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