A drill rod is made of high carbon steel and is used to manufacture drill bits, taps, dowel pins and roller bearings. The drill rod is also used in the manufacture of hammers, files and punches. The level of carbon used in the manufacture of steel determines its hardness. The drill rod is sold in lengths typically 36 inches (91 cm) long and in diameters ranging from 1/16 inch (1.5 mm) to 2 inches (5 cm) or larger. The rod can also be manufactured in a square shape.
There are two basic types of drill rod: water hardened and oil hardened. A water-hardened shank is used in the manufacture of hammers and files because the shank is not strongly bonded. This allows the material to be more easily machined than oil-hardened drill rod, although a water-hardened drill rod is not suitable for welding. On the other hand, the oil hardened shank is easily welded and machined, it is suitable for general tool making due to its long-lasting toughness.
In the water hardening process, the stem is heated to cherry red and then dipped in a vat of water and allowed to cool. This creates a hard, durable product that is still easily machined. When the shank is heated to a cherry red color and then dipped in a hot oil, the surface becomes extremely hard and damages most cutting tools. Therefore, these rods must have all machining completed before oil hardening.
Depending on the intended use, some shanks must be hardened prior to machining. To temper steel, it must be heated slowly after it has been hardened with water or oil. By heating the steel to about 800 degrees Fahrenheit (426 degrees Celsius), the hardness is relieved a little and the steel is more workable. Once brought to temperature, the steel can cool in air. After cooling, the part can be polished.
The difference in hardening of water and oil is that water is a much better conductor of heat and cools the rod faster. The parts should not be agitated in the water as this promotes much faster cooling on the side of the tool being pushed through the coolant. This can cause warpage as the sides cool at different rates. This is critical when creating precision workpieces. When building the knife, the steel should only be tempered in a straight up and down motion.