Holes for cutting pipe tapered threads. Pipe thread sizes. designation. GOST Thread hole diameter 1.1.4

Although slicing internal thread does not apply to complex technological operations, there are some peculiarities of preparation for this procedure. So, it is necessary to accurately determine the dimensions of the preparatory hole for threading, as well as to choose the right tool, for which special tables of diameters of drills for thread are used. For each type of thread, the appropriate tool must be used and the diameter of the preparation hole must be calculated.

Varieties and parameters of thread

The parameters by which the thread is divided into different types are:

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

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

cylindrical, which is designated by the letters MJ;
metric and conical, denoted respectively M and MK;
pipe, for which the letters G and R are used;
with a round profile, named after Edison and marked with the letter E;
trapezoidal, denoted by Tr;
round, used for the installation of sanitary fittings, - Kr;
resistant and resistant 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.

Tap application

Before proceeding with threading, the diameter of the preparation hole must be determined and drilled. To facilitate this task, the corresponding GOST was developed, which contains tables that allow you to accurately determine the diameter of the hole for the thread. This information makes it easy to select the drill size.

To cut a metric type thread on the inner walls of a hole made by 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 lateral surface there are special grooves located along its axis and dividing the working part into separate segments, which are called combs. Sharp edges dies are just the working surfaces of the tap.

To make the threads of the internal thread clean and neat, and its geometric parameters correspond to the required values, it must be cut gradually, by gradually removing thin layers of metal from the surface to be treated. That is why, for this purpose, either taps are used, 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 the help of which it is possible to perform sufficiently high-quality machining of the holes for the thread, is a set consisting of two taps - roughing and finishing. The first cuts holes for cutting from the walls metric thread a thin layer of metal and forms a shallow groove on them, the second not only deepens the formed groove, but also cleans it.

Combined two-way taps or sets of two tools are used for tapping small holes (up to 3 mm). For larger metric holes, use a combination 3-pass tool or a set of 3 taps.

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

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

The taps with which the metric hole is first processed is different minimum diameter among all the tools in the set and cutting teeth, the top of which is heavily cut.
The second tap has a shorter nose and longer flanges. Its working diameter is intermediate between the diameters of the rest of the tools from the set.
The third tap, with which the metric hole is machined last, has full cutting teeth and a diameter that must exactly match the size of the thread to be formed.

Taps are mainly used for tapping metric type threads. Significantly less often than metric taps are used designed for processing inner walls pipes. In accordance with their purpose, they are called pipe, and they can be distinguished by the letter G, which is present in their marking.

Internal threading technology

As mentioned above, before starting work, you need to drill a hole, the diameter of which must exactly fit the thread. 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 its poor performance, but also to the breakage of the tap.

Considering the fact that the tap, while forming the threaded grooves, not only cuts the metal, but also pushes it, the diameter of the drill for making the thread should be slightly less than its nominal diameter. For example, a drill for threading M3 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. In such tables, the diameters of the drills for making threads with both standard and reduced pitch are indicated, while it should be borne in mind that holes are drilled for these purposes different diameters... In addition, if the thread is cut in products made of brittle metals (such as cast iron), the diameter of the threaded drill obtained from the table must be reduced by one tenth of a millimeter.

You can familiarize yourself with the GOST provisions governing the cutting of metric threads by downloading the pdf document from the link below.

Drill diameters for a metric thread, you can calculate it yourself. From the diameter of the thread that you want to cut, you must 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 with a drill in the event that a three-way tap will be used for threading, use the following formula:

D o = D m x 0.8, where:

Before Is the diameter of the hole to be made with the drill,

D m- the diameter of the tap, which will be used to process the drilled element.

Download full version

GOST 21350-75

Group G13

STATE STANDARD OF THE UNION OF SSR

TAPERED PIPE CUTTING HOLES

Diameters

Holes for threading pipe taper screw thread.

Diameters

The validity period is set from 01.01.77

______________________________

* Expiration date removed

by the resolution of the USSR State Standard

N 2403 dated 06/29/84. (IUS N 11, 1984).

DEVELOPED, INTRODUCED AND PREPARED FOR APPROVAL by the All-Union Scientific Research Institute for Normalization in Mechanical Engineering (VNIINMASH)

And about. Director Gerasimov N.N.

Theme leader and performer of Zaroslov M.P.

APPROVED AND INTRODUCED BY Decree State Committee standards of the Council of Ministers of the USSR of December 12, 1975 N 3877

REPLACE MH 5389-64

1. This standard establishes the diameters of holes for cutting pipe tapered threads in accordance with GOST 6211-69 in steel products in accordance with GOST 380-71, GOST 4543-71, GOST 1050-74, GOST 5058-75 and GOST 5632-72 (except for alloys for nickel base) and copper in accordance with GOST 859-66.

2. Diameters of holes with reaming on a taper and their limit deviations must correspond to those indicated in Fig. 1 and in Table 1.

Table 1


	Hole diameter
Number of threads per				Drilling depth
		Pre Off	Pre Off

Note. For threads with a nominal size exceeding the nominal hole diameters and their maximum deviations should be equal to those established by GOST 6211-69 for inner diameter carving.

3. The diameters of the holes without reaming on the cone and their maximum deviations must correspond to those indicated in Fig. 2 and in Table 2.

table 2


Nominal thread size in inches	Number of threads per	Hole diameter		Drilling depth
			Prev off

4. It is allowed to use holes of other diameters obtained on the basis of experimental data for cutting pipe tapered threads.

5. Drill diameters for tapping holes are shown in the recommended appendix.

Drill diameters for holes for cutting pipe tapered threads


Nominal thread size in inches	Number of threads per	Drill diameter for hole
		with expansion on a cone	without tapering



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CUT HOLES
TAPERED PIPE THREAD

DIAMETERS

GOST 21350-75

STATE STANDARDS COMMITTEE
OF THE COUNCIL OF MINISTERS OF THE USSR

Moscow

DEVELOPED, SUBMITTED AND PREPARED FOR APPROVAL by the All-Union Scientific Research Institute for Normalization in Mechanical Engineering (VNIINMASH)

And about. director Gerasimov N.N.

Theme leader and performer Zaroslova M.P.

APPROVED AND INTRODUCED INTO ACTION by the Resolution of the State Committee of Standards of the Council of Ministers of the USSR No. 3877 dated December 12, 1975

STATE STANDARD OF THE UNION OF SSR

TAPERED PIPE CUTTING HOLES

Diameters

Holes for threading pipe taper screw thread.
Diameters

GOST
21350-75

Instead of
MN 5389-64

By the decree of the State Committee of Standards of the Council of Ministers of the USSR dated December 12, 1975 No. 3877, the validity period is established

from 01.01.77

2. Diameters of holes with reaming on a cone and their maximum deviations should correspond to those indicated in fig. 1 and in table. one.

Table 1

Dimensions in mm

Number of threads per 1 ²

Step R

Hole diameter

Drilling depthl

d c

d o

Nominal

Prev off

Nominal

Prev off

0,907

8,10

0,20

8,57

0,10

1,337

10,80

0,24

11,45

14,30

14,95

1,814

17,90

18,63

23,35

0,28

24,12

2,309

29,35

30,29

1 1/4

37,80

0,34

38,95

1 1/2

43,70

44,85

55,25

0,40

56,66

Note. For threads with a nominal size greater than 2² nominal hole diametersd o and their maximum deviations should be equal to those established by GOST 6211-69 for the internal thread diameter.

3. Diameters of holes without reaming on a cone and their maximum deviations should correspond to those indicated in fig. 2 and in table. 2.

4. It is allowed to use holes of other diameters obtained on the basis of experimental data for cutting pipe tapered threads.

5. The diameters of the drills for tapping holes are indicated in the recommended one.

table 2

Dimensions in mm

Nominal thread size in inches

Number of threads per 1 ²

Step R

Hole diameterd c

Drilling depthl

Nominal

Prev off

1 / 8

0,907

8,25

0,20

1 / 4

1,337

11,05

0,24

3 / 8

14,50

1 / 2

1,814

18,10

0,28

3 / 4

23,60

2,309

29,65

1 1 / 4

38,30

0,34

1 1 /2

44,20

56,00

0,40

Drill diameters for holes for cutting pipe tapered threads

Dimensions in mm

Nominal thread size in inches

Number of threads per 1 ²

Step R

Drill diameter for hole

with expansion on a cone

without tapering

1 / 8

0,907

1 / 4

1,337

10,8

11,1

3 / 8

14,25

14,5

1 / 2

1,814

3 / 4

23,25

2,309

1 1 / 4

38,25

1 1 /2

56,00

Internal threading is usually straightforward. But there are some peculiarities of using the tool and selection of holes for cutting metric threads.

Thread types

They differ in their main characteristics:

system of calculating diameter (inch, metric, others);
the number of calls (two-, three- or one-way);
profile shape (rectangular, trapezoidal, triangular, round);
direction of rotation of the screw (left or right);
placement on parts (internal or external);
part shape (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's round (E);
trapezoidal (Tr);
round for plumbing fixtures (Kp);
persistent (S, S45);
inch, including cylindrical and conical (BSW, UTS, NPT);
oil assortment.

Internal threading tools

To make internal cuts, you need a tap - a screw-shaped tool with sharp flutes. The rod can be in the form of a cone or a cylinder. The grooves go along and break the threads into sections called combs. It is the edges of the combs that are the working surfaces.

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

Single taps are also available commercially, and are more commonly used to fix stripped threads. To cut a new one, they buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing work... The first cuts a shallow groove, the second cleans and deepens it. There are also three-pass instruments. Thin taps, up to 3 millimeters, are sold in two, wider - in three. Three-way taps are inserted into the driver. The device of the cranks is different, but their size must match the size of the cutter.

In a set, tools are distinguished by the risks applied to the tail end. If you look closely, you can see the shape differences:

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

Taps are divided into pipe (marked with "G") for threading inside the pipe and metric - the more common.

The quality directly depends on the properties of the tap: it must be made of good metal and sharp. To prolong the life of the tool and improve the quality of the threads, a lubricant is used. Usually, it takes 3 - 5 attempts to acquire a stable cutting skill.

Slicing process

Before you start cutting, you should make a hole in the workpiece with the help of drills. The diameter of the hole from the drill must match inner dimension carving. When the size of the hole made by the drills is selected incorrectly, the tool may 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 pushed along the working surfaces of the tap, forming a groove profile on the workpiece. Given this feature, the size of the drill, which makes the hole for the thread, is selected slightly less 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. For cutting M4, the drill diameter should be 3.3 millimeters, and before working with the M6 tap, a hole is pre-drilled with a 5 mm drill. This indicator is calculated taking into account the thread pitch. The step can be calculated mathematically, but in practice they resort to correspondence tables, where for the M5 tap the step is 0.8, for the M4 this indicator is 0.7, for the M6 - 1. Subtract the step indicator 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 from the recommended size in the table.

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

Up = Dm * 0.8;

here: Dm - tap diameter.

A 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
М4	3,3	0,7
M5	4,1	0,8
M6	4,9	1
М8	6,7	1,25
M10	8,4	1,5

Table 1. Correspondence of thread diameters and preparation hole

Before starting work, the tap is inserted into a square shank - a knob. The gates can be conventional or with a ratchet. The thread is done carefully, the first pass is made with a tap number 1 to the end. Particular attention must be paid to the direction of movement: only clockwise, while it is necessary to apply some effort. It is carried out as follows: 1 \ 2 of a turn in the course alternates with 1 \ 4 of a turn against the screw to break the chips.

Thread in inches	Outer D, mm	Diameter in mm	Step, 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. Bore diameters for inch threads

A couple of drops of grease make it much easier to work on deaf people. threaded holes... 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 alloy parts, you can use homemade tool and drills from the usual set. Calibrated steel wire will do. With the help of 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. The cutting edges are sharpened with a bar or sharpener, after clamping the part in a collet chuck.

Video on how to cut an internal thread: