How to cut an internal thread with a tap: correct manual cutting in metal. Cutting an internal thread How to cut a thread

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 the hole. 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, paying special attention to maintaining 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 other similar fasteners have an external thread and, accordingly, you will need a die (lerka) or a screw clamp. 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.

Table 1. Recommended shank diameters for threads cut by dies

Thread diameter in mm	M 6	M 8	M 10	M 12	M 14	M 16	M 18	M 20
Stem diameter in mm	5,8	7,8	9,8	11,8	13,7	15,7	17,7	19,8

Table 2. Hole diameters for metric threads.

Designation	holes, mm
M1.0	0,75
M1.2	0,95
M1.4	1,1
M1.7	1,35
M2.0	1,6
M2.3	1,9
M2.6	2,15
M3x0.5	2,5
M3.5	2,9
M4x0.7	3,3
M5x0.8	4,2
M6x1	4,96
M7	6,0
M8	6,7
M9	7,7
M10x1.5	8,45
M11	9,4
M12x1.75	10,18
M14	11,8
M16	13,8
M18	15,3
M20	17,3

Table 3. Hole diameters for inch threads.

Thread designation, inch	Nar. diameter, mm	thread pitch		Hole diameter, mm
		thread per inch	mm
1/8"	2,095	24	1,058	0,74
3/16"	4,762	24	1,058	3,41
1/4"	6,350	29	1,270	4,72
5/16"	7,938	18	1,411	6,13
3/8"	9,525	16	1,588	7,49
7/16"	11,112	14	1,814	8,79

Table 4. Inch pipe threads.

Designation	Outer diameter, mm		thread pitch		Interior holes.mm
	pipes	carving	threads per inch	mm
pipes 1/4"	13,5	13,158	19	1,337	11,8
pipes 3/8"	17,0	16,663	19	1,337	15,2
pipes 1/2"	21,25	20,956	14	1,814	18,9
pipes 3/4"	26,75	26,442	14	1.814	24,3
pipes 1"	33,5	33.250	11	2,399	30,5

The question of how to cut threads with a tap arises when a pre-made hole needs to be prepared to accommodate a bolt, screw, stud, and any other type of threaded fastener. It is the tap in such situations that is the main tool that allows you to quickly and accurately cut the internal thread with the required geometric parameters.

Varieties and scopes of taps

Internal threading can be done manually or using machines various types(drilling, turning, etc.). The working tools that perform the main work of cutting internal threads are machine-hand or machine taps.

On different kinds taps are divided depending on a number of parameters. The following principles for classifying taps are generally accepted.

1. According to the method of bringing into rotation, machine-manual and machine taps are distinguished, with the help of which the internal thread is cut. Machine-hand taps equipped with a square shank are used in conjunction with special device with two handles (this is the so-called knob, tap holder). With the help of such a device, the tap is rotated and cuts the thread. Threading with a machine-type tap is carried out on various types of metal-cutting machines, in the chuck of which such a tool is fixed.
2. According to the method by which the internal thread is cut, universal (through) and complete taps are distinguished. The working part of the former is divided into several sections, each of which differs from the others in its geometric parameters. The section of the working part, which first begins to interact with the machined surface, performs roughing, the second - intermediate, and the third, located closer to the shank, - finishing. Threading with complete taps requires the use of several tools. So, if a set consists of three taps, then the first of them is intended for roughing, the second for intermediate, and the third for finishing. As a rule, a set of taps for cutting threads of a certain diameter includes three tools, but in some cases, when products made from especially hard material are processed, sets consisting of five tools can be used.
3. By hole type inner surface which needs to be threaded, there are taps for through and blind holes. The tool for processing through holes is characterized by an elongated conical tip (entry), which smoothly passes into the working part. Such a design is most often used for taps of a universal type. The process of cutting internal threads in blind holes is carried out by taps, the conical tip of which is cut off and performs the function of a simple cutter. This design of the tap allows you to cut threads with it to the entire depth of a blind hole. For threading this type, as a rule, a set of taps is used, which are driven manually using a wrench.
4. According to the design of the working part, the taps can be with straight, helical or shortened chip removal grooves. It should be borne in mind that taps with grooves of various types can be used for cutting threads in products made of relatively soft materials - carbon, low-alloy steel alloys, etc. steels, etc.), then for these purposes taps are used, the cutting elements of which are arranged in a checkerboard pattern.

Taps are usually used for cutting metric threads, but there are tools that cut pipe and inch female threads. In addition, taps also differ in the shape of their working surface, which can be cylindrical or conical.

Preparing for internal threading

In order for the process of cutting an internal thread with a tap not to cause any particular difficulties and to end with a quality result, it is necessary to properly prepare for this technological operation. All methods of threading with a tap assume that a hole with the appropriate diameter has already been made in the workpiece. If the internal thread to be cut has standard size, then a special table with data according to GOST can be used to determine the diameter of the preparatory hole.

Table 1. Hole diameters for standard metric threads

In the event that the thread to be cut does not belong to the standard category, the diameter of the hole for its execution can be calculated using the universal formula. First of all, it is necessary to study the marking of the tap, which necessarily indicates the type of thread being cut, its diameter and pitch, measured in millimeters (for metric). Then, to determine the size of the cross-section of the hole to be drilled for the thread, it is enough to subtract the pitch from its diameter. For example, if a tool marked M6x0.75 is used to cut a non-standard internal thread, then the diameter of the preparatory hole is calculated as follows: 6 - 0.75 \u003d 5.25 mm.

For standard threads belonging to the inch category, there is also a table that allows you to choose the right drill with which to perform the preparatory work.

Table 2. Hole diameters for inch threads

Important to get quality result is the question not only of what the thread is cut with, but also of which drill to make the preparatory hole. When choosing a drill, it is necessary to pay attention to the parameters and quality of its sharpening, as well as to ensure that it rotates in the chuck of the equipment used without beating.

The sharpening angle of the cutting part is selected depending on the hardness of the material to be drilled. The higher the hardness of the material, the greater the sharpening angle of the drill should be, but this value should not exceed 140 °.

How to cut a thread correctly? First you need to pick up tools and supplies:

1. an electric drill or drilling machine capable of operating at low speeds;
2. drill, the diameter of which is calculated or selected according to reference tables;
3. a drill or countersink, with which a chamfer will be removed from the edge of the prepared hole;
4. a set of taps of the appropriate size;
5. manual holder for taps (knob);
6. bench vise (if the product in which the thread is to be cut must be fixed);
7. core;
8. hammer;
9. machine oil or other composition, which during the processing process needs to lubricate both the tap and the thread section cut by it;
10. rag.

Technology features

When cutting an internal thread with a tap, the following algorithm is used.

• In the place on the surface of the workpiece where the hole for threading will be drilled, it is necessary to form a recess for a more accurate entry of the drill using a core and a conventional hammer. The drill is fixed in the chuck of an electric drill or drilling machine, on which low revolutions of rotation of the tool are set. Before starting drilling, the cutting part of the drill must be treated with a lubricant: the lubricated tool enters the structure of the material being processed more easily and creates less friction in the processing area. You can lubricate the drill with a piece of ordinary lard or grease, and when processing viscous materials, machine oil is used for this purpose.
• If threading is needed in detail small size, they should be pre-fixed using a bench vise for this. Starting drilling, the tool fixed in the equipment chuck must be positioned strictly perpendicular to the surface of the workpiece. You should regularly lubricate the tap and make sure that it does not warp and moves strictly in the specified direction.
• At the entrance to the hole, as mentioned above, it is necessary to chamfer, the depth of which should be 0.5–1 mm (depending on the diameter of the hole). For this purpose, you can use a larger diameter drill or countersink by installing them in the chuck of drilling equipment.
• The process of cutting internal threads begins with tap # 1, which is the first to be installed in the knob. We should not forget about the lubricant, which must be applied to the tap for threading. The position of the tap relative to the hole to be machined must be set at the very beginning of work, since later, when the tool is already inside the hole, this will not work. When cutting a thread with a tap, it is necessary to adhere to the following rule: 2 turns of the tap are made in the direction of threading, 1 - against the course. When the tap is made one turn back, chips are dropped from its cutting part and the load on it is reduced. Threading with a die is performed using a similar technique.
• Having cut the thread with tap No. 1, tool No. 2 is installed in the knob, and after it - No. 3. They are processed according to the method described above. When threading with taps and dies, you need to feel when the tool starts to rotate with force. As soon as such a moment comes, you should turn the knob in the opposite direction to throw chips from the cutting part of the tool.

Reading 3 min.

There are situations where a reliable connection cannot be made using welding machine. In such cases, threaded connections are used. It allows you to assemble, disassemble metal structures without deformation. However, to create a connection, you need to know how to properly cut a thread with a tap.

Tool varieties

The tool that is used to create a thread is called a tap. These are cylindrical metal rods, on the edges of which there are sharp incisors arranged in a certain sequence. Taps are divided according to several factors:

1. How to use. Together with hand tools a special wrench is supplied for work. Tooling for machine tools secures in the chuck thanks to the cylindrical shank.
2. According to the type of holes being processed. Devices are divided into two groups. Some are used for through holes, others for blind holes.
3. For cutting internal, metric, pipe threads.

The shape of the taps can be either cylindrical or conical.

Design features of the tool

If you need to cut the thread, before that you need to figure out what types of taps can be found in a hardware store:

1. Straight, screw fixtures stand out. A separate group are cylindrical rods, on which special grooves are cut to remove metal chips from the hole.
2. Another division by design is universal, complete tools. The first option is a tap, the working part of which is divided into three zones. They are needed for consistent rough, medium, finishing processing of the inside of the hole. The second option is a set of metal cylinders, each of which is responsible for its own type of threading.

To get a better connection, you need to choose a set of taps. Separate fixtures allow you to process metal more accurately, less vulnerable to great effort. Differ in reliability, durability, high accuracy.

How to determine the diameter of the hole?

If you take a large diameter drill, make a hole, take a tap of the same diameter, problems may arise. Before starting to cut the thread, you need to choose the size of the tool, the required hole diameter. For classic sizes drills if a special table that indicates the ratio of sizes. You can find it on the Internet.

How to cut a thread with a tap?

Tapping of internal threads is accurate technological process, which is carried out in a certain sequence.

Preparation

Initially, it is required to prepare tools, additional devices for work:

1. Small vise.
2. Electric drill with speed control, metal drills.
3. A set of taps.
4. Metal brush.
5. Kern with a hammer.

Threading with a tap by hand is carried out at low speeds of the power tool.

Slicing process

Threading step by step instructions:

1. Poke the hole with a punch with a hammer.
2. Drill a hole with an electric drill. Hold the tool exactly perpendicular to the work surface. Additionally, lubricate the drill with special oil.
3. Chamfer 1 mm in depth. To do this, use a drill with a larger diameter.
4. Fasten the snap in the collar. Perform two movements forward, one movement back. So the metal chips will come out of the hole, there will be no problems with cutting. Movements should be smooth.

During manual cutting, you can not make efforts on the clamp, continue to rotate the tool after it is stuck. If it breaks, you need to drill a tap with a drill, different drills for metal. Another option for extracting the debris is to grind the area around the hole with a grinder. Then you need to get it with pliers.

To create threaded connections, you need to buy the appropriate documents, learn how to work with them. Carrying out the work carefully, without haste, you can get a reliable connection in a short period of time.

The question of how to thread a bolt or nut is far from being idle. During repairs, the owners of apartments and houses are faced with the need to restore old threads of anchors, bolts, nuts, or simply threads in metal plates.

And even you need to cut a new thread on a bolt or nut. For professional turners or locksmiths, this task is not difficult, however, those who have never encountered such a process need to arm themselves with some theoretical knowledge, which is presented in this article.

Before proceeding with the practical steps of threading, you need to know its main parameters and types. In the construction and repair of housing, in most cases, metric threads are used. What does it mean? According to the shape of the tooth, the thread can be metric, inch, rectangular, trapezoidal, etc.

Metric Thread Specifications

The thread we are interested in has the shape of a triangle, the trapezoidal thread has the shape of a trapezoid. In addition, there is such a thing as the thread pitch, that is, the distance between its vertices: in the case of a metric thread, between the vertices of the thread triangle. And, of course, its diameter must be attributed to the characteristics of the thread.

Consider the above paragraph using the M 12 thread as an example, where the letter “M” indicates that the thread is metric, the number “12” determines the diameter of the thread. Where is the step size? The fact is that metric threads are divided into main and small ones, and if after the number there is no other digital value, then the thread is the main one. But if we have a thread M12 x 1.5 or M 12 x 1.25, then this means that the thread pitch is 1.5 and 1.25 mm, respectively. The pitch of the main thread M 12 is 1.75 mm.

All these values ​​for any type of thread can be found in reference books or on the pages of the relevant sites on the Internet. For internal threads (nuts), there is another reference value - the diameter of the threaded hole, which can be found there. For our M12 bolt, the inner diameter of the nut should be 12 mm minus the height of the tooth profile, that is, according to the reference books 10.2 mm. For fine thread M 12 x1.25, the diameter will be correspondingly smaller - 10.4 mm.

It is worth noting that something similar applies to the bolt or, as it is called in reference books, to the rod. Again, for the M 12 thread, the diameter of the rod should be slightly less than 11.7 mm, but for the M 12 X 1.25 thread, 11.9 mm. If you do not observe the dimensional tolerances for the thread for both the nut and the bolt, the thread will be of poor quality, weakened on one side, and on the other, if the tolerance is greater, it will simply break it.

Tooling and threading tools

Do not be afraid of the word "equipment" because, in fact, this is a device where a cutting tool is attached: taps and a die (lerka). The old name of the plate is given in brackets, but it can still be found. The equipment includes a collar of a rather simple design where a tap is inserted for threading nuts and another type of device where a die for threading a bolt is attached.

Tooling and cutting tools for threading

Taps, as well as dies, are made of high carbon cast iron, so they are fragile and are afraid of heavy loads. Threading in nuts is mainly carried out by two taps: N 1 and N 2. The first has an incomplete thread for preliminary penetration, following which the second tap produces the thread.

Taps for threading

As a result, the thread is complete and of high quality, which means it will firmly hold the connection with the nut. Another type of tap is used, called "machine", which combines two tap numbers.

Die holder and die set

It would seem convenient, but this type of tap is long and inconvenient to use. Used for cutting long threads. As for the dies, they have one number.

Another type of equipment, without which the threading process is almost impossible, is a medium-sized bench vise. What it is, probably, no one needs to explain. The only thing to remember is that the vise must be securely fastened.

Threading techniques

Immediately you need to make a reservation that in the rod at the end and in the threaded hole in the nut, chamfers must be chamfered by any accessible way. Chamfers are necessary for precise entry without distortion of the cutting tool, that is, a tap and a die. Next, we clamp the object for threading into the knob, clamp the rod or workpiece under the nut from the vise and proceed to threading.

Thread cutting with a die

This is done without the use of excessive force and always with a lubricant, which is ideal for sulfo-frezol. However, if this is not available, you can use an emulsion (a solution of mineral oil in water) or just vegetable oils.

By the way, if you decide to cut the thread of a stainless steel or copper bolt, there is no better lubricant than ordinary lard, which has been tested more than once in practice.

When cutting a thread, you need to feel the tap or die: if they begin to spring a little, that is, they strongly resist, you need to unscrew them and clean them from chips. If this is neglected, the cutting tool may simply crack and you will have to prepare again a new rod or blank for the nut.

And finally: if you don’t have the opportunity to order blanks for a bolt or nut from a turner, purchase (rolled metal in the form of a circle), which can be from five to 20 mm in diameter, and you don’t need more, because it’s almost impossible to manually cut a large diameter thread.

Threaded connections are simple, reliable, make it possible to adjust the tightening, as well as disassemble and assemble parts and mechanisms. They have received the widest application in various mechanisms, devices, devices.

The thread is external (screw) and internal (nut). There are threads cylindrical triangular (sawtooth), conical triangular, rectangular, trapezoidal, persistent, round. The most widely used is a cylindrical triangular or, as it is also called, a fastening thread, Figure No. 1.

Figure No. 1 - Thread elements on the bolt

1 - depth;

2 - top; 3 - step;

4 - depression;

5 - outer diameter;

6- inner diameter.

Internal thread cutting:

First of all, you need to choose the right drill for drilling the hole. You should be aware that if you drill a hole for the thread with a diameter exactly corresponding to the inner diameter of the thread, then the metal squeezed out during cutting will put pressure on the teeth of the tap, which may cause the thread to be broken, and the tap may break. When drilling a hole with a too large diameter, the thread depth will be incomplete and the connection will be fragile.
When drilling a blind hole for a thread, its depth must be made somewhat larger than the part being cut, otherwise the thread will turn out to be incomplete in length.

Threading is carried out in the following sequence: mark the place of drilling with a center punch; fix the part in a vice; drill a hole; insert a tap into the hole (Figure 2) strictly vertically (along the square); they put a collar on the tap, press it with the left hand to the tap, and turn it to the right with the right until the tap cuts several threads into the metal and takes a stable position; take the crank by the handles with both hands and rotate with the interception of hands every 1-2 turns. Threading is greatly facilitated if the tap is used to make 1-2 working turns to the right and 1-2 turns to the left; having finished cutting, the tap is turned out of the hole, then it is again driven along the resulting thread.

Figure No. 2 - Tapping an internal thread with a tap:

a - installation of the tap in the hole;

b - threading.

Rules for working with taps:

When cutting threads in deep holes, in soft and ductile metals (copper, aluminum, bronze, etc.), the tap must be periodically unscrewed from the hole and the grooves must be cleaned of chips; you need to cut the thread with a full set of taps - rough, medium and fine. The middle and finishing taps are inserted into the hole without a wrench, and only after the tap goes correctly along the thread, the wrench is put on the head and threading continues;
in the process of cutting, it is necessary to carefully monitor with the help of a square that there is no skew of the tap; the place of thread cutting should be lubricated with oil.

External thread cutting:

At home, it is done by hand with dies.
The diameter of the rod for external threading should be 0.3-0.4 mm less than the outer diameter of the thread being cut. Deviations from this rule are not allowed.

External thread cutting with a round die is carried out in the following order:
at the upper end of the rod, a chamfer is removed, which ensures that the die cuts into the metal;

The rod is clamped in a vice vertically so that its protruding end is 20-25 mm longer than the length of the cut part (Figure No. 3); a die fixed to the knob is placed on the rod and rotated with a little pressure so that the die cuts about 1-2 threads without skew. After that, the rod is lubricated with oil and the knob is smoothly rotated 1-2 turns to the right and 1/2 turn to the left.

Threading with sliding prismatic dies (Figure No. 3) is performed as follows: a chamfer is sawn at the end of the rod; install dies in the klupp; clamp the rod in a vice; put a screw cap on the rod and tightly shift the nuts with a clamping screw; lubricate the dies and the rod with oil; the screw cap is turned 1 - 1.5 turns clockwise, then 1-4, 1-2 turns back and so on until the end of the thread; having cut the thread, the klupp is screwed to the end of the rod, the dies are pressed with a screw and the thread is threaded again; check the thread with a nut of the appropriate diameter; at the end of the work, the dies are removed from the die, cleaned of chips, wiped and lubricated with oil; wipe the klupp.