Used for cutting threads in holes. Plumbing lesson on "cutting internal threads." Thread types and systems

Automechanical Lyceum

Saint Petersburg

LESSON PLAN ON THE TOPIC:

"Thread cutting"

Master p/o

Ivanova V.Ya.

The purpose of the lesson:

Teach students the techniques of cutting threads with a tap and die by hand.

- to form skills and develop skills in working with a tap and die.

To cultivate a sense of teamwork, the right attitude to learning, independence, respect, accuracy, and careful handling of tools and materials.

I. Organizational part, introductory part:

1) Checking absentees, assigning duty officers, availability of school supplies (notebooks, textbooks, pens, pencils, rulers, washing machines).

II. Repetition of the material covered.( pp. 79-83)

Questions: (p. 83 - questions).

What metals do you know?

What properties do different metals have?

What products are made from metals?

III. Main part:

1) Presentation of program material (in the form of a lecture).

Many parts of machines and building structures are fastened together using threaded connections. The following are used in threaded connections:

Bolt - a cylindrical rod with a head at one end and a thread at the other.;

Hairpin - a cylindrical rod with threads on both ends;

A screw is a cylindrical rod with a thread for screwing into one of the parts to be connected (Appendix Fig. 61 (poster or sketch on the board)).

Thread - these are protrusions on the surface of screws and nuts located along a helical line. There are two types of threads: external and internal.

These types of threads They are made on machines and manually. Depending on the lifting direction of the lifting direction of the turns on a cylindrical surface, the helix (i.e. thread) can be right-handed or left-handed. In mechanical engineering, right-hand threads are more often used.

Dies - used for cutting external threads.

Taps - used for cutting internal threads.

These tools come with holders (auxiliaries).

When showing the tool (on posters), name: design, main elements, main angles and set (according to posters).

Main thread elements:

The thread profile is considered in a section passing through the axis of the bolt or nut

Thread (turn) is the part of the thread formed during one full revolution of the profile.

Profile angle φ - the angle between the sides (edges) of the thread profile, measured in a plane passing through the axis of the bolt (in metric 60˚, and in inch 55˚).

Thread pitch P - the distance between the parallel sides or vertices of two adjacent turns, measured along the axis of the thread (in metric in mm, in inch the number of turns)

Profile height (thread depth) H1 – the distance from the top of the thread to the base of the profile, measured perpendicular to the axis of the bolt.

The outer diameter of the thread d is the diameter of the cylinder described near the threaded surface (for bolts along the tops of the thread profile, for nuts - along the depressions).

Internal diameter d1 is the diameter of the cylinder inscribed in the threaded surface (measured at the recesses for bolts, at the tops of the thread for nuts).

The average diameter d2 is the diameter of a cylinder coaxial with a thread, the generatrices of which are divided by the side sides of the profile into equal segments.

Thread profiles (on poster):

Cylindrical – triangular;

Conical – triangular;

Rectangular;

Trapezoidal;

Persistent;

Round;

Single-way (Used for reliable connection) and multi-way (used to transmit movement).

Types of threads (on poster):

Metric;

Inch;

Pipe;

Cylindrical.

Exercise: Name the main elements of carving according to Fig.

External thread execution sequence:

1) It is necessary to determine the diameter of the rod using the table (page).

2) Fix the workpiece in a vice vertically with a projection of 20-25mm.

3) Remove the chamfer at the end of the rod using a file.

Question: What safety precautions should be taken into account when working with a file?

4) The die is placed on the upper end of the rod and rotated with slight pressure without distortion.

5) Rotate the die holder 1-2 turns clockwise and 0.5 turns counterclockwise.

6) After cutting several turns, lubricate the rod with oil.

Sequence of internal threading:

1. Determine the diameter of the hole according to the table (page), for accuracy, drill on a metal lathe.
2. Pre-lubricate the tap with machine oil.
3. Place it in the hole without distortion.
4. Rotate smoothly, making 1-2 turns clockwise, half a turn counterclockwise.

Possible defects when cutting threads:

Torn cutting (lack of lubrication);

Threads with incomplete profile (discrepancy between the diameter of the rod and the hole);

Breakage of the tap or die (the diameter of the hole is less than normal or the rod is larger than normal).

IV. Practical work.

Completing tasks:

1. Cut threads on the rod.

2. Cut the thread with a tap.

V. Final part.

Lesson summary. Grade practical work students.

Cleaning the workshop.

Application of TCO: board, posters, manufactured sample (part or product).

Literature:

1 Textbook for 7th grade, V.D. Simonenko, 2007.

2 Lesson plans according to the 7th grade textbook edited by V.D. Simonenko (Volgograd 2006).

189. What is thread cutting?

Threading is the formation of a helical surface on the outer or inner cylindrical or [-tonic surfaces of a part.

190. What tools are used to cut a helical surface on the outer cylindrical surface of a part?

Cutting the helical surface on bolts, shafts and other external surfaces of parts can be done manually or by machine. Hand tools include: round split and continuous dies, as well as four- and hexagonal plate dies, dies for cutting threads on pipes. To fasten the dies, die holders and clamps are used. The round die is also used for machine thread cutting.

The number of chip holes g depends on the chip thickness azt removed by the teeth of one hole, the angle of the intake cone f and the thread pitch t:

As the number of chip holes g increases, the chip thickness a decreases and vice versa.

Depending on the diameter of the thread being cut, the number of chip holes ranges from 3 to 14.

Cutting external threads by machine can be done on lathes with thread cutters, combs, thread-cutting heads with radial, tangential and round dies, vortex heads, as well as on drilling machines with thread-cutting heads, on milling machines with thread-cutting cutters and on single-thread thread grinding machines nym and multi-strand circles.

Obtaining an external threaded surface can be achieved by rolling it with flat dies or round rollers on thread rolling machines. The use of thread rolling heads with axial feed allows you to roll external threads on drilling and turning equipment.

191. Name a tool for cutting threads in holes.

Threading in holes is carried out using taps manually and by machine. There are cylindrical and conical taps. Hand taps come in single, double and triple. Typically, a set consisting of three taps is used: a rough one, indicated by one dash or the number 1, a middle one, indicated by two dashes or the number 2, and a finishing one, indicated by three dashes or the number 3 (Table 12, Fig. 29).

There are special taps: for dies (die taps with a long cutting part), for nuts, for pipes, for light alloys, and also with a conical working part. Taps can be used to cut threads in through and blind holes or to calibrate previously cut threads with master taps. 77

A driver with a fixed or adjustable square hole is placed on the shank of a hand tap, ending in a square head.

In some cases, combined taps are used, which can be used for drilling and threading.

Machine taps are used for cutting internal threads on drilling and turning machines of all types. They can cut threads in one or more

Passages. In one pass, threads with a pitch of up to 3 mm are cut, and in 2-3 passes, threads with a larger pitch, especially long threads, as well as smooth threads in difficult-to-cut materials, regardless of the pitch, are cut.

For cutting threads in nuts on machines, nut taps are used. They operate without reversing and when cutting, the nuts are threaded onto the shank. There are nut taps with straight and curved shanks.

For cutting large-diameter internal threads, thread-cutting heads with adjustable dies or converging dies are used.

192. What elements does the tap consist of?

Tap elements are the working part, consisting of cutting and calibrating parts and a shank. On working T8
Parts are provided with spiral cutting and longitudinal grooves to remove chips. Cutting edges are obtained at the intersection of spiral cutting and longitudinal grooves for chip removal. The tail end ends with a square head for installation in the chuck. Taps are made from carbon tool steel U12 and U12A, high-speed steel R12 and R18, alloy steel X06, XV, IH.

193. What is a helical surface? A helical surface is a surface described by a generatrix curve uniformly rotating around

axis and at the same time performing a uniform translational movement along this axis. In relation to the threaded surface, the generatrix is ​​a triangle (for metric and inch threads), a trapezoid (for trapezoidal threads) and a rectangle (for rectangular threads, for example in jack lead screws).

194. What is a thread profile?

A thread profile is a contour obtained by cutting the screw surface with a plane passing through the axis of the screw.

The thread profile consists of the projections and valleys of the threads. The shaft axis is the axis of the helical surface (Fig. 30).

195. What parameters determine the thread in each screw and each nut?

The thread parameters are the outer diameter d, inner diameter du, average diameter d%, pitch R, thread profile angle oc. The thread profile is divided into two parts: projections and valleys. Threads can be single-start or multi-start.

196. What is a single-start thread pitch?

The thread pitch should be understood as the translational movement of the midpoint of the profile generatrix, corresponding to

Corresponding to one full revolution relative to the ssi thread.

The thread pitch is determined by the distance between the axes of two identical points of successive turns of the same name (Fig. 31), or the distance by which the nut moves along the screw when performing one full revolution for a single-start thread (Tables 13 and 14).

197. What is the progress of a multi-start thread?

The helical surface of a multi-start thread can be considered as several helical grooves having

Rdin is the nominal diameter (hence, one nominal pitch, which in a multi-start thread is called lead t) and formed on one smooth cylindrical surface with starts evenly spaced around the circumference. Thus, the thread stroke t is the distance between the nearest identical sides of the profile, belonging to the same screw surface, in a direction parallel to the thread axis. The thread lead is the relative axial movement of a screw or nut per revolution.

198. What is the relationship between the cutting stroke and the thread pitch?

If the thread is single-start, then the thread stroke t is equal to the thread pitch P. If the thread is multi-start, then the thread stroke t is equal to the product of the pitch P and the number of starts n:

199. Name the types of threads depending on the direction of cutting and the number of starts.

Threads can be single-start or multi-start, as well as right-handed and left-handed. A multi-start thread is when one cutting stroke involves two or more thread profiles.

200. How are threads designated?

The designation of threads is given in table. 15.

201. Name the types of threads depending on their configuration.

Depending on the thread configuration, there are metric (normal and small), inch, pipe, trapezoidal, symmetrical and asymmetrical, rounded, rectangular. They can be cylindrical or conical.

The profile angle of metric threads is 60°, inch cylindrical 55°, inch conch threads 60°, pipe cylindrical and conical 55°, trapezoidal 30°. 82

202. Name the types of threads depending on the profile.

Depending on the thread profile, they are divided into: triangular, trapezoidal, symmetrical and asymmetrical, rectangular and rounded (Fig. 31).

203. What pitches do the following threads have: M4, MB, M8, M10, M12, MI, M16, M18, M20, M22, M24, M27, MZO? with

The M4 thread has a pitch of 0.7 mm; MB - 1 mm; M8 - 1.25 mm; MU - 1.5 mm; M12 - 1.75 mm; M14 - 2 mm; M16 - 2 mm; M18 - 2.5 mm; M20 - 2.5 mm; M22 - 2.5 mm; M24 mm; M27 - 3 mm; M30 = 3.5 mm.

204. What types of carvings were used more often in the past, and which ones - now?

Previously, inch threads were more often used, now -■ metric, less often - inch.

205. What classes of thread accuracy are available?

In metric threads, there are 3 accuracy classes: precise (designation of fields for external threads Ah, for

Internal - 4Н5Н), medium (designation of tolerance fields for external threads 6gf, be and 6d, for internal threads - 5Н6Н, 6H, y6G), coarse (designation of tolerance fields for external |) threads 8ht 8g, for internal - 7Н, 7 G) .

For trapezoidal threads there are two accuracy classes: medium (designation of the tolerance field for long external threads is 7h, 7e, and 8e, internal 7H and 8H); rough (designation of the tolerance zone for long external threads 8е, 8с, 9с, internal 8Н and 9Н).

206. What diameters are distinguished in threads?

The threads are distinguished (Fig. 32) by the nominal diameter of the thread, which is most often the outer diameter of the screw surface d, the internal diameter dlf the average diameter of the screw^ and the internal diameter of the nut hole Dlt the diameter of the nut thread B, the average diameter of the nut thread Di, most often equal to rf2 Average screw diameter

_ D-~ Dx "2 o-*

207. What diameter should a hole for a metric thread have?

Example: The diameter of the M20 threaded rod should be

20 - 0.1 2.5 = 19.75 mm.

209. What coolants are used when cutting threads?

When cutting threads in parts made of carbon and alloy structural steels, use sulfofresol or a 5% solution of E-2 or ET-2 emulsion for taps; for dies, dies, thread-cutting heads - sulfofresol, Industrial 20 oil.

For stainless and hard-to-cut steels, sulfofresol, oleic acid or a liquid of the following composition is used: sulfofresol -60%, kerosene -25%, oleic acid - 15%.

For gray cast iron, kerosene or Industrial 20 oil is used for tapping.

® For aluminum and its alloys, use a 5% solution of emulsion E-2, ET-2 or a liquid of the following composition: Industrial 20 oil - 50%, kerosene - 50%.

For copper and its alloys, use a 5% solution of emulsion E-2, ET-2 or Industrial 20 oil.

Lubrication reduces friction, cools the tool, extends tool life and facilitates removal of waste.

210. How should a rod be prepared for threading?

Before cutting a thread, the rod must be cleaned of rust, and the lead-in chamfer must be removed from its end surface.

211. Name the reasons for defects when cutting threads.

The reasons for defects when cutting threads are as follows: discrepancy between the diameters of holes or rods and the thread being cut, damage to the tool, cutting threads without using lubrication, dull tools, poor fastening or poor installation of the tool, as well as inability to cut threads (Table 18).

212. What accidents can happen when cutting threads?

When cutting threads, a mechanic or a machine operator can injure the rueder with the sharp edge of a part or tool, so you should not clean hand tools of chips with your fingers; it is strictly forbidden to clean tools that are in motion with your fingers.

Type of damage I Causes of damage

Threads are torn

Partial thread

Breakage of the tap in the hole

Thread cutting without lubrication

Dull tool or improperly sharpened tool Incorrect tool position

The hole diameter is too large. Inattention of the mechanic.

Dull tap

Poorly hardened tap

The grooves of the tap and the hole are clogged with chips

Always use lubricant Do not use dull or poorly sharpened tools Check the installation of the tool before cutting threads Correctly select the diameters of the rod and hole for the threads Same

Pay attention at work

Check the tool before starting work, do not cut the thread with a blunt tool Replace the tap (remove the broken one) Clean the tap and hole from chips more often

The concept of a helix

If you take a piece of foil cut in the shape of a right triangle 2 and screw it onto cylinder 1 (Fig. 3.78), then the hypotenuse A C of this triangle forms a helix on the cylindrical surface. In this case, the circumference of the base of the cylinder must be equal to the length of leg AB of the triangle. The height of the cylinder along which the helix makes one full revolution (in our case this is the length of the CB leg) is called the pitch of the helix. The angle at which the helix rises along the surface of the cylinder (in the example under consideration, this is the angle between the leg A B and the hypotenuse A C) is called the angle of elevation of the helix.

Concept of carving

If a groove is cut on a cylindrical surface along a helical line, you will get a thread, the shape of which will be determined by the shape of the cut groove. The helical groove cut on the surface of the cylinder is called the root of the thread, and the helical protrusion formed as a result of cutting the groove during one turn of the cylinder is called the thread or thread. A cylindrical rod that has a screw surface along its entire length or some part of it is called a screw, and a hole that has a screw surface is called a nut.

Depending on the shape of the cut groove, several thread profiles are distinguished (Fig. 3.79): triangular; trapezoidal; chassis; rectangular (ribbon); trapezoidal thrust; round.

Based on the number of threads, threads are divided into single-, double-, triple- and multi-start threads. The number of starts of a particular thread can be determined by the number of thread ends exiting on the end surface of a screw part (screw or nut).

Thread elements

Each thread is characterized by certain numerical parameters - elements (Fig. 3.80), which are pitch, profile angle, profile height, outer, inner and average diameters.

Thread pitch P is the distance in millimeters between the tops of two adjacent thread turns, measured in the direction of its axis

Profile height t is the distance from the top of the thread to the base of the profile, measured in a direction perpendicular to the axis of the thread.

The base of the thread is the section of the thread profile located at the shortest distance from its axis.

Profile angle a is the angle between the straight sections of the sides of the thread profile.

Outside diameter thread d is the largest diameter measured along the tops of the thread perpendicular to its axis.

The internal diameter of a thread, dx, is the smallest distance between opposite thread roots, measured perpendicular to its axis.

The average thread diameter d2 is the diameter of a conditional circle drawn in the middle of the thread profile between the bottom of the recess (the base of the thread) and the top of the protrusion perpendicular to the thread axis.

Thread types and systems

The thread profile (see Fig. 3.79) depends on the shape of the working part of the tool used to produce the thread. According to their purpose, threads are divided into fastening and special. Fastening threads include triangular, and special threads include rectangular, trapezoidal, thrust and round. Fastening threads are cylindrical and conical, allowing for a tight connection. Special threads are used in most cases for motion conversion mechanisms; they are manufactured using special equipment and are not discussed in this textbook.

In mechanical engineering, three thread systems are accepted: metric, inch and pipe.

Metric threads (Fig. 3.81) have the profile of an equilateral triangle with an apex angle of 60°; the tops of the protrusions of the screw and nut are cut off to avoid jamming of the thread when screwing together. Metric threads are characterized by the size of the outer diameter and the pitch of the screw, expressed in millimeters. Metric threads come in coarse and fine pitch. Coarse pitch threads are designated by the letter M and a number corresponding to the diameter of the screw, for example M20. Metric threads with fine pitch are also designated by the letter M and numbers separated by a multiplication sign. The numbers respectively characterize the nominal diameter of the thread and its pitch.

Inch threads (Fig. 3.82) are used for repair work and the manufacture of spare parts for imported and old equipment. The profile of this thread is an isosceles triangle with an apex angle of 55° and flat cut ends of the screw and nut turns. The main characteristic of an inch thread is the number of threads per inch of thread length. The outer diameter of the thread (diameter bi nta) is also measured in inches. Fastening inch threads have diameters from 3/i6 to 4 inches and from 24 to 3 threads of thread per inch of its length.

Pipe thread (Fig. 3.83) has a profile similar to an inch thread and a smaller pitch. The tops of the turns are not cut flat, like inch and metric threads, but along a radius. In addition, pipe threads have no gaps between the threads of the screw and nut, which provides a higher connection density than metric and imperial threads. The main characteristic of pipe threads is the number of threads per inch of its length.

Pipe threads have diameters from 1/8 to 6 inches with the number of threads per inch from 28 to 11. The diameter of an inch thread is conventionally considered the diameter of the hole (lumen) of the pipe, and not the outer diameter. This thread is used for connecting pipes, pipeline fittings and other thin-walled parts. Indicate pipe threads in drawings indicating the diameter, for example Pipe. 3/8".

Determination of thread sizes (Fig. 3.84). When cutting threads, it becomes necessary to check their quality. To check the outer diameter of the thread, a caliper or micrometer is used, the inner diameter is checked using a caliper, the middle diameter is checked with a special thread micrometer, the thread pitch is controlled using a special thread pedometer (millimeter or inch).

produced on machines and manually using taps, dies and thread cutters.

Threads can be left or right; one, two, three and multi-pass.

The main elements of a thread: profile, pitch, outer and inner diameter.

Three thread systems are used: metric, inch and pipe.

Profile metric The thread has the form of a triangle with an apex angle of 60° with different pitch sizes - main and small ones from 1 to 5 - for fastening parts.

Profile inch The thread has an angle of 55° at the apex and is measured by the number of threads per 1”.

U pipe The thread profile also has an angle of 55° and is characterized by the number of threads per 1” (for various pipe connections).

Exist rectangular and trapezoidal thread profile (to transmit the movement of the part); persistent- (for mechanisms operating in one direction, hydraulic and mechanical presses); round - for water fittings and conical - for pipe connections operating at high pressures and temperatures.

Taps - are used for cutting threads in holes and consist of a working part and a shank.

The working part of the tap consists of a conical (intake) and calibrating parts.

The intake part does the main work of cutting threads, and the calibrating part serves to clean and calibrate the threaded connection. Typically, a set of three taps (rough, medium and finishing) is used. First, they cut rough, then medium, and the finishing thread is finally calibrated.

Dies used for cutting threads on rods (diameter 1 - 52 mm) both manually and on machines. The dies have a slot, thanks to which the thread diameter is slightly increased or decreased.

To determine d of a threaded hole, special tables are used. The diameter of the hole must be larger than the internal diameter of the thread, because When cutting a thread, the material is partially extruded. For example, for M14, d = 11.8. When cutting an external thread, the diameter of the rod must be slightly smaller than the outer diameter of the thread being cut, otherwise it will not be able to be screwed onto the rod and the end of the rod will be damaged.

There are combination taps consisting of rough tap, for pre-threading and finishing - for final thread cutting. Such a tap allows you to cut a thread with one tap, instead of a set, which saves auxiliary time for installing the tool. Exist drill taps combining drilling and threading operations, which will increase the productivity of threading operations. Dies are made from low-alloy steels (for example, 9ХС).

Scraping - this is the operation of final surface treatment by removing a very thin layer of metal with a special tool - scraper. This operation is used when it is necessary to ensure precise contact of rubbing surfaces.

To determine the part of the surface that needs to be scraped, the part is placed on a control plate covered with a thin layer of paint, and with light pressure the part is moved in different directions. Protruding areas of the surface to be scraped are covered with spots of paint and are subject to scraping. The quality of scraping is determined by the number of points of contact with the control plate (on a 25+25 mm plate the number of spots should be from 4 to 36).

The cutting tool for scraping is a scraper, and the testing tool is a plate. Scrapers of various configurations are made from high-carbon steel U10A - U12A. The cutting end of the scraper is hardened to give it high hardness.

Spanners are subdivided;

Open for hex and square nuts;

Overhead (snap-on) - nuts covering all edges, more durable and reliable;

Sockets, used when it is impossible to tighten (unscrew) the nut with a regular wrench;

Hinged, as well as rotary - used for screwing nuts in hard-to-reach places;

Adjustable torque wrenches are used to tighten nuts and bolts to the same torque.

Reversible pneumatic and electric impact wrenches are used when 2 to 20 nuts are screwed simultaneously.

Threads are widely used in mechanical engineering; they are used to connect parts together and to transmit movement. An example of the use of threads for connecting parts is the thread on the spindle of a lathe, intended for attaching a chuck; An example of the use of threads to transmit movement is the thread of a lead screw that transmits movement to the apron nut, the thread of screws in a vice, the thread of spindles in presses, etc.

The concept of a helix. The basis of any thread is the so-called helical line. Let's take a piece of paper in the shape of a right triangle ABC (Fig. 237, a), whose leg AB is equal to the circumference of a cylinder with diameter D, i.e. AB = πD, and the second leg BV is equal to the height of the helix rise in one revolution. Let's wrap the triangle onto a cylindrical surface, as shown in Fig. 237, a. The leg AB will wrap around the cylinder once, and the hypotenuse A B will wrap around the cylinder and form on its surface helix with pitch S equal to BV. The angle τ (tau) is called helix angle.

If the triangle is located to the right of the cylinder, as in Fig. 237, a, and the inclined line A B rises from left to right, then such a helix is ​​called right; with the reverse position of the triangle and the rise of the line from right to left(Fig. 237, b) we get left helix line.

Thread formation. If you bring the tip of the cutter to a cylindrical roller and then give rotation to the roller and at the same time uniform longitudinal movement of the cutter, then a helical line will first form on the surface of the roller (Fig. 238). When the tip of the cutter is deepened into the roller being processed and the cutter is repeatedly moved longitudinally, a helical groove called a thread (Fig. 239) will be obtained on the surface of the roller, with a profile corresponding to the shape of the cutting part of the cutter.

Thread profile. If the cutting part of the cutter is given a triangular shape, then on the surface of the processed cylinder during cutting you will get triangular thread(Fig. 239, a). If the cutting part of the cutter has a rectangular or trapezoidal shape, then accordingly when cutting you get rectangular or tape thread(Fig. 239, b) or trapezoidal(Fig. 239, c).

Basic thread elements. The main elements that determine the thread profile are as follows:

thread pitch S (Fig. 240) - the distance between two points of the same name (i.e. right or left) of two adjacent turns, measured parallel to the thread axis;

profile angle a - the angle between the sides of the coil, measured in the center plane;

the top of the profile E is the line connecting its sides along the top of the turn;

profile depression F - the line forming the bottom of the helical groove.

There are the following three thread diameters (Fig. 241):

outside diameter d thread - the diameter of the cylinder described near the threaded surface;

inner diameter d 1 thread - the diameter of the cylinder inscribed in the threaded surface;

the average diameter d 2 of the thread is the diameter of a cylinder coaxial with the thread, the generatrices of which are divided by the sides of the profile into equal sections.

Thread direction(right and left hand threads). If you look at the thread from the end, then on the right thread the rise of the groove is directed from left to right, and on the left, on the contrary, from right to left. The direction of the thread can also be detected by the direction of rotation of a screw when screwing it into a hole or a nut when screwing it onto a bolt: if the screwing is clockwise, then the thread is right-handed, if it is screwed counterclockwise, then the thread is left-handed. The most common right-hand thread.

2. Types of threads and their purpose

In mechanical engineering, the following types of threads are most often used: triangular- for connecting (fastening) parts together, trapezoidal And rectangular- to transmit movement.

Triangular threads are divided into metric, inch and pipe.

Metric threads. Most wide application In the USSR they received metric threads. According to GOST 9150-59, they are divided into threads with large pitches (for diameters 1-68 mm) and threads with fine pitches (for diameters 1-600 mm). Both threads differ in pitch sizes (for the same diameter) and other elements.

Metric threads have a triangular profile (Fig. 242) with a profile angle α = 60°. The tops of the profile of the bolt and nut are flat-cut, the cavity of the bolt can be flat-cut or rounded along the radius r.

The pitch of metric threads is measured in millimeters.

Inch thread (Fig. 243) has a profile angle a equal to 55°, and flat-cut peaks and valleys; There are gaps between the peaks and valleys. The outer diameter of an inch thread is indicated in inches. The pitch of an inch thread is expressed by the number of turns per length of 1".

In the USSR, inch threads are rarely used: only when repairing imported cars.

Pipe cylindrical thread (Fig. 244) has a profile in the form of a triangle with rounded tops and valleys, the angle a of the profile is 55°. The pitch of a cylindrical pipe thread is expressed by the number of turns over a length of 1". This thread is used mainly in gas and water pipes, as well as on couplings used to connect these pipes.

3. Thread measurement

Threads can be measured with a measuring ruler, thread gauge, thread gauges, special templates, etc.

A measuring ruler and thread gauge are used primarily to measure the pitch of an external thread. A measuring ruler is used to measure the length of a certain number of turns, for example ten; dividing the resulting length by the number of turns, find the size of one step. When measuring inch threads, determine the number of turns that fall on the length of one inch (25.4 mm).

Thread gauge(Fig. 245) serves to check the thread pitch. It consists of a set of steel plates, each of which is equipped with cutouts that precisely match the thread profile of a certain pitch. Each plate has numbers stamped on it indicating the thread pitch in millimeters or the number of turns per 1". When checking the thread pitch, the plate is applied to the thread being checked parallel to its axis (Fig. 245). The alignment of the thread gauge plate with the thread is checked for clearance.

One of the measuring tools for checking threads are normal thread gauges. External threads are checked normal threaded ring(Fig. 246), and the internal one - normal screw plug(Fig. 247). The right smooth end of the plug is used to check the diameter of the hole for the thread, and the left threaded end is used to check the thread itself. The correctness of the thread with normal gauges is determined by touch by the absence of wobble and the difficulty of screwing together the gauge and the part.

Checking threads using extreme gauges is much more accurate and productive.

External threads are checked limit threaded brackets.

The bracket (Fig. 248) has two pairs of rollers: the front pair is pass-through, and the rear pair is non-pass-through.

The method of measuring with a limit thread clamp is the same as when measuring smooth dimensions, i.e., the thread must pass freely through the go-through side of the gauge, and the non-go-through side of the gauge must hold back the thread.

Internal threads are checked limit screw plugs(Fig. 249). The bore end of the plug has a long, full profile thread; it must be completely screwed into the threaded hole along its entire length. The non-go end of the plug has two or three turns of a cut profile; it should not be screwed into the hole being measured.

Both smooth and threaded limit gauges are usually used in the manufacture of large quantity identical parts and in general in cases where parts must have exact dimensions with certain tolerances.

4. Cutting triangular threads with dies

External triangular thread small sizes can be cut into dies. Die(Fig. 250) is a solid or split ring with a thread on the inner surface and chip grooves 1; The grooves serve to form cutting edges 2, as well as to release chips.

Dies are made of carbon or alloy steel. Round dies are made whole(Fig. 250, a) or split(Fig. 250, b). The diameter of the split dies can be adjusted within small limits and thus somewhat restore the size of the tool after wear, which extends its service life. Split dies are used for cutting low-precision threads. Solid dies provide more accurate threads, as they have greater rigidity. The service life of solid dies is shorter.

Techniques for cutting threads with dies. To work, the die is inserted into a special die holder(Fig. 251) and secured with screws that fit into the recesses on the side surface of the die.

The cut part is fixed in the chuck; it must first be ground to the outer diameter of the bolt thread. You need to chamfer the end of the part so that the die can cut in easier. If the diameter of the part is too small, the thread is not deep enough and has an incomplete profile. If the diameter of the workpiece is too large, then during the cutting process the thread may be torn off, since the die will cut off a lot of metal; at best, the carving will be unclean.

Thread cutting with a die often begins with manually cutting several threads on a stationary workpiece using a die holder with two handles (Fig. 252, a). After this, turn on the machine and continue cutting, resting the handle of the die holder against the support (Fig. 252, b). When cutting threads with a die, holding the handle with your hands after starting the machine is not allowed. In order to give the correct direction to the die, you need to press it at the beginning of cutting with the tailstock quill, which is fed manually.

Cutting modes when cutting threads with dies. When cutting threads with dies, the cutting speed should be low, this increases the service life of the die. The following cutting speeds are recommended: for steel - 3-4 m/min; cast iron - 2.5 m/min; brass - 9-15 m/min. Sulfurized oils and boiled butter are recommended as cutting lubricants when cutting steel parts, and kerosene when cutting cast iron parts. Cooling should be plentiful.

5. Cutting triangular threads with taps

Small internal threads are cut with taps. Tap is a screw with several longitudinal grooves that form cutting edges and at the same time serve to release chips.

The design and elements of the tap are shown in Fig. 253. Its main parts are: conical intake part 1, calibrating part 2, grooves 5, smooth part 4, called the neck, square 5 for securing the tap in the driver or in the chuck.

The main work when cutting threads is performed by fence part 1, the tops of the teeth of which are cut off and have a variable profile. Following the intake part, the hole includes calibration part 2, which serves for cleaning (calibrating) the thread being cut.

On cervix The tap is always marked with the diameter of the thread: for metric threads with or without the letter M, and for inch threads - with the addition of the symbol " (inch).

Taps are made from carbon, alloy, and high-speed steel.

For manual cutting of metric or inch threads, use a kit hand taps, usually consisting of three pieces (Fig. 254), which sequentially pass through the hole to be cut. The first and second taps are used to pre-cut the thread, and the third is used to clean the thread, giving it its final dimensions and shape. The number of each tap in the set is recognized by the number of marks on the tail: No. 1 has one mark, No. 2 has two marks, and No. 3 has three marks. Sometimes, to cut small threads in through holes, a set of two taps is used, of which No. 1 is used for preliminary cutting, and No. 2 is used for final cutting.

For cutting threads in through holes with a length not exceeding the diameter of the thread, use nut taps(Fig. 255) with a long intake part, which is used to cut threads in one pass.

Preparing the threaded hole. When making threads with taps, small holes are usually tapped immediately after drilling; Large holes are pre-bored. It is very important to ensure the correct diameter of the thread hole; it should be slightly larger than the internal diameter of the thread. The material of the cut nut, under the action of the cutting force, flows somewhat into the grooves of the thread (Fig. 256). The more viscous the material of the part, the more it flows and, therefore, the larger the hole diameter should be.

The diameters of the threaded holes are selected according to the tables. In table 12 shows some hole diameters for metric threads.

Table 12

Threaded hole diameters

The length of the blind holes for threads should be greater than the length of the thread by at least the size of the tap part, i.e. by two or three threads.

Techniques for cutting threads with a tap. When cutting a thread with a tap on a lathe, the part to be cut is installed and secured in the chuck so that the axis of the part's hole coincides with the axis of rotation of the spindle. The tap is installed as shown in Fig. 257. Its intake part is inserted into the hole to be cut, and the tail part is fixed in the device. The device for securing the tap consists of a mandrel 4 with a key 3 and a sleeve 2 with a groove into which the key 3 fits. The tap is secured with two bolts in the square hole of the sleeve 1. The mandrel 5 has a conical shank inserted into the hole of the tailstock quill.

When cutting a thread, the tap is brought to the hole of the part using a handwheel that moves the quill; the tapping part of the tap is inserted into the holes being cut. To cut the first turns of the thread, you need to carefully and evenly press the tap while rotating the tailstock handwheel.

As soon as the tap cuts into the hole by 1-1.5 turns, its further movement will be carried out self-tightening due to the rotation of the part.

The device shown in Fig. 257, allows you to cut a thread to a specified length, upon reaching which thread cutting will automatically stop. When cutting threads in blind holes, before starting work with the next largest tap, it is necessary to remove chips from the hole.

Cutting modes when cutting threads with taps. The cutting speed when cutting threads with taps should be low; this extends the life of the tap and prevents chip jamming. The following cutting speeds are recommended: for steel 3-15 m/min; for cast iron, bronze and aluminum 6-22 m/min. Cooling should be plentiful. It is recommended as cutting fluids: for cutting parts made of steel - oil (sulfofresol), when cutting parts made of cast iron, bronze and aluminum - emulsion or kerosene.

6. Cutting triangular threads with cutters

The most common method of cutting triangular threads on screw-cutting lathes is cutting with thread cutters.

Cutter design. The shape of the cutting part of the thread cutter must correspond to the thread profile. The profile angle of the cutting part should be 60° for metric threads, 55° for inch and pipe threads. To avoid distortion of its profile when cutting a thread, thread cutters are usually sharpened with a rake angle γ = 0 and the tip of the cutter is set at the height of the machine center line.

There are thread cutters for cutting external thread(Fig. 258, a) and for cutting internal thread(Fig. 258, b). Both can be solid or inserted, rod, prismatic and disk, like shaped cutters. The head of a thread cutter for internal threads must be perpendicular to the axis of the cutter shank.

For finishing passes when cutting threads, spring-loaded holders are sometimes used to produce clean and smooth threads. Such a cutter, encountering a harder part of the metal on its way, is slightly pressed out and does not spoil the thread, but the latter turns out to be less accurate.

In Fig. 259 shows a spring holder 1 with a cutter. Bolt 2 is used to secure the insertion thread cutter 3 in the holder. The peculiarity of this Holder is that it can work as a spring or as a rigid one. This is achieved using screw 4; when the screw is inserted into the slot, the holder acts as rigid; when screw 4 is removed, it acts as springy. Rough cutting is carried out with a cutter fixed in a rigid holder, and finishing cutting is done with a cutter fixed in a spring holder.

Installation of thread cutter. Setting up the thread cutter requires a lot of attention. The cutter needs to be installed exactly at the height of the centers, otherwise the thread profile will be incorrect. In addition, the center line of the cutter profile must be perpendicular to the axis of the part(Fig. 260, a). This condition is mandatory when cutting both external and internal threads. If we neglect this, the thread profile will turn out to be asymmetrical (turned to the side), as shown in Fig. 260, b.

The thread cutter is installed using a template, as shown in Fig. 261 when cutting external threads and in Fig. 262 when cutting internal threads. To check, apply the template to the cylindrical (end) surface of the part in the horizontal plane and insert the cutter into the cutout of the template. The correct installation is judged by the clearance between the cutting edges of the cutter and the template cutout. If there is a large gap, it is eliminated by rearranging the cutter, after which the cutter is firmly fixed in the tool holder.

7. Threaded dies

External and internal triangular threads can also be cut using thread dies.

Thread dies Unlike conventional thread cutters, they have on the cutting part not one, but several teeth made according to the shape of the thread profile.

There are combs flat rod(Fig. 263, a); prismatic(Fig. 263, b); round with screw thread(Fig. 263, c).

The working part of the comb consists of cutting and calibrating teeth. The cutting teeth (there are usually two or three of them) are cut at an angle φ so that each subsequent tooth cuts slightly deeper than the previous one (Fig. 263, a and b). The calibrating part, which follows the cutting part, also has several teeth (two or three) and is intended for cleaning threads.

When cutting threads with combs, by distributing the load between several teeth, it is possible to increase the transverse feed and thereby reduce the number of passes compared to thread cutters. The combs last longer than threaded cutters. Prismatic combs are fixed in special holders, as shown in Fig. 263, b and install them in the tool holder exactly at the height of the centers.

Round screw combs (Fig. 263, c) are much more widely used when cutting triangular threads, both external and internal, as they are easier to manufacture. They consist of several screw turns. The working part of these combs also has several cutting teeth, cut at an angle, and several calibrating teeth.

When cutting external threads The thread direction of a round screw comb should be opposite to the direction of the thread on the part, i.e. if you need to cut a right-hand thread, then the comb should have a left-hand thread.

When cutting internal threads the direction of the thread of the round screw comb must coincide with the direction of the thread of the part, i.e., for example, when cutting a right-hand thread, the comb must have a right-hand thread.

Round threaded dies are fastened to mandrels, similar to round shaped cutters (see Fig. 224).

8. Setting up a lathe for thread cutting

To cut threads on a lathe, it is necessary that the spindle rotation speed be strictly linked to the speed of movement of the caliper, since the longitudinal feed of the cutter per revolution of the spindle must exactly correspond to the pitch of the thread being cut.

On lathes, adjustment to a given cutter feed is carried out as a result of the engagement of the corresponding gear wheels of the feed box and the feed guitar. Various combinations of traction of these wheels are carried out by corresponding handles and levers. Their rearrangement to obtain the desired feed is carried out in accordance with the table available on the machine.

As an example, we provide a table (Table 13, pp. 242-243) of the settings of a 1A62 screw-cutting lathe for cutting metric and inch threads.

As can be seen from table. 13, setting up the 1A62 machine for threading is done by changing the position of the handles 2 and 4 of the gearbox (see Fig. 36b), the coupling lever and handles A, B and C of the feedbox.

Replaceable gears a and b are installed with the working rims inward towards the tilt end of the guitar. To cut threads with metric and inch pitches, the wheels are installed inside with rims z = 42 and z = 100; for cutting modular threads - with crowns z = 32 and z = 97.

Let's look at examples of setting up a 1A62 machine for thread cutting.

Example 9. It is necessary to configure the machine to cut metric threads with a pitch of 2.5 mm.
In accordance with table. 13 set handle 2 (Fig. 36 b) to normal pitch, and handle 4 in any position.
We set handle A (see Table 13) of the feed box to the metric thread position; handle B - to position II, handle B - to position I, lever lever - to position 6.
Example 10. Set up the 1A62 machine to cut inch threads 16 threads per 1".
According to the table 13 set handle 2 of the gearbox (see Fig. 36 b) to normal pitch, set handle 4 in any position.
We set handle A (see Table 13) of the feed box to the inch thread position; handle B - to position I, handle B - to position I; the link lever is in position 3.
Example 11. It is required to configure the machine to cut strip threads with a pitch of 16 mm.
In accordance with table. 13 set handle 2 (see Fig. 36 b) to the increased pitch position, handle 4 to the orange position.
We set handle A of the feed box to the metric thread position; handle B - to position II, handle B - to position I, lever lever - to position 3.

9. Rules for counting the number of teeth of replaceable gears

In cases where the machine does not have a feed box, the machine is configured to cut threads of a given pitch by appropriately selecting replacement gears that transmit rotation to the lead screw from the spindle.

In Fig. 264 shows a diagram of the transmission of such movement. From the spindle to the lead screw with a pitch of 5, rotation is transmitted through a snaffle and interchangeable wheels z 1 z 2, z 3 and z 4 of the guitar, with the help of which the machine is adjusted to cut threads of a given pitch S p.

To properly set up the machine, you must be able to count the number of teeth on the replacement gears.

If the replacement wheels (Fig. 264) are selected so that the machine spindle and the lead screw make the same number of revolutions, then the part will have a thread of the same pitch as on the lead screw. Indeed, if the pitch of the lead screw is 6 mm, then in one revolution the screw will move the support with the cutter by 6 mm as well. Since during this time the part will make one revolution, the cutter will cut a thread, the pitch of which will also be 6 mm.

Let us assume that on the same lathe it is required to cut threads with a pitch of 3 mm, i.e., 2 times less than the pitch of the lead screw. If the part rotates twice as fast as the screw, then in one turn the screw will only have time to make half a turn. In this case, the support with the cutter will move by half a step, i.e. by 3 mm, therefore, the thread will be cut on the part with a pitch of 3 mm. If the spindle rotates three times faster than the lead screw, then the part will have a thread with a pitch of 2 mm.

Therefore, the following rule can be derived: how many times will the machine spindle rotate faster than the lead screw, how many times will the pitch of the thread being cut be less than the pitch of the lead screw?.

Let us assume that on a lathe with a lead screw pitch of 6 mm, it is required to cut threads with a pitch of 12 mm, i.e., 2 times larger than the lead screw pitch. Reasoning as before, we see that the part should rotate twice as slow as the lead screw. Indeed, if during one revolution of the part the lead screw makes two revolutions, then it will move the support with the cutter by two steps, i.e. by 12 mm, and the part will be threaded with a pitch of 12 mm.

Based on the above, we can formulate the second rule: how many times will the machine spindle rotate slower than the lead screw, how many times will the pitch of the thread being cut be greater than the pitch of the lead screw?.

Using the above reasoning, we can establish that the gear ratio of the replacement wheels is equal to the pitch of the cut thread S p divided by the pitch of the lead screw S, i.e.

This transmission ratio can be achieved using one of the methods shown in Fig. 265.

In the event that one pair of gears is sufficient to carry out the transmission, as shown in Fig. 265, a, the gear ratio for the case considered is determined as follows.

Example 12. Determine the gear ratio of the replacement wheels for cutting threads on a lathe with a pitch of 1.5 mm, if the lead screw pitch is 6 mm.
According to formula (13), the gear ratio Based on this gear ratio, we select replacement wheels and install them in such an order from the spindle to the lead screw that the ratio of the number of teeth of the drive wheel to the number of teeth of the driven wheel is exactly equal to the calculated gear ratio.

Selection of replacement wheels. For cutting threads, each screw-cutting lathe is supplied with a set of replacement wheels, most often with a number of teeth of 20, 25, 30, 35, etc. through 5 to 120 and, in addition, a wheel with 127 teeth. This set is called a heel set. The turner's task is to select a pair or two pairs of wheels from those available in the set that correspond to the calculated gear ratio.

Let us assume that on a lathe with a lead screw pitch of 6 mm, it is required to cut threads with a pitch of 2 mm. For this case, we obtain the gear ratio of the replacement wheels. Therefore, if you connect the spindle and the lead screw with any pair of wheels whose gear ratio is equal to , then the part will have a thread with a pitch of 2 mm.

In order to select the number of teeth of replacement wheels based on the gear ratio, you need to multiply the numerator and denominator of the fraction by the same arbitrary number so that the product turns out to be an integer and equal to the number of wheel teeth present in the set. For example, if the gear ratio is , then multiplying the numerator and denominator by 10, 15 or 20, respectively, we get:

The numbers 20 and 60, 30 and 90, 40 and 120 indicate the number of teeth of individual pairs of wheels, which on this machine provide threads with a pitch of 2 mm. You need to remember that the numerator is the number of teeth of the drive wheel, and the denominator is the number of teeth of the driven wheel. Thus, wheels with a number of teeth of 20, 30 and 40 are driving, and wheels with a number of teeth of 60, 90 and 120 are driven.

The first drive wheel is mounted on a snaffle shaft protruding from the headstock; The last of the driven wheels is placed at the end of the lead screw.

Example 13. On a lathe with a lead screw pitch S x = 8 mm, it is necessary to cut threads with a pitch S p = 1 mm.
Using formula (13), we determine the gear ratio: Multiplying the numerator and denominator by 15, we get: 15 tooth wheels are not included in the set. Then we multiply the numerator and denominator of the gear ratio by 20; The 20-tooth wheel is included in the set, but the 160-tooth wheel is missing. Therefore, this thread cannot be cut using one pair of replacement wheels. In such cases, it is necessary to decompose the gear ratio into two such fractions, multiplying which will give the same gear ratio. For our example it can be represented like this: Multiplying the numerator and denominator of the first fraction by 20, and the second fraction by 25, we find: or Thus, in order to cut threads with a pitch S p = 1 mm on this machine with a lead screw pitch S x = 8 mm, you can take two pairs of wheels 20 and 40 included in the machine set; 25 and 100. Wheels z 1 = 20 and z 3 = 25 should be driving, and wheels z 2 = 40 and z 4 = 100 should be driven.
The selected wheels can be installed in a different order.
1. You can swap the drive wheels, that is, install wheel z 1 = 25 in place of wheel z 1 = 20, and wheel z 1 = 20 in place of wheel z3 = 25.
2. In the same way, you can change the driven wheels z 2 = 40 and z 4 = 100.
Such rearrangements will not change the gear ratio. But the driving and driven wheels cannot be rearranged, since the gear ratio in this case will take on a completely different value.
3. It is possible to rearrange the first pair of wheels instead of the second, and the second pair instead of the first, i.e.

Checking the correct number of replacement wheels. To check the correctness of counting replacement wheels, you need to multiply the resulting gear ratio by the lead screw pitch, and the result of the multiplication should give the pitch of the thread being cut; this follows from formula (13)

If, according to formula (14), a thread pitch is obtained that does not correspond to the required one, this will show that the wheel count was made incorrectly.

Let's check the correctness of counting replacement wheels in the example on page 244, where

i.e. the wheels are selected correctly.

Checking the traction of replacement wheels

The wheels selected by calculation may not always be interlocked with each other; it may happen that one of them rests on the finger of the guitar. In order for replacement wheels to be installed on the guitar, ensuring their grip, the following conditions must be met:
The sum of the numbers of teeth of the first pair of wheels(z 1 + z 2) must be greater than the number of teeth of the second drive wheel z 3 by no less than 15, and the sum of the numbers of teeth of the second pair of wheels(z 3 + z 4) must be greater than the number of teeth of the first driven wheel z 2 also no less than 15.
Let's check the possibility of adhesion of the wheels selected in relation to our example, where

The difference between the sum of the numbers of teeth of the first pair of wheels z 1 + z 2 = 20 + 40 = 60 and the number of teeth z 3 = 25 is greater than 15 and equal to 35. The sum of the numbers of teeth of the second pair of wheels z 3 + z 4 = 25 + 100 = 125 is also much more than the number of teeth z 2 = 40 (the difference is 85). Therefore, the wheels can be coupled.

If the adhesion conditions have not been met, then you must first try to swap the driven or driven wheels. If such a rearrangement does not satisfy the adhesion conditions, it is necessary to re-do the calculation.

Example 14. Let the gear ratio of the replacement gears In this case, z 1 + z 2 = 20 + 30 = 50 is less than Z3 = 70, therefore, the adhesion condition is not met.
If you swap the numerators of the ratio, that is, write the gear ratio in this form: then the adhesion condition will be met
z 1 + z 2 = 70 + 30 = 100 will be greater than z 3 = 20 by 80; z 3 + z 4 = 20 + 35 = 55 will be greater than z 2 = 30 by 25.

10. Techniques for cutting triangular threads with cutters

After setting up the machine, they begin to cut the thread, slightly deepening the cutter. A screw mark is obtained on the surface of the part, the pitch of which is checked with a ruler, caliper or thread gauge. Before each next pass, the cutter is deepened along the limb by the required amount.

Cutting triangular threads with cutters can be done in the following ways.

First way. The cutter is installed perpendicular to the axis of the part (Fig. 267, a), using a template, as shown in Fig. 261. Before each new pass, the cutter is removed from the groove, moving the transverse part of the support towards itself. Then, using a handle located for convenience near the apron (machines 1A62, 1D62, 1K62), the friction clutch is switched to reverse the spindle. The spindle rotates in the opposite direction, and along with it, the machine lead screw rotates in the opposite direction, returning the longitudinal slide of the support to its initial position. Upon return of the longitudinal slide of the caliper, the cutter is given transverse movement (Fig. 267, b); The counting is carried out along the dial of the cross-feed screw. All these steps are repeated until the thread is cut to the full depth of the profile.

As can be seen from Fig. 267, the thread in this case is cut evenly by both cutting edges of the cutter. During rough cutting, the separated thick chips interfere with each other, so the cutter may jam and produce a rough thread surface. When finishing cutting, when small chips are removed, the surface is clean.

This method of feeding the cutter is used for cutting threads with a pitch S p less than 2 mm on both roughing and finishing passes; the cutter is fed for each pass to a depth of t=0.05 - 0.2 mm.

Second way. If the pitch of the thread being cut is more than 2 mm, the thread is cut with a special cutter (Fig. 268). It is installed in the upper part of the caliper, rotated at an angle (Fig. 268, a) equal to half the angle of the thread profile, and is fed by lateral cutting, moving the upper part of the caliper at an angle to the axis of the part. With this installation of the cutter, cutting is performed only with the left cutting edge (Fig. 268, b); the right cutting edge removes very thin chips and therefore wears out slowly.

After each pass, the cutter is removed from the groove, moving the transverse part of the caliper towards itself (the upper part of the caliper is not touched). Then the machine is reversed and the longitudinal slide of the support is returned to its initial position. Before each subsequent pass, move the transverse part of the caliper to its previous position along the dial or stop; The cutter is deepened by moving the upper part of the caliper along the limb.

To obtain a more accurate thread, the final cutting is performed using the first method.

Cutting right and left hand threads. When cutting a right-hand thread, the lead screw and spindle rotate on the turner, and the support with the cutter moves from the tailstock to the front. When cutting a left-hand thread, the lead screw must rotate in the opposite direction, that is, away from the lathe in the normal direction of spindle rotation. To change the direction of the thread being cut, turn the handle available for this purpose to the “left-hand thread” position (see Fig. 35, a - handle 26 and Fig. 40 - handle 3). In this case, the caliper will begin to move towards the tailstock. Therefore, cutting a left-hand thread should start from the left end of the part, i.e. from the headstock.

Cooling . The use of cutting fluids when cutting threads is mandatory. Abundant cooling keeps the cutter from becoming dull and helps to obtain clean thread flanks. Emulsion, rapeseed oil, sulfofresol (gives top scores); Cast iron parts can be cut dry or with kerosene.

11. Advanced Triangular Threading Techniques

When cutting threads, production innovators make extensive use of new labor methods; they use carbide thread cutters with special sharpening, significantly increase cutting modes, use not only the forward stroke of the cutter for cutting threads, but also the reverse stroke of the cutter, and use automatic switches, thereby significantly increasing labor productivity. For example, turner G. Bortkevich cuts metric threads with a pitch of 2 mm in three passes; cutting is carried out at a cutting speed of 100-270 m/min. Turner T. Biryukov cuts threads with a pitch of up to 2 mm with one cutter, and with a pitch of more than 2 mm - with two (roughing and finishing). The cutting depth for roughing passes is taken to be 0.5-0.6 mm; for the first two or three finishing passes - approximately 0.3 mm; for other passes - 0.15-0.2 mm. Thread cutting is carried out at a speed of 100-300 m/min.

Threaded cutters designed by Comrade Biryukov (Fig. 269) differ from ordinary threaded cutters; they have a bent head, which gives them some elasticity without sacrificing strength. The rake angle of the cutter is 3°, the back angle is 5°.

When cutting a thread at high speed, a slight collapse of its profile occurs: the profile angle of the thread being cut is always greater than the angle at the tip of the cutter by 30"-1°30". Therefore, Comrade Biryukov recommends in these conditions to use cutters with a profile angle equal to the profile angle of the thread being cut, reduced by 1°. For example, for cutting a metric thread with a profile angle of 60°, the profile angle of the finishing cutter is taken to be 59° (Fig. 269, b).

Comrade Biryukov also cuts threads in one pass, using simultaneously three cutters equipped with a hard alloy (Fig. 270) and representing, as it were, a comb: the rough cutter has a profile angle of 70°, semi-finishing - 65°, finishing - 59°.

To cut internal threads, the innovative turner V. Seminsky uses carbide cutters of his own design (Fig. 271).

These cutters are characterized by the fact that their head is rotated relative to the holder by 45°. This gives them increased rigidity, ensures a cleaner thread surface compared to conventional thread cutters (see Fig. 258, b) and allows them to work at high cutting speeds (up to 160 m/min).

12. Defects when cutting triangular threads with cutters and measures to prevent it

Most often, when cutting threads with cutters, defects of the following types are obtained:
1) inaccurate thread pitch;
2) inaccurate dimensions of the average thread diameter;
3) incorrect thread profile;
4) unsatisfactory cleanliness of the thread surface.

1. Inaccurate thread pitch is the result of incorrect selection of replacement gears or incorrect installation of feed box handles. This type of defect can be prevented by greater attention by the turner when setting up the machine. Marriage is irreparable.

2. Inaccurate dimensions of the average diameter are obtained due to insufficient or excessive metal removal when cutting threads. They are eliminated by more frequent measurements of thread elements with a caliper or calipers with sharp legs mounted on thread gauges, especially during the last passes, or by installing a hard stop on the depth.

3. An incorrect thread profile results from an incorrect cutter profile and inaccurate installation. This type of defect can be prevented by carefully checking the cutter profile and its installation.

4. Insufficient surface cleanliness (scratches, scuff marks on the thread) occurs when the cutter is sharpened incorrectly, the depth of cut is too high, the cutting speed is incorrectly selected, the cutter is too dull, the part or tool is not fastened tightly enough, there is no cooling or it is incorrectly selected, etc. To get rid of from this type of marriage, it is necessary to establish the reasons that caused the marriage and eliminate them.

13. Cutting rectangular and trapezoidal threads

Cutting rectangular and trapezoidal threads is considered one of the most difficult jobs in a turner's practice. Angle τ (Fig. 272), called helix angle, both rectangular and trapezoidal threads are significantly larger than triangular threads; this creates difficulties when sharpening thread cutters, their installation and when cutting threads and requires highly qualified turner.

Rectangular thread cutting. Rice. 273 gives an idea of ​​a cutter for cutting rectangular threads. The rectangular profile of its cutting part (if you look at the cutter from above) must be sharpened according to a template strictly according to the thread profile (Fig. 274). The rake angle γ of the cutter should be zero, the main relief angle α = 6 - 8°. The flanks of the cutter must be beveled so that none of them rub against the flanks of the thread flute. The steeper the thread, the greater the bevel on the side surfaces of the cutter.

There are two ways to install a thread cutter when cutting rectangular threads.

First way. The main cutting edge of the ab cutter can be installed parallel to the axis of the part (Fig. 272, left) exactly along the line of the centers of the machine. In this case, the resulting thread profile will exactly match the shape of the cutting part of the cutter, and the screw will receive the correct shape. However, the cutting angles at the left and right side cutting edges will be different. At the right edge, the cutting angle δ 1 will be obtuse, and the cutter in this place will not cut the metal, but scrape it; at the left edge, cutting conditions are more favorable, since the cutting angle δ 2 will be significantly less than 90°, but this edge will be greatly weakened and will quickly become dull.

Second way. The main cutting edge a"b" can be installed perpendicular to the side walls of the thread, as shown in Fig. 272, right. In this case, both side cutting edges will cut equally well, but the thread profile will not exactly match the cutter profile; the bottom of the groove will be concave rather than flat. For this reason, this setup is usually used only for rough groove cutting. For finishing passes, the cutter should be installed as in Fig. 272, left.

Cutting a rectangular thread is done either with one cutter sharpened to the full width of the groove, or with several cutters. Threads with pitches of up to 3-4 mm can be cut with one cutter with a measured cutting edge width. It is better to cut large (with a pitch of more than 4 mm) and precise threads first with a rough cutter with a width equal to ¾ of the width of the full thread profile, and then finally cut it with a finishing cutter across the entire width of the groove (Fig. 275, a). You can also do this: cut the thread with the same rough cutter, and then finish each side surface of the groove with a separate cut-off cutter(Fig. 275, b). This method produces cleaner and more accurate carvings.

Trapezoidal thread cutting. Trapezoidal threads have a trapezoidal profile with an apex angle of 30°. The inclination of the sides of the profile facilitates chip flow and allows trapezoidal threads to be cut cleaner and more accurately than rectangular threads.

Trapezoidal threads with a large lead angle are cut, like rectangular threads, with cutters with beveled side surfaces. The sharpening angles for these cutters and the methods for installing them remain the same as for rectangular threads (see Fig. 272); the advantages and disadvantages of this installation are the same for both types of cutters.

Depending on the size, accuracy and cleanliness, trapezoidal threads can be cut with one, two or three cutters. Smaller and less precise threads are cut with one cutter with a cutting part corresponding to the thread profile. Larger and more precise threads are cut with two or three cutters. Using a slotted cutter having a width equal to the width of the groove on the inner diameter, a cavity (groove) is first cut to a depth up to the inner diameter of the thread (Fig. 276, a). After this, install a trapezoidal cutter with an edge slightly smaller than the profile width of the thread being cut, and first cut the right side (Fig. 276, b) and then the left side of the cavity (Fig. 276, c). The final finishing of the profile is carried out with a normal trapezoidal thread cutter (Fig. 276, d), that is, a cutter whose cutting part profile corresponds to the thread profile. This method requires a lot of time.

Turner N. Chikirev achieved a significant increase in labor productivity when cutting trapezoidal and triangular threads by introducing high-speed cutting. To cut trapezoidal threads, they use cutters with T15K6 hard alloy plates. Cutting is carried out with two specially sharpened cutters - roughing and finishing (Fig. 277). The rough cutter (a) has a profile angle of 50°, the finishing cutter (b) has a thread profile. The rough cutter not only cuts the groove, but also expands it, while the finishing cutter gives the groove the desired profile.

Thread cutting is carried out in 6-7 passes with an insertion depth of 0.6-0.7 mm, with the last pass being a cleaning pass. Cutting speeds - from 155 to 450 m/min when processing steel with cutters equipped with T15K6 hard alloy.

To speed up machining when cutting threads on long shafts, innovators sometimes use a reverse idle slide for the cutting job. To do this, an additional support with a tool holder is installed on the rear part of the transverse slide. The cutter in the tool holder is installed with the front surface down.

14. Basic information about thread cutting with rotary cutters

Recently, a new high-performance method of cutting external and internal threads - rotating cutters - has become widely used. The essence of this method is as follows. On the carriage of a screw-cutting lathe, instead of a support with a tool holder, a special device is installed (Fig. 278), consisting of a rapidly rotating spindle 5 and a cutting head 4, in which a threaded cutter 6 equipped with a hard alloy plate is fixed. The cutting head receives rotation from an electric motor 1 with a power of 1.5 - 3.5 kW, installed on the carriage, through a belt drive 3 and a stepped pulley 2.

The head rotates at a speed of 1000-3000 rpm.

Part 7, on which the thread is cut, is fixed in chuck 8, and if it is longer, it is installed in the centers of the machine. The part receives a relatively slow rotation (3-30 rpm), i.e., for one revolution of the part there are approximately 100 to 300 revolutions of the cutting head. The cutter is set to the full depth of the thread, and the head is rotated in the direction opposite to the direction of rotation of the part. At the same time, the head, together with the caliper, receives a longitudinal feed movement; For one revolution of the part, it moves an amount equal to the thread pitch.

The diagram for cutting external threads with a rotating cutting head is shown in Fig. 279. As can be seen from the diagram, the axis of the cutting head is shifted relative to the axis of the part by a certain amount b. Thanks to this, during one revolution of the part, the cutter does not come into contact with it along the entire circumference, but only on a small part of it, cutting off thin short chips. Since the cutter makes from 100 to 300 revolutions per revolution of the part, instead of one continuous chip equal to the circumference of the part, it cuts off several hundred short, thin chips. These small chips fly away from the cutter in a whirlwind. This thread cutting method is sometimes called the whirlwind thread cutting method.

In Fig. 280 shows a diagram of vortex cutting of internal threads.

The advantages of this cutting method compared to the conventional one are: high speeds cutting and productivity, due to which machine time is reduced by 5-7 times, high precision of cut threads, cleanliness of the thread surface, operation without cooling.

Control questions 1. How is a helix formed when cutting threads on a lathe?
2. List the main thread elements.
3. What is the thread pitch? Thread profile?
4. What is the difference between metric thread and inch thread?
5. What types of threads do you know and what is the difference between them?
6. How to distinguish a right-handed thread from a left-handed one?
7. What tools can be used to cut threads?
8. How does the tap work?
9. List the main parts of a tap.
10. How are threads cut with taps?
11. How is the die constructed?
12. How is a thread cut with a die?
13. How to install a thread cutter when cutting external and internal threads?
14. How is a thread cut using a comb?
15. How is a thread cutting machine set up?
16. What is the gear ratio called?
17. What formula is used to determine the gear ratio of replaceable gears?
18. How to select replacement gears if the gear ratio is known?
19. State the rule for adhesion of replacement wheels on a lathe guitar.
20. When cutting a right-hand thread, the lead screw must rotate toward the turner. When installing the replacement wheels, the lead screw began to rotate from the turner. How to fix it?
21. What methods exist for cutting a triangular thread with a cutter?
22. What is the difference between cutting a right-hand thread and cutting a left-hand thread?
23. List the types of defects when cutting threads. What measures should be taken to prevent each type of marriage?
24. What tools are used to measure thread elements?
25. Tell us about the techniques for cutting rectangular threads.
26. Tell us about the techniques for cutting trapezoidal threads.
27. What is the principle of thread cutting with rotating cutters (whirlwind thread cutting)?

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