Knife making is the process of manufacturing a knife by any one or a combination of processes: stock removal, forging to shape, welded lamination or investment cast. Typical metals used come from the carbon steel, tool, or stainless steel families. Primitive knives have been made from bronze, copper, brass, iron, obsidian, and flint.
Different steels are suited to different applications. There is a trade off between hardness, toughness, edge retention, corrosion resistance, and achievable sharpness. Some examples of blade material and their relative trade offs:
Unusual non-metallic materials may also be used; manufacturing techniques are quite different from metal:
When forging, the blade material is heated to a high temperature or forging temperature in a forge and shaped with a hammer on an anvil to achieve the desired shape, often to near final dimension, where very little stock removal, if any, is required to finish. Steel can be folded either to form decorative pattern welded steel or to refine raw steel, or as the Japanese call it, tamahagane. Grain size is kept at a minimum as grain growth can happen quite easily if the blade material is overheated.
In a mass production environment, or in a well equipped private shop, the blanking process is used to make "blade blanks." This can be achieved by a number of different methods, depending upon the thickness of the material and the alloy content of steel to be cut. Thinner cross section, lower alloy blanks can be stamped from sheet material. Materials that are more difficult to work with, or jobs that require higher production volume, can be accomplished with water jet cutters, lasers or electron beam cutting. These two lend themselves towards larger custom shops. Some custom knife makers cut their blanks from steel using a metal-cutting bandsaw.
Knife makers will sometimes contract out to a shop with the above capabilities to do blanking. For lower production makers, or lower budgets, other methods must suffice. Knife makers may use many different methods to profile a blank. These can include hacksaws, files, belt grinders, wheel grinders, oxy-acetylene torches, CNC mills, or any number of other methods depending on budget.
If no power equipment is available, this can be done with files if the piece of steel has not yet been hardened. Grinding wheels, or small belt sanders are usually what a beginner uses. Well equipped makers usually use a large industrial belt grinder, or a belt grinder made specifically for knife making. Pre-polish grinding on a heat treated blade can be done if the blade is kept cool, to preserve the temper of the steel. Some knife makers will use a coolant mist on the grinder to achieve this.
Methods of heat treatment: atmosphere furnace, molten salt, vacuum furnace, coal (coke) forge, oxy/acetylene torch. Quenching after heat treatment differs according to type of metal and personal preferences. Quenching can be done with oil, animal tallow, water, air, or brine.
The finish quality of the blade is determined by the Grit of the finishing grind. These can range from a low-shine 150-250 grit finish to a mirror-shine. The high polish shine can be accomplished by buffing with chrome oxide (ex. white chrome, green chrome), hand rubbing with extremely fine wet-or-dry abrasive paper, or with a Japanese water-stone, which has an approximate grit of 10,000-12,000. Most high quality manufactured knives have about an 8000 grit finish.
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