To cut an internal thread on a part, you must first drill a hole. Its size is not equal to the thread diameter, but should be slightly smaller. You can find the diameter of the drill for the thread in a special table, but to do this you also need to know the type of thread.
Main settings
- diameter (D);
- pitch (P) - the distance from one turn to another.
They are determined by GOST 1973257-73. A large step is considered normal, but it corresponds to several smaller ones. A small pitch is used when applying to thin-walled products (pipes with a thin wall). They also make a small turn if the applied thread is a way to adjust any parameters. Also, a small step between turns is made to increase the tightness of the connection and to overcome the phenomenon of self-unscrewing of the part. In other cases, a standard (large) step is cut.
There are many types of threads, since each has its own formation characteristics; the diameter of the hole for the thread is different in each case. All of them are prescribed in GOST standards, but most often they use triangular metric and conical metric threads. We will talk about them further.
We usually see triangular threads on bolts and other similar fasteners, conical threads on most sanitary products, suggesting a detachable connection.
Adaptations
To apply carvings with your own hands, use small devices:
All these devices are made of alloys characterized by increased strength and abrasion resistance. Grooves and grooves are applied to their surfaces, with the help of which their mirror image is obtained on the workpiece.
Any tap or die is marked - they have an inscription on them indicating the type of thread that this device cuts - diameter and pitch. They are inserted into holders - collars and die holders - and secured there with screws. Having clamped the thread cutting device in the holder, it is put on/inserted into the place where you want to make a detachable connection. By turning the device, turns are formed. How correctly the device is positioned at the beginning of work determines whether the turns will “lay down” evenly. Therefore, make the first revolutions, trying to keep the structure level, avoiding shifts and distortions. After a few turns have been made, the process will go easier.
You can cut small or medium diameter threads by hand. Complex types (two- and three-way) or working with large diameters by hand are impossible - too much effort is required. For these purposes, special mechanized equipment is used - lathes with taps and dies attached to them.
How to cut correctly
Threads can be applied to almost any metals and their alloys - steel, copper, aluminum, cast iron, bronze, brass, etc. It is not recommended to do it on hot iron - it is too hard, it will crumble during operation and it will not be possible to achieve high-quality turns, which means the connection will be unreliable.
Tool for the job
Preparation
You need to work on clean metal - remove rust, sand and other contaminants. Then the place where the thread will be applied must be lubricated (except for cast iron and bronze - they must be worked “dry”). There is a special emulsion for lubrication, but if it is not there, you can use soaked soap. You can also use other lubricants:
You can often hear advice to use machine or mineral oil or even lard when cutting threads. They work well, but experts say that it is better not to do this - the chips will stick to the viscous substance, which will lead to rapid wear of the tap or die.
Slicing process
When cutting external threads, the die is placed strictly perpendicular to the surface of the pipe or rod. During operation, it should not wiggle, otherwise the turns will turn out uneven and the connection will be ugly and unreliable. The first turns are especially important. How they “lay down” determines whether the connection will then be skewed.
By applying the internal thread, the part is fixed motionless. If it is a small piece, you can clamp it in a vice. If the plate is large, ensure its immobility using available methods, for example, by fixing it with bars. M
The tap is inserted into the hole so that its axis is parallel to the axis of the hole. With little effort, little by little, they begin to twist in the given direction. As soon as you feel that the resistance has increased, unscrew the tap back and clear it of chips. After cleaning, the process continues.
Photo cutting process
When cutting a thread in a blind hole, its depth should be slightly greater than required - this excess should include the tip of the tap. If this is structurally impossible, the tip of the tap is cut off. At the same time, it is not suitable for further use, but there is no other way out.
In order for the turns to be of high quality, two taps or dies are used - rough and finishing. The first pass is done as a rough pass, the second as a finishing pass. There is also combined devices for threading. They allow you to do everything in one pass.
Another practical advice: to prevent chips from falling into work area, when cutting, make one full turn clockwise, then half a turn counterclockwise. After this, return the tool to the place where you stopped and make one revolution again. Continue this way until the required length.
Tables for selecting the diameter of a drill for threading
By doing internal thread a hole is pre-drilled for it. It is not equal to the diameter of the thread, since when cutting, part of the material is not removed in the form of chips, but is squeezed out, increasing the size of the protrusions. Therefore, before application, it is necessary to select the diameter of the drill bit for the thread. This can be done using tables. They are available for every type of thread, but here are the most popular ones - metric, inch, pipe.
| Metric thread | Inch thread | Pipe thread | |||||
|---|---|---|---|---|---|---|---|
| Thread diameter, inches | Thread pitch, mm | Drill diameter, mm | Thread diameter, inches | Thread pitch, mm | Drill diameter, mm | Thread diameter, inches | Threaded hole diameter, mm |
| M1 | 0.25 | 0,75 | 3/16 | 1.058 | 3.6 | 1/8 | 8,8 |
| M1.4 | 0,3 | 1,1 | 1/4 | 1.270 | 5.0 | 1/4 | 11,7 |
| M1.7 | 0,35 | 1,3 | 5/16 | 1.411 | 6.4 | 3/8 | 15,2 |
| M2 | 0,4 | 1,6 | 3/8 | 1.588 | 7.8 | 1/2 | 18,6 |
| M2.6 | 0,4 | 2,2 | 7/16 | 1.814 | 9.2 | 3/4 | 24,3 |
| M3 | 0,5 | 2,5 | 1/2 | 2,117 | 10,4 | 1 | 30,5 |
| M3.5 | 0,6 | 2,8 | 9/16 | 2,117 | 11,8 | - | - |
| M4 | 0,7 | 3,3 | 5/8 | 2,309 | 13,3 | 11/4 | 39,2 |
| M5 | 0,8 | 4,2 | 3/4 | 2,540 | 16,3 | 13/8 | 41,6 |
| M6 | 1,0 | 5,0 | 7/8 | 2,822 | 19,1 | 11/2 | 45,1 |
| M8 | 1,25 | 6,75 | 1 | 3,175 | 21,3 | - | - |
| M10 | 1,5 | 8,5 | 11/8 | 3,629 | 24,6 | - | - |
| M12 | 1,75 | 10,25 | 11/4 | 3,629 | 27,6 | - | - |
| M14 | 2,0 | 11,5 | 13/8 | 4,233 | 30,1 | - | - |
| M16 | 2,0 | 13,5 | - | - | - | - | - |
| M18 | 2,5 | 15,25 | 11/2 | 4,33 | 33,2 | - | - |
| M20 | 2,5 | 17,25 | 15/8 | 6,080 | 35,2 | - | - |
| M22 | 2,6 | 19 | 13/4 | 5,080 | 34,0 | - | - |
| M24 | 3,0 | 20,5 | 17/8 | 5,644 | 41,1 | - | - |
Once again, please note that the diameter of the drill bit for the thread is given for large (standard thread).
Table of rod diameters for external threads
When working with external threads, the situation is very similar - part of the metal is extruded rather than cut off. Therefore, the diameter of the rod or pipe on which the thread is applied should be slightly smaller. How accurate - see the table below.
| Thread diameter, mm | 5,0 | 6 | 8 | 10 | 12 | 16 | 20 | 24 |
|---|---|---|---|---|---|---|---|---|
| Rod diameter, mm | 4,92 | 5,92 | 7,9 | 9,9 | 11,88 | 15,88 | 19,86 | 23,86 |
The question of how to cut a thread with a tap arises in cases where a pre-made hole needs to be prepared to accommodate a bolt, screw, stud or any other type of threaded fastener. In such situations, it is the tap that is the main tool that allows you to quickly and accurately cut an internal thread with the required geometric parameters.
Types and areas of application of taps
Internal thread cutting can be done manually or using machines various types(drilling, turning, etc.). The working tools that perform the main work of cutting internal threads are machine-hand or machine taps.
On different kinds Taps are divided depending on a number of parameters. It is generally accepted the following principles classification of taps.
- According to the method of rotation, a distinction is made between machine-manual and machine taps, with the help of which internal threads are cut. Machine-hand taps equipped with a square shank are used in combination with special device with two handles (this is the so-called knob, tap holder). With the help of such a device, the tap is rotated and cuts the thread. Thread cutting with a machine tap is carried out on metal cutting machines of various types, in the chuck of which such a tool is fixed.
- Based on the method by which internal threads are cut, a distinction is made between universal (through) taps and complete taps. The working part of the former is divided into several sections, each of which differs from the others in its geometric parameters. The section of the working part that first begins to interact with the surface being processed performs rough processing, the second - intermediate, and the third, located closer to the shank - finishing. Cutting threads with complete taps requires the use of several tools. So, if a set consists of three taps, then the first of them is intended for roughing, the second for intermediate, and the third for finishing. As a rule, a set of taps for cutting threads of a certain diameter includes three tools, but in some cases, when products made of particularly hard material are processed, sets consisting of five tools can be used.
- According to the type of hole inner surface which needs to be threaded, there are taps for through and blind holes. A tool for processing through holes is characterized by an elongated conical tip (approach), which smoothly passes into the working part. Taps most often have this design universal type. The process of cutting internal threads in blind holes is carried out using taps, the conical tip of which is cut off and performs the function of a simple milling cutter. This design of the tap allows it to cut threads to the full depth of a blind hole. To cut a thread of this type, as a rule, a set of taps is used, driven manually using a wrench.
- According to the design of the working part, taps can have straight, helical or shortened chip removal grooves. It should be borne in mind that taps with grooves of various types can be used for cutting threads in products made of relatively soft materials– carbon, low-alloy steel alloys, etc. If threads need to be cut in parts made of very hard or viscous materials(stainless, heat-resistant steels, etc.), then taps are used for these purposes, cutting elements which are arranged in a checkerboard pattern.
Taps are typically used for cutting metric thread, but there are tools that can be used to cut pipe and inch internal threads. In addition, taps differ in their shape work surface, which can be cylindrical or conical.
Preparing to cut internal threads
In order for the process of cutting internal threads using a tap to not cause any particular difficulties and result in a high-quality result, it is necessary to properly prepare for this technological operation. All methods of cutting threads using a tap assume that a hole with the appropriate diameter has already been made in the workpiece. If the internal thread to be cut has standard size, then to determine the diameter of the preparation hole, a special table with data in accordance with GOST can be used.
Table 1. Diameters of holes drilled for standard metric threads
If the thread that needs to be cut does not belong to the standard category, you can calculate the diameter of the hole to make it using a universal formula. First of all, it is necessary to study the marking of the tap, which must indicate the type of thread being cut, its diameter and pitch, measured in millimeters (for metric). Then to determine the size cross section The hole that needs to be drilled for the thread is enough to subtract the pitch from its diameter. For example, if a tool marked M6x0.75 is used to cut a non-standard internal thread, then the diameter of the preparation hole is calculated as follows: 6 – 0.75 = 5.25 mm.
For standard threads belonging to the inch category, there is also a table that allows you to choose the right drill with which to carry out the preparatory work.
Table 2. Diameters of holes drilled for inch threads
An important question to obtain a high-quality result is not only the question of what is used to cut the thread, but also what drill to use to make the preparation hole. When choosing a drill, you need to pay attention to the parameters and quality of its sharpening, as well as to ensure that it rotates in the chuck of the equipment used without runout.
The sharpening angle of the cutting part is selected depending on the hardness of the material that needs to be drilled. The higher the hardness of the material, the greater the sharpening angle of the drill should be, but this value should not exceed 140°.
How to cut threads correctly? First you need to select tools and consumables:
- an electric drill or drilling machine capable of operating at low speeds;
- a drill whose diameter is calculated or selected using reference tables;
- a drill or countersink, with the help of which a chamfer will be removed from the edge of the prepared hole;
- a set of taps of the appropriate size;
- hand holder for taps (drivers);
- bench vice (if the product in which the thread needs to be cut needs to be fixed);
- core;
- hammer;
- machine oil or another composition that during processing must be used to lubricate both the tap and the thread section being cut by it;
- rags.
Features of the technology
When cutting internal threads with a tap, the following algorithm is used.
- In the place on the surface of the workpiece where the hole for threading will be drilled, it is necessary to form a recess for a more accurate entry of the drill, using a core and a regular hammer. The drill is fixed in the chuck of an electric drill or drilling machine, at which low tool rotation speeds are set. Before starting drilling, the cutting part of the drill must be treated with a lubricating compound: a lubricated tool enters more easily into the structure of the material being processed and creates less friction in the processing area. You can lubricate the drill with a piece of ordinary lard or grease, and when processing viscous materials, machine oil is used for these purposes.
- If threading is necessary in details small size, they should first be fixed using a bench vice. When starting drilling, the tool fixed in the equipment chuck must be positioned strictly perpendicular to the surface of the workpiece. You should lubricate the tap regularly and ensure that it does not warp and moves strictly in the given direction.
- At the entrance to the hole, as mentioned above, it is necessary to remove the chamfer, the depth of which should be 0.5–1 mm (depending on the diameter of the hole). For this purpose, you can use a larger diameter drill or countersink, installing them in the chuck of drilling equipment.
- The process of cutting internal threads begins with tap No. 1, which is the first to be installed in the driver. We should not forget about the lubricant, which must be applied to the tap for threading. The position of the tap relative to the hole being machined must be set at the very beginning of the work, since later, when the tool is already inside the hole, this will not be possible. When cutting a thread with a tap, you must adhere to the following rule: 2 turns of the tap are made in the direction of cutting the thread, 1 - against the direction. When the tap makes one revolution back, chips are thrown off its cutting part and the load on it is reduced. Thread cutting with a die is performed using a similar technique.
- After cutting the thread with tap No. 1, tool No. 2 is installed in the driver, and after it – No. 3. They are processed according to the method described above. When cutting threads with taps and dies, you need to feel when the tool begins to rotate with force. As soon as such a moment occurs, you should turn the knob reverse side to clear chips from the cutting part of the tool.
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
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 threads, 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 spicy. 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
Before you start cutting, you should use drills to make a hole in the workpiece. The diameter of the hole from the drill must match internal size thread. 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 required diameter 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. Special attention it is necessary to pay attention to the direction of movement: clockwise only, and some force 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 instrument and drills from the usual 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. Cutting edges are sharpened using a whetstone or sharpener, having previously clamped the part into a collet chuck.
Video on how internal threads are cut:
Goal of the work
1. Practically master the technique of hole processing.
2. Learn thread cutting techniques.
Brief theoretical information
Many parts of machines, instruments and mechanisms have holes of different sizes and shapes, which are obtained by various processing methods using a variety of cutting tools, equipment and devices. In plumbing practice, the following methods for processing holes are most often used: drilling, reaming, countersinking, reaming, etc. (Fig. 11).
Drilling is one of the widespread operations in plumbing practice, which is encountered quite often. Drilling is carried out with a cutting tool-drill. Various types of drills are used for drilling holes, but the most common are feather and twist.
Twist drills, compared to feather drills, have the ability to remove chips during drilling and supply coolant to the cutting surface. This improves cutting conditions and ensures a more accurate and clean hole, allowing you to resharpen the drill while maintaining almost the same diameter. The working part of a twist drill is a cylindrical rod with two spiral grooves, usually directed at an angle of 60° to the drill axis. This inclination of the grooves provides the most favorable cutting angle when drilling steel and cast iron and free movement of the forming chips.
Drills are sharpened on special machines or manually on sharpeners with fine-grained abrasive wheels. The sharpening angle is selected depending on the hardness of the material being drilled. The most favorable sharpening angles for drilling some materials are given in Table 3. The correct sharpening of the drill is controlled using a template.
Table 3
Drill sharpening angles for drilling some materials
To increase the durability of the drill and reduce the cutting forces during drilling, multi-stage sharpening of drills is used.
In order for a drill to work, it needs to be provided with two movements: rotational and translational (the latter is called feed). These movements are carried out using portable devices or stationary machines in which drills are secured with chucks or conical bushings. Chucks are used to secure drills with cylindrical shanks.
To drill holes of small diameters, hand, electric and pneumatic drills are used. The most advanced and productive way to produce holes is drilling on special vertical drilling, horizontal drilling and radial drilling machines.
Before drilling, the centers of future holes are marked and marked on the products. The depth of the core (center) depends on the diameter of the drill. As the diameter of the drill increases, the length of its bridge increases, i.e. the drill becomes “dumber”, so the depth of the core should also increase with increasing drill diameter.
When preparing a product for drilling large holes, first fill a shallow center and draw one or more control circles with a compass. Control circles serve for timely detection of drill drift to the side. The diameters of the circles, except for the last one, should be smaller than the diameter of the hole being drilled, and the diameter of the last one should be larger, since the first circles are cut off with a drill, and the last one should remain to control the correctness of the finally drilled hole.
When installing drilling products on the machine, the following guidelines should be followed:
the accuracy of drilling largely depends on the condition of the table of the drilling machine, therefore the table must be protected from nicks, local wear and rust, and the products must be installed on the table carefully, without impacts or significant movements; before installation on the table, the products must be cleaned of dirt, and any existing items on them burrs are removed;
when drilling through hole, the cleanliness and possible transfer of which do not matter, a wooden plank with parallel sides should be placed under the product; if the distortion is unacceptable, a metal ring or a metal tile with a hole for the drill to pass must be placed under the product;
if there is a hole in the machine table for the passage of a drill, drilling must be done without supports;
there should be no shavings or pieces of metal under the drilled product that could cause the hole to skew;
when drilling deep holes you need to check the perpendicularity of the surface of the table and the spindle of the machine, for which you should fix a cranked needle in the spindle and, after whitening the table with chalk, manually turn the spindle so that the needle draws a circle on the table. If the needle draws full circle, which means that the spindle is perpendicular to the surface of the table, the formation of an incomplete circle will indicate a violation of perpendicularity and a skew of the table towards the undrawn section of the circle. When installing products on a skewed table, it is necessary to level it with wedges, focusing on the control vertical lines drawn during marking, coinciding with the direction of future holes. The correct installation of the product must be checked using a surface planer with two scribers. At
correct position
product, the tip of the upper scriber should coincide with the upper end, and the lower one with the lower end of the control line. After securing the product, you need to check again that it is installed correctly, since when tightening the nuts it may again be distorted;
incomplete holes on the side of the products must be drilled, clamping the products in pairs, or using a gasket;
With a drill diameter over 15 mm, an incorrectly started hole can be moved by pressing firmly on the workpiece from the side while the machine is running. However, this technique should be used in extreme cases and with great caution.
Countersinking is used to chamfer a hole and produce conical and cylindrical recesses for the heads of screws and rivets, and counterbore is used to clean the end surfaces.
Countersinking is performed on drilling machines. Fastening countersinks is no different from fastening drills. The cutting speed when countersinking should be approximately one and a half times less than when drilling with a drill of the same diameter.
When countersinking, chips are removed with a strong jet of compressed air or water or by tipping the part if it is not heavy. When countersinking parts made of steel, copper, brass, duralumin, cooling with soap emulsion is used.
Reaming can be done both on drilling and lathe machines, and manually with special tools called reamers. A reamer, unlike a drill and a countersink, removes a very small layer of metal (allowance for the reamer), within tenths of a millimeter. Reamers for machine reaming are called machine reamers, while reamers for manual reaming are called manual reamers. Processing holes with reamers allows you to obtain high precision and surface cleanliness. Holes with a diameter of more than 6 mm are processed with two reamers: rough and finishing.
To prevent the occurrence of longitudinal marks (edges) in the hole being processed and to achieve the specified surface finish and processing accuracy, the teeth of the reamers are arranged around the circle with an uneven pitch. If the step were uniform, then with each turn with the handle the teeth would stop in the same places, which would inevitably lead to a wavy surface, therefore, when manually reaming, reamers with an uneven tooth pitch are used, and machine reamers are made with a uniform tooth pitch. The number of teeth must be even (from 6 to 14).
The helical surface formed on bodies of revolution is called a thread. Threads are widely used in technology as a means of connecting, sealing or ensuring specified movements of machine parts, mechanisms, devices, etc.
Threads on parts can be obtained by cutting with chip removal and rolling, i.e. by plastic deformation method.
Taps are used to cut internal threads, and dies, runners and other tools are used to cut external threads. The tools for rolling threads are rolling dies, rolling rollers and rolling heads. The tap consists of two main parts: working and tail (Fig. 12).
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Fig. 12. Tap |
Hand taps are used for cutting threads by hand. Hand taps for metric and inch threads are standardized and are manufactured as a set of two taps for threads with pitches up to 3 mm inclusive (for basic metric threads with a diameter of 1 to 52 mm and for inch threads with a diameter of 1/4 to 1") and a set of three taps for threads with pitches greater than 3 mm (for metric threads from 30 to 52 mm and for inch threads with a diameter of 1 1/8 to 2").
The first (roughing) tap cuts the rough thread, removing up to 60% of the metal; the second (middle) tap gives a more accurate thread, removing up to 30% of the metal; The third (finishing) tap removes up to 10% of the metal, has a full thread profile and is used for final precision thread cutting and calibration. In order to determine which tap is rough, which is medium, and which is fine, one, two or three circular marks (rings) are made on the tail section, respectively, or the corresponding number is placed.
Dies are used for cutting external threads both manually and on machines. Depending on the design, dies are divided into round, rolling, sliding (prismatic). Round dies are made whole, split.
To cut an internal thread, a drilled hole in which the thread is cut with a tap is processed with a countersink or machined.
When cutting, the material is partially “squeezed out,” so the diameter of the drill should be slightly larger than the internal diameter of the thread.
If you drill a hole for a thread with a diameter that exactly matches the internal diameter of the thread, then the material squeezed out during cutting will put pressure on the teeth of the tap, causing them to become very hot as a result of high friction and metal particles stick to them. In this case, the thread may end up with torn threads, and sometimes the tap may break. When drilling a hole that is too large in diameter, the threads will be incomplete.
When determining the diameter of the drill for cutting metric and pipe thread use special tables from reference books, for example, Appendix 3.
The diameter of the hole for a metric thread is approximately calculated using the formula:
Where D- hole diameter, mm; d- diameter of the thread being cut, mm; t- thread depth, mm.
The dimensions of the driver for securing the tap are selected depending on the diameter of the thread. The approximate length of the knob can be determined by the formula:
Where d- thread diameter, mm.
After preparing the hole for the thread and selecting the driver, the workpiece is secured in a vice and a tap is inserted vertically (without distortion) into its hole.
Pressing the knob against the tap with your left hand, turn it to the right with your right hand until the tap cuts into the metal on several threads and takes a stable position, after which the knob is taken by the handles with both hands and rotated with the hands intercepted every half turn. To make work easier, the crank with the tap is rotated in a clockwise direction (one or two turns to the right and half a turn to the left, etc.). Thanks to this reciprocal rotational movement of the tap, the chips break, become short (crushed), and the cutting process is greatly facilitated.
Having finished cutting, turn the knob in the opposite direction to unscrew the tap from the hole, then drive it through.
In order to obtain a clean thread with the correct profile and not spoil the tap, you need to use cutting fluids when cutting threads, for example, diluted emulsion (1 part emulsion to 160 parts water). In addition to diluted emulsion, it can be used when cutting internal threads in parts made of steel and brass. linseed oil, from aluminum - kerosene, from red copper - turpentine. Thread cutting in bronze and cast iron parts is done dry.
When cutting threads, machine and mineral oils should not be used, as they significantly increase the resistance that the tap or die must overcome during operation, negatively affect the cleanliness of the hole surfaces and contribute to rapid tool wear.
When cutting an external thread with a die, you must keep in mind that in the process of forming a thread profile, the metal of the product (especially steel, copper) “stretches” and the diameter of the rod increases. As a result, the pressure on the surface of the die increases, which leads to its heating and adhesion of metal particles, so the thread turns out torn.
When choosing the diameter of a rod for external threads, you should be guided by the same considerations as when choosing holes for internal threads. Good quality threads can be obtained if the diameter of the rod is slightly smaller than the outer diameter of the thread being cut. If the diameter of the rod is significantly smaller than required, the thread will be incomplete; if the diameter of the rod is larger, then the die either cannot be screwed onto the rod and the end of the rod will be damaged, or during cutting the teeth of the die may break due to overload.
The diameter of the workpiece should be 0.3...0.4 mm less than the outer diameter of the thread.
When cutting a thread with a die manually, the rod is secured in a vice so that its end protruding above the level of the jaws is 20...25 mm longer than the length of the part being cut. To ensure penetration, a chamfer is removed at the upper end of the rod. Then a die attached to the clamp is placed on the rod and the clamp is rotated with slight pressure so that the die cuts into approximately one or two threads. After this, the part of the rod to be cut is lubricated with oil and the die is rotated with uniform pressure on both handles in the same way as when cutting with a tap, i.e. one or two turns to the right and half a turn to the left. To prevent defects and breakage of the die, it is necessary to ensure that the die is perpendicular to the rod: the die must cut into the rod without distortion.
Manual thread cutting is a low-productivity and labor-intensive operation. There are various ways to mechanize thread cutting: the use of hand-powered devices, for example, hand-held electric drills increase the productivity of cutting in comparison with the manual method (wrench) by three to four times, threading machines (drilling machines of electric and pneumatic action), which increase productivity by 8. .. 10 times compared to the manual method, self-closing thread-rolling heads (Frezer plant), providing threads of the first and second accuracy classes.
Work order
1. Obtain a blank for the instrument from the teacher.
2. Read the drawing.
3. Draw up a technological process map (see Table 2).
4. Complete the task.
5. Clean the workplace and return the received tool.
The report must contain technological map for the manufacture of a part and answers to questions that the teacher gives to the group after familiarizing students with the topic of laboratory work,
BIBLIOGRAPHY
MAKIENKO N.I.
Plumbing. - M.: Higher school, 1982.
Practice program in UPM / Comp. M.G.Klyuchko, Yu.A.Kazimirchik. - Kyiv: KNIGA, 1983. ZHURAVLEV A.N.
Tolerances and
Locksmith tool
|
Tool name |
Tool group |
Note |
|
large-scale verification Squares Scribblers Marking compasses Reismas Height gauges Center finders
Nibblers
Pipe cutters General purpose files: pugnacious velvet Special purpose files |
Marking |
For marking For cutting For filing metals |
|
Pneumatic files Mechanical (machine) files cylindrical end Sweeps: cylindrical expansion conical Countersinks Countersink drills Reamer drill Countersink drills Step drills countersinks Countersink reamers Combined countersinks Combined sweeps
Tap sockets round (lerks) thread rolling sliding, prismatic Drivers for round dies (holder holders) Oblique clamps Electric thread cutters Pneumatic threading machines locksmith (handbrake) mechanized blacksmith's |
Auxiliary |
For machining holes For multiple operations For thread cutting For chopping |
|
Chisel, crosspieces Ditchers Punchers Notches marking mechanical electric Support
Pneumatic scrapers Sanding blocks Sanding paper Sanding heads Electric sanders Pneumatic sanding machines Ironers Lappings are different Spanners: cap end adjustable Screwdrivers:
Impact wrenches Hairpin drivers Pipe wrenches Pliers Pliers Needle nose pliers (biters) Pneumatic clamps ( hand presses) |
Plumbing and assembly shop Plumbing and assembly shop |
For chopping For marking For riveting For scraping For cleaning and polishing For polishing For lapping For screwing and unscrewing For gripping and clamping small metal parts For riveting |
|
Soldering irons:
electric gasoline Blowtorches |
Plumbing and assembly shop auxiliary |
For soldering |
Appendix 2
Metric thread day hole diameters
Note. Data for the third small thread is not given.
