The strength of the fastening of the parts to each other is ensured by screwing the carrier of the external thread into the internal of the second product. It is important that their parameters are maintained in accordance with the standards, then such a connection will not be broken during operation and will provide the necessary tightness. Therefore, there are standards for the execution of threads and its individual elements.

Before cutting, a threaded hole is made inside the part, the diameter of which should not exceed its inner diameter. This is done using metal drills, the dimensions of which are given in the reference tables.

Hole Options

There are the following thread parameters:

• diameters (internal, external, etc.);
• profile shape, height and angle;
• step and entry;
• others.

The condition for connecting the parts to each other is the complete coincidence of the indicators of the external and internal threads. If any of them is performed without compliance with the requirements, then the fastening will be unreliable.

Fastening can be bolted or studded, which, in addition to the main parts, include nuts and washers. Holes are formed in the parts to be fastened before joining, and then cutting is carried out.

To perform it with maximum accuracy, it is necessary to pre-form a hole by drilling, equal to the value of the inner diameter, that is, formed by the tops of the protrusions.

With through execution, the diameter of the hole should be 5-10% over size bolt or stud, then the condition is fulfilled:

d resp = (1.05..1.10)×d, (1),

where d is the nominal diameter of the bolt or stud, mm.

To determine the hole size of the second part, the calculation is carried out as follows: the step value (P) is subtracted from the value of the nominal diameter (d) - the result obtained is the desired value:

d resp = d - P, (2).

The calculation results are clearly demonstrated by the table of thread hole diameters, compiled according to GOST 19257-73, for sizes 1-1.8 mm with small and main steps.

Nominal diameter, mm	Pitch, mm	Hole size, mm
1	0,2	0,8
1	0,25	0,75
1,1	0,2	0,9
1,1	0,25	0,85
1,2	0,2	1
1,2	0,25	0,95
1,4	0,2	1,2
1,4	0,3	1,1
1,6	0,2	1,4
1,6	0,35	1,25
1,8	0,2	1,6
1,8	0,35	1,45

An important parameter is the drilling depth, which is calculated from the sum of such indicators:

• screwing depth;
• stock of external thread of the screwed-in part;
• her undercut;
• chamfers.

At the same time, the last 3 parameters are reference, and the first is calculated through the accounting factors for the material of the product, which are equal for products from:

• steel, brass, bronze, titanium - 1;
• gray and malleable cast iron - 1.25;
• light alloys - 2.

Thus, the screw-in depth is the product of the material factor and the nominal diameter, and is expressed in millimeters.

Download GOST 19257-73

Thread types

Threads according to the measurement system are divided into metric, expressed in millimeters, and inch, measured in the corresponding units. Both of these types can be made in both cylindrical and conical shapes.

They may have profiles various forms: triangular, trapezoidal, round; divided according to the application: for fasteners, plumbing elements, pipe and others.

The diameters of the preparatory holes for threading depend on its type: metric, inch or pipe - this is standardized by the relevant documents.

Holes in pipe connections, expressed in inches, are prescribed in GOST 21348-75 for a cylindrical shape and GOST 21350-75 for a conical one. The data is valid for copper and nickel-free steel alloys. Cutting is carried out inside the auxiliary parts into which pipes will be screwed - slates, clamps and others.

GOST 19257-73 shows the diameters of holes for cutting metric threads, where the tables show the size ranges of nominal diameters and pitches, as well as the parameters of holes for metric thread taking into account the values ​​of limit deviations.

The data given in the GOST19257-73 table confirm the calculation given above, in which the parameters of holes for metric types are calculated from the nominal diameter and pitch.

GOST 6111-52 normalizes the diameters of holes for inch conical threads. The document indicates two diameters with a divergence by a cone and one without reaming, as well as drilling depths, all values ​​except the nominal value are expressed in millimeters.

fixtures

manual or automatic ways slicing deliver results various classes precision and roughness. So, the main tool remains a tap, which is a rod with cutting edges.

Markers are:

• manual, to perform metric (M1-M68), inch - ¼-2 ʺ, pipe - 1/8-2 ʺ;
• machine-manual - nozzles for drilling and other machines are used for the same sizes as manual ones;
• nut, which allow you to cut a through version for thin parts, with nominal sizes of 2-33 mm.
• For cutting metric threads use a set of rods - taps:
• draft, having an elongated intake part, consisting of 6-8 turns, and marked with one risk at the base of the shank;
• medium - with an intake part of an average length of 3.5-5 turns, and marking in the form of two marks;
• the finishing one has an intake part of only 2-3 turns, without marks.

When manually cutting, if the pitch exceeds 3 mm, then 3 taps are used. If the step of the product is less than 3 mm, two are enough: roughing and finishing.

Taps used for small metric threads (M1-M6) have 3 flutes for chip removal and a reinforced shank. In the design of the rest - 4 grooves, and the shank is through.

The diameters of all three rods for metric threads increase from rough to finish. The last threaded rod must have a diameter equal to its nominal diameter.

Taps are attached to special devices– tool holder (if it is small size) or collar. With the help of them, the cutting rod is screwed into the hole.

Preparation of holes for cutting is carried out using drills, countersinks and lathes. It is formed by drilling, and by countersinking and boring, its width is increased and the surface quality is improved. Fixtures are used for cylindrical and conical shapes.

The drill is a metal rod consisting of a cylindrical shank and a helical cutting edge. to their main geometric parameters relate:

• helix angle, typically 27°;
• taper angle, which can be 118° or 135°.

Drills are rolled, dark blued, and shiny - polished.

Countersinks for cylindrical shapes are called twigs. They are metal rods with two cutters twisted into a spiral and a fixed guide pin to insert a countersink into the cavity.

cutting technique

You can cut with a hand tap following the following steps:

• drill a hole for the thread of the appropriate diameter and depth;
• carry out its countersinking;
• fix the tap in the holder or collar;
• set it perpendicular to the working cavity in which cutting will be carried out;
• screw the tap with light pressure clockwise into the hole prepared in advance for threading;
• turn the tap back every half turn to cut chips.

For cooling and lubricating surfaces during the cutting process, it is important to use lubricants: machine oil, drying oil, kerosene and the like. Incorrectly selected lubricant can lead to poor cutting results.

Drill size selection

The drill diameter for a hole for a metric thread is also determined by formula (2), taking into account its main parameters.

It should be noted that when cutting in ductile materials such as steel or brass, the turns increase, therefore it is necessary to choose a larger drill diameter for threading than for brittle materials such as cast iron or bronze.

In practice, drill sizes are usually slightly smaller than required hole. So, table 2 shows the ratio of nominal and external threaded diameters, pitch, diameters of the hole and drill for it for cutting metric threads.

Table 2. The ratio of the main parameters of the metric thread with a normal pitch and the diameters of the hole and drill

Nominal diameter, mm	Outer diameter, mm	Pitch, mm	Largest hole diameter, mm	Drill diameter, mm
1	0,97	0,25	0,785	0,75
2	1,94	0,4	1,679	1,60
3	2,92	0,5	2,559	2,50
4	3,91	0,7	3,422	3,30
5	4,9	0,8	4,334	4,20
6	5,88	1,0	5,153	5,00
7	6,88	1,0	6,153	6,00
8	7,87	1,25	6,912	6,80
9	8,87	1,25	7,912	7,80
10	9,95	1,5	8,676	8,50

As can be seen from the table, there is a certain dimensional limit, which is calculated taking into account thread tolerances.

The size of the drill is much smaller than the hole. So, for example, under the M6 ​​thread, outside diameter which is 5.88 mm, and its highest value holes should not exceed 5.153 mm, it is worth using a 5 mm drill.

An M8 threaded hole with an outer diameter of 7.87 mm will only be 6.912 mm, which means that the drill for it will be 6.8 mm.

The quality of a thread depends on many factors when cutting it: from the choice of tool to a correctly calculated and prepared hole. Too little will lead to increased roughness and even breakage of the tap. High forces applied to the tap contribute to non-compliance with tolerances and, as a result, dimensions are not maintained.

Screws, bolts and studs are the most common external threads. Most often, they fall into the hands of a home master ready-made. But it happens that you need to make some tricky bolt or non-standard stud. 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 external threading depends on the nominal diameter of the thread and the size of the thread pitch. All this information is usually indicated on the detail drawing as the designation M10 × 1.5. The letter "M" denotes a metric thread, the number after the letter is the nominal diameter, the number after the sign "x" is the thread pitch. When using the main (large) step, it may not be indicated. Main thread pitch defined by the standard and is the most preferred.

When choosing the diameter of the rod for external threads, the same principles are followed as for selection of holes for internal threads. Determined that the 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 squeezed out a little and the thread profile is complete.

If the diameter of the rod is much less than required, 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 break during operation.

For each combination of diameter and thread pitch, there is optimum 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. Bold type in the table indicates the main thread pitch for each nominal diameter.

Basic cutting tool external thread- plate. The most commonly used round solid dies in the form of a hardened steel nut.

For the formation cutting edges the thread of the die is crossed by through longitudinal holes, which also provide chip exit. To facilitate entry, the extreme threads of the thread have an incomplete profile. To rotate the plate, use die holder- a tool with a socket for a die and long handles. There are also split and sliding (klupp) dies, but this is rare in the home workshop.

To reduce friction and obtain a clean thread on steel rods, a lubricant is used - mineral oil or kerosene, on copper - turpentine. At the end of the rod, to facilitate entry, a chamfer must be made with a width not less than the thread pitch.

Metric threads. Rod diameters and tolerances for metric thread M3-M50, performed by dies. Drill diameters M1-M10 for drilling holes for metric threads. Threading P

Metric threads. Rod diameters and tolerances for metric thread M3-M50, performed by dies. Drill diameters M1-M10 for drilling holes for metric threads. Cutting die threads and markers.

• External thread: The die is clamped in the collar with screws located along its contour.
• At the end of the rod on which the thread is to be cut, on grinding machine chamfer at an angle<60 о до диаметра, равного 80% диаметра резьбы. Затем плашку смазывают густым маслом (напр. солидол), животным жиром (салом) или растительным маслом — жидкое моторное масло лучше не использовать, так как оно зачастую портит резьбу.
• At the end of a rod firmly clamped in a vice with a chamfer in the form of a truncated cone, a wrench with a die is installed exactly in the horizontal plane and the wrench is rotated clockwise with both hands (looking from above), if the thread is right-handed, with a slight pressure on the die. Sometimes it is recommended to smoothly rotate the knob clockwise, sometimes - after each half turn, turn it back a little to break the chips. The main thing is to lubricate all the working blades well so that the thread does not break and the die does not become dull.
• The diameter of the rods for external metric thread should be selected according to Table 1.

Table 1. Diameters of rods for metric threads made with dies

• Internal thread: cut with cutters. A tap is a metal-cutting tool for cutting internal threads in pre-drilled holes. There are manual (rotate with a knob) and machine, nut and tool (uterine and ram). When cutting deep threads, a set of three taps is usually used: the first tap (designation - one risk) is preliminary, the second (two risks) cuts the thread and the third (three risks or no bottom) calibrates it. Nut taps are suitable for cutting short threads (as in a nut) and have successive cutting edges; after passing the entire length, a full thread is obtained.
• The correct choice of hole diameters is of great importance. If the diameter is larger than it should be, then the internal thread will not have a full profile and a weak connection will result. With a smaller hole diameter, the entry of the tap into it is difficult, which leads to the breakdown of the first turns of the thread or to jamming and breakage of the tap. The diameter of a hole for a metric thread can be approximately determined by multiplying the thread size by 0.8 (for example, for an M2 thread, the drill should have a diameter of 1.6 mm, for M3 - 2.4-2.5 mm, etc. (see. . table).
• It is necessary to lubricate the cutting part of the tap with thick oil (eg grease), animal fat (lard) or vegetable oil - it is better not to use liquid engine oil, as it often spoils the thread - and insert it into the hole.
• Then you need to carefully monitor that the tap goes exactly along the axis of the hole in order to avoid breakage. After cutting 4-5 turns, the tap is removed from the hole and cleaned of chips. After that, it is lubricated again and screwed into the hole again, another 4-5 turns are cut, continuing the operation until it stops (with a blind hole or until the tap exits (with a through hole).
• Then they clean the first tap, put it in place and take a tap with two risks, lubricate it, manually screw it into the hole and, as soon as it starts to cut into the metal, put a collar on it. After cutting every 5-6 turns, the tap is cleaned of chips and lubricated until the hole is completely passed.
• Then they clean the second tap, put it in place, take the last tap with three risks, also grease it, screw it into the hole by hand until it engages, put on the knob and carefully calibrate the thread. Chip cleaning and lubrication are repeated as before.
• Inch taps thread is cut in the same way as metric. For threading pipes, die cutters are used, usually with adjustable cutting elements in the thread range for pipes with an internal diameter of 1/4 to 4 inches. Threads on pipes and stubbles of large diameter are best cut on screw-cutting lathes.
• The diameter of the drill bits for drilling holes for metric threads should be selected according to Table 2.

Table 2. Drill diameters for drilling holes for metric threads

Article rating:

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

The diameters of the 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 designed to connect and seal various types of structural elements using pipe threads. The quality of the grooving work 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 on which it is applied.

When threading by hand using a die, concentricity 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 thread-cutting machine, the application threading heads with precise threading knife, then the indicators of the applied thread are comparable with the theoretical values.

The ROTHENBERGER concern manufactures threading machines, threading die cutters, heads, knives, which ensure the performance of work with high precision. All equipment fully complies with international standards in this area.

Pipe thread cylindrical, G (BSPP)

Also known as the Whitward carving ( BSW (British Standard Whitworth)). This type is used to organize cylindrical threaded connections. Also used in cases where an internal cylindrical thread is connected to an external conical thread (GOST 6211-81).

• GOST 6357-81: Basic norms of interchangeability. The thread is pipe cylindrical.
• ISO R228
• EN 10226
• DIN 259
• BS2779
• JIS B 0202

Thread parameters

• theoretical profile height (H) - 960491R;
• designation according to the shape of the profile - inch thread (profile in the form of an isosceles triangle with an angle at the top of 55 degrees);
• maximum pipe diameter is 6 inches (pipe over 6 in. welded).

Symbol example:

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

G1 1 / 2 - conditional passage (measured in inches);

A - accuracy class (may be A or B).

To designate a left-hand thread, the LH index 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 size of the thread in this case conditionally characterizes the lumen of the pipe, despite the fact that in fact the outer diameter is much larger.

table 2

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

D - outer diameter of the internal thread (coupling);

D1 - internal diameter of the internal thread;

d1 - internal diameter of the external thread;

D2 - the average diameter of the internal thread;

d2 is the average diameter of the external thread.

Conical pipe thread, R (BSPT)

It is used for organizing conical pipe connections, as well as for connecting cylindrical and external conical threads (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 crushing at the junction when the fitting is screwed in). Therefore, the application of BSPT should always be accompanied by the use of a sealant.

This type of thread is characterized by the following parameters:

• GOST 6211-81 -Basic norms of interchangeability. The thread is pipe conical.
• ISO R7
• DIN 2999
• BS21
• JIS B 0203

designation according to the shape of the profile - inch thread with a taper (profile in the form of an isosceles triangle with an angle at the apex 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 numerical 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 a left-hand thread.

Thread parameters

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

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

Table 3

Thread size designation, pitches and nominal values ​​of the outer,
average and internal diameters of pipe taper thread (R), mm