Threaded connection is the main way to connect parts. In the manufacture of their own hands of any device of metal arises the need for self-threading. Cutting allows you to form your own threads in various holes.
In practice, one has to deal with various materials that differ in their properties. Cutting should take into account the characteristics of the material. There are certain rules that have been developed over the years, which allow you to perform high-quality thread cutting of various sizes and types.
Features of the structure of taps
The tap belonging to the group of metalworking turning tools, has the form of a rod, on which the cutting element is made. It is intended for cutting internal threads, that is, inside the hole in various materials, as well as for restoring damaged internal threads.
A set of cutting tools: a - drills, b - countersinks, c - reamers, d - taps, d - dies.
Tools consist of working and tail parts. In turn, the working part is divided into intake (cutting) and calibrating section. The cutting area is responsible for the main function of the tap - thread cutting, and, most often, has a tapered shape. He has teeth in the form of incisors placed around the circumference. The calibration section performs the task of final formation. It is made in the form of a cylinder with teeth, which are a continuation of the teeth of the cutting section. This area is much longer than the fence. The working part in the longitudinal direction is cut by grooves, which are intended for the formation of incisors and chip output. In taps with a diameter of up to 22 mm there are three grooves. Special-purpose devices can be manufactured without grooves. Grooves can be straight or helical.
The tail part is shaped like a cylinder. At the end of the section there is a square for installation in the mounting tool. In this part of the label is knocked in diameter. With the help of the shank tool is fixed in a manual holder or machine chuck.Back to table of contents
Main types of taps
By the way of using taps are divided into two types - manual and machine. The first ones are installed in manual holders (knobs) and are intended for cutting the internal thread manually. Machine mounted in special holders for lathe chucks.
By type of thread, cut by a tap, they are divided into several types. Metric is designed for cutting the most common metric thread. Pipe forms internal threads on the pipes, as well as reinforced in the holes of metal parts. Inch is a device for special inch thread, as well as tapered. Specialized nut taps are made of very strong steel (Р6М5) and have a special shape of shanks.
In addition, taps are divided into single and complete. Complete sets are used to cut in several passes. The kit may contain two taps - finishing and roughing; or three taps - roughing, medium processing and finishing. Completeness is indicated on the tail of the instrument. Taps in the kit differ in the shape of the tooth: the draft tooth has a trapezoidal shape; the middle has a triangle with a rounded top; near the finish one - a triangle with a sharp apex.Back to table of contents
In the general case, threading is to make a protrusion on the inner surface of the hole so that it forms a helix. Such a protrusion, like the whole thread, is characterized by the following main parameters: the angle of elevation of the spiral line, the pitch, the type of profile of the protrusion and the angle of elevation of the profile, the outer and inner diameter. In addition, it is customary to allocate a depth determined by the outer and inner diameters.
In the direction of the thread can be right, when the helical protrusion rises counterclockwise, and left, when the direction of the elevation of the protrusion coincides with the clockwise movement. According to the shape of the profile of the protrusion, two main types are distinguished: carving with a rectangular profile and with a triangular profile. There are also special forms of the profile, but they are practically not used in the living conditions.
The main one is metric thread. Such a profile is a triangle with a profile angle of 60º. By step metric is divided into threads with a large pitch and fine pitch. An example of a complete designation of a metric thread is M10x1-6H. The designation should be understood as follows:
The table of the choice of taps for cutting threads.
- M - metric thread;
- 10 - nominal diameter;
- 1 - thread pitch;
- 6H - tolerance limits for size deviations.
In the normal (large step) designation is reduced (for example, M10). In the case of a left thread, the designation LH is entered.
The second most common in everyday life is a tubular cylindrical type. The profile is a triangle with an apex angle of 55º. This type is used when connecting pipes and cylinders where an increased tightness of the connection is needed. A cylindrical pipe thread is designated by the letter G with the diameter in inches.
The resistant thread is based on a trapezoidal profile with angles of inclination on one side 3º, on the other - 30º. The designation includes the letter S, diameter and pitch.Back to table of contents
Choosing the right tap
The scheme of cutting external and internal thread.
First, select the type of tap on the type of thread and its purpose (profile shape, thread pitch, tolerances). According to the requirements (class) of accuracy, it is determined whether a single tap should be used or a kit is necessary. In addition, taps are available with different cleanliness of processing of their cutting element, which affects the accuracy of threading profile cutting.
The material in which to cut the thread affects the choice of the tap. So, you should consider the front angle sharpening teeth. It is for steel - 5-10º, for copper alloys - 0-5º, for aluminum and alloys - 25-30º. Devices can be made from ordinary steels, high-strength steels, or high-strength taps, which should be taken into account when considering what kind of strength material is processed.
The main choice is made according to the diameter of the hole in which internal threading is performed. The diameter of the tap should be slightly smaller than the diameter of the hole. So, for the metric thread M20 (tap diameter 20 mm) the hole diameter is 19 mm. With metric thread, if there are no special requirements, then the standard step is performed. For example, M4 thread - 0.7 mm pitch; M5 - 0.8 mm; M10 - 1.5 mm; M12 - 1.75 mm, etc.Back to table of contents
Scheme of threading dies.
In order to ensure the threading, the tap must be given a rotational movement with the application of force. This function is performed by a handgrip holder. It provides a vertical mounting tool and the ability to apply a significant load due to the levers. The standard design of the knob contains the attachment of the tap and the elongated handles with which you can rotate the device manually with force.
Fastening the device is carried out in two ways. One of the designs of the crank consists of two parts. With the articulation of these parts inside, a hole is formed to install the tap. Both parts are closer to an adjustable distance, which is set by screws. The second option provides for a single knob design with a hole in the center. The tap is inserted into this hole and clamped with 3-4 locking screws. Handles knob made on both sides. Handle lengths can be 15-25 cm.Back to table of contents
Preparation for cutting
Internal threading begins with the drilling of the desired hole - through or deaf. The main condition: the hole must be smaller than the diameter of the thread. When drilling a hole, it is recommended to choose a drill from the following condition:
Classification of thread types.
- when threading M3 - drill diameter 2.5 mm;
- with M4 - 3.4 mm;
- with M5 - 4.2 mm;
- with M6 - 5 mm;
- when M8 - 6.7 mm;
- with M10 - 8.4 mm.
If it is necessary to cut a large thread, the diameter of the hole is determined by multiplying approximately the diameter of the thread by 0.8.
The hole for tapping an internal thread is made on a drilling machine or an electric drill. In the latter case, the workpiece is clamped in a vice. Care must be taken that the drill is directed vertically. A chamfer is removed at the upper edge of the hole to facilitate the entry of the tap. It can be made with a larger drill bit or a file. After drilling, the hole is thoroughly cleaned of chips, which is especially important for blind holes.Back to table of contents
The part in which the hole for internal thread is drilled is secured in a vice so that the chamfer on the hole is at the top. The axis of the hole should be strictly perpendicular to the table. The tap is securely fastened in the socket of the driver and vertically inserted into the face of the hole in the workpiece. Holding the knobs of the knob with both hands, the tap is pressed against the part and rotated clockwise. Rotation is performed smoothly and evenly with gentle pressure. This is two turns ahead. Then turn back a half turn (counterclockwise). In this sequence, the entire hole is drilled.
When threading the bolt must be fixed.
When threading is necessary to periodically cool the tool. It is recommended to use the following substances: when working with aluminum and its alloys - kerosene, with copper - turpentine, with steel parts - emulsion. For metals such as bronze or cast iron, cooling lubricants can not be used.
Cutting internal threads with a tap is best done using complete taps. Initially, thread is cut. Then the middle tap is similarly passed, and only then the thread is finally formed with the help of finishing. The exclusion from the process of any tap will not lead to a noticeable acceleration of the process, but will significantly impair the quality of work.Back to table of contents
Basic rules for slicing
Internal thread tap should be done with the obligatory observance of certain rules. In the case of cutting in long holes, in blind holes, in aluminum or copper, the tap must be removed from time to time, and the hole must be carefully cleaned from metal particles.
Cutting is recommended to make a complete set of the device. The middle and finishing are first rotated in the hole by hand without being fixed in the crank, and only after that they are fixed in it and driven off with a slight effort. The thread inside the blind holes is cut to a length greater than the calculated thread length to the length of the cutting section of the tap.
The introduction of the tap into the hole must be carefully controlled vertically.
Every three turns of the knob, check the verticality with a square.
Be sure to use coolant.
When cutting there may be characteristic defects, the appearance of which must be closely monitored. A rough or uneven thread appears when there is insufficient cooling or tipping of the tap. Incomplete profile formation can occur when drilling a hole incorrectly. For the same reason, directional distortions and tool breakage may occur.Back to table of contents
For tapping you will need the following tool:
- a set of taps;
- electric drill;
- set of drills;
In the manufacture of their own hands various devices can not do without threaded connections. Taping is the most important stage of such work. When you follow certain rules, you can make it yourself.