How to cut a thread on a lathe with a cutter

Threading technique

The cutter moves evenly along the workpiece and cuts the line in the form of a screw with its tip. The inclination of the line to the axis perpendicular to the movement of the torch is called the angle of extension of the helical line. This indicator depends on:

• the speed of rotation of the part in the machine;
• cutting torch feed features.

How To Cut Threads On A Lathe

When the cutter is buried in the blank, it becomes covered with a helical groove. The thread ensures secure fastening, sealing or movement of elements in the planned direction.

Depending on the configuration of the blank, the name of the mount is given: cylindrical or conical. The profile, which is at the same time the cross section of the projection onto the plane of the thread, is selected taking into account the purpose. The following profiles are most applicable:

• rectangular;
• trapezoidal;
• acute-angled.

They are cut by single-pass or multi-pass. The second ones are created by several grooves located at equal intervals from each other, the first ones. by a single groove.

Thread properties are defined by concepts such as pitch and stroke. the distance between the same elements of the thread. It is equal to the product of the number of calls per step.

Incisors

The scheme of threading on a lathe with a cutter

To obtain a thread, craftsmen use a different cutter:

• Pipe-cutting tools;
• Threading heads;
• Taps;
• Dies.

Due to the design of the lathe, threading on the lathe allows you to obtain an internal and external variation of its performance.

At the same time, a device that allows you to process wood by cutting threads is divided into three large categories:

• Prismatic group. This cutter can be used to machine the outer sides of workpieces. At the same time, the device of the prismatic group allows working with large-sized workpieces. The tool is held in the machine holder by a special device called a dovetail. Threading elements of the prismatic group are subject to multiple regrinding, which compares favorably with rod tools.
• Core group. The simplest tool for cutting. The rod can have any cross-sectional shape, it has a working head. The profile is determined depending on the shape of the head. Shaft fixture is a shaped category of woodworking tools. The most popular of these has soldered carbide edges to cut off excess wood. They are distinguished by a long service life, less often than others need sharpening.
• Round group. The heads of such devices allow you to cut internal and external threads. With such a cutter, you can perform a wide range of operations, which makes them compare favorably with the prismatic group. An important feature is the susceptibility to multiple regrinding of the tool without losing the original characteristics.

Internal and external threading with a tool

It is the threading cutter (GOST 18876-73) made of high-speed steel that is most often used for threading. Such cutters, the geometry of which is similar to the geometry of shaped cutting devices, are divided into three types:

The internal thread is made with straight cutters mounted in a mandrel or curved varieties of them, the external thread is bent or straight. In this case, the edges of the tool must be similar to the thread profile.

Important features of the use of the devices in question:

• The rake angle of the cutters depends on the material being cut. It varies from 0 to 25 °. For workpieces made of steels, the rake angle is 0 °, for high-alloy steels, characterized by increased resistance to high temperatures, it is from 5 to 10 °. In general, for non-ferrous and viscous materials, this angle has high values, for brittle and hard materials. small ones.
• The tip of the cutting tool depends on the root configuration that is performed. It can be chamfered or rounded.
• The size of the rear side angles of the cutters is selected so that in the process of performing work on the machine, the side parts of the tool do not rub against the screw threaded surface. Most often, the indicated angles on the left and right sides are chosen to be the same. Their value is equal to 6-8 ° if the angle of rise of the thread is more than 4 °, or 3-5 ° in cases where the angle is less than 4 °.
• Threads are cut in the holes after boring or immediately after the drilling operation.

It should be added that steel products are processed on lathes with tools with carbide inserts T15K6, T14K8, T30K4 and T15K6. But for parts made of cast iron, plates made of VK4, VK6M, B2K and VKZM alloys are most often used.

Threading with taps and dies

Taps are usually used to make metric internal threads. If machine taps are used on the lathe, any thread is cut in one pass of the tool. Turning of viscous and hard workpieces is carried out using a set of taps.

In sets of three tools, one tap is finishing (it does 10% of the total work), the second is semi-finishing (30%), the third is rough (60%). If there are only two tools in the kit, one (rough) accounts for 75% of the work performed, the second. 25%. You can distinguish a rough tap from a finishing and semi-finishing tap by the intake part. The roughing tool has the longest.

The high-speed modes of threading with the use of taps are as follows:

• from 6 to 22 meters per minute for parts made of bronze, cast iron and aluminum;
• 5 to 12 meters per minute for steel parts.

When using taps, it is imperative to cool them with oil or a special emulsion.

Dies are designed to be made on bolts, screws, male thread pins. Before the operation, pre-processing of that workpiece zone is performed on which the thread will be cut. The cross-section (external) of the thread is larger than the processed area by the following values:

• 0.14. 0.28 mm (threads with a diameter of 20 to 30 mm);
• 0.12–0.24 mm (11 to 18 mm);
• 0.1-0.2 mm (6 to 10 mm).

In the tailstock (in the quill) of the lathe there is a ram holder, which is a special chuck. It carries out the installation of the tool we are considering.

The speed of the cutting operation with the use of dies is as follows:

How to cut a thread on a manual lathe (Intermediate method ideal for home workshop & hobby engineer)

• 10-15 m / min (brass products);
• 2-3 m / min (cast iron products);
• 3-4 m / min (steel products).

At the end of the workpiece, before starting the procedure, be sure to chamfer. This allows you to create the thread lead necessary for processing. high-quality and efficient The chamfer has the same height as the thread profile.

Types of incisors

The lathe is designed to cut internal and external threads. For this, many varieties of incisors have been created, belonging to three large groups:

Rods are the simplest type of cutting tool. This is a rod (of any cross-sectional shape) with a working head. The profile is determined by the shape of the head. One of the varieties of rod cutters. with soldered carbide working edges. They are more resistant to abrasion and do not require frequent sharpening. Round and prismatic belong to the shaped category.

Prismatic cut only the outside. Compared to rod, they are able to work with large surfaces. The cutter is held in a dovetail holder. Capable of more resharpening than rod.

Round ones perform external and internal threads. They cut more conveniently and have a wider range of applications than prismatic ones. They can be resharpened more times. They are installed in the holder relative to the end and the hole.

Slicing rules

Threading instructions in the video:

Using various tools, threading is carried out on a lathe. To perform this operation, dies and taps, cutters, special heads are used.

Classification of threads

• conical;
• cylindrical.

Without specifying the direction, the thread is cut with the left direction. It is considered standard. The tool is used the same. Changes to reverse rotation and the cutting edge is reversed 180⁰. the slide moves in from the opposite side.

The sectional profile of the tooth has different shapes. Used types of threads made on lathes:

• metric;
• metric-conical;
• tubular cylindrical;
• pipe conical;
• inch;
• trapezoidal;
• persistent;
• round.

To use taps and dies, the part is mounted in a chuck. The threaded cutting tool is pressed against the center of the tailstock. When cutting with a cutter, a long part is pressed by a tailstock, a short one by a mushroom. The tool is mounted on a support and aligned in the axis of the part.

Lathe threading. cutters, taps, dies, heads and combs

Threading on a lathe is one of the operations for which a variety of tools can be used. This problem is most often solved with the help of a cutter. In addition to it, taps, dies, and special-purpose working heads are also used. In addition, on lathes, such an operation can be performed using the knurling technology.

The process of threading on a lathe with a cutter

Rules for obtaining thread

Threading operations provide that the master uses pipe-threading conical, pipe-threading cylindrical, inch, thrust types of thread.

In order for the execution of the pipe-cutting structure to proceed correctly and without errors, it is necessary to rely on certain rules when working with a die, a head, a tap, etc.

• First, the setup of the machine itself is performed. Thread-cutting, pipe-cutting operations cannot be performed with high quality, provided that there is no equipment that is appropriate in terms of characteristics and capabilities. The setting provides for the adaptation of the device for a specific type of thread, used threading, pipe-cutting heads, taps, dies. The setting is carried out according to the instructions for the machine and working tools. It will not be superfluous to reinforce your pipe-cutting skills with video lessons.
• Further, based on important rules and recommendations, work is carried out to create a thread with the required parameters.
• The cleanliness of the resulting thread depends on the correct setting of the working tool and its movement relative to the workpiece. To achieve the desired result, it uses a template that is installed parallel to the centers of the lathe on the workpiece. The torch projection and template are superimposed on one another and clearance is checked. The cutting tool must be positioned strictly on the center line of the lathe.
• A curved working tool is used to cut internal threads. If you take a mandrel, you can use a straight tool. External cutting is carried out mainly by bent, but sometimes even cutters. Select cutters based on the type of material being cut and the requirements for thread characteristics.
• The location of the working edges of the cutters depends on the profile to be made. Triangular provide for the production of a thread at the top of 55 or 60 degrees for inch and metric threads, respectively.
• The selection of the rake angle is based on the workpiece material. It can be between 0 and 25 degrees. At the same time, a smaller angle is chosen for harder and more brittle materials.
• The lateral corners of the tool at the back must have such parameters that when cutting the lateral elements do not touch the surface of the thread. In most cases, they are the same on the left and right sides. So, if the angle of the threaded lift is more than 5 degrees, the lateral angles will be 6-8 degrees, or 3-5 degrees with the threaded angle less than 4 degrees.
• Internal grooving is performed after boring or drilling a hole. During processing, the metal is subject to deformation, which is why the diameter of the hole should be chosen slightly larger than the inner diameter. For brittle metal, 0.02 is added to the value, and for ductile metal. up to 0.4.
• Sometimes the pipe-tapping machine requires you to complete the grooving. Internal diameters are made 0.3 millimeters smaller compared to the same parameter of the thread.
• Using a pipe-cutting unit in order to get high-quality cutting at the end, make a shoulder of 3 mm (no more), without changing the diameter. This projection will mark the finishing pass of the cutting tool. When the work is finished, the ledge can be removed.
• Roughing with a cutting head is carried out at a speed not exceeding 30 m / min. Finishing allows turning the head at speeds up to 55 m / min.
• Working with cast iron involves the passage of the cutting die head at a speed of up to 25 m / min. For carbide materials, this figure is up to 150 m / min.
• If the thread pitch is less than 2 mm, work is performed at higher speeds, but decreases with a pitch of 6 mm.
• The thread is cut on a lathe in several passes. At the end of each approach, the cutting tool returns to the starting position.

How to cut tapered threads on a lathe

Threading with a cutter on a lathe is not the most technologically complex process, but it requires increased attention, certain skills and theoretical knowledge. It is about the latter that we will tell you, which will allow you to get as close as possible to the desired quality of processing workpieces by threading with cutters.

• 1 Incisors
• 2 Slicing technique

• 2.1 Rules for obtaining a thread

The scheme of threading on a lathe with a cutter

To obtain a thread, craftsmen use a different cutter:

• Pipe-cutting tools;
• Threading heads;
• Taps;
• Dies.

Due to the design of the lathe, threading on the lathe allows you to obtain an internal and external variation of its performance.

At the same time, a device that allows you to process wood by cutting threads is divided into three large categories:

• Prismatic group. This cutter can be used to machine the outer sides of workpieces. At the same time, the device of the prismatic group allows working with large-sized workpieces. The tool is held in the machine holder by a special device called a dovetail. Threading elements of the prismatic group are subject to multiple regrinding, which compares favorably with rod tools.
• Core group. The simplest tool for cutting. The rod can have any cross-sectional shape, it has a working head. The profile is determined depending on the shape of the head. Shaft fixture is a shaped category of woodworking tools. The most popular of these has soldered carbide edges to cut off excess wood. They are distinguished by a long service life, less often than others need sharpening.
• Round group. The heads of such devices allow you to cut internal and external threads. With such a cutter, you can perform a wide range of operations, which makes them compare favorably with the prismatic group. An important feature is the susceptibility to multiple regrinding of the tool without losing the original characteristics.

How to cut tapered threads on a lathe?

Threading tool

The productivity of work is increased due to the use of die heads. They have 4 segments with incisors. Having cut to the end, the device opens up, freeing the part. The tool does not need to be twisted. The thread is cut quickly, like a tap. Diameters up to 100 mm can be processed.

Die heads have a complex design and are used in mass production of parts.

The cutter is sharpened according to a flat template, regardless of the type of thread. The angle should exactly match the cavity, following its contours. After cutting, the tops of the threads should be cleaned and slightly blunt.

In trapezoidal profiles, the corners of the peaks and valleys are rounded off to R 0.3–0.5 mm. Otherwise, the thread will twist poorly and abut against the tops. With peeled tops, when screwing in, the threads slide along the lateral surface, creating a strong connection.

The value of the maximum load and the tightness of the connection increase.

The highest productivity when machining holes is provided by the tap for tapping internal threads. Exposed in the axis of the part, it cuts through all the turns, regardless of the number of passes.

Application of incisors

Tapping tools are required for tapping with a lathe. They are made of high-speed steel, and the requirements for their characteristics are stipulated by the corresponding GOST (18876-73). By design, such cutters are divided into the following types:

• prismatic;
• rod;
• round (disc).

A helical threaded groove on the surface of the workpiece is cut with a bent or straight cutter, and to form an internal type thread, straight and curved tools are required, which are fixed in a special mandrel. The top of the turning tool, which is used to cut the turns, must have a configuration that fully corresponds to the profile of the thread being formed.

Cutters for threading: a. rod; b. prismatic multidisciplinary; c. prismatic single-profile; d. multi-profile disk; d. disc single-profile; e. disk for internal thread; α is the back angle; γ is the rake angle; φ is the angle of the intake cone; h. height of the cutter axis

When forming a thread with a cutter, a number of features of this technology should be taken into account.

• The rake angle of a turning tool for tapping depends on the characteristics of the material being machined. You can choose such an angle within a fairly wide range: 0–250. So, if a thread is cut with a machine on workpieces from ordinary steels, the rake angle should be 0 degrees, for high-alloy steels that withstand temperature loads well, the rake angle can be 5–100. It can be the greater, the higher the viscosity of the material, and the lower, the higher the hardness and brittleness of the metal from which the workpiece being machined is made.
• The tip of the turning tool, which forms the helical line on the workpiece, must have a shape identical to the thread profile.
• The rear side corners of the tool are chosen so that the surfaces of the cutter with which they are formed do not rub against the newly formed helical groove. Usually, these angles on both sides of the turning tool are made the same. If the angle of rise, which the thread is characterized by, is less than 4 degrees, then such angles are chosen in the range of 3-50, if more than 40, then 6-8 degrees.
• Internal threads are cut in already prepared holes, which are obtained by boring or drilling.

Billets, which are made of steel, are processed on a lathe using tools with plates made of hard alloys T15K6, T14K8, T15K6, T30K4. If the part is made of cast iron, then a tool with plates from the following grades of hard alloys is used to cut threads on it: VK4, B2K, VK6M, VK3M.

Thread parameters

Before dwelling in more detail on how to cut a thread on a lathe with a cutter, let’s take a closer look at the main elements of the helical groove. You can meet it both on steel rods or nuts, and on pipe fittings in gas, heat and water pipelines. To characterize the thread, the following main elements of its profile (longitudinal section) are distinguished:

• Outside diameter;
• Thread pitch;
• Apex angle.

In terms of diameter, standard metric threads up to 6 mm have a pitch of 1 mm, then 2 mm. If necessary, it is not difficult to cut a seven-millimeter or nine-millimeter thread on the machine. It is impossible to perform such work with manual threading tools. taps and dies.

By pitch, threads are divided into standard (1 mm), small (less than 1 mm) and large (more than 1 mm). Typically, all taps are designed for standard thread spacing. You can get fine or coarse threads only on a screw-cutting lathe.

According to the angle at the top of the threads, they are divided into metric (the angle is 60 °) and inch (the angle is 55 °). For manual cutting, it is necessary to have a set of tools for each diameter with different angles. For mechanical cutting, it is sufficient to purchase only two threaded cutters with the required sharpening angles.

How to thread on a lathe with a cutter?

Threads are the most common element in fasteners. It is subdivided according to a number of characteristics, has wide application and can be obtained on parts with hand tools or cutters on screw-cutting lathes. Despite the fact that the for turning work can be quite high, the quality of the resulting thread is incomparably higher. The key to this, for example, is the experience of SibPromDetal specialists.

Thread cutting technology

Based on the specified parameters, the appropriate cutter and thread cutting modes are selected. Before proceeding to obtain on the surface of the part a helical groove of a triangular, rectangular or trapezoidal section, it is necessary to turn the workpiece to the required diameter.

This type of work is carried out with a standard through cutter at appropriate speeds. Due to the partial expansion of the metal during cutting, the diameter of the workpiece must be made 0.1 mm less than the required diameter of the future thread.

The next stage is setting up the machine, and more specifically, the guitar mechanism that regulates the feed rate of the cutter. Using the appropriate tables, depending on the desired pitch, it is necessary to install the required gears. After that, you can cut the threads on a lathe.

To do this, a threaded cutter with the required sharpening angle is installed in the tool holder and the handle for connecting the support to the lead screw is used to control it. Thanks to this device, the tip of the cutting tool carries out a spiral movement along the surface of the part, gradually going deeper pass by pass to the required depth until a full triangular profile is obtained.

Remember to periodically lubricate the surface of the part with machine oil to obtain the highest quality of the produced threads. This will reduce the roughness and partially cool the core to be machined. You can see in more detail the technology of obtaining a thread on a lathe on the proposed

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Lathe threading. cutters, taps, dies, heads and combs

Threading on a lathe is one of the operations for which a variety of tools can be used. This problem is most often solved with the help of a cutter. In addition to it, taps, dies, and special-purpose working heads are also used. In addition, on lathes, such an operation can be performed using the knurling technology.

The process of threading on a lathe with a cutter

Tapping with turning equipment

When threading a workpiece installed on a lathe, using a cutter, such a process looks like this: a tool moving along the axis of the rotating part (feed movement) draws a screw-type fishing line on its surface with its pointed tip. The characteristic parameter of the helical mowing line, formed by the cutter on the surface of the workpiece, is the angle of its rise or increase. The value of this angle, measured between the tangent located to the helical mowing line and a plane that is perpendicular to the axis of rotation of the part, is determined by:

• the amount of feed of the cutting tool moving along the axis of the workpiece;
• the frequency with which the part rotates.

An equally important parameter of a helical mowing line is its pitch, which characterizes the distance between its adjacent turns. This distance is measured along the axis of the workpiece.

Moving along the axis of the rotating workpiece, the cutter cuts into it and creates a helical surface, which is commonly called a thread. Elements with a threaded surface are used to solve various problems: ensuring the movement of elements relative to each other, their articulation and sealing of the formed joints.

The most common types of thread profile: a. triangular, b. rectangular, c. trapezoidal, d. persistent, e. round

The surface of the threaded workpiece can be cylindrical and conical. The characteristics of a threaded connection are significantly influenced by the profile of the thread, that is, its contour in the plane. Allocate profiles:

• triangular;
• trapezoidal;
• rectangular;
• persistent;
• round.

The thread on the surface of the part can be formed with one screw thread (single-start) or several (multi-start). If several screw threads are cut, then they are located equidistantly in relation to each other.

You can count the number of threads at the beginning of the threaded surface. A multi-start thread, in addition to a pitch, is characterized by such a parameter as a stroke. This is the distance measured between two points of the same type of two adjacent turns, which are formed by one thread. This distance is measured along the mowing line, which is parallel to the axis of the threaded part. For a single-start thread formed by one thread, the stroke is equal to the pitch, and for a multi-start thread it can be calculated by multiplying the pitch by the number of starts.

All types of threads with diagrams, parameters and GOST regulating them

Technology of using taps and dies

With the help of taps, which are a screw with several longitudinal grooves that form cutting edges and facilitate chip evacuation, predominantly metric threads are cut on a lathe in small diameter holes. If machine taps are used for threading, the operation is performed in one pass.

Machine taps differ from conventional taps in that they consist of two parts. intake and calibration. If ordinary taps are used for threading with a lathe, then the technology for performing this process involves the use of a set of tools. The set for tapping internal threads includes three types of taps: roughing, which does 60% of the work, semi-finishing (30%), finishing (10%). Sometimes there may be two tools in such a set: the rough, which does 75% of the work, and the finishing, which does 25% of the work. To distinguish a rough tap from a finishing tap, just look at its intake part: it is much longer than that of a finishing tap.

Tapping design

The speed of threading on a lathe using taps can be quite high:

• 6-22 m per minute. for parts made of cast iron, bronze and aluminum;
• 5-12 m per minute. for steel billets.

With the help of dies, which are a ring with an internal thread and several chip grooves, the external thread is made on screws, bolts and studs. The surface of the part must be pre-ground to the value of the required diameter, which must take into account the tolerance:

• 0.14–0.28 mm. for threads with a diameter of 20–30 mm;
• 0.12–0.24 mm. for threads with a diameter of 11–18 mm;
• 0.1-0.2 mm. for threads with a diameter of 6-10 mm.

The dies with which the external thread is cut are fixed in a special chuck (die holder) located in the quill of the tailstock of the lathe.

Using dies, the threads are cut at the following speeds (their setting also takes into account the minimum tool wear during operation):

• 10-15 m per minute. on items made of brass;
• 2-3 m per minute. on cast iron parts;
• 3-4 m per minute. on steel blanks.

In order for the die to freely enter the part, a chamfer is removed at the end of the latter, which coincides in height with the height of the thread profile.

Application of incisors

Tapping tools are required for tapping with a lathe. They are made of high-speed steel, and the requirements for their characteristics are stipulated by the corresponding GOST (18876-73). By design, such cutters are divided into the following types:

• prismatic;
• rod;
• round (disc).

A helical threaded groove on the surface of the workpiece is cut with a bent or straight cutter, and to form an internal type thread, straight and curved tools are required, which are fixed in a special mandrel. The top of the turning tool, which is used to cut the turns, must have a configuration that fully corresponds to the profile of the thread being formed.

Cutters for threading: a. rod; b. prismatic multidisciplinary; c. prismatic single-profile; d. multi-profile disk; d. disc single-profile; e. disk for internal thread; α is the back angle; γ is the rake angle; φ is the angle of the intake cone; h. height of the cutter axis

When forming a thread with a cutter, a number of features of this technology should be taken into account.

• The rake angle of a turning tool for tapping depends on the characteristics of the material being machined. You can choose such an angle within a fairly wide range: 0–25 0. So, if a thread is cut with a machine on workpieces from ordinary steels, the rake angle should be 0 degrees, for high-alloy steels that withstand temperature loads well, the rake angle can be 5 –10 0. It can be the higher, the higher the material’s viscosity, and the lower, the higher the hardness and fragility of the metal from which the workpiece being machined is made.
• The tip of the turning tool, which forms the helical line on the workpiece, must have a shape identical to the thread profile.
• The rear side corners of the tool are chosen so that the surfaces of the cutter with which they are formed do not rub against the newly formed helical groove. Usually, these angles on both sides of the turning tool are made the same. If the angle of rise, which the thread is characterized by, is less than 4 degrees, then such angles are chosen in the range of 3-5 0. If more than 4 0. then 6-8 degrees.
• Internal threads are cut in already prepared holes, which are obtained by boring or drilling.

Billets, which are made of steel, are processed on a lathe using tools with plates made of hard alloys T15K6, T14K8, T15K6, T30K4. If the part is made of cast iron, then a tool with plates from the following grades of hard alloys is used to cut threads on it: VK4, B2K, VK6M, VK3M.

Application of die heads

When threading using lathes, special heads are used much less often than the tools described above. These heads can be used to cut any type of thread. Their working elements are combs: prismatic ones are used when it is necessary to cut an internal thread, for cutting an external one, radial, round and tangential ones are needed. The peculiarity of such heads is that their working bodies automatically diverge when they reverse, so they do not come into contact with the newly cut thread.

Combs for cutting internal threads (their number in the set may be different) are made with a lead-in taper. When cutting external threads, round-type dies are mainly used, which are distinguished by their simplicity of design. In addition, combs of this type are characterized by high durability, they can be repeatedly reground, bringing their geometric parameters to their original values.

In the event that on a lathe it is necessary to cut a helical surface on worms or screws with a large length, then the threading heads are fixed on the machine support, which contributes to an increase in the productivity of the technological process. Such heads can be equipped with both conventional cutters and a cup-type tool.

You can understand the technology of threading using a lathe from the video, which clearly shows how this process is carried out. Below are several videos showing the process of making threads in different ways.

Methods for obtaining threads

Threaded connections are used in mechanical engineering and construction. The use of threaded hardware allows you to connect parts of mechanisms and structural elements during construction by using bolts, nuts, screws, studs. Threaded products are also designed to transmit forces or movement in mechanisms such as a jack, gearbox, press, machine.

Tapping scheme on a lathe

Jacks and lead screws are made with trapezoidal thread.

There are the following methods for making threads:

• manually (tap or die);
• on machines:

• screw-cutting lathe (mod. 16K20);
• thread rolling with rollers and flat dies;
• milling (mod. RTS 161F4) to obtain threads with a large pitch;
• grinding wheels with a given profile for the manufacture of fine and precise threads;
• screw-cutting (mod. 1622);
• for threading nuts (mod. 2064);
• providing vortex threading using multi-cutter heads.

Vortex cutting is provided by 4 cutters located in the rotating head from its own motor. This device is fixed to the lathe support. Due to the alternate plunge of the cutters, a high machining speed is ensured, since the cutters do not heat up significantly. This also provides a lower roughness of the resulting threaded surface and increased profile accuracy.

Classification of threads

A thread is a helical line formed on the surface of a body of revolution by the apex of a protrusion of a certain shape. The distance between adjacent protrusions is equal to the thread pitch. The shape of the protrusion depends on its type. There is a depression between two adjacent protrusions.

• Direction of the spiral cutter line:
• right (it is lifted from left to right, and the bolt is screwed in clockwise);
• left (screwing takes place counterclockwise).
• The shape of the protrusion in the form:
• triangle,
• trapezium,
• unequal trapezoid,
• rectangle,
• semicircle.
• The outer surface of the part (cylindrical or conical).
• Locations on the part (internal or external).
• Number of visits (one, two, three);
• Purpose (mounting and chassis).

• with a profile angle:

• 60⁰ (metric, tapered inch);
• 55⁰ (tubular cylindrical, tubular conical);

stubborn;

round;

trapezoidal (angle 30⁰).

Trapezoidal thread is characterized by greater strength than rectangular thread, with less laboriousness of manufacture. The purpose of the trapezoidal thread is to convert rotary motion into translational.

In addition, a thread called modular is used. It is used where rotation is transmitted from a worm to a worm wheel, the axes of which are at an angle of 90⁰.

Decoding the spelling of the threads

The thread is designated: М12х1.25–7Н. This means: metric internal (7H), diameter 12 mm, pitch. 1.25 mm, tolerance field 7H. For an external thread, the tolerance field is recorded: 6h. The coarse step value is not given in the designation (М16–8g). The letters LH (М16–8g – LH) are added to the left thread in the designation. GOST 8724-81 contains a table indicating the diameter and pitch of the required size.

Threading on lathes

Threading is an extensive topic in metalworking using lathes. This technology is used in more than 40% of works. The strength of the connection of detachable structural elements or mechanisms depends on the quality of the threads. Read more about this in the article.

Threading tool

Die. On the outer surface, the thread is cut with dies. They are made in the form of a nut. Holes are drilled in them to obtain cutting elements and to evacuate chips. On each side, the die has cutting elements that form an intake cone (angle 20⁰ – 30⁰). In the middle there is a calibrating zone.

The die is fixed in the knob with screws. It is necessary after each turn of the plate to turn it back by a third of the circle. This is necessary to clean the holes from chips and obtain a high-quality threaded surface.

Tap. The tap is used to cut internal threads. It has cutting edges obtained by making longitudinal or helical grooves. The grooves form the front surfaces of the teeth. The working area of ​​the tap forms the intake and calibrating sections. The fence is also called cutting. It is tapered and plunges gradually.

There are hand, machine and nut taps. Hand taps are made single and complete: for roughing and finishing cuts when cutting threads. The set also consists of 3 taps. Its number is indicated by the number of circular notches on the shank (1. rough, 2. semi-finishing, 3. finishing).

The largest intake part is at the rough tap. The shank of the taps is made in the form of a square in order to transmit the working force with a wrench. Taps are subdivided for tapping in through and blind holes. Nut taps are available with straight or curved shank.

Cutter. The thread is cut by the tip of the cutter, fixed in the support, when it is moved relative to the rotating workpiece. In this case, the thread pitch formed by the cutter is equal to the distance between the vertices of adjacent protrusions along the axis of the part.

Cutters for threading constructively perform:

• solid (made of high speed steel or hard alloy);
• with brazed carbide plates (GOST 18885–73);
• prefabricated with mechanical fastening SMP (replaceable polyhedral plates).

A threaded cutter with a brazed or replaceable multi-faceted plate (MPS) must have sharpening angles that ensure that the corresponding profile is obtained on the thread. These cutters are used for cutting metric and trapezoidal threads.

Cutters with MPS are used on CNC turning and milling machines, which can provide the necessary cutting conditions and obtain a finished part in one processing cycle (machining centers).

To ensure the quality of the thread when cutting it, coolant must be used (emulsion, sulfofresol and others).

High speed steel grades for cutters: R6M5K5, R6M5, R9M4K8, R9K5, R12F3, R9M4K8.

Equipment used

The thread is cut by hand or on a screw-cutting lathe. When cutting by hand, a vice and a tool are used: dies and taps. You can cut a thread using a screw-cutting lathe 16K20 with a cutter, a tap, a die and other types of tools. They are used for cutting both external and internal threads.

On the feed box of the 16K20 machine there is a table in which the positions of the handles are indicated in order to adjust the desired thread pitch. Setting the processing modes allows you to get a high-quality part. Cutter technology provides for:

• its correct sharpening;
• setting up the operating modes of the machine;
• correct installation of the cutter in the center of the part using a fixture. a template;
• measurement of the obtained dimensions with threaded gauges or gauges.

When threading is not allowed: scuffing, crushing, torn threads, risks.

Special attachment or separately driven swirl heads expand the functionality of the lathes.

Turret lathes increase productivity by reducing tool change times.