Cobalt Drill Bits
Cobalt drill bits can be used on extremely hard, high tensile strength materials like hardened stainless steel (precipitation-hardened), Inconel alloys, cast iron, and titanium but they are also used on softer materials like plastic. They are often used in the aviation industry.
There are two grades of cobalt bit. M35 has 5% cobalt added to raise resistance to heat and M42 has 8% of cobalt added to utilize its wear resistance properties as it is less prone to breaking and chipping compared to other bits. The most popular types of cobalt drill bit are jobber length, numbered measured, fractional measured, 6 inch and 12 inch extended length.
Bosch cobalt drill bits include an alloy that enables bits to heat to 1,100 degrees Fahrenheit and drill for an extended length of time at these higher temperatures. These temperatures that would normally destroy other bits made from less heat resistant material. They last longer in highly abrasive materials. The overall bit hardness can be increased to 68 HRC which is ideal for drilling in abrasive or tough materials. A thick web design increases the rigidity and prevents the drill bit from snapping when drilling in very hard and abrasive materials. The higher red hardness of cobalt allows speeds of up to 30% higher than other drills.
Twist drill bits are made from a range of materials including cobalt, carbon, black oxide and titanium. The functionality of the drill dictates which of these materials is included – each is designed for a particular purpose. Some materials are hard and require a drill that is resistant to wear and tear and high temperatures. Some materials are softer, so softer metals can be used in making the bit. Each bit has its specific purpose. Bits with black oxide in their formula are for general purpose use for heavy duty drilling in carbon, plastic, soft cast iron and aluminum.
Cobalt alloys hold their hardness at extremely high temperatures, more so than standard bits but their main disadvantage is that they are more brittle and can therefore snap more easily than regular drill bits. Cobalt bits are not coated, they are made solely of cobalt. When manufacture is almost complete, the bit is baked at high temperatures in a special industrial oven which changes the surface color to a subdued golden color. This is mainly done to enable color identification from other bits. Even if the gold color wears away through use or sharpening, it is still solid cobalt steel through and through.
Irwin is a popular drill manufacturer who use M42 grade (contains 8% cobalt) in their bits. A correctly sharpened a cobalt bit is still as good as a brand new bit – its performance is not affected. However, sharpening other coated or tipped drill bits such as titanium for example, the performance is decreased in effectiveness as the coating is worn away.
Companies that supply drill bits and accessories include Makita, Hilti and Irwin as mentioned. Along with cobalt drill bits, there are many other types on the market including tile drill bits and brad point bits, long and short bits, glass and metal, ceramic, flexible, step drill bits.
Tagged with: Abrasive Materials • Aluminum Alloys • Aviation Industry • Black Oxide • Cast Iron • Cobalt Alloys • Cobalt Drill Bit • Cobalt Drill Bits • Degrees Fahrenheit • Dictates • Heat Resistant Material • High Temperatures • Hrc • M42 • Resistance Properties • Rigidity • Strength Materials • Tensile Strength • Thick Web • Wear And Tear • Wear Resistance
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