![]() ![]() 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. Materials Titanium nitride coated twist bit 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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