fans of the Okinawans.
Concealable and Versatile
This is perhaps the most effective flexible weapon I’m aware of, being not so long as to make it impossible to control, but long enough to create considerable reach. There are no rules, but a typical gusari is between 18 and 36 inches, with 20–24 inches being fairly typical. It’s quite versatile and can be used for strikes, chokes, traps, and throws. It’s also very small and concealable. One favored technique is to hold the coiled chain in one hand and throw one weight while holding on to the other.
Although not impossible to control, this weapon is very difficult to learn and use effectively.
Volumes upon volumes have been written about steel chemistry and properties, and which steel is best for a particular job. The kobolds prefer if I keep it to around 500 words (kobolds have short attention spans), so I’ll quickly cover simple carbon steels and low alloy tool steels. Although stainless and high alloy steels have their uses, they cannot be used effectively for high impact weapons such as swords and axes, so perhaps we’ll deal with them at another time.
There are literally hundreds of types of steel, so we’ll only be scratching the surface and focusing on the most common types used in common cutting tools.
Simple Carbon Steels; or the Power of 10’s
Simple carbon steels, also sometimes referred to as 10 series steels, or spring steels, have the simplest chemistry of any of the hardenable steels. Although they can contain small amounts of alloying elements, for the most part they are iron and carbon. They are called 10 series steels because they are described by a 10 followed by a second two digit number. The ten simply means that it is iron and carbon without any significant alloying elements added. The second number tells how much carbon is in the steel. For example, 1075 contains approximately 0.75% carbon.
There are three basic edge geometries used on cutting tools, and those three types have some variations. Each has advantages and disadvantages, and some are useful only on specialized tools. Each type has its advocates, and some makers like one type so much that they specialize in making only that type of edge.
The Hollow Grind
The hollow grind, or concave grind, is probably the most familiar; you’ve probably at least heard of it, even if you don’t know what it is. It’s created on a wheel, either on a stone or a belt grinder’s contact wheel. Its primary advantages are extreme sharpness and the ability to approach a cut at a very acute angle and bite without sliding. Its biggest disadvantage is that it doesn’t have much steel behind the edge, so it’s fragile compared to other grinds. You have to be careful when initiating this grind to get it established at the same height on both sides of the blade. Once established, it’s the easiest grind to finish because the grinder wheel wants to stay in the hollow that’s created. This grind is often used on fine cutting instruments, such as razors and scalpels.