Taps for thread cutting. Types and size table
Any technical product consists of individual parts fastened together using fasteners. Although threaded connections were known back in Ancient Rome, China, as well as the Mayan civilization, the tap began to be used as a thread-forming tool only at the end of the Middle Ages (XV-XVI centuries). Before this, the inner spiral of the nut was made by other methods, including using a lathe.
Device Features
At first, a three- or four-sided rod was used, on which the teeth were cut. The end was sharpened into a shallow cone. When screwing such an artifact into the hole of a nut or body, toothed bridges cut an internal thread.
It is clear that such a tool was far from perfect, since the cutting teeth did not have a back angle, and the front angle was negative. However, its design was gradually improved until it became more rational.
Today, any tap for threading has similar design elements:
- Grooves for the release of chips and the supply of cooling and lubricating fluid (coolant). Their number is usually from 2 to 6 .
- The profile of the depressions can be different: single-radius, straight front and rear surfaces, straight front and radius rear.
- Groove direction: straight, spiral right and left . The former are used in conventional universal taps. Flutes with a left-handed helical line are used to cut threads for passage. In this case, the chips go in front of the tap so as not to spoil the cutting. Right-hand recesses are used for blind holes so that the chips are brought back, otherwise they, being compressed, will break the tool.
- The intake part is made conical in order to facilitate cutting of the cutting teeth into the material of the part . The tilt angle is from 3 to 20 degrees, depending on the purpose of the tap (roughing, intermediate, finishing).
- The calibrating part is cylindrical, has a reverse lowering of up to 0.1 mm, which serves to reduce the friction force . For the same purpose, the calibrating teeth are backed at a distance of 1/3 of the width of the feather from the top of the tooth. The reduction is about one tenth of a millimeter for threads with a diameter of 12 to 30 mm.
By purpose
- Bench (hand) taps are used to make threads using a crank. In order to reduce the effort, they are made in a set, which includes 2-3 tools, each of which removes only part of the processing allowance. The first tap is the rough tap, the last tap is the finishing tap. To distinguish them from each other, markings in the form of dashes (one, two, three dashes) are applied to the shank. Bench taps are mainly used for cutting threads in body parts.
- Machine (machine-manual) . They are used for mechanized thread cutting on machines: drilling, turning, aggregate, such as a machining center. Structurally they do not differ from metalwork ones, except that they have a shortened fence part and higher durability. The main purpose is cutting threads in parts.
- Nuts . As the name suggests, they are used for cutting nuts. They always consist of one tap with an elongated intake cone. During operation, the tap is not unscrewed from the nut, but the finished nuts are threaded onto an elongated shank, which has 2 designs: straight and radius (curved). The first is used on drilling and turning machines. After filling the storage part of the shank, the tool is removed from the quick-release chuck and the finished nuts are shaken off. The curved tap is used on automatic threading machines. In this case, the nuts, under the pressure of each other, move to the end of the tool, where they fall into the container.
Design versions
- Taps with short flutes (fluteless). Used for cutting threads in aluminum alloys, tough low-carbon or high-strength alloy steels.
- With screw grooves. Used on machining centers for cutting blind threads.
- With staggered teeth. The latter on the calibrating part are cut off one at a time, thereby reducing the friction force, which is important for viscous materials.
- Stepped. The cutting part of the tool is divided into two sections, each of which operates according to its own shaping scheme. For example, the 1st section cuts according to a generator circuit, the 2nd - according to a profile circuit. Or, the 1st one works as a cutting tool, the 2nd one as a smoothing tool.
- Combined. The 1st stage is a drill, the 2nd is a tap. As they say - two in one.
- Broach tap. It is used to cut threads of any diameter and pitch in parts with a through hole on a lathe. The part is put on the tool shank, after which it is clamped into the machine chuck, and the shank is secured in the tool holder. Set the automatic feed equal to the cutting pitch and turn on the corresponding spindle rotation. Once the broach leaves the workpiece, the thread is ready.
- With internal coolant supply. Used on specialized or multi-operational machines to increase productivity.
- Bell type. Used when cutting through threads of large diameter (50–400 mm). The tool is made as a composite tool, consisting of individual cutting sectors. Coolant is supplied inside, the number of feathers reaches 16, and spacious grooves accommodate a large volume of chips.
According to the type of thread being cut
- Metric, designated by the letter M. Dimensions, including thread pitch, are measured in millimeters . Below is a table of parameters for taps with a main (large) pitch. For each standard size, GOST 8724–2002 establishes several additional (small) steps. Three millimeters is the maximum that can be cut using a wrench.
Designation Dimensions, mm Main step Tap drilling
M 3 0.5 2.5
M 4 0.7 3.3
M 5 0.8 4.2
M 6 1.0 5.0
M 8 1.25 6.7
M 10 1.5 8.5
M 12 1.75 10.2
M 14 2 12.0
M 16 2 14.0
M 18 2.5 15.4
M 20 2.5 17.4
M 22 2.5 19.4
M 24 3 20.9
M 27 3 23.9
- Inch conical. The diameter is expressed in English units of length - inches (25.4 mm) , and instead of the pitch, the inverse value is written - the number of turns per 1 ", or in the technical lexicon - the number of threads. The more threads, the smaller the thread pitch. The middle surface of the thread has a slope of 1° 47′ 24", so the tap reaches the stop at the end of cutting, which should be borne in mind so as not to break it.
- Pipe cylindrical. A variety of inch threads, limited to the range of standard metal pipes . Pitch is also expressed in threads per inch.
- Pipe conical. The same as cylindrical ones, but with a slope. The diameter of the drilling for the thread is several tens smaller . The thread is cut all the way.
The summary table contains the parameters of taps with inch thread pitch
Conical
Designation Thread pitch (threads per inch) Hole diameter, mm
K 1/16” 27 6.0
K 1/8” 27 8.3
K 1/4” 18 10.7
K 3/8” 18 14.3
K 1/2” 14 17.5
K 3/4” 14 23.0
K 1” 11.5 28.7
Pipe cylindrical
G 1/8” 29 8.6
G 1/4” 19 11.5
G 3/8” 19 15.0
G 1/2” 14 18.7
G 5/8” 14 20.6
G 3/4” 13 24.2
G 7/8” 12 27.9
G 1” 11 30.3
Pipe conical
Rc 1/8” 28 8.2
Rc 1/4” 19 11.0
Rc 3/8” 16 14.5
Rc 1/2” 14 18.1
Rc 3/4” 12 23.6
Rc 1” 11 29.6
Instrumental material
Hand taps heat up slightly during operation, so they are made from high-carbon tool steels U10A, U12A. For machine taps operating at high speeds, high-speed steels R6M5, R6M5K5, R6M5K8 are used. The best quick cutter is P18. Finally, high-performance machines are equipped with carbide tools. Small taps are made entirely of carbide, medium ones are brazed, and large ones usually have a prefabricated design.
Source: https://proinstrumentinfo.ru/metchiki-dlya-narezaniya-rezby-tablitsa-razmerov/
Threaded hole size: choice of drill, procedure for calculating diameter, expert advice
A threaded joint is the best option when it is necessary to create a detachable connection.
The use of these elements is widespread, 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 hole for the thread.
It is worth saying that hardware with an externally applied threaded section are widely available on sale and choosing an option according to the required diameter is not a problem; all that remains is to determine what it should be so that the connection is tight and the fastening element does not fall out of it.
Some of the recommendations for thread cutting
There are several options for threading devices on the market. Devices of this kind are used everywhere. This makes it possible to apply threads for parts that are characterized by rotation.
The presence of such notches gives this process translational movements, which is important for connections of this kind in equipment parts and mechanisms. It is in this case that it is important to choose the correct hole size for the thread, relying on tables and formulas.
After all, poor-quality or unreliable joints can lead to serious damage.
Regarding the direction of movement of the guide, there are:
- external;
- internal;
- single-pass;
- multi-pass;
- rights;
- left.
There is a special sizing system for applying threads and determining the size of the hole for the thread. According to it, there are such thread options that are cut using taps, such as:
- Metric.
- Inch, with a different profile. The characteristic angle here is 55°, the diameter designation is shown not in millimeters, but in inches, and the number of threads determines the pitch.
- Pipe is characterized by differences in the initial diameter, based on the size of the pipe opening. Suitable for external cutting only. The dimensions of the hole for the half-inch pipe thread are determined according to the table below.
Metric thread
It is characterized by a special profile, externally resembling the shape of a triangle, the angle is 60°. 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 threads using this technology, special markings are applied for large steps using digital and letter designations. In this design option, the number means the outer size of the hole for the thread, that is, the diameter.
Studying any of the drawings, you can come across this kind of designation - “M4”, “M6”, etc. Sometimes a designation has to be drawn up with a non-standard 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 threads
Remember that a hole with a diameter of 0.5 cm is suitable for an M6 thread, while for an M3 thread you should take a drill with a diameter of no more than 0.21 cm.
Remember that a special formula is used to calculate the size of a threaded hole, but often this need does not arise, since the public domain is full of special tables developed by specialists. Such formulations will help both a beginner in carpentry and a 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 use the workpiece to create a hole with a diameter corresponding to the size of the tool you have chosen, which will be used during further cutting.
It is worth noting that accuracy is important in such work, and any hole must correspond to the dimensions of the 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 choosing and purchasing drills, because on the market you can choose any model for any size, from the minimum diameter to a large caliber.
Based on specific tasks, you can order the production of a drill for the required hole size for an inch or millimeter thread.
How and with what help you can form a thread in a product
In order to form a high-quality thread, and even inside the workpiece, you will have to arm yourself with a device called a tap. Outwardly, it resembles a screw with some recesses with pointed edges. One of the structural elements is the rod that complements the tap, which can be conical or cylindrical. The arrangement of the grooves is longitudinal, due to which they divide the threaded connections into small elements called ridges - working parts.
When applying threads, do not rush, make sure the groove is clean and remove the steel layer gradually. Remember that the further quality of the parts and the strength of their connection depends on this.
In order to do everything correctly when selecting the size of the hole for an M6 thread or another diameter, you need to take a device with a long length or stock up on several corresponding elements. Buying single taps is also not a problem.
Such elements are often used during the restoration of threads damaged as a result of long-term use. To cut a new relief for the correct screwing of parts, taps are taken in pairs.
It is recommended to use one for forming rough threads, the second for finishing.
Some features of using taps
The peculiarity of the taps in the kit lies in the fact that the first makes small recesses, and the second is used to clean them and enlarge them to the required size with an accuracy of a fraction of a millimeter.
Interestingly, three-pass thread forming devices 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 sizing standard can lead to poor quality results.
Therefore, it is suggested that before you start work, determine the size of the hole for the M10 (0.85 mm), M12 (0.96 mm) or other thread with which you have to work.
How to make an aluminum alloy tap at home
Sometimes there is a need to cut internal threads on the surface of a brass or light alloy coating of a part. To do this, you can use a homemade tool and drills taken from a classic set.
To make a tap with your own hands, prepare steel wire, which is cut and hardened using a die. After hardening, it is recommended to release the part to the color of ripe straw, and sharpen the cutting edges using a whetstone or sharpener, having previously fixed the part in a collet chuck.
Now that you know the basic concepts, you will sooner understand the need to calculate the size of a threaded hole. Whatever parts and whatever tools you work with, remember the recommendations given, and if you are in doubt about the parameters, rely on special tables, which are best printed out and always kept at hand.
Source: https://FB.ru/article/424943/razmer-otverstiya-pod-rezbu-vyibor-sverla-poryadok-rascheta-diametra-sovetyi-spetsialistov
Selecting a drill according to the diameter of the thread: special tables and cutting features
Any detachable type connection must have a thread. It is worth noting that all hardware with external threads, bolts in particular, can be purchased anywhere: in a construction supermarket or at the market. But with internal threads everything is much more complicated. It should be cut with your own hands or using special machines.
Today we will tell you how to correctly select drills of a particular diameter for a specific thread, and you can also familiarize yourself with the table of these diameters.
The need to select drills for threading
To make your own internal thread, take your workpiece and drill a hole in it that will match the diameter of the tool that is intended for cutting. And each of these holes must strictly correspond to the size of the tool. This is why you need to carefully select the diameter of the drill according to the thread.
Today there are drills on sale with different diameters and sizes. Starting from a minimum size of 0.5 mm and ending with large conical drills measuring about 0.05 mm. Depending on the type of work performed, holes of different diameters can be made by drilling to suit certain needs.
Parameters for selecting a drill for threading: table
If you need to drill a hole with a large diameter, you will need to take a special machine, where the drills are equipped with conical tails, but ordinary drills are equipped with cylindrical tails. On a large drill, the cone has a fifth size. Thus, the parameters of the cone directly depend on the diameter of the drill; the larger the diameter of the drill, the larger the cone is needed. For example:
- diameter from 6 to 10 mm;
- the required cone size is from 11 to 22 mm.
You can select the drill diameter for a particular thread as accurately as possible using a special size selection table.
If there is a need to create an internal thread, the hole diameter should be selected according to the thread diameter and thread pitch parameters. This data in the tables is designated as M8×1 , where:
- M is a metric thread;
- the number is the thread pitch;
- if it is simply M8 and without numbers, then you need to use a standard large step. This parameter step is the most common and is adjusted according to standards for most drill sizes.
Diameters require selection of the appropriate hole size. The table includes a list of the most common sizes that you usually have to deal with in everyday life when performing certain jobs.
Thread classification
Externally, the thread looks like a helical groove with a constant cross-section. There are two types of it:
We have already mentioned these types earlier. Threaded connections are used everywhere. They are needed so that the part can rotate through translational movements. Without threaded connections, it is difficult to imagine the normal operation of mechanisms or complex machines. They can also be single-pass or multi-pass.
And according to the direction of movement of their guides, they are divided into:
If we talk about classification by size , then it comes in the following types:
- metric;
- inch;
- pipe
Metric threads are distinguished by their special triangular profile, the angle of which is 60 degrees. All thread parameters are calculated in millimeters. If the thread pitch is large, then, as already mentioned, we have a number and a letter designation.
The number indicates the size of the outer diameter of the thread, according to which you can select a particular drill. Technical drawings must certainly include characteristics of the thread or its analogues.
If a metric thread needs to be represented with a small non-standard pitch, then you need to add a number that indicates the pitch.
Another profile angle value is specific to an inch-type threaded connection. This angle can be equal to 55 degrees , and the size of the hole is calculated in inches, the pitch varies by the number of threads.
And the pipe threaded type differs from others in its initial diameter, which depends directly on the size of the pipe hole. In this case, cutting is carried out only externally.
Features of thread cutting
Various equipment is used for thread cutting, for example:
- drill type machine;
- turning park;
- various cutting devices.
In this case, cutting can be done either mechanically or manually. For example, for internal use you can use special threaded taps, and for external use - dies. Taps, like drills, are selected depending on the diameter of the hole. They are divided into the following categories:
- inch;
- metric;
- pipe
Basically, sets of hand taps consist of three devices, two of which are needed for preliminary work, and the last one is a finishing tool, with the help of which the final shape of the thread is made and adjusted to certain dimensions. The taps have numbers. If the die holder is supplied with not three, but two devices, then the first is preliminary, and the second is finishing. Taps are made on the basis of high-alloy steel.
External threads are obtained by using a die. These tools can be round or prismatic in shape. For round dies use a knob .
Methods for producing internal threads
To make a hole where you will need to tap, you must first select the correct size drill bit.
To use a tap, its hole must be processed with a countersink until the desired degree of cleanliness is obtained. When cutting, the metal is gradually squeezed out.
The size of the drill should be slightly larger than the internal threaded diameter of this tool.
When cutting, the hardness of the metal does not greatly affect the diameter of the hole. But if a low thread material is used, the diameter of the hole can change significantly. So, if the size of the hole and the internal diameter of the drill exactly correspond to each other, then during cutting the material is squeezed out, and its excess acts on the teeth of the tap. When heated, the chips stick, as a result of which the tap may break and the threads will have torn threads .
When working with drills and threaded connections, you need to very carefully select the parameters so that the work is ultimately completed efficiently. Special tables will help you with this, indicating the parameters for a particular thread and other valuable tips.
Source: https://stanok.guru/metalloobrabotka/tokarnye-raboty/podborka-diametra-sverla-pod-rezbu-tablicy-i-osobennosti.html
Drill and tap hole size charts: metric, inch
Making internal threads is usually not difficult. But there are some features of using the tool and selecting holes for cutting metric threads.
Types of thread
internal thread on the barrel coupling
They differ in their main characteristics:
- diameter calculation system (inch, metric, others);
- number of passes (two-, three- or single-pass);
- profile shape (rectangular, trapezoidal, triangular, round);
- direction of rotation of the screw (left or right);
- placement on the part (internal or external);
- shape of the part (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 round (E);
- trapezoidal (Tr);
- round for plumbing fasteners (Kp);
- persistent (S, S45);
- inch, including cylindrical and conical (BSW, UTS, NPT);
- oil range.
Tools for internal threading
To make internal cutting, you need a tap - a screw-shaped tool with sharp grooves. The rod can be shaped like a cone or a cylinder. The grooves run lengthwise and break the thread into sections called combs. It is the edges of the combs that are the working surfaces.
To ensure a clean groove, the metal is removed gradually, in layers. This requires one very long tool or set.
Single taps are also found on sale; they are often used to correct broken threads. To cut a new one, buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing work.
The first one cuts a shallow groove, the second one cleans and deepens it. There are also three-pass tools. Thin taps, up to 3 millimeters, are sold in twos, wider ones - in threes. Three-pass taps are inserted into the gates.
The design of the knobs is different, but their size must match the size of the cutter.
The tools in the set are distinguished by the marks marked on the tail end. If you look closely, you will notice differences in shape:
- the first tap has heavily cut tooth tips, the outer diameter is slightly smaller than the other tools in the set;
- second tap with shorter fence segment, longer ridges. Its diameter is slightly larger than that of the first;
- the third tap has full ridges of teeth, and its diameter should match the dimensions of the future thread.
Taps are divided into pipe taps (marked “G”) for cutting threads inside the pipe, and metric taps, which are more common.
The quality directly depends on the properties of the tap: it must be made of good metal and sharp. To extend the life of the tool and improve the quality of the thread, lubricant is used. Usually, to acquire a stable cutting skill, you need to make 3 - 5 attempts.
Cutting process
diameters of thread holes depending on the type of metal
Before you start cutting, you should use drills to make a hole in the workpiece. The diameter of the drill hole must match the internal thread size. When the size of the hole made with drills is chosen incorrectly, the tool can 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 pressed along the working surfaces of the tap, forming a groove profile on the workpiece. Taking this feature into account, the size of the drill used to make the hole for the thread is selected slightly smaller 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. To cut M4, the diameter of the drill must be 3.3 millimeters, and before working with an M6 tap, a hole is first made with a 5 mm drill. This indicator is calculated taking into account the thread pitch.
The pitch can be calculated mathematically, but in practice they resort to correspondence tables, where for an M5 tap the pitch is 0.8, for M4 this figure is 0.7, for M6 - 1. We subtract the pitch index from the diameter and get the required diameter of the drill.
When working with brittle metals, such as cast iron, the drill diameter should be reduced by 0.1 mm compared to the size recommended in the table.
The formula for calculating the hole diameter when working with three-pass taps:
Up=Dm * 0.8;
here: Dm is the diameter of the tap.
| 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 |
| M4 | 3,3 | 0,7 |
| M5 | 4,1 | 0,8 |
| M6 | 4,9 | 1 |
| M8 | 6,7 | 1,25 |
| M10 | 8,4 | 1,5 |
Table 1. Correspondence between thread diameters and preparation hole
Before starting work, the tap is inserted into a square shank - a knob. The collars can be regular or ratchet. The carving is done carefully, the first pass is made with a No. 1 tap to the end. Particular attention must be paid to the direction of movement: only clockwise, and some effort must be applied. It is done like this: 1/2 turns along the stroke alternate with 1/4 turns against the screw stroke to destroy the chips.
| Thread in inches | External D, mm | Diameter, mm | Pitch, 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. Hole diameters for inch threads
A couple drops of lubricant will make working on blind threaded holes much easier. 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 light alloy parts, you can use homemade tools and drills from a regular set. Calibrated steel wire will do. Using 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 using a whetstone or sharpener, after first clamping the part into a collet chuck.
about how internal threads are cut:
Complete GOST for hole diameters for cutting metric threads
Source: http://StanokGid.ru/osnastka/diametr-otverstij-pod-rezbu.html
What drill to use for M10 threads?
They differ in their main characteristics:
- diameter calculation system (inch, metric, others);
- number of passes (two-, three- or single-pass);
- profile shape (rectangular, trapezoidal, triangular, round);
- direction of rotation of the screw (left or right);
- placement on the part (internal or external);
- shape of the part (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 round (E);
- trapezoidal (Tr);
- round for plumbing fasteners (Kp);
- persistent (S, S45);
- inch, including cylindrical and conical (BSW, UTS, NPT);
- oil range.
Threaded hole: diameter, classification of types, size table - Machine
18.12.2019
The strength of fastening the parts to each other is ensured by screwing the external thread carrier into the internal thread of the second product. It is important that their parameters are maintained in accordance with the standards, then such a connection will not be damaged during operation and will ensure the necessary tightness. Therefore, there are standards for the execution of carvings and its individual elements.
Threaded hole diameter
Before cutting, a hole is made inside the part for the thread, the diameter of which should not exceed its internal diameter. This is done using metal drills, the dimensions of which are given in the reference tables.
Hole parameters
The following thread parameters are distinguished:
- diameters (internal, external, etc.);
- profile shape, height and angle;
- step and entry;
- others.
The condition for connecting parts to each other is the complete coincidence of the external and internal threads. If any of them are not performed in accordance with the requirements, the fastening will be unreliable.
External thread
The fastening can be bolted or stud, which, in addition to the main parts, includes nuts and washers. Before joining, holes are formed in the parts to be fastened, and then cutting is carried out.
To perform it with maximum accuracy, you should first form a hole by drilling, equal to the size of the internal diameter, that is, formed by the tops of the protrusions.
When performing a through design, the diameter of the hole must be 5-10% larger than the size of the bolt or stud, then the following condition is met:
dresponse = (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 pitch value (P) is subtracted from the value of the nominal diameter (d) - the resulting result is the desired value:
- dresponse = d - P, (2).
- The calculation results are clearly demonstrated by the table of threaded hole diameters, compiled according to GOST 19257-73, for sizes 1-1.8 mm with small and main pitches.
| 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 the following indicators:
- screw-in depth;
- reserve of external thread of the screwed-in part;
- her undercut;
- chamfers.
In this case, the last 3 parameters are for reference, and the first is calculated through the coefficients for taking into account the material of the product, which are equal for products from:
- steel, brass, bronze, titanium – 1;
- gray and ductile cast iron – 1.25;
- light alloys – 2.
Internal thread on barrel coupling
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
Types of carving
According to the measurement system, threads are divided into metric, expressed in millimeters, and inch, measured in corresponding units. Both of these types can be made in either cylindrical or conical shapes.
Classification of threads
They can have profiles of various shapes: triangular, trapezoidal, round; divided according to application: for fasteners, plumbing elements, pipes and others.
The diameters of the preparation 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 specified in GOST 21348-75 for cylindrical shapes and GOST 21350-75 for conical shapes. The data is valid when using copper and nickel-free steel alloys. The cutting is carried out inside the auxiliary parts into which the 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 threads, taking into account the values of maximum deviations.
Thread types according to GOST
The data given in the GOST 19257-73 table confirms 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 inch tapered threads. The document indicates two diameters with a taper and one without a taper, as well as drilling depths; all values, except the nominal value, are expressed in millimeters.
Adaptations
Manual or automatic cutting methods provide results in various classes of accuracy and roughness. Thus, the main tool remains a tap, which is a rod with cutting edges.
Tap device
Taps are:
- manual, for metric (M1-M68), inch – ¼-2ʺ, pipe – 1/8-2ʺ;
- machine-manual - attachments for drilling and other machines, used for the same sizes as manual ones;
- nuts, 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:
- rough, having an elongated intake part, consisting of 6-8 turns, and marked with one mark at the base of the shank;
- medium - with a fence of average length of 3.5-5 turns, and markings in the form of two marks;
- the finishing part has a fence of only 2-3 turns, without marks.
Tolerance control of metric thread placement
When cutting manually, if the pitch exceeds 3 mm, then use 3 taps. If the product pitch is less than 3 mm, two are enough: roughing and finishing.
Taps used for small metric threads (M1-M6) have 3 grooves that carry chips and a reinforced shank. The design of the others has 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.
The taps are attached to special devices - a tool holder (if it is small) or a crank. They are used to screw the cutting rod into the hole.
Preparing holes for cutting is carried out using drills, countersinks and lathes. It is formed by drilling, and by countersinking and boring it is increased in width and improves the quality of the surface. The fixtures are used for cylindrical and conical shapes.
Thread pitch
A drill is a metal rod consisting of a cylindrical shank and a helical cutting edge. Their main geometric parameters include:
- the helical lift angle is usually 27°;
- point angle, which can be 118° or 135°.
Drills are rolled, dark blued, and shiny - ground.
Countersinks for cylindrical shapes are called counterbores. They are metal rods with two cutters twisted into a spiral and a fixed guide pin to insert the countersink into the cavity.
Cutting technique
Using a hand tap, cutting can be carried out following the following steps:
- drill an opening for a thread of the appropriate diameter and depth;
- countersink it;
- secure the tap in the holder or driver;
- align 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 off the chips.
Thread system
To cool and lubricate 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.
Selecting drill size
The diameter of the drill for a hole for a metric thread is also determined by formula (2), taking into account its main parameters.
Drill parametersDiameter of the thread hole and its other characteristics
It is worth noting that when cutting in ductile materials, such as steel or brass, the turns increase, so it is necessary to choose a larger drill diameter for the thread than for brittle materials, such as cast iron or bronze.
In practice, drill sizes are usually slightly smaller than the required hole. Thus, Table 2 shows the ratio of the nominal and outer thread diameters, the pitch, the diameters of the hole and the drill for cutting metric threads.
Table 2. The relationship between the main parameters of metric threads with 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, for an M6 thread, the outer diameter of which is 5.88 mm, and its largest hole value should not exceed 5.153 mm, you should use a 5 mm drill.
A hole for an M8 thread with an outer diameter of 7.87 mm will be only 6.912 mm, which means the drill for it will be 6.8 mm.
The quality of the thread depends on many factors when cutting it: from the choice of tool to the correctly calculated and prepared hole. Too little 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.
Source: https://regionvtormet.ru/stanki-i-oborudovanie/otverstie-pod-rezbu-diametr-klassifikatsiya-vidov-tablitsa-razmerov.html
Selection of drill for tap table
A thread drill is a metal-cutting tool that is used before using a tap or similar device. It is necessary that all parameters comply with current requirements and standards. Otherwise, the fastening will be unreliable.
To select the optimal drill diameter for threads, special tables have been developed. The value depends on the type of cut. Requirements for drill size and metric hole parameters are regulated by the interstate standard GOST 19257-73. As an auxiliary tool, it is necessary to use a caliper or other device to calculate the size and pitch of the thread.
Drill and hole size chart for metric and inch threads
Let's consider the calculation results from GOST 19257-73:
- For M3 threads, a tap is required, for which the standard pitch is 0.5, drills are 2.5 mm.
- For M4 threads, a tap is required, for which the standard pitch is 0.7, drill bits are 3.3 mm.
- For M5 threads, a tap is required, for which the standard pitch is 0.8, drill bits are 4.2 mm.
- For M6 threads, a tap is required, for which the standard pitch is 1.0, drill bits are 5.0 mm.
- For M8 threads, a tap is required, for which the standard pitch is 1.25, drill bits are 6.75 mm.
- For M10 threads, a tap is required, for which the standard pitch is 1.5, drills are 8.5 mm.
- For M12 threads, a tap is required, for which the standard pitch is 1.75, drill bits are 10.25 mm.
- For M16 threads, a tap is required, for which the standard pitch is 2.0, drills are 13.5 mm.
Despite the fact that the metric system is the most popular, we recommend that you familiarize yourself with the table of threaded drill diameters:
Drilling tool selection formula
Selecting the optimal drill size for threading is the key to high-quality operation of the threading device.
The easiest way to calculate is to use the well-known formula: the step size is subtracted from the nominal diameter. For example, for M8 you need a device with a cross section of 8-1.25 (standard pitch) = 6.75 mm.
It should be remembered that when working with plastic materials, the calculated number of turns increases. Thus, to drill into brass, it is necessary to prepare a gimlet with a larger diameter than is necessary for brittle metals and alloys such as cast iron or bronze.
Source: https://crast.ru/instrumenty/podbor-sverla-pod-metchik-tablica
Hole diameter for metric thread: size table according to GOST
Despite the fact that cutting internal threads is not a complex technological operation, 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.
The thread diameter and through hole must comply with the standards, otherwise the grooves will come out too small and the threaded connection will be unreliable
Types and parameters of thread
The parameters by which threads are divided into different 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).
Metric thread parameters
Depending on the above parameters, the following types of thread are distinguished:
- 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.
Tap: design and parameters
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 a thin layer of metal from the walls of the hole for cutting metric threads and forms a shallow groove on them, the second one not only deepens the formed groove, but also cleans it.
Types of thread taps and their differences
Minimum set of taps
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.
Some types of tap drivers
When using a set of three taps that differ 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.
- The tap, with which the hole for cutting metric threads is processed first, has the smallest diameter among all the tools in the set and cutting teeth, the upper part of which is heavily cut off.
- The second tap has a shorter fence and longer combs. Its working diameter is intermediate between the diameters of the other tools in the set.
- 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.
Set of three taps
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
Table 2. Diameters of holes for inch 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 from the link below.
GOST 19257-73 Holes for cutting metric threads. Diameters Download
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:
To = Dm x 0.8, where:
Do is the diameter of the hole that must be made using a drill,
Dm is the diameter of the tap that will be used to process the drilled element.
Scheme of cutting internal threads with a tap
The drivers into which the threaded tap is inserted can have a simple design or be equipped with a ratchet. You should work with such devices with tools fixed in them very carefully. To obtain high-quality and clean threads, rotating the tap clockwise, performed half a turn, must be alternated with turning it one-fourth of a turn against the thread.
The thread will be cut much easier if you use a lubricant during this procedure. The role of such a lubricant when cutting threads in steel products can be played by drying oil, and when processing aluminum alloys - alcohol, turpentine or kerosene. If such technical fluids are not at hand, then ordinary machine oil can be used to lubricate the tap and the thread being cut (however, it has less effect than the substances listed above).
Source: http://met-all.org/obrabotka/prochie/diametr-sverla-pod-rezbu-metricheskuyu-tablitsa-razmerov.html
