HOW OUR KNIVES ARE MADE
We use a combination of high-tech automated processes and skilled handwork to build our knives. All labor is performed in the USA.
Generally each design starts as a pencil sketch or paperboard cutout. Once the initial concept is established, the design is traced into a computer drawing program and converted into a CAD file. At this stage, overall weight and balance are calculated, while ergonomics and performance are thoroughly considered. The shape is exhaustively adjusted until a final draft settled upon. We build prototypes to test each prospective design, and make further adjustments until the design is finalized.
We outsource the shape cutting to a metal fabrication shop. The CAD files are used to program a computer-controlled (CNC) laser or waterjet machine. We supply the tool-steel plates, and the shop accurately cuts our knife patterns.
Prep grinding and machining
In our shop, we perform some preparatory grinding and machining on the shapes, one at a time. The grinding is done manually on a 2×72 inch belt grinder. Lanyard holes are drilled and chamfered on a drill press.
We outsource the heat treatment to a shop that specializes in cutlery. The shop processes our knives in accordance with our requirements, and tests each batch to confirm that target specifications have been met. Occasionally the knives are heat-treated and tested in our shop.
After heat treatment, we tumble the knives in our shop. The knives are placed in a rotating drum along with abrasive ceramic polishing stones and a cleansing solution. The tumbling process cleans and polishes the steel, and smooths any sharp corners or edges.
Final bevel grinding
In our shop, we perform the final bevel grinding on a 2×72 belt grinder. Each knife is ground by hand, one at a time.
In our shop, we mark each knife with the Flying Steel logo, using an electro-etching machine with custom stencils.
Final inspection and cleaning
We carefully inspect and clean each knife. Finally, we apply a food-grade oil to deter corrosion.
We use US-made virgin 1075 for our knives. 1075 is a simple high-carbon steel with a long history of use as a spring steel, and a long standing reputation for toughness. We rely on 1075 to provide the right blend of performance, quality and value.
We use German-made virgin 1075+Cr for our knives. This steel is 1075 with extra chromium, which provides additional toughness and corrosion resistance. 1075+Cr is a perfect steel for high-impact applications.
We use US-made virgin 6150 for our knives. 6150 is a medium-carbon alloy steel – similar to 5160 – with enhanced toughness, impact strength, and abrasion resistance. 6150 is suited to provide the ideal properties for professional-grade throwing knives. 6150 is essentially 1050 steel with additional chromium and vanadium.
We use German-made virgin 8670 for our knives. 8670 is a high-carbon tool steel that is commonly used to manufacture large metal-cutting circular saw blades. Its composition provides the framework for a tool with excellent resilience and toughness. 8670 is essentially 1070 steel with additional chromium and nickel.
We use German-made virgin 80CrV2 for our knives. 80CrV2 is also a high-carbon tool steel that is ideal for tough knives. 80CrV2 is essentially 1075 or 1080 steel with additional chromium, nickel, and vanadium.
We use US-made virgin S7 steel for our high-end knives and spikes. S7 is the king of premium shock-resistant tool steels – providing extremely high toughness and hardness – and is known around the world for its incredible mechanical properties.
The hardness of medium and high-carbon steel can be altered by the set of processes known as heat treatment. In the context of knives and tools, the phrase refers to the hardening and tempering processes. Hardening transforms the steel into a very brittle crystal structure known as martensite. The tempering process dials down some of the hardness and brittleness to gain toughness and resilience.
We are proud to employ the expertise of Peter’s Heat Treating for our production batches. Smaller batches are occasionally hardened in our shop, using proven methods and equipment. All batches are tested for quality.
HARDNESS VS. TOUGHNESS
Hardness and toughness are the two qualities that make a durable throwing knife. Simply put, hardness is the resistance to deformation, while toughness is resistance to breaking. When a knife becomes bent, or the tip curls over, it means the hardness was overcome. Conversely, when the knife breaks, or the tip shears off, it means the toughness was overcome. In a throwing knife, high hardness and high toughness are required, but unfortunately these two qualities are inversely related – it could be said that they are opposites. As hardness increases, toughness decreases. Because of this, when the toughness of two steels is compared, the comparison is meaningful only when both steels have the same hardness. Mild steel from the hardware store is always far tougher than the best tool steel!
Each steel has a maximum potential hardness, and in the tempering process, it is possible to achieve any final hardness up to the maximum potential hardness. Again, the maximum potential hardness is also the minimum potential toughness, and for this reason, some hardness is sacrificed in order to gain toughness during the tempering process. Low and medium-alloy steels such as 1075 and 6150 are limited by toughness – meaning that they are tempered to 50 RC (a moderately hard value) to gain sufficient toughness. If they were made any harder, they would be too brittle. In contrast, special steels such as S7 are designed to provide the best of both worlds – high hardness AND high toughness. An S7 knife at 55 RC is tougher than a 1075 knife at 50 RC.
What this means on the throwing range is that the softer 50 RC steels will suffer more damage caused by deformation than the 55 RC knives. Specifically, the softer 50 RC knives will require periodic tip maintenance and will bear more dents, gouges, and burrs. The harder 55 RC knives will be nearly maintenance-free.