How to tap an internal thread: correct hand cuts in metal. Internal threading How threads are cut

You can talk for a very long time about how to cut the thread correctly. Whole books and monographs are devoted to this. But, the vast majority of threads used do not require special skills when cutting, and we will stop our attention on the basic methods.

Internal threading

To cut internal threads, taps are used - tools like a screw with cutting grooves. Typically, two taps are required for the black cut and the finish cut. The difference is in the grooving depth. There are also three-way taps and other cutting options. To work with them, special wrenches are needed, which may be different in design, but must necessarily be suitable in size for the working tool.

It is very important to prepare the hole before threading required diameter... Otherwise, you will either break the tap (if the hole diameter is less than required), or get a poor-quality thread. So, if an internal thread M10 is required, i.e. 10 mm in 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 \u003d 8.5 mm. Thread steps 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 considering the issue of how to properly cut the thread. We attach the tap to the holder and slowly start screwing it into the hole, paying special 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 good quality. The duration of its operation and the likelihood of breakdown depend on the use of the lubricant. A few drops of oil will not only make cutting easier, but also improve the quality of the threads. This is especially important for cutting blind holes. Naturally, it doesn't hurt to have certain skills that come with practice. However, this operation is relatively simple and skills are acquired after 3-4 threads.

How to properly thread a bolt or stud

Bolts, studs and other similar fasteners have external threads and, accordingly, you will need a die (lerka) or klupp. The first ones are used for metric threads, and die plates are used for pipe threads. Cutting with a die is a little easier - they have special pipe runs (put it on and start cutting) and ratchet holders. To work with a die, it is very important to make the first turns exactly, therefore it is strongly recommended to first make a small chamfer with a file.

Unlike internal threads, there are no difficulties with diameters. So, for the 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 good quality, and lubricant must be used when cutting. Sometimes it is more difficult to start the carving 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 firmly clamped in a vice.

Finally…

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

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

Table 1: Recommended shank diameters for dies

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

Table 2. Diameters of holes 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
М5х0.8	4,2
М6х1	4,96
M7	6,0
М8	6,7
M9	7,7
М10х1.5	8,45
M11	9,4
М12х1.75	10,18
M14	11,8
М16	13,8
M18	15,3
M20	17,3

Table 3. Bore 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	Outside diameter, mm		Thread pitch		Interior holes mm
	pipes	carvings	thread per inch	mm
pipes 1/4 "	13,5	13,158	19	1,337	11,8
3/8 "pipes	17,0	16,663	19	1,337	15,2
pipes 1/2 "	21,25	20,956	14	1,814	18,9
3/4 "pipes	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 tap a thread arises when a pre-drilled hole must be prepared to accommodate any other type of bolt, screw, stud, and threaded fastener. It is the tap that in such situations is the main tool that allows you to quickly and accurately cut an internal thread with the required geometric parameters.

Varieties and scopes of taps

Internal threading can be done manually or using machine tools different types (drilling, turning, etc.). Working tools that perform the main work on 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 the classification of taps are considered generally accepted.

1. According to the method of rotation, machine-hand 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 combination with special device with two handles (this is the so-called 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 metal-cutting machines of various types, in the chuck of which such a tool is fixed.
2. According to the way in which the internal thread is cut, there are universal (through) and complete taps. The working part of the former is divided into several sections, each of which differs from the others in its geometrical 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. Complete taps require multiple tools to thread. So, if the set consists of three taps, then the first of them is intended for roughing, the second for intermediate, the third for finishing. Typically, a set of taps for tapping a certain diameter includes three tools, but in some cases, when products made of particularly hard material are processed, sets of five tools can be used.
3. By the type of hole, on the inner surface of which it is necessary to cut a thread, taps are distinguished for through and blind holes. The through-hole tool is characterized by an elongated tapered tip (lead-in) that merges smoothly into the working end. This design is most often used by universal taps. The process of tapping internal threads in blind holes is carried out with taps, the tapered tip of which is cut off and performs the function of a simple cutter. This design of the tap allows you to use it to cut threads to the full depth of the blind hole. For threading of this type, as a rule, a set of taps is used, which are manually rotated using a wrench.
4. By the design of the working part, the taps can be with straight, screw or shortened chip-removing grooves. It should be borne in mind that taps with grooves of various types can be used to cut threads in products made of relatively soft materials - carbon, low-alloy steel alloys, etc. If the thread needs to be cut in parts made of very hard or viscous materials (stainless, heat-resistant steels, etc.), then taps are used for these purposes, the cutting elements of which are staggered.

Taps are usually used for cutting metric threads, but there are tools with which to 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 to not cause any particular difficulties and end with a high-quality result, it is necessary to properly prepare for this technological operation. All tapping methods 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 preparation hole.

Table 1. Diameters of holes drilled for standard metric threads

In the event that the thread that needs to be cut does not belong to the standard category, you can calculate the hole diameter for its implementation using the universal formula. First of all, it is necessary to study the marking of the tap, in which the type of thread to be cut, its diameter and pitch, measured in millimeters (for metric), must be indicated. Then, in order to determine the size of the cross-section of the hole that must be drilled for the thread, it is enough to subtract the pitch from its diameter. For example, if a tool marked M6x0.75 will be used to cut a non-standard internal thread, then the diameter of the preparation 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 preparatory work is performed.

Table 2. Diameters of holes drilled for an inch thread

Important to get quality result the question is not only about what the thread is cut with, but also about 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 the fact 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 larger the sharpening angle of the drill should be, but this value should not exceed 140 °.

How to cut the threads correctly? First you need to pick up tools and consumables:

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 the help of 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. locksmith's vice (if the product, in which it is necessary to cut the thread, must be fixed);
7. core;
8. a hammer;
9. machine oil or other compound, which during processing must be lubricated both the tap and the section of the thread cut by it;
10. rags.

Technology features

When tapping an internal thread, the following algorithm is guided.

• In the place on the surface of the workpiece where the hole will be drilled for threading, it is necessary to form a recess for a more accurate drill entry using a core and a conventional hammer. The drill is fixed in the chuck of an electric drill or drilling machine, at which low rotation speed of the tool is set. Before starting drilling, the cutting part of the drill must be treated with a lubricating compound: the lubricated tool easily enters the structure of the material being processed 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 necessary in detail small size, they should be previously fixed using a bench vice. When starting drilling, the tool fixed in the chuck of the equipment must be positioned strictly perpendicular to the surface of the workpiece. The tap should be lubricated regularly and ensured that it does not tilt and moves strictly in the specified direction.
• At the entrance to the hole made, as mentioned above, it is necessary to remove a chamfer, the depth of which should be 0.5–1 mm (depending on the diameter of the hole). For this purpose, a larger diameter drill or countersink can be used by installing them in the chuck of the drilling equipment.
• The internal threading process begins with the # 1 tap, which is the first to be inserted into the driver. Do 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 the work, since later, when the tool is already inside the hole, this will not work. When tapping with a tap, you must adhere to the following rule: 2 turns of the tap are made in the course of threading, 1 - against the course. When the tap is made one turn backward, chips are thrown off the cutting end and the load on it is reduced. Die tapping is performed in a similar manner.
• Having cut the thread with a tap No. 1, tool No. 2 is installed in the knob, and after it - No. 3. Their processing is carried out according to the above described method. When threading with taps and dies, you need to feel when the tool starts to rotate with effort. As soon as such a moment comes, the wrench should be turned in the opposite direction to dump the 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 and disassemble metal structures without deformation. However, to create a connection, you need to know how to properly tap the threads.

Tool varieties

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

1. Method of use. Together with hand tools a special knob is supplied for work. Tooling for machine tools is fixed in the chuck thanks to the cylindrical shank.
2. By the type of holes to be machined. The devices are divided into two groups. Some are used for through-hole machining, others for deaf people.
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 a thread, before that you need to figure out what types of taps can be found in a hardware store:

1. Straight, screw fittings stand out. A separate group is 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 version represents taps, the working part of which is divided into three zones. They are needed to consistently conduct rough, medium, and finishing 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 devices allow more accurate metal processing, less vulnerable to great force. They are distinguished by reliability, durability, high accuracy.

How to determine the correct hole diameter?

If you take a large diameter drill, make a hole, take a tap of the same diameter, problems can arise. Before starting to cut a thread, you need to select the size of the tooling, the required hole diameter. For classic sizes drills if there is a special table in which the ratio of dimensions is indicated. You can find it on the Internet.

How to tap threads?

Internal tapping is accurate technological process, which is carried out in a certain sequence.

Training

Initially, you need to prepare tools, accessories for work:

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

Tapping by hand is done at low power tool speeds.

Slicing process

Step-by-step instructions for threading:

1. Beam the hole with a punch and hammer.
2. Drill a hole with an electric drill. Hold the tooling exactly perpendicular to the work surface. Lubricate the drill bit with special oil.
3. Chamfer 1 mm in depth. To do this, use a larger drill bit.
4. Fasten the snap in the collar. Perform two forward movements, one backward movement. This will allow the metal shavings to come out of the hole and there will be no cutting problems. Movements should be smooth.

During manual cutting, do not make any clamping efforts, continue to rotate the tool after it gets stuck. If it breaks down, you need to drill out the tap with a drill, different drills for metal. Another option for removing the debris is to grind the area around the hole with a grinder. Then you need to get it out with pliers.

To create threaded connections, you need to buy the appropriate documents, learn how to work with them. By working 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 idle. During the renovation, the owners of apartments and houses are faced with the need to restore old threads of anchors, bolts, nuts, or just a thread that is in metal plates.

Otherwise, you just 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 a similar process need to arm themselves with some theoretical knowledge that is set out in this article.

Before embarking on practical steps on 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 characteristics

The thread of interest to us is in the shape of a triangle, the thread trapezoidal is in the shape of a trapezoid. In addition, there is such a thing as a 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 characteristic of the thread.

Consider the above paragraph using the example of the M 12 thread, where the letter "M" indicates that the thread is metric, the number "12" defines the thread diameter. Where is the step size? The fact is that metric threads are divided into main and small, and if there is no other digital value after the number, then the main thread is. 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 main thread pitch M 12 is 1.75 mm.

All these values \u200b\u200bfor any type of thread can be found in reference books or on the pages of the corresponding sites on the Internet. For internal threads (nuts), there is another reference value - the diameter of the hole for the thread, 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 accordingly be less - 10.4 mm.

It is worth noting that something similar applies to the bolt or, as it is called in the 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, loosened on one side, and on the other, if the tolerance is larger, it will simply break.

Rigging and threading tools

Do not be intimidated by the word "equipment" because, in fact, this is a device where the cutting tool is attached: taps and dies. The old name of the plate is given in brackets, but you can still find it. The equipment includes a wrench of a rather simple design where a tap is inserted for threading in nuts and another type of device where a die for threading a bolt is attached.

Tooling and cutting tools for threading

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

Tapping taps

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 work with. Used for long thread cutting. As for the dies, they have one number.

Another type of equipment, without which the process of threading is almost impossible, is a medium-sized locksmith vice. Probably, nobody needs to explain what it is. The only thing to remember is that the vise must be securely fastened.

Thread cutting techniques

Immediately it is necessary to make a reservation that in the rod at the end and in the hole for the thread in the nut, any chamfers must be removed in an accessible way... Chamfers are necessary for accurate entry without skewing the cutting tool, that is, the tap and the die. Next, we clamp the object for threading into the knob, clamp the rod or workpiece under the nut from the vice and proceed to threading.

Die cutting

This is done without the use of excessive force and always with a lubricant, which is ideal for sulfo-fresol. However, if this is not available, you can use an emulsion (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 fat, which has been proven 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, strongly resist, you need to turn them out and clean them of chips. If this is neglected, the cutting tool may crack corny and you will have to prepare again a new rod or blank for the nut.

And finally: if you do not 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 any more, because it is almost impossible to manually cut large-diameter threads.

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

The thread can be external (screw) and internal (nut). Distinguish between cylindrical triangular (sawtooth), conical triangular, rectangular, trapezoidal, thrust, round threads. The most widely used is a cylindrical triangular or, as it is also called, a fastening thread figure No. 1.

Figure # 1 - Bolt thread elements

1 - depth;

2 - top; 3 - step;

4 - depression;

5 - outer diameter;

6- inner diameter.

Internal threading:

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 that exactly matches the inner diameter of the thread, then the metal squeezed out during cutting will press on the teeth of the tap, which can cause the thread to have torn threads, and the tap may break. Drilling too large a hole will result in an incomplete thread depth and a loose connection.
When drilling a blind hole for a thread, its depth must be slightly larger than the cut part, 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 punch; fix the part in a vice; a hole is drilled; insert a tap into the hole (Figure 2) strictly vertically (in a square); put a knob on the tap, press it with the left hand to the tap, and turn it with the right hand to the right until the tap cuts into the metal for several threads and takes a stable position; take the knob by the handles with both hands and rotate with the interception of the hands every 1-2 turns. Threading is greatly facilitated if the tap makes 1-2 working turns to the right and 1-2 turns to the left; after finishing cutting, the tap is twisted out of the hole, then once again driven along the resulting thread.

Figure №2 - Tapping the internal thread:

a - installation of the tap into the hole;

b - threading.

Rules for working with taps:

When threading in deep holes, in soft and viscous 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. Medium and fine taps are inserted into the hole without a wrench, and only after the tap has gone correctly along the thread, a wrench is put on the head and the threading continues;
in the process of cutting, you need to carefully monitor with the help of a square so that there is no misalignment of the tap; the threading point should be lubricated with oil.

External threading:

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

Cutting an external thread with a round die is performed in the following order:
at the upper end of the rod, a chamfer is removed, which ensures that the die is cut into the metal;

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

Thread cutting with sliding prismatic dies (Figure No. 3) is performed as follows: a chamfer is cut at the end of the rod; dies are installed in the die; clamp the rod in a vice; put on the stem of the die and tightly move the nuts with a clamping screw; grease the dies and the rod with oil; the klupp is turned 1 - 1.5 turns clockwise, then 1-4, 1-2 turns back and so on until the end of the thread; after cutting the thread, screw the screw to the end of the rod, tighten the dies with a screw and pass the thread 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 from shavings, wiped and oiled; wipe the klupp.