Slim long drill bits11/20/2023 Most drill bits have a diameter-to-length ration of 1:1 to 1:10. These systems reduce work time by bypassing the need to loosen and tighten the chuck during bit transitions. ![]() ![]() There are also specialty shanks, such as those with hex-shaped shafts, and various proprietary quick-release systems for situations in which several bits are used in rapid succession. Some shanks, used mainly in heavy-duty industrial situations, have tapered shanks to cut down on overall weight and cost. Most drill bit shanks are straight – they are the same diameter at the top of the shaft as they are along the length and at the bottom. Bits are available in a variety of functional lengths, including standard lengths (called ‘stub-length’ or ‘screw-machine-length), which are relatively short ‘jobber lengths’, which are considered medium-length and ‘taper-length’ or ‘long-series’ which are, as the name indicates, the longest of the three categories. A shorter functional length results in a more rigid shaft (in relation to the girth) and the axis of cut will therefore be truer and there will be less chance of breakage under a certain amount of torque resistance. This advantage has its drawbacks or limitations, however, as a longer shaft will be more flexible and may cause warping of the hole trajectory, and has a higher risk of breakage. Longer functional length is achieved by the drill bit having a longer shaft. The longer the functional length, the deeper the hole that can be drilled. This is the length of the bit beyond the chuck, or the length of the bit that can be extended into the hole being cut. A flat bit has a smaller surface area and will therefore be more sensitive to changes in lip angle. An acute point angle requires more aggressive lip angle to ensure adequate web surface area. The point angle will determine the proper amount of lip angle a bit requires. A lesser lip angle will create a less aggressive cut for the given amount of pressure. A greater lip angle will bite deeper (and therefore more quickly) into the material through a rotation, causing a more aggressive cut for a given amount of pressure. ![]() This is the angle of the wedge of the tip after the cutting edge. Sharper point angles will tend to dull when used with harder materials, or may bite in and bind the bit to a halt – possibly breaking the tip or shaft. Harder materials require a larger point angle, as a larger angle will bite into the material, and will also hold up better to the higher impact and resistance of a harder material. Softer materials require a sharper point angle (a duller point angle will tend to skitter along the surface, failing to bite into the material). This has an effect on the way the bit will cut through certain materials. Aluminium and copper are common examples. This is usually used in situations where the material being drilled out tends to gall on the bit or clog the hole. This tends to cut more slowly (per rotation) and uses a higher spindle speed. A ‘compact flute’ is a flatter spiral, resulting in more loops of the groove along the length of the bit. This is called an ‘elongated flute.’ It usually uses lower spindle speeds. ![]() If this is steep, the bit will tend to cut more quickly (per rotation). The spiral (sometimes called the rate of twist) is the steepness of the groove that spirals along the edge of the bit. There are several standard aspects of drill bit geometry: the spiral, the point angle, the lip angle, and the functional length. For clarity, this article will use the term ‘drill’ for the machine itself, without the bit, and ‘bit’ for the bit itself, without the machine. Sometimes the term ‘drill’ is used for the machine portion of the tool, and sometimes for the bit and machine together. Lists of non-circular cross-section drill bits are also available. Charts are available for these, as are tables indicating required screw tap sizes for each. There are standard sizes for drill bits, in both metric and imperial units. The drill has a piece called a chuck, which can be tightened onto the upper end of the bit, called the shank, to hold it firmly in place during drilling. The electricity is supplied via a cable or battery. The drill bit is attached to a rotating piece on the end of the drill, which is in turn attached to a motor, usually powered by electricity. This is nearly always a circular hole, though some specialised bits can cut holes in other shapes for specialised purposes. Drill bits are tips placed on the end of drills that cut holes in material.
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