When slicing external thread It is important to choose the diameter of the rod on which the cutting will be done. If selected incorrectly, here, as in the case of internal threads, defects may occur.
The procedure for cutting external threads is as follows:
· select a workpiece required diameter, fix it in a vice and at the end of the workpiece intended for cutting threads, remove a chamfer 2...3 mm wide;
· we fix the die (round or sliding) in the die-holder collar with persistent screws so that the marking on the die is on outside;
lubricate the end of the rod (workpiece) machine oil and place a die on it strictly at an angle of 90º (the marking on the die should be at the bottom);
· pressing the die firmly against the workpiece, we begin to rotate the die holder handle clockwise until the thread is cut on desired length. We perform rotational movements in the following order:
one or two turns clockwise, ½ turn counterclockwise;
· after cutting the thread to the required distance, remove the die from the workpiece using reverse rotational movements.
When cutting threads on pipes intended for laying pipelines, the order of rotational movements of the die holder has one feature. At the beginning of the thread, as usual: one or two turns forward (clockwise) and ½ turn back (counterclockwise), and when cutting the last few threads, the reverse rotation should not be performed. The thread cut in this way has a so-called run-out, that is, the last threads of the thread are cut to a shallower depth, which contributes to better locking of the pipeline.
To cut a thread to a specific, fixed length, you can proceed in two ways. Or periodically take measurements of the cut threads measuring instruments, or use a die holder with a guide flange and bushing: put the die holder on the workpiece until the die stops, unscrew the bushing to the required thread length and secure it; during rotational movements of the die holder, the flange will be screwed onto the bushing, dragging the die along with it.
If it is necessary to cut particularly precise external threads on a cylindrical workpiece with a diameter of 4 to 42 mm and in increments of 0.7 to 2 mm, then thread rolling dies can be used instead of conventional dies.
In addition to the fact that such dies produce cleaner threads, they are also more durable (metal fibers are not cut off during such an operation, but undergo plastic deformation and are, as it were, compressed).
Quality of cut external threads We check by external inspection to detect broken threads or burrs. For accuracy checks We use a control nut to tighten the threads: it should be screwed on without effort, but should not have any play (swing).
Pipe clamp Thread cutting is carried out in the following sequence:
· the clamp is placed on the preparatory end of the pipe;
· then the guide dies are pressed against the pipe by turning the corresponding faceplate, fixed with a clamping bolt;
External thread cutting
TO category:
Threading
External thread cutting
External threads are cut into dies manually and on machines.
Depending on the design, dies are divided into round, rolling, sliding (prismatic).
Round dies (lerks) are made whole and split.
A solid die is a hardened steel nut in which through threads are cut through longitudinal holes, forming cutting edges and serving for the release of chips. On both sides of the die there are fence parts 1/2 - 2 threads long. These dies are used for cutting threads with a diameter of up to 52 mm in one pass.
The diameters of solid round dies are provided by the standard for basic metric threads - from 1 to 76 mm, for inch threads - from 1/4 to 2”, for pipe threads - from 1/8 to 1 72”.
When cutting threads, round dies are manually secured in a special driver.
Split dies, unlike solid ones, have a slot (0.5 -1.5 mm) that allows you to adjust the thread diameter within 0.1-0.25 mm. Due to the reduced rigidity, the threads cut by these dies have an insufficiently accurate profile.
Thread rolling dies are used for rolling precise thread profiles. Thread rolling dies have a body on which threaded rolling rollers are installed. The rollers can be adjusted to the size of the thread being cut. The dies are rotated by two handles screwed into the body.
Using thread rolling dies, threads with a diameter of 4 to 33 mm and a pitch of 0.7 to 2 mm of 6-8 grades are cut. Knurling is performed on machines and also manually. The thread is stronger because the metal fibers in the screws are not cut. In addition, due to the pressure of the dies, the fibers are strengthened. Since the thread is only extruded, the surface is cleaner. Thread rolling is done in the same way as cutting with clamps.
In Fig. Figure 2, b shows a small-sized thread-rolling die of the NPN type, used for rolling Mb and M12 threads on drilling and lathes.
The die shown in Fig. 2, c, is designed for rolling threads on thin-walled pipes on drilling and turning machines, as well as manually.
Sliding (prismatic) dies, unlike round ones, consist of two halves, called half-dies. Each of them indicates the size of the external thread and the number or for correct fastening in the device (clamp). On the outside of the half-dies there are angular grooves (grooves) with which they are installed into the protrusions of the die.
To evenly distribute the pressure of the screw on the half-dies, in order to avoid distortion, a cracker is placed between the half-dies and the screw.
Sliding (prismatic) dies are made in sets of 4-5 pairs each; each pair is inserted into the die as needed. Sliding dies are manufactured for metric threads with a diameter from MB to M52 mm, for inch threads - from 1/4 to 2” and for pipe thread- from ‘/8 to 1 3/4’. The sliding die is fixed in a clamp (Fig. 271, b), which consists of an oblique NPN type, c - for rolling a frame with two handles and a clamping screw on thin-walled pipes. The half-dies are inserted into the protrusions of the frame, a cracker is inserted and secured with a screw. Cluppies in which prismatic dies are installed are manufactured in six sizes - from No. 1 to No. 6. The work of the clamp is shown in Fig. 3, c.
Rice. 1. Solid (a), split (b) dies: 1 - die, 2 - thread, 3 - intake part
Rice. 2. Thread rolling dies: a - small-sized type MI1H, b - thread rolling
Rice. 3. Sliding prismatic dies: a - half dies, b - die, c - thread cutting
Rice. 4. Thread cutting with a die
External thread cutting. When cutting a thread with a die, you must keep in mind that during the formation of the thread profile, the metal of the product, especially steel, copper, etc., “stretches”, and the diameter of the rod increases. As a result, the pressure on the surface of the die increases, which leads to its heating and adhesion of metal particles, so the thread turns out torn.
When choosing the diameter of a rod for external threads, you should be guided by the same considerations as when choosing holes for internal threads. Good quality threads can be obtained if the diameter of the rod is 0.3 - 0.4 mm less than the outer diameter of the thread being cut. If the diameter of the rod is significantly smaller than required, the thread will be incomplete; if the diameter of the rod is larger, then the die either cannot be screwed onto the rod and the end of the rod will be damaged, or during cutting the teeth of the die may break due to overload.
When cutting a thread with a die manually, the rod is secured in a vice so that its end protruding above the level of the jaws is 20 - 25 mm longer than the length of the part being cut. To ensure penetration, a chamfer is removed at the upper end of the rod.
Then a die attached to the clamp is placed on the rod and the clamp is rotated with slight pressure so that the die cuts into approximately one or two threads. After this, the cut part of the rod is lubricated with oil and the die is rotated with uniform pressure on both handles as when cutting with a tap, i.e. one or two turns to the right and half a turn to the left.
To prevent defects and breakage of the die teeth, it is necessary to ensure that the die is perpendicular to the rod: the die must cut into the rod without distortion.
The cut internal thread is checked with thread plug gauges, and the external thread is checked with thread micrometers or thread ring gauges and thread templates.
Thread cutting with clamps is carried out in the following order. Place the dies in the die and move them apart to a size slightly larger than the diameter of the workpiece being cut, clamp the workpiece in a vice in a vertical position and file a chamfer at the end; put the die on the workpiece rod and move the dies tightly with a screw.
The die with dies lubricated with mixed or sulfurized oil is turned 1 -1 V2 turns clockwise, then V4 - X2 turns back. Having cut the thread, the die is moved by rotating it in reverse side for descending to the end of the rod; then tighten the die with a screw and pass the thread a second time.
Checking the thread with a gauge or nut (as a last resort), repeat the passes until the thread is obtained the right size. At the end of the work, the dies are removed from the die, cleaned of chips, thoroughly wiped and lubricated with oil.
High-performance thread cutting methods. Many machine parts are connected using threaded connections (tractors, cars, metal-cutting and other machine tools), which is a labor-intensive process. Hardened self-extrusion screws are used to connect sheet parts through punched holes.
The Volzhsky Automobile Plant widely uses hardened self-tapping screws for cast iron and steel parts. When the screws rotate with feed, they extrude threaded grooves.
The same plant uses self-locking threaded connections: a hexagonal head with recesses at the lower end and holes and radial grooves at the upper end; Serrated shoulder bolts. All this significantly reduces the labor intensity of assembly work.
To prevent the bolts from unscrewing, adhesives (anaerobic resins) of the TEN-3 type are used, which are recommended for locking joints operating under vibration load conditions.
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External thread cutting
Thread represents helical groove formed on rotating parts. Widely used for connecting parts together (fastening) and for transmitting motion (as, for example, in the lead screw of a lathe or a vice).
Used in threaded connections bolts, hairpins And screws. Bolt – a cylindrical rod with a head at one end and a thread at the other (see figure on the right A). Hairpin - a cylindrical rod with threads at both ends. One end of the stud is screwed into one of the parts to be joined, and the part to be fastened is installed on the other end and a nut is screwed on ( b). Screw - a cylindrical rod with a thread for screwing into one of the parts to be connected and a head of various shapes ( V).
Basic thread elements
: helix angle A,
thread pitch R, profile angle at, outdoor and inner diameter s(picture on the left). Depending on the purpose threaded connection apply different types threads
By direction of turns carving happens right And left(picture on the right). Most often, right-hand threads are cut.
To cut external fastening threads, use a special tool - dies. They are round(picture left A), thread rolling(b) And sliding(V).
Round die (Fig. on the right) is made in the form of a nut made of hardened steel. The thread of the die is crossed by through longitudinal holes. The resulting wedge-shaped cutting edges and grooves ensure cutting of the workpiece and simultaneous release of chips. In order for the end of the rod (workpiece) to fit better into the die from the end sides, its thread has a lower profile height. This is the so-called fence part. Round dies in accordance with the standard are provided for cutting metric threads with a diameter from 1 to 76 mm. They are placed in nests die holder and fix it there with studs (or bolts) with a slot for a screwdriver.
Die 4 (Fig. left) with special cutouts 6 attached to die holder 5 or in collar three or four screws, depending on its size and operating conditions. One or two screws 7 serve to secure screws 1 And 3 - to secure and compress the die when adjusting its size after cutting the jumper. The die is expanded using screw 2 .
In the building thread rolling die (rice. b above) installed rolling adjustable threaded casters. The metal of the workpiece is not cut, but extruded. Due to this, the surface of the thread is cleaner, and the thread itself is of higher quality and more accurate.
Sliding prismatic dies
(rice. V above) consist of two sliding and retractable half-plates.
Of particular interest is the knob for installing and fastening dies (Fig. on the right) with an additional guide ring 16
, which helps maintain direction on cylindrical workpieces 12
(rods, mold pushers and screws, die pullers). The additional device can be used in conventional gates.
In the inner part of the clip 1
The collar has a processed square window with inserted prismatic dies. There is a screw installed on the side of the holder 15
, pressing the dies 9
during operation, and from the sides of the clip into the body 11
two handles screwed in 13
for hand gripping. There is a washer installed at the bottom of the cage 14
, secured with screws 8
, and two guide pins 10
, along which the ring moves 16
.
In order to cut a thread with a die on a rod, you must first know outside diameter threads d and her step R(see picture on the left). These data are indicated on the plate. Then, using the table (see table below), determine the diameter of the rod for this thread and select the workpiece.
| Thread diameter | Step(R ) | Rod diameter | |
| Least | Largest | ||
| M 5 | 0,75 | 4,8 | 4,8 |
| M 6 | 1 | 5,8 | 5,8 |
| M 8 | 1,25 | 7,8 | 7,9 |
| M 10 | 1,5 | 9,75 | 9,85 |
| M 12 | 1,75 | 11,76 | 11,88 |
In this case, it is necessary to take into account that when cutting threads, metal, especially copper, mild steel, “stretches.” As a result, the diameter of the rod increases slightly and the pressure on the threaded surface of the die increases. It heats up, chips stick to the cutting edges, and the thread becomes “ragged.” All this reduces its quality. That's why the diameter of the rod should be 0.1...0.3 mm less than the outer diameter of the thread, depending on the size of the thread. If the diameter of the rod is 0.4...0.5 mm smaller than the outer diameter of the thread, then the thread profile is incomplete.
The selected workpiece must be straightened, marked, cut according to the markings and, securing it in a vice, chamfered with a file (Fig. right A) so that the intake part of the die captures the metal more easily. You should check the quality of the die by external inspection and by screwing it onto a bolt or stud with an intact thread. It is also necessary to carefully check the quality of fastening of the die in the die holder in order to exclude possible distortion and slippage in the socket.
Before cutting the thread, its length is marked on the rod, the rod is secured in a vice so that the end protruding above the upper plane of the jaws is 20...25 mm larger than the part being cut. The rod is placed on the square at an angle of 90° to the upper planes of the jaws (Fig. b). The die, fixed in the die holder, is placed on the upper end of the rod and, with slight pressure, preventing the die from skewing, rotate it (Fig. V). After cutting 1-2 threads, once again check the coincidence of the axes of rotation of the die and the rod.
After that lubricate the threaded part of the rod with oil, cutting the die and rotating the die, pressing evenly on both handles of the die holder (Fig. G). The rotation should be reciprocating: one or two turns to the right and half a turn to the left. In this case, the chips break and exit through the longitudinal hole. This makes thread cutting easier and improves thread quality. 
The quality of cut threads is checked under production conditions thread micrometers, thread gauges-rings and screw plugs(see picture on the left). IN school conditions It is allowed to check the threads with nuts.
After finishing work, the die is removed from the die holder, thoroughly cleaned from chips with a brush, wiped with a rag and lubricated with oil.
Thread cutting with a die can also be performed on lathe.
When cutting threads, the die should be securely secured in the die holder.
When working, be careful not to get your hand between the die holder handle and the support.
Use a brush or oil can for lubrication.
Do not blow the chips off the die, but use a broom brush.
Do not allow oil to get on clothes or hands.
Enterprises use hardened screws, which are screwed through punched holes in two or more connected parts made of sheet metal. Screws, cutting threads in holes, connect these parts. This method of threaded connection is economical and speeds up the assembly process. Many enterprises now use hardened self-extruding screws for steel and cast iron parts, the hardness of which is less than the hardness of the screws.
Threads on bolts and studs of small diameter are made on automatic lathes simultaneously with the manufacture of the bolts themselves. Screws and bolts also stamped on the presses.
Widely used in mass production external thread rolling. After passing between the rollers, a thread is formed on the rod. Some threading machines use carbide inserts instead of rollers.
Below we describe the basic terms and concepts that are necessary to master the material.
Main thread elements:
Outer thread diameter- this is the diameter of an imaginary cylinder, the surface of which coincides with the tops of the external thread and the valleys of the internal thread.
Internal thread diameter- the diameter of the cylinder, the surface of which coincides with the crests of the internal thread and the valleys of the external thread.
Average thread diameter- the diameter of an imaginary cylinder coaxial with the thread, the generatrix of which intersects the thread profile at the point where the width of the groove is equal to half the thread pitch.
Profile angle- the angle between the sides of the profile, measured in the axial section.
Top of profile- section of the profile connecting the sides of the protrusion.
Profile cavity- section of the profile connecting the sides of the groove.
Thread pitch is the distance between adjacent profile sides of the same name in a direction parallel to the thread axis.
Thread angle- the angle formed by the tangent to the helical line to a point lying on the average diameter of the thread, and a plane perpendicular to the axis of the thread.
Profile angle- the angle between the sides of the thread, measured in a plane passing through the axis of the thread.
Thread system
The following threads are used in industry:
Metric thread- has a triangular profile and serves mainly to connect parts together.
Metric threads are divided into two groups: metric thread with coarse pitch And metric fine pitch thread for diameters 0.25-600 mm.
Pipe tapered thread- has the same purpose as the cylindrical one. The required connection density is achieved by deforming the turns of the conical pipe thread.
Tapered inch thread with a profile angle of 60 degrees. Tapered inch threads are used to obtain tight connections.
Inch thread- used for fastening connections of machine parts with bolts, screws and studs.
Trapezoidal threads- used mainly for lead screws of machine tools and other power transmissions.
Trapezoidal threads are divided into large, normal and small.
Thrust threads- large, normal and small - used mainly for running and cargo (with heavy load) screws with one-sided effective load. In rare cases they are used as fasteners.
Rectangular thread- used for cargo and lead screws. Threads are difficult to manufacture and have disadvantages that limit their use.
Cylindrical pipe thread- cylindrical pipe threads are used in connections of hollow thin-walled parts, when the connection must be especially tight.
Modular thread- used for worms.
Helix diagram: A- development of a helix line; b- cylindrical triangular thread; V- cylindrical square thread; G- cylindrical rectangular thread; d- cylindrical
trapezoidal thread; e- cylindrical round thread; and- single-start thread; h- double thread; and - three-start thread.
In order to find out the thread pitch, special gauges are used (see figure on the right).
What are the threads used for cutting?
The main methods for creating threads are as follows: 1 - cutting with thread cutters or thread dies; 2 - cutting with dies, threading heads and taps; 3 - rolling using flat or round rolling dies; 4 - milling using special thread cutters; 5 - grinding with abrasive wheels.
Thread cutting with cutters. Using thread cutters and combs on screw cutting lathes cut both external and internal threads (internal threads, starting with a diameter of 12 mm and above).
The method of cutting threads with cutters is characterized by relatively low productivity, so at present it is used mainly in small-scale and individual production, as well as in the creation of precision screws, gauges, lead screws, etc. The advantage of this method is the simplicity of the cutting tool and relatively high accuracy the resulting thread. Schematically, it is as follows (Fig. 32): with simultaneous rotational movement of the part on which the thread is being cut and the translational movement of the cutter (on a lathe - II), the latter removes (cuts out) part of the surface of the part in the form of a helix (I).
Rice. 32
Thread cutting with dies and taps. In Fig. 33 shows the dies, which in their own way design features They are divided into round ones - I and II (chairs) and sliding ones - III (cloud ones).
Round dies, used in installation, procurement and other work, are designed for cutting external threads with a diameter of up to 52 mm in one pass. For larger threads, dies of a special design are used, which actually serve only to clean the thread after preliminary cutting it with other tools.
Sliding dies consist of two halves that are inserted into the die and gradually move closer together during the cutting process.
Rice. 33
When cutting threads on metal cutting machines(II) the die is installed and secured in a special cartridge or device (Fig. 34). The part is fed into the calibrating part of the rotating die. Internal mounting thread in the vast majority of cases they are cut with taps.
The tap (Fig. 35) is a threaded steel rod divided by longitudinal straight or helical grooves that form cutting edges. These same grooves serve to release chips. According to the method of application, taps are divided into manual and machine.
Rice. 35
The sequence for obtaining threads in blind holes is as follows (Fig. 36): first, drill a socket into which a pin or screw will later be screwed. The drill diameter must be selected from the table. values recommended by GOST 9150-81 standard. The thread is cut with a set of two or three taps (small, medium and normal, fine) depending on the size of the thread. It is impossible to cut a thread with one tap (normal) in one go. This leads to breakage of the tap.
For metric threads with coarse pitch and inch thread the set consists of three taps, for metric threads with fine pitch and pipe threads - two.
Thread rolling. The main industrial method of thread production at present is rolling on special thread rolling machines having a three-roller head housing 1, a roller holder 2 and a rolling roller 3 (Fig. 37). Part 4 is clamped in a caliper vice. In this case, high productivity ensures high quality of the product (shape, size and surface roughness).
The thread rolling process involves creating a thread on the surface of a part without removing chips due to plastic deformation of the surface of the workpiece. Schematically it looks like this. The part is rolled between two flat dies (Fig. 38. I) or cylindrical rollers (Fig. 38. II, III) having a threaded profile, and a thread of the same profile is extruded onto the rod. Largest diameter rolled thread 25 mm, smallest 1 mm; length of rolled thread 60...80 mm.
Rice. 36
Rice. 37
Thread milling. Milling of external and internal threads is carried out on special thread milling machines. In this case, a rotating comb cutter, when fed radially, cuts into the body of the part and mills threads on its surface. Periodically, an axial movement of the part or cutter occurs from a special copier by an amount equal to the thread pitch during one revolution of the part (Fig. 39).
Grinding precision threads. Grinding as a method of creating threads is used mainly to obtain precise threads on relatively short threaded parts, for example, threaded plugs - gauges, threaded rollers, etc.
Rice. 38
Rice. 39
Rice. 40
The essence of the process is that the grinding wheel, located to the part at an angle of the lifting thread, with fast rotation and simultaneous slow rotation of the part with feed along the axis by the value of the thread pitch in one revolution, cuts out (grinds) part of the surface of the part. Depending on the design of the machine and a number of other factors, the thread is ground in two to four or more passes (Fig. 40).
Internal threads are cut with taps, external threads are cut with dies or runs.
Tap - cutting tool, which is a hardened screw on which several longitudinal straight or helical grooves are cut, forming cutting edges. The tap has a working part and a shank ending in a square.
The working part of the tap consists of a sampling and calibrating parts. The intake - the front conical part does the main work. Calibrating – calibrates the thread.
Thread cutting. Drilled hole must be countersinked or machined. When cutting a thread, the material is partially extruded, so the diameter of the drill must be slightly larger than the internal diameter of the thread. Changing the size of holes when cutting threads in hard and brittle less metals than soft and viscous ones. If the drill exactly matches the diameter of the hole, then the material squeezed out during cutting will put pressure on the teeth of the tap, causing it to become very hot and metal particles sticking to them. The thread will end up with torn threads, and the tap may break.
In order to facilitate the work, the crank with the tap is rotated one to two turns to the right and half a turn to the left. The shavings break. When cutting deep threads in soft and tough metals, the tap must be periodically unscrewed and the grooves cleared of chips.
Cutting should be done with a full set of taps, first with roughing taps, then with medium and finishing taps. They are indicated on the shank by a circular mark (groove), rough - one, medium - two and finishing three.; The type of thread and its size are also indicated there. By appearance the rough one has a large intake part (cone) and a cut-off thread on the calibrating one. The finishing has a slight taper and full profile threads. To get a clean thread and not damage the tap, you need to use cutting fluids.
Collars used to rotate taps manually. There are non-adjustable ones - having one or three holes, and adjustable ones with movable crackers.
External thread cutting.
Sliced with dies– a hardened nut with chip grooves forming cutting edges.
The working part of the die consists of an intake and calibrating parts. The intake part is located on both sides of the die, the calibrating part usually contains 3-5 turns.
Collars and clamps. Threading with hand taps is carried out using cranks that fit onto the square ends of the shanks. The dies are inserted into gates or dies. The driver is a frame with two crackers: movable and fixed, forming a square hole.
The clamp consists of a body with handles. Before cutting the thread, the end of the pipe is ground to the required diameter, and a chamfer is removed at the very end. Under the influence of the cutting force, the metal of the part begins to flow, and the workpiece increases in diameter. As the diameter increases, the pressure on the die teeth increases, they heat up more and metal particles stick to them, which leads to thread failure or tooth breakage. To prevent these phenomena, the diameter is made 0.2-0.4 mm smaller than the outer diameter of the thread. At the beginning of cutting, it is necessary to apply pressure and ensure that the die cuts in without distortion. Then oil the rod and cut it like a tap. The die can be cut in several passes by pressing the die with a screw.
