Internal metric threads, which are cut by taps by hand or machine, have certain parameters.
Diagram of the device drill.
However, simply knowing these parameters is not enough, you need to choose the right drill bit in diameter for the future thread and be able to drill metal under it.
Drills as a tool for making holes in materials of different composition and hardness are made of different types:
Types of drills: a - spiral centerless, b - spiral with center and trimmers, c - spiral with screw center, d - center feather, d - center, e - gimlet, w - razzenkovka, z - groove, and - plug.
- Cylindrical spiral - the most common type of tool. They are used for drilling a wide range of different materials, ranging from wood products to various steel grades. The tool, which has proved itself well since the times of the USSR, is made of high-speed steel of grade Р6М5 or Р18. The drill of steel P18 (in the people - rapid) has a high indicator of hardness and is very high quality, only to find it on sale became problematic. Currently, there are products labeled HSS, but they are significantly inferior to the Soviet in performance and, as a rule, are made in China.
- Cylindrical spiral with a dusting or napayka from solid materials. If the tool is yellow, then it has a titanium coating, it does not improve its characteristics, but simply allows to extend the longevity of the working part. For the same purpose drills with burnishing are produced, they are black in color. For the processing of hard materials or alloyed and hardened steels, products with tipped from hard tungsten alloy with cobalt VK-9 or VK-10 are used (in the people - pobeditovye). Cobalt can be introduced as an alloying element in the composition of high-speed steel drills, the marking of such a product - R6M5K5.
- Step tools are designed to make holes in materials of small thickness, for example, for sheet metal. One such product can drill several holes of different diameters depending on the number of steps on it.
- Ring drills are used to make holes of large diameter with low accuracy requirements. The working part of such a tool is a crown, which “bites” into the material, inside it there is a void. Products are very common in construction, used for processing stone or concrete.
- Flat tools can only be used for drilling wood and wood products.
- Centering and countersinks. The first serve to perform the deepening in the metal, which will set the correct direction of the working part of a conventional drill. A countersink is needed for machining the edges of the finished holes (chamfering, burrs, making secret recesses for the screw head).
Selection of tools for work
Recommended diameters of bores and rods.
Most often for drilling holes for different threads take the usual cylindrical tools of the desired diameter. To determine what diameter you need to take a drill for internal thread, you need to know its parameters: diameter and pitch of turns. For example, marking M6 x 1 means that it is a metric thread with a diameter of 6 mm with a pitch of 1 mm, respectively, to select a tool for making the hole and a tap for cutting. The formula for calculating the hole diameter is:
DR - b = do
In this formula:
- DR - thread diameter, mm;
- b - step of turns, mm;
- do - bore diameter.
Under the M6 x 1 you need to drill a hole: 6 - 1 = 5 mm. The above formula is valid for metric thread with any step turns. To simplify the selection of hole diameters, Table 1 lists their values for the standard metric thread series.
|Metric threading options||M 1||M 2||M 3||M 4||M 4.5||M 5||M 6||M 8||M 10|
|Metric threading options||M 12||M 14||M 16||M 18||M 20||M 22||M 24||M 27||M 30|
|Diameter of a drill, mm||five||ten||25||50|
|Size of breakdown, mm||0.08||0.12||0.2||0.28|
A tool of any size slightly turns the hole, as a result of which it actually turns out to be somewhat larger in diameter. For example, some indicators of the increase in the size of the holes can be seen from Table 2.Back to table of contents
The scheme of drilling metal.
Ideally, drilling work is best done on a special machine, then you can simply take the required diameter value from Table 1. However, not everyone has this kind of equipment, so most of the time you have to drill metal using a conventional hand drill. In this case, you should follow some recommendations:
- The tool must be properly sharpened and have no deviations from the longitudinal axis (beats). The sharpening angle depends on the hardness of the material being processed; the harder the metal to be drilled, the greater the angle of the cutting part must be observed. At the same time, its value cannot exceed 140⁰.
- No matter how hard you try to hold the drill firmly and confidently during the drilling process, the hole will be broken down more than if the work was done on the machine. The breakdown values shown in Table 2 will certainly be exceeded if you drill the metal with a drill. As a result, the threaded turns in the profile will look like a beveled cone, and it should be pointed. In such a connection will be increased backlash, its reliability is questionable. In order to avoid such a situation, it is necessary to take a drill 0.1 mm smaller than the one shown in Table 1 to make the hole. This tenth part of a mm should be broken down. Perhaps when tapping the tap will not be very easy, but if you do the work carefully, then the thread will turn out to be full-fledged and play in the joint is excluded.
- Before you drill metal, you need to make a markup and find out the exact location of the hole. Then this place should be nacked, making a sufficiently deep notch, otherwise at the very beginning of drilling the tool will “walk” on the surface of the part. Ideally, it is best to deepen the notch by centering, which will make a small blind hole in the metal, the drill will not leave it.
- The workpiece should be well secured in a comfortable position. If it is convenient for you to work in a standing position, holding the drill horizontally, the part should be firmly fixed in a vice. In the case when it is impossible to do this, it is better to lay it on a horizontal surface low above the floor and fix it with a clamp. You can drill vertically, from top to bottom, pointing the drill to the intended location.
- The tool requires lubrication during operation. A piece of old lard is best suited for this purpose, you need to turn on the drill and dip the end of the drill into it on the go. If fat is absent, you can use grease or other grease. When working with viscous or heat-resistant steels (stainless steel, copper), it is necessary to use engine oil as a lubricant.
The rotational speed of the cartridge should be as low as possible. Surely many were faced with a situation when, after passing a couple of mm, the process stopped, the drill rotated in one place. At the same time, a visual study of its edges showed that the tool was not blunt.
The reason is different: the cutting edge of the drill overheated at high speed loses its hardness and is unable to cope with the metal. If we continue in the same vein, the working part of the tool will “lick itself”, this is more difficult to fix. In any case, rework is required.
Do not try to drill from the very first hole of a large diameter, as a rule, for hand drills the inconvenience begins with a size of 10 mm. It is better to first make a hole of small diameter (3-4 mm), and then drill out to the required. Sometimes it has to be done in three steps. When drilling, you need to be careful at the moment when the drill comes out on the other side. There is a sharp resistance of the last layer of metal under the cutting edge, you need to hold the drill firmly with both hands, otherwise it can turn and just pull out of your hands.
Making holes for metric threads is a simple matter, but it requires attention and care.
This will help properly selected tools and accessories.