Rod diameter for thread m6. What is the diameter of the rod to choose for an external metric thread? External thread cutting. Diameters of rods for thread when cutting with dies

The strength of the fastening of the parts to each other is ensured by screwing the carrier of the external thread into the internal one 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 norms for the implementation of the thread and its individual elements.

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

Hole parameters

The following thread parameters are distinguished:

• diameters (inner, outer, and so on);
• 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 observing the requirements, then the fastening will be unreliable.

The 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, you must first form a hole by drilling, equal to the size of the inner diameter, that is, formed by the tops of the protrusions.

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

d hole = (1.05..1.10) × d, (1),

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

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

d hole = 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 basic steps.

Nominal diameter, mm	Step, 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 the following indicators:

• screw-in depth;
• stock of external thread of the screwed-in part;
• its undercut;
• chamfers.

In this case, the last 3 parameters are reference, and the first is calculated through the factors of accounting for the material of the product, which are equal for products from:

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

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

Download GOST 19257-73

Varieties of carving

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

They can have profiles of various shapes: triangular, trapezoidal, round; divided by 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 normalized 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 shape. The data is valid when copper and nickel-free steel alloys are used. Cutting is carried out inside auxiliary parts into which pipes will be screwed - shale, 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 threads, taking into account the values ​​of the maximum deviations.

The data given in the table GOST19257-73 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 standardizes the diameters of holes for an inch tapered thread. The document indicates two diameters with a divergence per taper and one without reaming, as well as drilling depths, all values, except for the nominal value, are expressed in millimeters.

Gadgets

Manual or automatic cutting methods provide results in various accuracy and roughness grades. So, the main tool remains a tap, which is a rod with cutting edges.

Taps are:

• manual, for metric (M1-M68), inch - ¼-2 ʺ, pipe - 1 / 8-2 ʺ;
• machine-hand - nozzles for drilling and other machines, used for the same sizes as hand-held;
• nut, which allow you to cut a through version for thin parts, with nominal dimensions of 2-33 mm.
• A set of tap rods is used for cutting metric threads:
• rough, having an elongated intake part, consisting of 6-8 turns, and marked with one line 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 lines;
• the finishing part has an intake part of only 2-3 turns, without risks.

For manual cutting, if the pitch exceeds 3 mm, then use 3 taps. If the step of the product is less than 3 mm, two are enough: rough and final.

Taps applied to small metric threads (M1-M6) have 3 flutes, along which the chips are removed, and a reinforced shank. In the design of the rest there are 4 grooves, and the shank is through.

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

The taps are attached to special devices - a tool holder (if it is small) or a knob. With the help of them, the cutting rod is screwed into the hole.

Holes are prepared for cutting using drills, countersinks and lathes. It is formed by drilling, and by countersinking and boring, it increases its width and improves the surface quality. Fixtures are used for cylindrical and conical shapes.

The drill is a metal rod consisting of a cylindrical shank and a helical cutting edge. Their main geometric parameters include:

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

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

Countersinks for cylindrical shapes are called counterbores. They are metal rods with two helical cutters and a fixed guide pin to guide the countersink into the cavity.

Cutting technique

Using a hand tap, you can perform cutting by observing the following steps:

• drill an opening for the thread of the corresponding diameter and depth;
• to carry out its countersinking;
• fix the tap in the holder or wrench;
• 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 the chips.

To cool and lubricate surfaces during the cutting process, it is important to use lubricants: engine oil, drying oil, kerosene, and the like. An improperly selected lubricant can lead to poor quality cutting results.

Drill size selection

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

It is worth noting that when cutting in plastic materials, such as steel or brass, an increase in turns occurs, therefore it is necessary to choose a drill diameter larger for the thread than for brittle materials such as cast iron or bronze.

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

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

Nominal diameter, mm	Outside diameter, mm	Step, 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 you can see from the table, there is a certain dimensional limit, which is calculated taking into account the tolerances for the thread.

In this case, the size of the drill is much smaller than the hole. So, for example, for the M6 ​​thread, the outer diameter of which is 5.88 mm, and its maximum hole value should not exceed 5.153 mm, it is worth using a 5 mm drill.

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

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

Metric threads. Rod diameters and tolerances for metric threads 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 threads M3-M50, performed by dies. Drill diameters M1-M10 for drilling holes for metric threads. Tapping with dies and taps.

• External thread: The die is clamped in the knob with screws located along its contour.
• At the end of the rod, on which it is necessary to cut the thread, a chamfer is removed on a sharpening machine 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 knob with a die is installed exactly in the horizontal plane and the knob with a die is rotated with both hands clockwise (looking from above), if the thread is right-hand, 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 working blades well so that the thread does not break and the die does not become blunt.
• Diameter of rods for external metric thread should be selected according to table 1.

Table 1. Diameters of rods for metric thread made by dies

• Internal thread: cut with taps. Tap is a metal-cutting tool for cutting internal threads in pre-drilled holes. There are manual (rotated with a wrench) and machine, nut and tool (uterine and die) .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 (like in a nut) and have sequential 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 female thread will not have a full profile and a loose 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 threads 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 M2 threads, 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 it is necessary to carefully monitor that the tap goes exactly along the axis of the hole 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 comes out (with a through hole).
• Then they clean the first tap, put it in place and take the tap with two risks, lubricate it, manually screw it into the hole and, as soon as it starts to cut into the metal, put the knob on it. After cutting every 5-6 turns, the tap is cleaned of chips and lubricated until the hole is fully bored.
• Then they clean the second tap, put it in place, take the last tap with three risks, also lubricate it with grease, screw it into the hole by hand until it engages, put on the knob and carefully calibrate the thread. The chip cleaning and lubrication is repeated as before.
• Inch taps threads are cut in the same way as metric. For pipe threading, die cutters are used, usually with adjustable cutters ranging from 1/4 to 4 in. ID pipe threads. It is better to cut threads on pipes and stubble with large diameter on screw-cutting lathes.
• The diameter of the shafts for drilling holes for metric threads should be selected according to table 2.

Table 2. Diameters of drills for drilling holes for metric threads

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Screws, bolts, and studs are the most common male threads. Most often, they fall into the hands of a home craftsman ready-made. But it happens that you need to make some clever bolt or non-standard stud. A blank for such a part is a rod, the diameter of which must correspond to the thread to be cut.

Male thread shank diameter depends on nominal thread diameter and thread pitch. All this information is usually indicated in the drawing of the part in the form of 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 “x” sign is the thread pitch. When using the main (large) step, it may not be specified. Basic thread pitch is defined by the standard and is most preferred.

When choosing the diameter of a rod for an external thread, the same principles are followed as when choosing holes for an internal thread. It has been found that the best thread quality is obtained if the diameter of the shank is slightly less than the nominal diameter of the thread to be 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 the required one, then the tops of the threads will be cut, if more, then the die simply will not screw on the rod or break during operation.

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

The main tool for cutting external threads is a die. The most commonly used round continuous dies in the form of a hardened steel nut.

To form the cutting edges, the thread of the die intersects the through longitudinal holes, which also provide the exit of chips. To facilitate lead-in, the extreme threads have an incomplete profile. To rotate the plate, use ram holder- a tool with a socket for a die and long handles. There are also split and sliding (klupp) dies, but this is a rarity in the home workshop.

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

Despite the fact that tapping is not a complex technological operation, 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.);
• the 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 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 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 dies are precisely 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 off a thin layer of metal from the walls of the hole for cutting metric threads 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.

1. The tap, with which the hole for cutting metric threads is first processed, has the smallest diameter among all the tools in the set and cutting teeth, the upper part of which is heavily cut.
2. 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.
3. The third tap, with which the metric hole is machined last, is characterized by the full ridges of the cutting teeth and a diameter that must exactly match the size of the thread to be formed.

Taps are mainly used for tapping metric threads. Significantly less often than metric taps are used for processing the inner walls of 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 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 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, 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 are indicated for making threads with both standard and reduced pitch, while it should be borne in mind that holes of different diameters are drilled for these purposes. 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.

The diameters of drills for metric threads can be calculated independently. 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 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 mx 0.8, where:

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

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