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Screws, bolts and studs are the most common externally threaded items. Most often, they fall into the hands of a home craftsman ready-made. But it happens that you need to make some tricky bolt or non-standard pin. The blank for such a part is a rod, the diameter of which must correspond to the thread being cut.

The diameter of the rod for an external thread depends on the nominal diameter of the thread and the size of the thread pitch. All this information is usually indicated on the drawing of the part in the form of the designation M10 × 1.5. The letter "M" stands for metric thread, the number after the letter is the nominal diameter, the number after the “x” sign is the thread pitch. When using the main (large) step, it may not be indicated. Basic thread pitch defined by the standard and is the most preferred.

When choosing the diameter of a rod for external threads, they are guided by the same principles as when choosing holes for internal threads. Determined that best quality thread is obtained if the diameter of the rod is slightly less than the nominal diameter of the thread being cut. When cutting, the metal is slightly squeezed out and the thread profile is complete.

If the diameter of the rod is much smaller than the required one, then the tops of the threads will be cut off; if it is larger, then the die simply will not screw onto the rod or will break during operation.

For each combination of diameter and thread pitch there is optimal rod diameter. The easiest way to determine this diameter is from the table, which shows the most common threads that can be encountered House master. The main thread pitch for each nominal diameter is highlighted in bold in the table.

Basic cutting tool external thread- die. Most often, round continuous dies in the form of a hardened steel nut are used.

To form the cutting edges, the die threads are crossed by through longitudinal holes, which also provide chip exit. To facilitate entry, the outer threads have an incomplete profile. To rotate the dies use die holder- a tool with a socket for a die and long handles. There are also split and sliding (clump) dies, but these are rare in the home workshop.

To reduce friction and obtain clean threads, a lubricant is used on steel rods - mineral oil or kerosene, and on copper rods - turpentine. At the end of the rod, to facilitate entry, a chamfer must be made with a width of at least the size of the thread pitch.

This table will help you understand cutting metric threads and possibly reduce waste. The table values ​​can be useful for machine operators, shop foremen, and engineers.

The diameters of rods for cutting metric threads are regulated by GOST 16093-2004.

The standard metric thread pitch is indicated(*)

Pipe thread

Pipe thread is a group of standards intended for connecting and sealing various types of structural elements using pipe threads. The quality of work when cutting grooves has a great influence on the reliability of the connection and the structure obtained in this way. Particular attention should be paid to the correlation of the thread with the axis of the pipe to which it is applied.

When cutting threads manually using a die, the alignment is far from ideal, which can affect the reliability and quality of the connection. As for the use of tools such as a lathe or tapping machine, applications threading heads with precision threading blade, then here the indicators of the applied thread are comparable with the theoretical values.

The ROTHENBERGER concern produces thread-cutting machines, thread-cutting dies, heads, knives that ensure the performance of work with high accuracy. All equipment is fully compliant international standards in this area.

Cylindrical pipe thread, G (BSPP)

Also known as Whitward carving ( BSW (British Standard Whitworth)). Applicable this type for organizing cylindrical threaded connections. Also used in cases of connecting internal cylindrical threads with external tapered threads (GOST 6211-81).

• GOST 6357-81 - Basic standards of interchangeability. Cylindrical pipe thread.
• ISO R228
• EN 10226
• DIN 259
• BS 2779
• JIS B 0202

Thread parameters

• theoretical profile height (H) - 960491Р;
• designation according to the profile shape - inch thread (profile in the form of an isosceles triangle with an apex angle of 55 degrees);
• maximum pipe diameter is 6 inches (for pipes with a diameter over 6, a welded connection is used).

Example of a symbol:

G - designation of the profile shape (cylindrical pipe thread);

G1 1/2 - nominal diameter (measured in inches);

A – accuracy class (can be A or B).

To designate a left-hand thread, the index LH is used (example: G1 1/2 LH-B-40 - cylindrical pipe thread, 1 1/2 - nominal bore in inches, accuracy class B, make-up length 40 millimeters).

The thread pitch can have one of four values:

Table 1

The main dimensions of cylindrical pipe threads are determined by GOST 6357-81 (BSP). It should be remembered that the thread size in this case conditionally characterizes the lumen of the pipe, despite the fact that in fact outside diameter significantly more.

table 2

d - outer diameter of the external thread (pipe);

D - outer diameter internal thread(couplings);

D1 - internal diameter of internal thread;

d1 - internal diameter of the external thread;

D2 - average diameter of internal thread;

d2 is the average diameter of the external thread.

Tapered pipe thread, R (BSPT)

Used for organizing pipe conical connections, as well as for connecting internal cylindrical and external tapered thread(GOST 6357-81). Based on BSW, compatible with BSP.

The sealing function in connections using BSPT is performed by the thread itself (due to its compression at the connection point when the fitting is screwed in). Therefore, the use of BSPT must always be accompanied by the use of a sealant.

This type of thread is characterized by the following parameters:

• GOST 6211-81 - Basic standards of interchangeability. Conical pipe thread.
• ISO R7
• DIN 2999
• BS 21
• JIS B 0203

designation based on the profile shape - inch thread with a taper (profile in the form of an isosceles triangle with an apex angle of 55 degrees, cone angle φ=3°34′48").

When designating, a letter index of the thread type is used (R for external and Rc for internal) and a digital indicator of the nominal diameter (for example, R1 1/4 - conical pipe thread with a nominal diameter of 1 1/4). The index LH is used to designate left-hand threads.

Thread parameters

Inch thread with a taper of 1:16 (cone angle φ=3°34′48"). Profile angle at the apex 55°.

Symbol: letter R for external thread and Rc for internal thread ( GOST 6211-81- Basic norms of interchangeability. Pipe thread is conical), the numerical value of the nominal diameter of the thread in inches (inch), the letters LH for a left-hand thread. For example, a thread with a nominal diameter of 1.1/4 is designated as R 1.1/4.

Table 3

Designation of thread size, pitches and nominal values ​​of external,
average and internal diameters of conical pipe threads (R), mm

Despite the fact that cutting internal threads is not a complex technological operations, there are some features of preparation for this procedure. Thus, it is necessary to accurately determine the dimensions of the preparation hole for threading, 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, there are the following types thread:

• 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, a 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 holes from the walls for cutting metric threads thin layer metal and forms a shallow groove on them, the second 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 designs, 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 must be strictly observed. They can be distinguished from each other both by special marks applied to the shanks and by design features.

1. The tap, with which the hole for cutting metric threads is processed first, has the minimum diameter among all the tools in the set and cutting teeth, top part which are heavily cropped.
2. The second tap has a shorter fence and longer combs. Its working diameter is intermediate value between the diameters of the other tools from the set.
3. The third tap, with which the hole for cutting metric threads is processed last, is 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:

Before- 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.