Threaded hole 3 4 pipe. Pipe thread sizes. designation. guests. Homemade tap for aluminum alloys

To cut an internal thread on a part, you must first drill a hole. Its size is not equal to the diameter of the thread, but should be slightly smaller. Find drill diameter and for threading it is possible in a special table, but for this you also need to know the type of thread.

main parameters

• diameter (D);
• step (P) - the distance from one turn to another.

They are determined by GOST 1973257-73. A large step is considered normal, but several smaller ones correspond to it. A small pitch is used when applied to thin-walled products (thin-walled pipes). They also make a small turn if the applied thread is a way to adjust any parameters. Also, a small step between the turns is made to increase the tightness of the connection and to overcome the phenomenon of self-unscrewing of the part. In other cases, a standard (large) step is cut.

There are many types of threads, since each has its own formation characteristics, the diameter of the threaded hole in each case is different. All of them are spelled out in GOSTs, but most often they use triangular metric and conical metric thread. We will talk about them further.

We usually see triangular threads on bolts and other similar fasteners, conical threads on most plumbing products that require a detachable connection.

fixtures

For threading with your own hands, small devices are used:

All these devices are made of alloys that differ increased strength and abrasion resistance. Grooves and grooves are applied to their surface, with the help of which their mirror image is obtained on the workpiece.

Any tap or die is marked - they have an inscription indicating the type of thread that this device cuts - diameter and pitch. They are inserted into holders - knobs and die holders - fixed there with screws. Clamping the threading tool in the holder, put it on / insert it into the place where you want to make a detachable connection. By scrolling the device, turns are formed. It depends on how correctly the device is set at the beginning of work whether the turns “lie down” evenly. Therefore, make the first turns trying to keep the structure even, avoiding shifts and distortions. After a few turns have been made, the process will become easier.

You can cut threads of small or medium diameter manually. Complex types (two- and three-way) or working with large diameters by hand is not possible - too much effort is required. For these purposes, special mechanized equipment is used - on lathes with taps and dies attached to them.

How to cut correctly

You can thread almost any metal and their alloys - steel, copper, aluminum, cast iron, bronze, brass, etc. It is not recommended to do it on a red-hot iron - it is too rigid, it will crumble during operation and it will not be possible to achieve high-quality turns, which means that the connection will be unreliable.

Tool for the job

Training

It is necessary to work on clean metal - remove rust, sand and other contaminants. Then the place where the thread will be applied must be lubricated (except for cast iron and bronze - they must be worked “dry”). There is a special emulsion for lubrication, but if it is not available, soaked soap can be used. You can also use other lubricants:

You can often hear advice to use machine or mineral oil or even lard when threading. They work well, but experts say that it is better not to do this - the chips will stick to a viscous substance, which will lead to rapid wear of the tap or die.

Slicing process

When cutting an external thread, the die is placed strictly perpendicular to the surface of the pipe or rod. During operation, it should not wag, otherwise the turns will turn out to be uneven and the connection will be ugly and unreliable. The first turns are especially important. It depends on how they “lie down” whether the connection will then be skewed.

By applying an internal thread, the part is fixed motionless. If it is a small piece, it can be clamped in a vise. If the plate is large - ensure its immobility available methods, for example, fixing with bars. M

The tap is inserted into the hole so that its axis is parallel to the axis of the hole. With a little effort, little by little, they begin to twist in a given direction. As soon as you feel that the resistance has increased, unscrew the tap back and clean it of chips. After cleaning, the process continues.

The process of slicing in a photo

When threading in a blind hole, its depth should be slightly more than required - this excess should include the tip of the tap. If this is structurally impossible, the tip is cut off from the tap. At the same time, it is not suitable for further operation, but there is no other way out.

In order for the turns to turn out to be of high quality, two taps or dies are used - roughing and finishing. The first pass is a rough pass, the second is a finish pass. There are also combined threading devices. They allow you to do everything in one pass.

Another practical advice: so that the chips do not fall into working area, when cutting, make one full turn clockwise, then half a turn counterclockwise. After that, the tool is returned to the place where it stopped and again make one revolution. So continue to the required length.

Tapping drill diameter selection tables

When making an internal thread, a hole is pre-drilled under it. It is not equal to the diameter of the thread, since during cutting, part of the material is not removed in the form of chips, but is squeezed out, increasing the size of the protrusions. Therefore, before applying, it is necessary to select the diameter of the drill for the thread. This can be done in tables. They are for each type of thread, but we will give the most popular ones - metric, inch, pipe.

Once again, we draw your attention to the fact that the diameter of the drill for threading is given for large (standard threads).

Table of rod diameters for external thread

When working in external thread the situation is very similar - part of the metal is squeezed out, not cut off. Therefore, the diameter of the rod or pipe on which the thread is applied should be slightly smaller. How accurate - see the table below.

Threaded joint - best option if necessary, create a detachable connection. The use of these elements is ubiquitous, and self-taught craftsmen or beginners in this business, faced with such a need, often ask the question of what should be the size of the threaded hole. It is worth saying that hardware with an externally applied threaded section is widely distributed on sale and it is not a problem to choose an option according to the required diameter, it remains only to determine what it should be in order for the connection to be tight, and fastener did not fall out of it.

There are several options for threading devices on the market. Devices of this kind are used everywhere. This makes it possible to thread parts that are characterized by rotation. The presence of such notches gives this process translational movements, which is important for joining this kind in equipment parts and mechanisms. It is in this case that it is important to choose right size threaded holes, based on tables and formulas. After all, poor-quality or unreliable articulation can lead to serious damage.

Groups and cutting options

Regarding the direction of movement of the guide, there are:

• outdoor;
• internal;
• single pass;
• multi-pass;
• rights;
• left.

There is a special sizing system for threading and determining the size of the threaded hole. According to her, there are such threading options that are cut with taps, such as:

Metric thread

It is characterized by a special profile, outwardly resembling the shape of a triangle, the angle is 60 o. All measurements when determining the parameters of the thread and holes for it are carried out in millimeters. It is recommended to pay attention to this!

In the factory, when creating a thread using this technology, a special marking is applied, which is produced for large steps using digital and letter designation. In this design option, the number means outer size threaded holes, that is, the diameter.

Studying any of the drawings, you can find this kind of designation - "M4", "M6", etc. Sometimes the designation has to be drawn up with an atypical step, then a digital marker is additionally introduced into the description, indicating the step size, for example, “M8x0.8”.

Based on these tables, a certain list of the “thread - drill size” format has been formed, which is often used by craftsmen in practice:

• M5 - 0.42 cm;
• M4 - 0.33 cm;
• M8 - 0.67 cm;
• M12 - 0.96 cm.

Features of choosing a drill for metric thread

Remember that a hole with a diameter of 0.5 cm is suitable for the M6 ​​thread, while a drill with a diameter of no more than 0.21 cm should be taken for the M3 thread.

Remember that a special formula is used to calculate the size of a threaded hole, but often such a need does not arise, since the general access is full of special tables developed by specialists. Such formulations will also help a beginner in carpentry, and master. Using ready-made values ​​is much easier and more practical, because you don’t have to calculate the required indicator every time.

Features of choosing a drill for cutting

For example, knowing the size of the hole for the M8 thread (0.67 cm), you can create a hole on the basis of the workpiece with a diameter corresponding to the size of the tool you have chosen, which is used during further cutting.

It is worth noting that accuracy is important in such work, and any hole must correspond to the dimensions cutting tool and nothing else. It is this rule that is fundamental in the need to accurately select a drill strictly in size for subsequent cutting.

Today, there are no difficulties with the choice and purchase of drills, because on the market you can choose any model for any size, from the minimum diameter to a large caliber.

Based specific tasks, you can order the manufacture of a drill for the required hole size for an inch or millimeter thread.

How and with what you can create a thread in the product

In order to form a high-quality thread, and even inside the workpiece, you will have to arm yourself with such a device, which is called a tap. Outwardly, it resembles a screw with some recesses with pointed edges. One of structural elements- the rod that complements the tap can be conical or cylindrical. The location of the grooves is longitudinal, due to which they separate the threaded connections into small elements, called ridges - working parts.

When applying the thread, do not rush, keep the groove clean and remove the steel layer gradually. Remember that the further quality of the parts and the strength of their connection depend on this.

In order to do everything right by choosing the size of the hole for the M6 ​​thread or another diameter, you need to take a fixture with a long length or stock up on several appropriate elements. Single taps are also not a problem to buy. Such elements are often used during the restoration of threads damaged as a result of long-term operation. To cut a new relief for the correct screwing of parts, taps are taken in pairs. It is recommended to use one for forming a rough thread, the second for finishing.

Some features of the use of taps

The peculiarity of the taps in the kit lies in the fact that the first one makes recesses small size, and the second is used to clean them up and increase them already under required size accurate to a fraction of a millimeter.

Interestingly, three-pass thread forming tools are also appearing on the market.

When faced with work involving drills and threaded connections, carefully select the tool, taking into account its quality and characteristics. Even the smallest deviation from the dimensional grid standard can lead to poor quality results.

Therefore, before starting work, it is proposed to determine the size of the hole for the thread M10 (0.85 mm), M12 (0.96 mm) or another with which you have to work.

How to make an aluminum alloy tap at home

Sometimes there is a need to cut an internal thread on the surface of a brass or light alloy coating of a part. For this you can use homemade tool and drills taken from the classic set.

To make a tap with your own hands, prepare a steel wire, which is cut and hardened with a die. After hardening, it is recommended to release the part to the color of ripe straw, and cutting edges sharpen, working with a bar or sharpener, having previously fixed the part in a collet chuck.

Now, knowing the basic concepts, you will soon understand the need to calculate the dimensions of the thread hole. With what details and with what tools you work, remember the recommendations given, and if in doubt about the parameters, rely on special tables that are best printed out and always kept at hand.

Despite the fact that the cutting of internal threads is not a complex technological operation, there are some features of the preparation for this procedure. So, you should accurately determine the dimensions of the preparatory hole for threading, as well as choose the right tool, for which special tables of drill diameters for threading are used. For each type of thread, you must use the appropriate tool and calculate the diameter of the preparation hole.

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 entries (one-, two- or three-way);
• the shape in which the profile elements are made (triangular, rectangular, round, trapezoidal);
• the direction of the rise of the turns (right or left);
• location on the product (external or internal);
• surface shape (cylindrical or conical);
• purpose (fixing, fixing and sealing, running).

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

• cylindrical, which is indicated by the letters MJ;
• metric and conical, denoted respectively by 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, designated Tr;
• round, used for the installation of sanitary fittings, - Kr;
• persistent and persistent 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 preparatory 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 choose the size of the drill.

To cut metric threads on the inner walls of a hole made with a drill, a tap is used - a helical 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. The sharp edges of the combs are precisely the working surfaces of the tap.

In order for the turns of the internal thread to turn out to be clean and neat, and 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 machined. 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 which you can perform the processing of threaded holes with sufficient quality, is a set consisting of two taps - roughing and finishing. The first cuts holes for cutting metric threads from the walls 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 threading in holes with small diameters (up to 3 mm). Larger metric holes require a combination 3-pass tool or a set of 3 taps.

For manipulations with a tap, it is used special device- collar. The main parameter of such devices, which can have a different design, is the size mounting hole, which must exactly match the size of the tool shank.

When using a set of three taps that differ both in their design and geometric parameters, the sequence of their application should be strictly observed. You can distinguish them from each other both by special risks applied to the shanks, and by design features.

1. The tap with which a hole for cutting a metric thread is machined first is different minimum diameter among all the tools of the set and cutting teeth, the upper part of which is heavily cut off.
2. The second tap has a shorter chamfer and longer combs. Its working diameter occupies an intermediate value between the diameters of other tools from the set.
3. The third tap, with which the hole for cutting metric threads is finished 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 threading metric threads. Much less frequently than metric taps are used for processing the inner walls of pipes. They are called pipe pipes in accordance with their purpose, and they can be distinguished by the letter G present in their marking.

Thread cutting technology

As mentioned above, before starting work, it is necessary to drill a hole, the diameter of which must exactly fit the 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 its poor quality, but also to breakage of the tap.

Given the fact that the tap, forming threaded grooves, not only cuts off the metal, but also pushes it through, the diameter of the drill for threading should be somewhat smaller 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 thread - 5 mm, M8 - 6.7 mm, M10 - 8.5 mm, and for M12 - 10.2.

Table 1. Main hole diameters for metric threads

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

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

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

D o \u003d D m x 0.8, where:

Before- this is the diameter of the hole to be made with a drill,

D m- the diameter of the tap with which the drilled element will be processed.

It would seem that in the pipes of the complex? Connect and twist ... But, if you are not a plumber or an engineer with a specialized education, then questions will definitely arise for answers to which you will have to go where your eyes look. And they most likely look first on the Internet)

Earlier we talked about diameters metal pipes in this material. Today we will try to clarify the threaded pipe connections for various purposes. We have tried not to clutter up the article with definitions. Basic terminology contains GOST 11708-82 which everyone can see for themselves.

Pipe cylindrical thread. GOST 6357 - 81

Direction: Left

Accuracy class: Class A (increased), Class B (normal)

Why in inches?

The inch size came to us from Western colleagues, since the requirements of the current post-Soviet space GOST and formulated on the basis of the thread BSW(British Standard Whitworth or Whitworth thread). Joseph Whitworth (1803 - 1887), a design engineer and inventor, back in 1841, demonstrated the screw profile of the same name for detachable connections and positioned it as a universal, reliable and convenient standard.

This type of thread is used both in the pipes themselves and in the elements of pipe connections: locknuts, couplings, elbows, tees ( see picture above). In the section of the profile, we see an isosceles triangle with an angle of 55 degrees and roundings at the tops and bottoms of the contour, which are made for high tightness of the connection.

Threading is carried out on sizes up to 6”. All pipes bigger size to secure the connection and prevent rupture, they are fixed by welding.

Symbol in the international standard

International: G

Japan: PF

UK: BSPP

The letter G is indicated and the bore diameter (inner Ø) of the pipe in inches. The outer diameter of the thread itself is not present in the designation.

Example:

G 1/2- a pipe thread cylindrical external, internal Ø of a pipe 1/2 "". The outer diameter of the pipe will be 20.995 mm, the number of steps for a length of 25.4 mm will be 14.

The accuracy class (A, B) and the direction of the turns (LH) can also be indicated.

For example:

G 1 ½ - B- cylindrical pipe thread, internal Ø 1 ½ inches, accuracy class B.

G1 ½ LH-B- cylindrical pipe thread, internal Ø 1 ½ inches, accuracy class B, left.

The make-up length is indicated last in mm: G 1 ½ -B-40.

For an internal cylindrical pipe thread, only the Ø of the pipe for which the hole is intended will be indicated.

Parallel pipe thread size chart

How to determine the pitch of an inch thread

I give you a picture from the English-speaking Internet, which clearly demonstrates the technique. Pipe threads are characterized not by the size between the tops of the profile, but by the number of turns per 1 inch along the axis of the thread. To help the usual tape measure or ruler. We apply, measure one inch (25.4 mm) and visually count the number of steps.

In the picture with an example ( see above) threads - from English it is literally "thread threads". In this case, there are 18 of them. one inch.

It's even easier if you have an inch thread gauge lying around in your toolbox. It is very convenient to carry out measurements, but it must be remembered that inch threads may differ in the apex angle of 55 ° and 60 °.

Tapered pipe threads

drawing pipe taper threads

Tapered pipe thread GOST 6211-81 (1st standard size)

Parameter unit: Inch

Corresponds to the rounded profile of a cylindrical pipe thread with an angle of 55°. Cm. top part (I) of the three-dimensional image "picture of pipe taper threads".

Symbol

International: R

Japan: PT

UK: BSPT

The letter R and the nominal diameter Dy are indicated. The designation R means appearance threads, Rc internal, Rp internal cylindrical. By analogy with cylindrical pipe threads, LH is used for left-hand threads.

Examples:

R1½- external pipe conical thread, nominal diameter Dy = 1 ½ inches.

R1 ½ LH- external pipe taper thread, nominal diameter Dy = 1 ½ inches, left hand.

Conical inch thread GOST 6111 - 52 (2nd standard size)

Parameter unit: Inch

Has a profile angle of 60°. Cm. lower part (II) of the three-dimensional image "picture of pipe conical threads". It is used in pipelines (fuel, water, air) of machines and machine tools with relatively low pressure. The use of this type of connection assumes tightness and thread locking without additional special means(linen threads, yarn with red lead).

Symbol

Example: K ½ GOST 6111 - 52

It stands for: inch conical thread with an outer and inner diameter in the main plane approximately equal to the outer and inner Ø of a cylindrical pipe thread G ½

Table of the main parameters of the conical inch thread

Metric taper thread. GOST 25229 - 82

Parameter unit: mm

Manufactured on surfaces with a taper of 1:16

It is used when connecting pipelines. The angle at the top of the coil is 60°. The main plane is offset relative to the end ( see pic above).

Symbol

The letters MK are followed by an indication of the diameter in the main plane and the thread pitch in mm: MK 30x2

Metric Taper Thread Size Chart

Characteristics of cylindrical pipe / inch threads relative to metric

The main characteristics of "inch" and "pipe" cylindrical threads in relation to the "metric" thread for the main dimensions.

Many of you have encountered cutting internal threads with a tap and many have a question - what diameter should the drill bit be, for example, M8 or M10. Indeed, when threading, the initial task is to drill a hole of a suitable diameter so that the tap does not cut the metal too tight and at the same time does not hang out. Therefore, I will tell you how you can calculate the correct drill diameter for any metric thread yourself.

In fact, everything is simple, as you know, there are only 2 thread parameters: this is the diameter and the pitch. You can also notice (for those who do not know) that the thread is standard (with a standard pitch) and any other. For example, the standard thread for 10 mm is 1.5 mm, that is, M10 * 1.5. But after all, threads 10 * 1.25 and 10 * 1 are quite common. The letter M on the thread means that the thread is metric.

Drill diameters for metric (M) threads

So, as I said, we take the diameter and step as the basis for calculations. Just subtract the thread pitch from the diameter and the resulting figure will be the diameter of the required drill. Let's calculate the diameter of the drill for M8 thread (standard).

8 minus 1.25 (standard pitch) we get 6.75 mm - this is exactly the drill you need to cut the M8 thread. And for example, a thread 8 * 1 - the drill will turn out with a diameter of 7 mm.

I hope everything is clear. I will also provide you with the necessary plate of standard threads (that is, you can find out which pitch is standard for a certain diameter) and the diameter of the drills for them.

Table of standard threads and drill diameter for them.

In addition to the standard thread, there are steps of 0.75 (for small threads up to M10), 1 mm, 1.25 mm, 2 mm (for large taps and dies).

I hope this article helped you independently calculate the required drill diameter for threading.

By the way, cut the thread not “dry”, but add machine or household oil. This will reduce the load on the die-tap, and cutting is much easier this way.

More related articles:

Drill and Tap Hole Size Charts: Metric, Inch

Hole diameter (drill) for threading

For threaded connections most often used metric thread. In addition to metric threads, there are quite a few more various kinds carving, we will not dwell on them.

Internal threads are cut with taps. Tap - a metal-cutting tool for cutting internal threads in a pre-cut drilled holes. There are hand and machine taps. When cutting deep threads, a set of two or three taps is usually used: the first tap cuts a rough thread, the second tap cuts a full thread, and if there is a third sword, the thread is calibrated.

Of great importance correct selection tap hole diameters. If the hole diameter is larger than it should be, then the internal thread will not have a full profile - the connection will be fragile. If the diameter is less than required, the entry of the tap into it is difficult, this leads to the breakdown of the first turns of the thread or, in the worst case, to jamming and breakage of the tap.

The first column of the table below shows metric threads from M2 to M48. The second column shows the coarse pitch applied to each metric thread. When cutting threads, these pitch values ​​should be followed whenever possible. The third column indicates the diameters of the hole (drill) for metric threads with coarse pitch. In some exceptional cases it is necessary to use a finer pitch. Fine pitch hole diameters are presented in the following columns of the table.

Metric Hole Chart

GOST 19257-73 - Holes for cutting metric threads.