How to cut a thread. Cutting internal and external threads

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Cutting internal thread

Internal thread (thread in the hole) is cut tap(fig. right). Taps are made from tool carbon, alloyed or high speed steel. The tap consists of shank and working part .

shank the tap is attached to crank or machine chuck.

Working part tap is a screw with longitudinal or helical grooves for threading. As with dies, the working part of the tap has a chamfer to facilitate the entry of the tool into the hole. Helical grooves, similar to the longitudinal holes in the die, form cutting edges. The shavings come down on them.
Hand taps for cutting metric threads are produced in a set that includes two taps for threads up to 3 mm in diameter and three ( № 1 -draft , № 2 - average and № 3 - finishing ) for threads larger than 3 mm. Rough tap performs the main work and cuts up to 60% of the metal layer to be removed. Semi-finishing tap cuts up to 30% of the metal layer. Fine tap gives the thread its final shape and dimensions and cuts off the remaining 10% of the metal layer. The taps included in the kit have different diameters of the threaded part and different shape profiles. On the tail part of all taps of the set, circular risks are knocked out ( 1,2,3 ) or tap numbers are affixed, as well as thread sizes are indicated - diameter and step.

To rotate the tap when cutting threads manually use the device knob(fig. left). Gates are - unregulated(rice. a) and adjustable(rice. b).

Before proceeding with threading in the hole, mark the place of the hole with its obligatory punching. Taking into account the dimensions future carving according to the table (see table below), the diameter of the drill is selected.

Sometimes you can use in a simple way- to find out the diameter of the hole for the desired thread, subtract the pitch from the diameter of the thread and get the diameter of the hole.

The size of the threaded hole diameter can be calculated by the formula D=d-1.6t,
where D - hole diameter, mm;
d is the diameter of the thread being cut, mm; t - thread depth, mm.

The dimensions of the knob for fixing the tap when threading are selected depending on the diameter of the thread being cut. The approximate length of the collar can be determined by the formula
L=20D+100mm,
where D is the thread diameter.

When cutting an internal thread, the metal is squeezed out, as it were, reducing the diameter of the hole. Therefore, the diameter of the drill should be slightly larger than the inner and smaller than the outer diameter of the thread. If the hole diameter is less than required, the tap will break, and if it is larger, the thread will be incomplete, weakened.
The drilled hole is processed countersink. The use of this tool allows you to improve the quality, reduce the taper, ovality of the side surface of the hole. A countersink works in the same way as a drill.

For high-quality threading, it is important to correctly fix the part in a vice and install the first tap in the hole (fig. above a). The part is fixed so that the surface with the hole is parallel to the planes of the vise jaws, and the tap is perpendicular to the plane of the part and the jaws. Perpendicularity (90° angle) is checked with a square (Fig. b).
Threading in the following way(rice. in). First, tap No. 1 is installed. Its threaded part is preliminarily lubricated with oil. Pressing the collar with the left hand to the tap, with the right hand smoothly rotate it to the right until the tap cuts 1-2 threads. At the same time, they monitor the preservation right angle, guiding the tap if necessary. After the tap has taken the correct stable position and threading has begun, the knob is taken with both hands and rotated with light pressure, intercepting every half turn. In order for the chips to break and go into the grooves of the tap, it is rotated back and forth: one and a half turns forward and half a turn back.
Having finished the passage with tap No. 1, it is turned out, tap No. 2 is inserted, threaded, the knob is installed and cut. The thread is finally finished with tap No. 3 and the thread is checked (Fig. d).
Blind threaded holes are drilled to a depth slightly greater than the length of the thread.
The quality of the thread can be checked in the workshop by screwing the appropriate bolt into the hole.

When threading, the following defects sometimes occur, which should be avoided:
1) rough or torn cut- it turns out if there is no lubrication, and also due to a skewed tap or die;
2) partial profile thread- if the diameter of the hole is greater than the norm or the diameter of the rod is less than the norm;
3) thread misalignment or tap breakage- if the diameter of the hole is less than the norm or the diameter of the rod is more than the norm.

When cutting threads in ductile and soft metals, it is necessary to periodically unscrew the tap and clean the grooves from chips.
The thread must be cut in sequence full set taps.
Care must be taken to ensure that there is no distortion of the tap.
Special care must be taken when threading blind holes.
Be sure to periodically lubricate the cut thread with oil.

You can talk about how to properly cut a thread for a very long time. Entire books and monographs are devoted to this. But, the vast majority of threads used do not require special skills when cutting, and we will focus on the main methods.

Internal threading

For cutting internal threads, taps are used - tools like a screw with cutting grooves. As a rule, two taps are required for cutting for a black and a finishing pass. The difference is in the depth of grooving. There are also three-pass taps, and other cutting options. To work with them, special knobs are required, which can be of different designs, but must be suitable in size to the working tool.

Before threading, it is very important to prepare a hole of the desired diameter. Otherwise, you will either break the tap (with a hole diameter less than required), or get a poor-quality thread. So, if an M10 internal thread is required, i.e. 10 mm along the groove diameter, then the hole diameter should be 8.5 mm. This is determined based on the thread pitch. For M10, it is 1.5 mm and, accordingly, the required hole diameter will be 10-1.5 = 8.5 mm. Thread pitches can be found using special formulas, although more simple option will not calculate the diameter, but find out its value from the table.

After preparing the hole, we proceed directly to the consideration of the question of how to properly cut the thread. We fix the tap in the holder and slowly begin to screw it into the hole, Special attention paying attention to the accuracy of the direction. Cutting is done clockwise with the application of certain efforts.

For successful cutting, the tap must be sharp and of high quality. The duration of its operation and the likelihood of breakage depend on the use of lubricant. A few drops of oil will not only make cutting easier, but will also improve the quality of the thread. This is especially important for cutting blind holes. Naturally, the presence of certain skills that come with practice will not interfere with work. However, this operation is relatively simple and skills are acquired after 3-4 carvings.

How to properly cut a thread on a bolt or stud

Bolts, studs and similar fasteners have an external thread and, accordingly, you will need a die (lerka) or a klupp. The former are used for metric threads, the kluppy for pipe threads. Cutting with a klupp is a little easier - they have special pipe entries (put on and started cutting) and ratchet holders. To work with a die, it is very important to make the first turns evenly, so it is highly recommended to first make a small chamfer with a file.

Unlike internal threads, there are no difficulties with diameters. So, for an M10 thread, you need a workpiece with a diameter of 10 mm. The basic rules for cutting are not much different from working with a tap. The dies must be sharp and of high quality, and lubricant must be used when cutting. Sometimes it is more difficult to start a thread and if a skew is noticeable, then it is necessary to cut off the defective section and start again. For any type of thread, the workpiece must be tightly fixed in a vise.

Finally…

In conclusion, I would like to warn that there is another formula for determining the diameter of a hole for an internal thread - tap diameter x 0.8. But it is relevant only for manual three-pass taps. For all other cases, it is better to use the appropriate tables.

And, of course, the success of cutting and the quality of the thread largely depend on the quality of the tool itself. However, this problem is easily solved - after all, in the Mecca Tool online store you will find any required tool at an attractive price.

Every person involved in the installation of metal structures or performing various tasks should know how to cut threads with a tap manually. repair work. This is one of the basic plumbing skills that experienced workers have brought to automatism.

Taps are designed to be gripped by a rotating tool (knob) or fixed in a machine chuck.

Basic tool

To make internal threads by hand, various taps are used, made of carbon or high speed steels. They are a metal rod with working part and a shank designed to be gripped by a rotating tool (knob) or fixed in a machine chuck. The working part with an external thread has a conical shape; longitudinal grooves are provided in it for the exit of chips.

There are several types of taps, but not all of them are suitable for manual internal threading. For example, machine tools can only be used on machine tools due to their design. For production handmade fit the following types taps:

1. Complete. From the name it follows that this is a set of several products (3-5 pieces) of the same diameter, used alternately. Allows you to achieve a clear thread profile, although the operation takes some time.
2. Machine-manual. A type of machine tool in which the end of the shank has a rectangular cross section for wrapping with a wrench. The thread is cut in one pass.

In addition, taps can have different designs depending on the type of thread. The most common is metric, less often - cylindrical and pipe.

As a rule, during the installation of metal structures industrial buildings(hangars, greenhouses and other structures) not subject to vibrations, metric threads are used.

Also, some of the taps are made with a cut off working part, this is necessary for working with blind holes. Separately, work with alloyed steels of increased hardness should be considered. Products to overcome this hardness have grooves on the working part, arranged in a checkerboard pattern or crosswise.

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Drill selection

An electric drill is required to perform the work of cutting internal threads.

Before cutting a thread with a tap, you must first drill a hole for it. It is clear that the diameter of the hole must be smaller size tap, but how much? Exist universal way calculating this difference. Any thread is characterized by two parameters:

• diameter, indicated on tools with a capital letter M in front, for example, M6;
• the pitch of the turns is written as a number after the first parameter, for example, M6x1.

Looking at the marking of the tap, it is easy to choose a drill for the job. It is necessary to subtract the thread pitch from the diameter value, in the above example M6x1 you will need a hole with a size of 6 - 1 = 5 mm. The drill should be taken as an ordinary cylindrical one; for metal processing, such drills are made of R6M5 high-speed steel. To facilitate sizing, Table 1 lists recommended hole diameters for the most common metric threads.

Table 1

Since it is about manual processing metal, then when selecting drills, one feature should be taken into account. When working with an electric drill, no matter how hard you try to keep it level and motionless, the hole will break and its size will be somewhat larger than necessary. As a result, after the tap passes, the threads will have a sheared profile. When tightening the bolt there, a backlash will appear, and with a high tightening torque, the turns can simply be deformed. The amount of hole stakeout depends on two factors:

Countersinks are needed for chamfering when cutting internal threads.

1. The larger the diameter, the more the hole unfolds. For example, at D = 5 mm there is an increase of 0.08 mm, and at D = 10 mm - already 0.12 mm.
2. Working conditions. The locksmith may be in an uncomfortable position or at a height, this will cause an increased breakdown of the hole, which will then affect the quality of the connection.

The problem is solved as follows: in order for the internal thread to turn out to be full-profile, you must initially take a drill with a diameter of 0.1 mm less than required. It is possible that in some cases the rotation of the tap will be difficult, but usually there is no difficulty.

Preparation of tools

To perform the work of cutting an internal thread, you will need:

• marking tools (tape measure, ruler, pencil);
• electric drill with a set of drills;
• countersink for chamfering;
• a set of taps with a manual knob;
• a hammer;
• core

Drills should be filled (sharpened) in accordance with the hardness of the material being processed. The harder it is, the more you need to withstand the sharpening angle. During drilling and cutting, the working parts of drills and taps must be lubricated. The choice of type of lubricant depends on the toughness of the steel. For ordinary and carbon steel, old lard or grease is suitable, for stainless steel - machine oil.

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Work order

In order to properly perform the entire range of threading work, it is recommended to follow a certain sequence. This is important when you need to provide a good hundred connections, as in assembly metal structures. You need to start with the markup, which is done using a tape measure or ruler in accordance with the drawing. Having measured the indicated distances from the base sides, a mark is made at the found point with a pencil. Marking is carried out for all holes at once or for those where the worker is able to reach while at a height.

Further, having pointed the core at the intended place, one calculated and accurate blow is applied to make a clear depression. Naturally, before starting the procedure, the core must be sharpened properly. In the same way, you need to outline all the places for future holes. Then the drill is fixed in the drill chuck and lubricated, after which you can start making a hole. The speed of the drill must be adjusted in advance so that they are low.

Drilling is done carefully, with medium pressure, holding the drill without distortion at an angle of 90 ° to the surface. Do not allow the power tool to stagger in different directions, this enhances the breakdown of the hole. It should be noted that at the moment the drill exits on the other hand, some effort and a slight increase in the number of revolutions will be required. If the metal is thick, then the lubrication of the working part must be carried out several times during the process. When all the holes are ready, a countersink is inserted into the chuck and chamfers are removed.

The last step is threading. The sequence of this operation is the same for all types of taps. Having clamped it in the knob and previously lubricated, the end of the tool is inserted into the hole, also observing an angle of 90 °. Lightly pressing the knob from above, so that the first turns of the working part can catch on the edge of the chamfer, make the first turn. Further rotation goes without pressure according to the algorithm: one turn forward, half a turn back to dump chips. With machine taps that make threads in one pass, care must be taken: the tool is fragile and breaks easily. Complete products go easier, but here you need to drive the thread with the first number, then the second, and so on.

There are quite a few ways to connect parts, but the most common and affordable is still screw (bolt) fasteners. It is about such fasteners that we will talk. More precisely, we will consider the types of taps, the technology of threading in holes for screws and bolts of different diameters.

Taps are divided depending on the method of threading, and also depending on what hole they are intended for.

Specification by cutting method

According to the method of cutting, they distinguish:

1. Pass-through markers. A feature of such a tool is that it has both marking cutting teeth and teeth for finishing cutting of coils. Most often, such tools are used when working with parts made of soft metals, for example, aluminum, copper, brass.
2. Complete taps. In this case, we are talking about several tools for carving at once. The minimum set consists of three taps for different stages cutting: the first is for roughing, the second is for intermediate, the third is for final. Of course, the performance of work with such a set requires more time compared to using a single tap, but the quality of the turns is much higher.

Specification by hole type

Technological openings can be deaf or through. For each hole type the appropriate tap type should be used. through holes processed with a tool sharp end, and deaf ones - with a tool with a cut end. Working with a tap for a blind hole is more difficult, since very often when it reaches the bottom of the hole it can stall and break, however, with successful cutting, a quality thread is obtained along the entire length of the hole.

Separately, it should be noted that, in addition to the above, taps are divided into machine and machine-manual. The former have an elongated shank and can be installed in any electric machine, with the help of which the cutting of the turns will be carried out. The latter can be used both when doing work manually, and when doing work using an electric tool.

Tap marking

Taps for cutting internal metric threads marked with the letter "M". In this case, the letter “M” is followed by the value of the diameter of the thread being cut. In addition to the diameter, the thread pitch is also indicated on the tool. For example, marking M4 × 1 means that the tool can carve a hole with a diameter of 4 mm in 1 mm increments. When it comes to cutting tool for left-hand threads, the tool is marked LH . The diameter and pitch of the thread is indicated in a manner similar to that described above.

How to cut a thread with a tap - technology

Internal threading looks like this:

For maximum clarity, we offer you see short video, which discusses in detail the process of cutting an internal thread.

Summing up

For really good threading in the workpiece of a particular metal, you do not need to have any special knowledge and experience. As practice shows, even a master far from plumbing can cope with such work.

The main advice is to exclude haste, and approach all operations, including preparatory ones, responsibly . Equally important is the choice tool to get the job done - not worth saving. Remember: cheap low-quality taps often break off during operation, and it is extremely problematic to remove a piece of a tool from a hole.

Tapping internal thread

For threading, a variety of tools can be used, among which we highlight a tap. It is used to create a threaded surface designed to accommodate a screw, stud, bolt, or other fastener. Relatively low cost, ease of use determined the wide distribution of the considered hand tool. Let's take a closer look at how to properly cut a thread with a tap at home.

Classification of taps and their scope

For threading for a sufficiently long period, turning or drilling machines. They are designed to rotate workpiece or tool. The tap becomes the working tool in almost all cases.

The classification of such an instrument is carried out according to a number of different criteria:

As a rule, high-quality tool steel is used in the manufacture of tools. She can withstand long-term operation, do not heat up during operation. Tap High Quality has a strict geometric shape, looks neat. A similar tool is often used for cutting metric threads, but there are options for obtaining inch threads. The shape of the base can be cylindrical or conical.

Preparatory stage

In order for the work of obtaining a thread not to cause many difficulties, careful preparation should be made for such technological operation. All applied methods related with internal thread cutting, provide that a hole of the required diameter has already been obtained in advance. Get standard size threads is possible when creating a hole according to the correspondence table. For example, for an M10 thread, a hole with a diameter of 8.5 mm is created.

Often there is a situation when you should get a thread custom size. In this case, the required hole diameter is calculated using the universal formula. The calculations are carried out as follows:

1. The marking of the tool used is being studied. It is necessary to pay attention to the type of thread being cut, the pitch and the diameter.
2. You can determine the required hole diameter when using the M5X0.75 tap as follows: 5−0.75=5.25 mm.

The easiest way to work is when you need to get a standard thread, since the entire the necessary information can be taken from various tables of normative documentation.

To get a quality hole, you need to choose the right drill. When drilling, it is recommended to use equipment that prevents the occurrence of runout during operation. When choosing a drill, it is worth remembering that it must have a high-quality sharpening. Experts recommend choosing the sharpening angle depending on the hardness of the material being processed. With increasing hardness index the recommended sharpening angle also increases, but it should not exceed 140 degrees.

Required Equipment

Threading with a tap by hand only possible with the following tool:

After finding everything you need, you can proceed to the direct execution of work.

Features of the applied technology

Carry out the work in question you can do it yourself at home. To do this, consider the following recommendations:

It is not recommended to apply a large load to the handle by using a lever or gas wrench. Do not forget that the tap may burst due to high load, then remove the remaining the inside part will be quite difficult. AT While working, the master should feel how the tool goes: easily or with great effort. The form cutting edge does not allow the removal of chips from the working part at the moment of rotation along the thread.