Drill bits are some of the most common and versatile parts of any machine shop or home tool shed. They can drill into metals, solid wood furniture, porcelain and even glass, and with a variety of different drill bits available, one can find an appropriate bit for almost any situation. One major aspect of drill bit selection is the material makeup of the drill bit itself. Not all twist bits will work on all applications. It’s important to match the material of the bit to the material being drilled to produce the best results.
Low and high carbon steels are both used for drill bits, but for different purposes. Soft low carbon steel cannot cut hard metals due to their poor tempers, but they can cut wood. They require sharpenings to extend their lifespan. The primary bonus of low carbon steel is its relative inexpensiveness, especially when compared to some more exotic drill bit materials.
High carbon steels have better tempers than low carbon steels, so they require less maintenance, such as sharpening, and hold their form and effectiveness longer. They can cut both woods and metals, and if available, are preferred to low carbon steels when cutting extremely hard woods.
High Speed Steel
High Speed Steel (HSS) is a special type of carbon steel that is prized for the way it can withstand high temperatures while maintaining structural integrity, specifically its hardness. Friction created by high speed turning can raise temperatures dramatically, but HSS can undergo these types of drillings. HSS can function at normal temperatures, as well, but only at a level equal to standard carbon steel. HSS can also take coatings, such as titanium nitrade, which give the drill bit better lubricity, decreasing friction and helping to extend the bit’s life.
Titanium is a corrosion resistant metal, and is reasonably light compared to its strength. It is similar to steel in that it has a good fatigue limit, and also a high heat limit, although both are less than steel’s. This longevity makes it attractive for use in repetitive, large runs. It is a very versatile drill bit coating and it can cut a broad variety of surfaces, including many types of steels and irons, as well as wood and plastic.
While not a primary material for drill bits, zirconium coated metals function very well for drill bits. The zirconium nitride coating can increase strength for hard but brittle materials, like steel. The makeup of the zirconium also decreases friction for improved precision drilling.
Cobalt is used for materials that HSS cannot cut, such as stainless steel. It is less succeptible to high temperatures than even HSS so it is not affected by extremely high heat. As a drawback, though, cobalt coatings are excessively brittle.
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