How to cut a thread on a pipe: an overview of the main methods. How to cut internal threads - types of taps, technology, tips Table for cutting internal threads

Often during repairs there is a need strong fastening parts of any structure, and the connection with a screw and nut still remains one of the most reliable. However, it happens that there is a screw, but no suitable nut. There is only one way out - to cut the thread yourself.

A little theory

First of all, you need to choose suitable tool. Assortment of all kinds cutting devices quite wide - these are grinding wheels, cutters, files, taps, dies and others. Often both specialists and craftsmen Many of them are easy to use, while not everyone knows how to cut threads.

When making a nut or in any other case where an internal thread is required, taps are used. Appearance The tap quite expectedly resembles a screw - absolutely right, it is the screw that is screwed into the nut!

But in this case, this “screw” is turned into cutting tool. Taps are made from hard tool steel, and the cutting edges are quite sharp. If the tap is worn out, with traces of corrosion or worn out cutting edges, then it will not be possible to cut a good thread.

The top of the tap has the shape of a cone - this makes it easier to center the tool during the thread cutting process, and on the sides there are special grooves into which the resulting chips fall. It must be said that there are also “grooveless” taps.

Taps are produced by hand and machine. Important difference hand tools The point is that the tap does not cut through the workpiece to the full depth of the profile, but divides it into parts. Therefore, there are several taps for the size of one thread, and they differ in the number of annular grooves applied to the “tail” of the tool (respectively - number one, number two, etc.) There is also a special “roughing” tap, which is marked with an annular rim.

First, determine the diameter of the thread. Here it is necessary to take into account the thread pitch length. If M20x1 is required (diameter 20, thread pitch 1), then the internal diameter of the future nut will be 19 mm.

The hole for the thread in the workpiece can be made using a drill. The drill must be directed only perpendicular to the surface, otherwise the workpiece will be hopelessly damaged.

The first step is rough thread cutting, for which an appropriate tool is used, then all other stages of work are carried out. The tap is secured using a special wrench, but in extreme cases, an adjustable wrench will do.

Important Notes

You should work with taps carefully - hard steels, as a rule, are characterized by increased fragility, so there is a risk of tool breakage. In any case, it is advisable to have spare taps.
Thread cutting is carried out using the entire set of taps sequentially. If you skip at least one stage in a hurry, you won’t get high-quality carving.
When working with non-ferrous alloys (copper, tin or aluminum), it is necessary to periodically unscrew the tap and remove chips.
Ferrous metal shavings are removed by turning the tool in reverse.
To reduce friction, you can use turpentine, kerosene or linseed oil. No need to use lubricant when working with cast iron and bronze.
During work, periodically check the position of the cutting tool in relation to the workpiece - the tap should only be at a right angle to the surface.
If the thread is cut in a blind hole, then the depth of the hole itself should be slightly greater than the depth of the threaded part.

We must remember that if work rules are violated good carving will not work, and the tap may break during operation. Removing a broken cutter can be problematic; in addition, the workpiece may be completely damaged.

To receive good result skill is always required, so if the work is being done for the first time, it is advisable to stock up on several thread blanks. It is better to first learn in practice how to properly cut a thread with a tap. A certain number of initially damaged samples will ensure reliable operation in the future.

How to cut thread video

A threaded connection is the main method of connecting parts. When making any metal device with your own hands, the need arises to cut threads yourself. Tapping allows you to create threads in various holes with your own hands.

In practice, we have to deal with various materials that differ in their properties. Cutting should take into account the characteristics of the material. There are certain rules, developed over the years, that allow you to perform quality thread cutting different sizes and types.

Features of the structure of taps

The tap, which belongs to the group of metalworking and turning cutting tools, has the shape of a rod on which the cutting element is made. It is intended for cutting internal thread, that is, inside the hole in various materials, as well as for restoring damaged internal threads.

A set of metal-cutting tools: a - drills, b - countersinks, c - reamers, d - taps, d - dies.

The tools consist of a working and a tail part. In turn, the working part is divided into an intake (cutting) and calibrating section. The cutting section is responsible for the main function of the tap - cutting threads, and, most often, has a conical shape. It has teeth in the form of incisors placed around a circle. The calibrating section performs the task of final formation. It is made in the form of a cylinder with teeth that are a continuation of the teeth of the cutting section. This section is much longer than the fence. The working part is cut in the longitudinal direction with grooves, which are designed to form cutters and remove chips. Taps with a diameter of up to 22 mm have three grooves. Devices special purpose can be manufactured without grooves. The grooves can be straight or helical.

The tail part has the shape of a cylinder. At the end of the section there is a square for installation in the fastening tool. In this part the diameter marking is stamped out. Using a shank, the tool is fixed in a hand holder or machine chuck.

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Main types of taps

According to the method of use, taps are divided into two types - manual and machine. The first ones are installed in manual holders (knobs) and are designed for cutting internal threads manually. Machine ones are mounted in special holders for lathe chucks.

Based on the type of thread cut with a tap, they are divided into several types. Metric is designed for cutting the most common metric threads. Pipe forms internal threads on pipes, as well as reinforced ones in the holes of metal parts. Inch is a device for special inch threads, as well as cone-shaped ones. Specialized nut taps are made of very strong steel (P6M5) and have a special shank shape.

In addition, taps are divided into single and complete. Complete ones are used to cut in several passes. The set may contain two taps - finishing and rough; or three taps - roughing, medium finishing and finishing. Completeness is indicated on the tail of the instrument. The taps included in the set differ in the shape of the tooth: the roughing one has a trapezoidal tooth; the middle one has a triangle with a rounded top; the finishing one has a triangle with a sharp apex.

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Basic parameters

In general, cutting a thread means making a projection on the inside surface of a hole so that it forms a helix. Such a protrusion, like all threads, is characterized by the following main parameters: the helix angle, pitch, type of protrusion profile and profile elevation angle, outer and inner diameter. In addition, it is customary to distinguish another depth, determined by the outer and inner diameters.

In direction, the thread can be right-handed, when the helical protrusion rises counterclockwise, and left-handed, when the direction of rise of the protrusion coincides with the clockwise movement. Based on the shape of the protrusion profile, there are two main types: threads with a rectangular profile and with a triangular profile. There are also special forms profile, but they are in living conditions are practically not used.

The main thread is metric. This profile is a triangle with a profile angle of 60º. According to the pitch, metric is divided into threads with a large pitch and with a fine pitch. An example of the full designation of a metric thread is M10x1-6N. The designation should be understood as follows:

M - metric thread;
10 - nominal diameter;
1 - thread pitch;
6H - tolerance limits for dimensional deviations.

With normal (large pitch) the designation is abbreviated (for example, M10). In the case of a left-hand thread, the designation LH is entered.

The second most common type in everyday life is the cylindrical pipe type. The profile is a triangle with an apex angle of 55º. This type is used when connecting pipes and cylinders, where increased tightness of the connection is required. Straight pipe threads are designated by the letter G, indicating the diameter in inches.

The thrust thread is based on a trapezoidal profile with inclination angles of 3º on one side and 30º on the other. The designation includes the letter S, diameter and pitch.

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Choosing the right tap

First, the type of tap is selected based on the type of thread and its purpose (profile shape, thread pitch, tolerances). According to the accuracy requirements (class), it is determined whether a single tap should be used or a set is required. In addition, taps are produced with different finishes of their cutting element, which affects the accuracy of cutting the thread profile.

The material in which the thread must be cut influences the choice of tap. Thus, the rake angle of the teeth must be taken into account. For steel it is 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 brazed steels, which must be taken into account when considering what strength of material is being processed.

The main choice is made based on the diameter of the hole in which the internal thread is cut. The diameter of the tap should be slightly smaller than the diameter of the hole. So, for a metric M20 thread (tap diameter 20 mm), the hole diameter is 19 mm. With metric thread, if not special requirements, then the standard step is executed. For example, M4 thread - pitch 0.7 mm; M5 - 0.8 mm; M10 - 1.5 mm; M12 - 1.75 mm, etc.

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Fastening tool

In order to ensure thread cutting, the tap must be given a rotational movement with the application of force. This function is performed by a manual holder - a knob. It provides vertical mounting of the tool and the ability to apply significant loads using levers. The standard design of the driver contains a tap fastening unit and elongated handles, with which you can rotate the device manually with force.

The device is mounted in two ways. One of the knob designs consists of two parts. When these parts are joined, a hole is formed inside for installing the tap. Both parts come together at an adjustable distance, which is set with screws. The second option provides a single knob design with a hole in the center. The tap is inserted into this hole and clamped with 3-4 locking screws. The handles of the knob are made on both sides. Handle lengths can be 15-25 cm.

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Preparing for slicing

Cutting internal threads begins with drilling the desired hole - through or blind. The main condition: the hole must be smaller than the thread diameter. When drilling a hole, it is recommended to select a drill from the following condition:

for M3 thread - drill diameter 2.5 mm;
at M4 - 3.4 mm;
at M5 - 4.2 mm;
at M6 - 5 mm;
at M8 - 6.7 mm;
at M10 - 8.4 mm.

If it is necessary to cut a large thread, the hole diameter is determined by approximately multiplying the thread diameter by 0.8.

The hole for cutting internal threads is made on drilling machine or an electric drill. In the latter case, the workpiece is clamped in a vice. It is necessary to ensure that the drill is directed strictly vertically. The top edge of the hole is chamfered to facilitate entry of the tap. It can be done with a larger diameter drill or file. After drilling, the hole is thoroughly cleaned of chips, which is especially important for blind holes.

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Tapping threads

The part in which the hole for the 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 fixed in the driver socket and inserted vertically into the chamfer of the workpiece hole. Holding the handles of the driver with both hands, the tap is pressed against the part and rotated clockwise. Rotation is smooth and even with light pressure. This is done two times forward. Then turn it half a turn back (counterclockwise). The entire hole is drilled in this sequence.

When cutting threads, the bolt must be secured.

When cutting threads, it 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 may not be used.

It is best to use complete taps for cutting internal threads with a tap. First, the rough thread is cut. Then the middle tap is passed in the same way, and only then the thread is finally formed using a finishing tap. Excluding any tap from the process will not significantly speed up the process, but will significantly degrade the quality of work.

How to cut a thread for a bolt or screw? To perform thread cutting, you need to understand the issue and have a minimum set of tools, the main one of which is a tap.

General information about the tool

Internal threads in holes are cut manually or by machine using special tools - taps, which are found in two versions: machine-hand and machine. Types and versions of tools for cutting internal threads:

Machine products are designed to be secured in a chuck or collet clamp metalworking machine on which this type of work can be performed. Machine-manual execution includes a shank square section, so that the tool can be installed in a hand crank.
Depending on the cutting method, taps can be universal (through) or complete. The latter are a set of two or three tools of the same diameter, which should be used in the same hole alternately: first - roughing No. 1, then - No. 2 and 3, if available. In the case of some alloys, sets of five products are used. A universal tap makes all the threads at once, but requires great physical effort and breaks more often.
According to the thread configuration, cutting products are divided into pipe, metric and cylindrical.
Based on the type of holes, there are tools for through and blind holes. The first ones have a long lead-in part. Most often they are universal, while the latter have a cut-off approach. Such work is performed in a set of 2-3 products.
According to the design of the working part, the products come with straight, screw or shortened grooves. They are used to work with regular, carbon or low-alloy steels. For stainless or heat-resistant ductile steels, a tool with a staggered arrangement of teeth is used.

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Preparing for thread cutting

Before cutting the thread, you need to required diameter. It is clear that it will be smaller than the thread diameter, but by how much? For standard cases The hole sizes are shown in Table 1.

Table 1

Thread designation	Hole diameter, mm	Thread designation	Hole diameter, mm
M 1	0.75	M 10	8.5
M 1.1	0.85	M 11	9.5
M 1.2	0.95	M 12	10.2
M 1.4	1.1	M 14	12.0
M 1.6	1.25	M 16	14.0
M 1.8	1.45	M 18	15.4
M 2	1.6	M 20	17.4
M 2.2	1.75	M 22	19.4
M 2.5	2.05	M 24	20.9
M 3	2.5	M 27	23.9
M 3.5	2.9	M 30	26.4
M 4	3.3	M 33	29.4
M 4.5	3.8	M 36	31.9
M 5	4.2	M 39	34.9
M 6	5.0	M 42	37.4
M 7	6.0	M 45	40.4
M 8	6.7	M 48	42.8
M 9	7.7	M 52	46.8

What to do if the thread is non-standard? There is a universal formula for determining the diameter of the hole. Each tap has a marking indicating the type, diameter and thread pitch in millimeters, for example, one of the non-standard ones is M 6 x 0.75. The hole size is determined as follows: its pitch is subtracted from the thread size (6-0.75 = 5.25 mm). Pitch is the distance between two turns.

Pipe internal cylindrical threads are measured in inches. The diameters of the holes for this type of connection are shown in Table 2.

Table 2

Designation in inches	1 / 8	1 / 4	3 / 8	1 / 2	5 / 8	3 / 4
Hole diameter, mm	8.8	11.7	15.2	18.9	20.7	24.3
Designation in inches	7 / 8	1	1 1 / 8	1 1 / 4	1 3 / 8	1 1 / 2
Hole diameter, mm	28.1	30.5	35.2	39.2	41.6	45.2

The drill must be properly sharpened, without runout. Otherwise, the hole will come out larger in diameter, and subsequently there will be play in the connection due to defective turns.

The sharpening angle of the drill must correspond to the hardness of the material.

The harder the metal being processed, the larger the angle should be (but not more than 140°).

Before performing work, you should prepare the following tools or devices:

electric low-speed drill or drilling machine;
drill of the required size;
a drill 10 mm larger than the pass-through drill or a countersink for chamfering;
set of taps;
hand crank;
hand vice(if necessary);
hammer;
core;
lubricant;
rags.

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Work order

When preparatory stage finished, you can drill the hole and tap the thread in the following order:

Decide on the location of the hole by marking the part and placing a mark in the right place. Place the core and one with a strong blow Use a hammer to make a recess where the drill enters. Clamp the drill bit into the chuck of an electric drill or machine tool, set the rotation speed to low, and lubricate the cutting part of the tool. Old lard is best suited for these purposes; if you don’t have it, you can lubricate it with grease. When working with viscous steel grades (stainless or heat-resistant), lubrication is carried out with machine oil.
If necessary, clamp the part in a hand vice. Attach the drill to the recess on the part, visually align the electric drill so that the cutting tool is at an angle of 90° to the surface. Drill a hole at low speed, periodically lubricating the drill with lard or pouring machine oil on it if the part is thick. Avoid distortion and overheating of the tool. When finished, insert a countersink into the chuck and make a high-quality chamfer; the beginning of the cutting process depends on it. Distortion during countersinking is also unacceptable. The chamfer depth is up to 1 mm, with very small hole diameters - up to 0.5 mm.
Place the shank of tap No. 1 into the sliding prism of the driver, fix it by rotating the handles, and lubricate the working part well. After removing the drilling chips from the part, insert a tap with a driver into the hole and cut the thread. Do not try to forcefully change the position of the incoming tool; it will go in as smoothly as you drilled the hole and chamfered it. Correct the position of the tap relative to the part at the very beginning so that there is no obvious distortion. Cut according to the algorithm: make 2 turns forward, then 1 turn back. This is necessary to discharge chips and reduce the load on the tool.
Repeat the operation with taps No. 2 and 3 (if any). You don't have to count the revolutions, you need to cut the threads until you feel an increase in resistance. Then turn back to dump the chips. After the operation is completed, you can verify the quality of the work performed by screwing a bolt into the hole. It may be tight and require turning with a wrench, then you can try to screw in another bolt. If it also goes with tension, you should

Despite the fact that cutting internal threads is not a complex technological operation, there are some features of preparation for this procedure. Thus, it is necessary to accurately determine the dimensions of the preparation hole for cutting threads, and also select the right tool, for which special tables of drill diameters for threads are used. For each type of thread, it is necessary to use the appropriate tool and calculate the diameter of the preparation hole.

Types and parameters of thread

The parameters by which threads are divided into various types, are:

units of diameter (metric, inch, etc.);
number of thread starts (one-, two- or three-thread);
the shape in which the profile elements are made (triangular, rectangular, round, trapezoidal);
direction of rise of turns (right or left);
location on the product (external or internal);
surface shape (cylindrical or conical);
purpose (fastening, fastening and sealing, chassis).

Depending on the above parameters, the following types of thread are distinguished:

cylindrical, which is designated by the letters MJ;
metric and conical, designated M and MK respectively;
pipe, designated by the letters G and R;
with a round profile, named after Edison and marked with the letter E;
trapezoidal, designated Tr;
round, used for installation of sanitary fittings, – Kr;
thrust and thrust reinforced, marked as S and S45, respectively;
inch thread, which can also be cylindrical and conical - BSW, UTS, NPT;
used to connect pipes installed in oil wells.

Application of the tap

Before you start threading, you need to determine the diameter of the preparation hole and drill it. To facilitate this task, the corresponding GOST was developed, which contains tables that allow you to accurately determine the diameter of the threaded hole. This information makes it easy to select the drill size.

To cut metric threads on the inner walls of a hole made with a drill, a tap is used - a screw-shaped tool with cutting grooves, made in the form of a rod, which can have a cylindrical or conical shape. On its side surface there are special grooves located along its axis and dividing the working part into separate segments, which are called combs. The sharp edges of the combs are precisely the working surfaces of the tap.

In order for the turns of the internal thread to be clean and neat, and for its geometric parameters to correspond to the required values, it must be cut gradually, by gradually removing thin layers of metal from the surface being treated. That is why for this purpose they use either taps, the working part of which is divided along the length into sections with different geometric parameters, or sets of such tools. Single taps, the working part of which has the same geometric parameters along its entire length, are needed in cases where it is necessary to restore the parameters of an existing thread.

The minimum set with which you can sufficiently perform machining of threaded holes is a set consisting of two taps - rough and finishing. The first one cuts a thin layer of metal from the walls of the hole for cutting metric threads and forms a shallow groove on them, the second one not only deepens the formed groove, but also cleans it.

Combination two-pass taps or sets consisting of two tools are used for tapping small diameter holes (up to 3 mm). To machine holes for larger metric threads, you must use a combination three-pass tool or a set of three taps.

To manipulate the tap, a special device is used - a wrench. The main parameter of such devices, which can have different design, is the size of the mounting hole, which must exactly match the size of the tool shank.

When using a set of three taps, differing both in their design and geometric parameters, the sequence of their use should be strictly observed. They can be distinguished from each other both by special marks applied to the shanks and by design features.

The tap, with which the hole for cutting a metric thread is processed first, has the minimum diameter among all the tools in the set and cutting teeth, upper part which are heavily cropped.
The second tap has a shorter fence and longer combs. Its working diameter is intermediate between the diameters of the other tools in the set.
The third tap, with which a hole for cutting metric threads is processed in last resort, characterized by full ridges of cutting teeth and a diameter that must exactly match the size of the thread being formed.

Taps are used primarily for cutting metric threads. Much less often than metric ones, taps designed for processing the internal walls of pipes are used. In accordance with their purpose, they are called pipe, and they can be distinguished by the letter G present in their markings.

Internal thread cutting technology

As mentioned above, before starting work, you need to drill a hole, the diameter of which must exactly fit a thread of a certain size. It should be borne in mind: if the diameters of the holes intended for cutting metric threads are chosen incorrectly, this can lead not only to poor quality execution, but also to breakage of the tap.

Considering the fact that the tap, when forming threaded grooves, not only cuts the metal, but also pushes it, the diameter of the drill for making threads should be slightly smaller than its nominal diameter. For example, a drill for making M3 threads should have a diameter of 2.5 mm, for M4 - 3.3 mm, for M5 you should choose a drill with a diameter of 4.2 mm, for M6 threads - 5 mm, M8 - 6.7 mm, M10 - 8.5 mm, and for M12 - 10.2.

Table 1. Main diameters of holes for metric threads

All diameters of drills for GOST threads are given in special tables. Such tables indicate the diameters of drills for making threads with both standard and reduced pitches, but it should be borne in mind that holes of different diameters are drilled for these purposes. In addition, if threads are cut in products made of brittle metals (such as cast iron), the diameter of the thread drill obtained from the table must be reduced by one tenth of a millimeter.

You can familiarize yourself with the provisions of GOST regulating the cutting of metric threads by downloading the document in pdf format follow the link below.

The diameters of drills for metric threads can be calculated independently. From the diameter of the thread that needs to be cut, it is necessary to subtract the value of its pitch. The thread pitch itself, the size of which is used when performing such calculations, can be found out from special correspondence tables. In order to determine what diameter the hole needs to be made using a drill if a three-start tap is used for threading, you must use the following formula:

D o = D m x 0.8, Where:

D o- this is the diameter of the hole that must be made using a drill,

D m– the diameter of the tap that will be used to process the drilled element.

Making internal threads is usually not difficult. But there are some features of using the tool and selecting holes for cutting metric threads.

Types of thread

They differ in their main characteristics:

diameter calculation system (inch, metric, others);
number of passes (two-, three- or single-pass);
profile shape (rectangular, trapezoidal, triangular, round);
direction of rotation of the screw (left or right);
placement on the part (internal or external);
shape of the part (cone or cylinder);
purpose (running, fastening and sealing or fastening).

According to the listed characteristics, the following types are distinguished:

cylindrical (MJ);
metric and conical (M, MK);
pipe (G, R);
Edison round (E);
trapezoidal (Tr);
round for plumbing fasteners (Kp);
persistent (S, S45);
inch, including cylindrical and conical (BSW, UTS, NPT);
oil range.

Tools for internal threading

To make internal threads, you need a tap - a screw-shaped tool with sharp grooves. The rod can be shaped like a cone or a cylinder. The grooves run lengthwise and break the thread into sections called combs. It is the edges of the combs that are the working surfaces.

To ensure a clean groove, the metal is removed gradually, in layers. This requires one very long tool or set.

Single taps are also found on sale; they are often used to correct broken threads. To cut a new one, buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing work. The first one cuts a shallow groove, the second one cleans and deepens it. There are also three-pass tools. Thin taps, up to 3 millimeters, are sold in twos, wider ones - in threes. Three-pass taps are inserted into the gates. The design of the knobs is different, but their size must match the size of the cutter.

The tools in the set are distinguished by the marks marked on the tail end. If you look closely, you will notice differences in shape:

the first tap has heavily cut tooth tips, the outer diameter is slightly smaller than the other tools in the set;
second tap with shorter fence segment, longer ridges. Its diameter is slightly larger than that of the first;
the third tap has full ridges of teeth, and its diameter should match the dimensions of the future thread.

Taps are divided into pipe taps (marked “G”) for cutting threads inside the pipe, and metric taps, which are more common.

The quality directly depends on the properties of the tap: it must be made of good metal and spicy. To extend the life of the tool and improve the quality of the thread, lubricant is used. Typically, it takes 3 to 5 attempts to acquire stable cutting skills.

Cutting process

Before you start cutting, you should use drills to make a hole in the workpiece. The diameter of the hole from the drill must match internal size threads. When the size of the hole made with drills is chosen incorrectly, the tool can break or the grooves will turn out to be of poor quality.

During cutting, part of the metal does not fall out with chips, but is pressed along the working surfaces of the tap, forming a groove profile on the workpiece. Taking this feature into account, the size of the drill used to make the hole for the thread is selected slightly smaller than the nominal diameter of the future thread.

For example, when cutting M5 (groove diameter is 5 mm), you should choose a drill for a 4.2 mm hole. To cut M4, the diameter of the drill must be 3.3 millimeters, and before working with an M6 tap, a hole is first made with a 5 mm drill. This indicator is calculated taking into account the thread pitch. The pitch can be calculated mathematically, but in practice they resort to correspondence tables, where for an M5 tap the pitch is 0.8, for M4 this figure is 0.7, for M6 - 1. We subtract the pitch index from the diameter and get the required drill diameter. When working with brittle metals, such as cast iron, the drill diameter should be reduced by 0.1 mm compared to the size recommended in the table.

The formula for calculating the hole diameter when working with three-pass taps:

Up=Dm * 0.8;

here: Dm is the diameter of the tap.

Type	Diameter	Step
M1	0,75	0,25
M1,2	0,95	0,25
1,4	1,1	0,3
1,7	1,3	0,36
2,6	1,6	0,4
2,8	1,9	0,4
M3	2,1	0,46
M3	2,5	0,5
M4	3,3	0,7
M5	4,1	0,8
M6	4,9	1
M8	6,7	1,25
M10	8,4	1,5

Table 1. Correspondence between thread diameters and preparation hole

Before starting work, the tap is inserted into a square shank - a knob. The collars can be regular or ratchet. The carving is done carefully, the first pass is made with a No. 1 tap to the end. Special attention it is necessary to pay attention to the direction of movement: clockwise only, and some force must be applied. It is done like this: 1/2 turns along the stroke alternate with 1/4 turns against the screw stroke to destroy the chips.

Thread in inches	External D, mm	Diameter, mm	Pitch, mm
1\8″	2,095	0,74	1,058
1\4″	6,35	4,72	1,27
3\16″	4,762	3,47	1,058
5\16″	7,938	6,13	1,411
7\16″	11,112	8,79	1,814
3\8″	9,525	7,49	1,588

Table 2. Hole diameters for inch threads

A couple drops of lubricant will make working on blind threaded holes much easier. Although machine oil is sometimes used as a lubricant, drying oil is optimal for working with steel. WITH aluminum alloys It is preferable to use kerosene, alcohol or turpentine. Technical oil can also be used, but with less effect.

Homemade tap for aluminum alloys

To create internal threads in brass or light alloy parts, you can use homemade instrument and drills from the usual set. Calibrated steel wire will do. Using a die, an external thread is cut on it, after which the workpiece is hardened. After hardening, it is necessary to release the part to the color of ripe straw. Cutting edges are sharpened using a whetstone or sharpener, having previously clamped the part into a collet chuck.

Video on how internal threads are cut: