In very small sizes it is difficult to fit carbide tips in some industries, most notably printed circuit board manufacturing, requiring many holes with diameters less than 1 mm, solid carbide bits are used. However, it is becoming common in job shops to use solid carbide bits. The material is expensive and much more brittle than steels consequently they are mainly used for drill-bit tips, small pieces of hard material fixed or brazed onto the tip of a bit made of less hard metal. Tungsten carbide and other carbides are extremely hard and can drill virtually all materials, while holding an edge longer than other bits.The main disadvantage of cobalt steels is that they are more brittle than standard HSS. They hold their hardness at much higher temperatures and are used to drill stainless steel and other hard materials. Cobalt steel alloys are variations on high-speed steel that contain more cobalt.They can be used to drill metal, hardwood, and most other materials at greater cutting speeds than carbon-steel bits, and have largely replaced carbon steels. High-speed steel (HSS) is a form of tool steel HSS bits are hard and much more resistant to heat than high-carbon steel.If they are overheated (e.g., by frictional heating while drilling) they lose their temper, resulting in a soft cutting edge. Bits made from high-carbon steel are more durable than low-carbon steel bits due to the properties conferred by hardening and tempering the material.They are used only for drilling wood even working with hardwoods rather than softwoods can noticeably shorten their lifespan. Soft low-carbon steel bits are inexpensive, but do not hold an edge well and require frequent sharpening.Many hard materials, such as carbides, are much more brittle than steel, and are far more subject to breaking, particularly if the drill is not held at a very constant angle to the workpiece e.g., when hand-held. Many different materials are used for or on drill bits, depending on the required application. The following table lists geometries recommended for some commonly drilled materials. The best geometry to use depends upon the properties of the material being drilled. Much higher ratios are possible (e.g., "aircraft-length" twist bits, pressured-oil gun drill bits, etc.), but the higher the ratio, the greater the technical challenge of producing good work. The diameter-to-length ratio of the drill bit is usually between 1:1 and 1:10. Other types of shank used include hex-shaped, and various proprietary quick release systems. For heavy duty drilling in industry, bits with tapered shanks are sometimes used. Most drill bits for consumer use have straight shanks. Twist drill bits are available in standard lengths, referred to as Stub-length or Screw-Machine-length (short), the extremely common Jobber-length (medium), and Taper-length or Long-Series (long). While longer bits can drill deeper holes, they are more flexible meaning that the holes they drill may have an inaccurate location or wander from the intended axis.
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