Guide to the drills

Perov Perov or flat drill bits are easy to design, they are cheap to manufacture and are not very sensitive to distortion in the work. Feather drills are bilateral and unilateral. The difference lies only in their form of sharpening the cutting edges. Feather drill Perovs or flat drills are simple structures, they are cheap to manufacture and are not very sensitive to distortion in the work. Feather drills are bilateral and unilateral. The difference lies only in their form of sharpening the cutting edges. Feather bits have a flat cutting part with two cutting edges symmetrically arranged about the axis of the drill and forming a cutting angle of 45 °, 50 °, 75 °, 90 °. Drill diameter is measured by the width of the blade. The thickness of the pen at the cutting edge depends on the diameter of the drill and is: 1.u drill diameter 5 ... 10 mm from 1.5 to 2 mm; 2.diametrom 10 ... 20 mm 2 to 4 mm; 3.diametrom over 20 mm from 6 to 8 mm. Cutting edge at its intersection form a straight line, which is called the transverse edge, or a jumper. The main drawback of feather drill is the lack of an automatic chip removal in drilling, which spoils the cutting edge and often makes removing the drill from the drilled hole. In addition, feather drill in the process of losing direction and decrease in size of diameter for regrinding. Twist drills Twist drills, perhaps, the most in demand at the consumer. They represent a cylindrical rod, the working part of which is provided with two helical spiral grooves, intended for chip disposal and the formation of cutting elements. The slope of the grooves to the axis of the drill is 10 to 45 ° The working end has a conical drill. On the generators of the cone there are two, symmetrically placed relative to the drill cutting edges. Twist drills are made with cylindrical, conical and hexagonal. shanks. Drill shank diameter are made up to 12 mm, with cone - from 6 to 60 mm. All twist drills are standardized. Therefore, the purchase is necessary to select only those dimensions of the openings for which there is a corresponding drill diameter. Angle and at the top of the drill (the angle between the cutting edges) should be chosen depending on the workpiece material and be: for drilling of soft metal 80 ... 90 ° for drilling steel and cast iron of medium hardness 116 ... 118 ° for drilling very hard metals 130 ... 140 ° Such drills are distinguished long service life and good reliability. Well, if we talk about the shortcomings - denote a relatively high price performance. Sharpening drills Experts say that the purity of drill holes and high productivity in drilling can be achieved only when working with sharp and properly sharpened drill. In the process of cutting part of the drill bit wears out, and therefore requires a systematic restoration of their geometric dimensions. Restoration is done by grinding. Sharpening drills carried out on special grinding machines or hand-grinding wheels. Hand-sharpening drill bit sharpening When manually keep your left hand for the working part, perhaps closer to the cutting edge, and the right hand of the shank. Cutting edge of drill bit is pressed against the side of the grinding disc and smooth movement of the right hand turn the drill bit, ensuring that the cutting edges have the correct slope to the axis and the desired shape. Strongly press the drill should not be, because it lengthens the process of sharpening. In the process of sharpening drill bit heated. Therefore, to avoid losing hard grind necessary to produce cooling. The cutting edges properly sharpened drill bit should be straight. The angle of them to cross the edge must be equal for drill diameter up to 15 mm - 50 °, more than 15 mm - 55 °, and the length of the lateral edge - 10 ... 20 times smaller than the diameter of the drill. When defects are sharpening hand sharpening drill bits, the following defects: 1. The length of the cutting edges can get uneven: the middle of the transverse edge does not coincide with the axis of the drill bit. The length of the cutting edge will be more loaded than the short edge, and soon becomes blunt. Outwardly, it is often expressed in the form of pitting near the corner of her long edge. In addition, under the influence of a large load from the edge of the long edges of the bit will be wrung out in the direction of the axis of rotation and get a hole of larger diameter than the drill diameter. The deeper the hole, the smaller will be its accuracy. 2. Cutting edge sharpened at different angles to the axis of the drill bit. In this case, the middle transverse edge coincides with the axis of the drill bit. Since the slope of a cutting edge longer than the second, then the latter will not work. Whittle in this case is only one edge. Under the influence of one-sided burden of cutting edge drill will sidetrack and thereby increase the diameter of the hole. 3. Two defects simultaneously. If, after sharpening drill cutting edges are not equal in length and are inclined to the axis of the drill in different angles, then the middle of the transverse edge shifted from the axis of the drill and when the work will revolve around an axis. Cutting Speed ??One of the main issues drilling technology - the most suitable cutting conditions, that is the definition of such a combination of speed and flow drills, which ensures maximum productivity. Rotational speed drill is characterized by its speed in a minute. This rate represents the path traversed by the outer points of the cutting edge of drills, and is measured in meters per minute. The optimum cutting speed in drilling - this is such a speed, which delivers high performance for a sufficiently long operation bit (from 10 to 100 minutes) without resharpening. Practically established that the economic cutting speed drill should work without resharpening: The Drill 5 ... 20 mm for 15 minutes at a diameter drill 25 ... 35 30 minutes At a diameter greater than 40 mm drill 90 minutes Allowable cutting speed in drilling depends of material quality drill bits. Thus, high-speed steel drills allow higher cutting speeds than carbon steel drill bit. The speed depends on the mechanical properties of the material. Than the plastic material, the harder it is given chip, heats up quickly drill and lowers the cutting properties. Therefore, brittle materials can be drilled at a higher rate than viscous. Not last in this list is, and this characteristic, as diameter drill bit. With an increase in the diameter of the cutting speed can be increased, as a massive drill bit has a higher strength and better heat dissipation from the cutting edges. Drilling depth is not less important. The deeper the hole drilled, the more difficult removal of chips, more friction and higher heat of cutting edges. Therefore, ceteris paribus drilling shallow holes can be performed with greater speed and deep - with less. The intensity of the cooling drills also affects the process of drilling. The drill works better at higher cutting speed and low pitch. If during the drill quickly blunt the cutting edge in the corners (at the beginning of cylindrical part of the drill), it says that the cutting speed is taken too large and must be reduced. If a blunt drill or chip on the cutting edges, this indicates that the flow is too great. Dulling and breakage of the drill more likely to occur at the end of drilling through holes (for output of metal). To prevent dulling or breakage of the drill to pass, it is necessary at the end of drilling to reduce the flow. Typically, for cooling the bit in the paper apply: when drilling hard materials - kerosene or turpentine, when drilling soft materials - soda solution, when drilling cast iron - kerosene or jet of compressed air. The use of cooling during drilling can increase the cutting speed for steel by 20% and iron 50% and get a cleaner surface holes. The choice of diameter drill in practice, depending on destination, there are different kinds of drilling, such as through-the deaf, a scan, a thread, etc. In all these cases for the same nominal bore diameter is selected drill diameters. It should be borne in mind that in the process of drilling a hole drill develops and makes it somewhat larger diameter. Averages development drill holes (the difference between the diameter of the resulting hole and the drill diameter) can take the following: Drill, Develop mm holes, mm 5 0.08 10 0.12 25 0.20 50 0.28 75 0.35 For the holes with the exact diameter should take into account the value of development and, accordingly, to select the bit slightly smaller diameter. Causes damage to the drill Practice the following main reasons for failure of drills: 1) the meeting on its way shell drill deviates to the side and breaks, and 2) if the lower part of the hole in the product is not limited to horizontal and inclined plane, the drill goes out of the product evenly, gets stuck in a hole and breaks, and 3) when drilling deep holes, when the depth of drilling more cutting edge drills, grooves, plunging into the product, clogged wood shavings, and the drill is extremely hot, dull and breaks, and 4) during the exit drill from the product, ie at the end of drilling, if the supply has not decreased, but remained the same, the drill breaks down frequently, and 5) failure also occurs when working with a blunt drill. Source: http://www.stroynet.ru/article_id111.htm