Threaded connections are simple, reliable, make it possible to adjust the tightening, as well as disassemble and assemble parts and mechanisms. They are widely used in various mechanisms, devices, devices.
The thread is external (screw) and internal (nut). Distinguish between cylindrical triangular (sawtooth), conical triangular, rectangular, trapezoidal, thrust, and round threads. The most widely used is cylindrical triangular or, as it is also called, the fastening thread figure No. 1.
Figure №1 - Elements of the thread on the bolt 1 - depth;
2 - top; 3 - step;
4 - depression;
5 - outside diameter;
6- inner diameter.
Internal threading:
First of all, you need to choose the right drill bit for drilling the hole. You should know that if you drill a hole for the thread with a diameter that exactly matches the inner diameter of the thread, then the metal squeezed out during cutting will press on the teeth of the tap, which can cause the thread to have torn threads, and the tap may break. When drilling a hole, too large diameter the depth of the thread is incomplete and the connection is weak.
When drilling a blind hole for a thread, its depth must be slightly larger than the cut part, otherwise the thread will turn out to be incomplete in length.
Threading is carried out in the following sequence: mark the place of drilling with a punch; fix the part in a vice; drill a hole; insert a tap into the hole (Figure 2) strictly vertically (in a square); put a knob on the tap, press it with the left hand to the tap, and turn it to the right with the right hand until the tap cuts into the metal for several threads and takes a stable position; take the knob by the handles with both hands and rotate with the interception of the hands every 1-2 turns. Threading is greatly facilitated if the tap makes 1-2 working turns to the right and 1-2 turns to the left; after finishing cutting, the tap is twisted out of the hole, then once again driven along the resulting thread.
Figure №2 - Tapping the internal thread: a - installation of the tap into the hole;
b - threading.
Rules for working with taps:
When threading in deep holes, in soft and viscous metals (copper, aluminum, bronze, etc.), the tap must be periodically unscrewed from the hole and the grooves must be cleaned of chips; you need to cut the thread with a full set of taps - rough, medium and fine. The middle and finishing taps are inserted into the hole without a wrench, and only after the tap goes correctly along the thread, a wrench is put on the head and the threading continues;
in the process of cutting, it is necessary to carefully monitor with the help of a square so that there is no misalignment of the tap; the threading area should be lubricated with oil.
External threading:
At home, it is done manually with dies.
The diameter of the rod for an external thread should be 0.3-0.4 mm less than the outer diameter of the thread to be cut. Deviations from this rule are not allowed.
Cutting an external thread with a round die is performed in the following order:
at the upper end of the rod, a chamfer is removed, which ensures the plunging of the die into the metal;
The rod is clamped in a vice vertically so that its protruding end is 20-25 mm more than the length of the cut part (Figure No. 3); a die fixed in the knob is placed on the rod and rotated with slight pressure so that the die cuts about 1-2 threads without skewing. After that, the rod is lubricated with oil and smoothly rotate the knob 1-2 turns to the right and 1/2 turn to the left.
Thread cutting with sliding prismatic dies (Figure No. 3) is performed as follows: a chamfer is cut at the end of the rod; dies are installed in the die; clamp the rod in a vice; put on the stems on the rod and tightly move the nuts with a clamping screw; grease the dies and the rod with oil; the klupp is turned 1 - 1.5 turns clockwise, then 1-4, 1-2 turns back and so on until the end of the thread; having cut the thread, screw the screw to the end of the rod, tighten the dies with a screw and pass the thread again; check the thread with a nut of the appropriate diameter; at the end of the work, the dies are removed from the die, cleaned of shavings, wiped and lubricated with oil; wipe the klupp.
Tapping internal threads begins with the selection of the desired tool. After that, the first step is to drill a hole. In fact, this stage is the most important, since if you make a mistake with the selection of the diameter, then either the bolt will dangle, or the tap will break from overload when threading. It is best to determine the diameter of the holes from the tables, but you can also make a rough estimate: subtracting its pitch from the diameter of the thread, you can get an approximate value of the required hole diameter.
For example, if the outer diameter of the thread is 18 mm, and the pitch is 1 mm, then you need to drill a hole of 17 mm. Drilling must be strictly perpendicular to the surface of the part (due to deviations, rejects are possible when cutting). It is advisable to make a small chamfer at the drilled hole. For blind holes, the depth must be greater than the length of the cut part so that the tool goes beyond the required thread length when cutting. If this margin is not provided, then the thread will be incomplete.
Detail with drilled hole fixed in a vice. The tap is fixed in the knob (if not, use an adjustable wrench) or in the chuck of the machine. The quality of the thread, cutting speed and tool life are greatly influenced by the correct selection of cutting fluid (coolant). In order not to spoil the tool, and to get the thread clean and with the correct profile, it is necessary to use the following coolant:
diluted emulsion (one part of the emulsion mixed with 160 parts of water);
for parts made of brass and steel, linseed oil can be used;
for aluminum products- kerosene;
for parts made of red copper - you can use turpentine;
in cast iron and bronze products, cutting should be carried out dry.
Mineral and machine oils must not be used - they contribute to a significant increase in the resistance that the tool overcomes during operation, have a negative effect on the roughness of the thread and lead to rapid wear of the tap.
1.2. Tapping rules for internal threading
For manual threading, the tool is inserted vertically into the hole (without skewing). The knob is rotated in the desired direction (for right-hand thread clockwise) not all the time, but periodically make 1-2 turns per reverse side.
With this rotational-return movement of the tap, the cut chips break, become short (crushed) and are easier to remove from the working area, and the process of forming the thread is greatly facilitated. At the end of cutting, the tool is turned out by rotating the knob in the opposite direction, then it is driven through the finished thread or until it stops for blind holes. You must also adhere to the following rules:
When forming threads in viscous and soft metals (aluminum, copper, babbits, etc.), as well as in deep holes, the tool should be periodically unscrewed from the hole to clean the grooves from chips.
When using a tap set, all tools in the set must be used. Cutting immediately with a fine or medium tap, and then with a finishing one without a roughing pass does not speed up, but only slows down and complicates the cutting process. In addition, the thread is of poor quality, and the tool may break. The finishing and middle taps are screwed into the hole by hand (without a wrench) until the tool goes along the thread correctly, and only then the wrench is installed and work continues.
In the process of cutting, it is required to carefully monitor the correct insertion of the tool so that there is no distortion. To do this, it is necessary to check the position of the tap relative to the upper plane of the part with the help of a square every 2–3 threads of shavings cut again. Particular care should be taken when working with blind and small holes.
Tap design
Tap(Fig. 1) is a hardened screw, on which several straight or helical grooves are cut, forming the cutting edges of the tool. The grooves also accommodate cutting chips and chips can be driven out of the cutting area.
The tap consists of two parts- working and shank, at the end of which a square is made (for hand taps). The working part of the tap includes: the cutting (intake) part, which ensures the removal of the main part of the machining allowance; a gauging part for finishing the thread; chip grooves; nibs (threads separated by chip flutes) and a core that provides the tap with sufficient strength and rigidity for machining. The tail part of the tap serves to fix it in the wrench, which is used for working and idle movements of the tap.
The working part of the tap is made from tool carbon steel grades U11, U11A, high-speed steel or hard alloy. The choice of the material of the working part depends on the physical and mechanical properties of the workpiece being processed. In solid taps, the material of the tail part is the same, and for taps consisting of two parts, connected by welding, the tail part is made of structural steel grades 45 and 40X: The number of flutes made on the tap depends on its diameter (three grooves for taps with a diameter up to 20 mm and four - for taps with a diameter over 20 mm).
The main work when threading is performed by cutting edges formed by the intersection of the front surfaces of the groove with the rear (relief, made along the Archimedean spiral) surfaces of the working part. Backing the rear surface of the cutting teeth allows them to keep their profile constant after regrinding, which is carried out centrally in the sharpening shops.
Typically, taps are made with straight flutes, however, taps with helical flutes are used to improve cutting conditions and produce accurate and clean threads. The angle of inclination of such a groove to the tap axis is 8 ... 15 °. For precise and clean threaded surfaces in through holes when processing soft and viscous materials, flute taps are used.
Fig. 1 Tap:
a - construction: 1 - thread (turn); 2 - square; 3 - tail; 4 - groove; 5 - cutting pen; b - geometric parameters: 1 - front surface; 2 - cutting edge; 3 - backed surface; 4 - back surface; 5 - cutting pen; α is the back angle; β - cutting angle;δ is the tapering angle;γ is the rake angle; c - with a screw flute: 1 - groove; d - cutting a blind thread; ω is the angle of inclination of the helical groove.
In the process of building radio-controlled models, especially ships, you almost always have to cut the threads, since a rather large number of detachable connections are used.
Today I want to tell and show, with examples, how this is done. To begin with, it must be said that the thread can be right and left, has a diameter and a pitch, for the right, the helix rises counterclockwise, and for the left, clockwise. It follows from this that the name corresponds to the direction of twisting of the product. Metric threads are designated by the letter "M", then there is a number indicating the ee diameter, and the value after the "x" sign indicates the pitch, if it is not indicated, then the basic pitch is implied, which is preferred for each diameter.
If it is necessary to cut a thread in a hole, then taps are used to perform this work.
They are universal or complete, which represent a set of two or three tools, which work in turn: first - roughing, and then - finishing.
With a universal tap, all work is done in one pass. Previously, a hole is drilled in the place where it is necessary to perform internal cutting. Its diameter is selected according to the table.
If the hole is drilled larger, then the connection will not have a full profile and will not be of high quality. If the diameter is taken to be smaller, then the stroke of the tap will be difficult and this can lead to its jamming and breakage, especially in hard materials. After drilling, the square shank is securely fixed in the wrench and, having lubricated well, for example, with grease, is inserted into the hole. Then, smoothly rotating the knob, making two turns forward and half a turn backward, cutting is performed. Every 4-5 turns, the tap is removed, chips are removed from it, and after lubrication the actions are repeated.
Sometimes it is necessary to repair or re-thread a rod, stud, bolt or shaft. For this, a die is used. Unlike cutting in a hole, all work on a bar is done in one pass.
One end of the rod is well fixed, for example, in a vice. On the second in the form of a cone and well lubricated, you can use a grease, a die is installed, clamped in a knob. Then smooth movements the knob rotates, and, after every half-turn, it is advisable to slightly turn the tool back to remove the chips. Good lubrication ensures ease of movement and prevents premature bluntness of the working surfaces of the tool.
For threading on shafts, such a "fit" is used.
It works as a guide, since it is quite difficult to accurately position the die, even on a cone, and cut the thread exactly in the center. A hole with a shaft diameter, in our case 2 mm, is drilled in the thin part of the "fit". In the thick part, the tool is fixed under the M2. During operation, the thin part is put on the shaft and then cutting is performed. This guide allows the die to move exactly in the center of the shaft. Such a detail is made on lathe, individually for each section of the shaft.
The question of how to thread a bolt or nut is far from idle. During the renovation, the owners of apartments and houses are faced with the need to restore old threads of anchors, bolts, nuts, or just a thread that is in metal plates.
Otherwise, you just need to cut a new thread on a bolt or nut. For professional turners or locksmiths, this task is not difficult, however, those who have never encountered such a process need to arm themselves with some theoretical knowledge that is set out in this article.
Before proceeding to practical action for threading, you need to know its main parameters and types. In the construction and renovation of housing, in most cases, metric threads are used. What does it mean? According to the shape of the tooth, the thread can be metric, inch, rectangular, trapezoidal, etc.
Metric thread characteristics
The thread of interest to us is in the shape of a triangle, the thread trapezoidal is in the shape of a trapezoid. In addition, there is such a thing as a thread pitch, that is, the distance between its vertices: in the case of a metric thread, between the vertices of the thread triangle. And, of course, its diameter must be attributed to the characteristic of the thread.
Consider the above paragraph using the example of the M 12 thread, where the letter "M" indicates that the thread is metric, the number "12" defines the thread diameter. Where is the step size? The fact is that metric threads are divided into main and small, and if there is no other digital value after the number, then the main thread is. But if we have a thread M12 x 1.5 or M 12 x 1.25, then this means that the pitch of the thread is 1.5 and 1.25 mm, respectively. The pitch of the main thread M 12 is 1.75 mm.
All these values for any type of thread can be found in reference books or on the pages of the corresponding sites on the Internet. For internal threads (nuts), there is another reference value - the diameter of the hole for the thread, which can be found there. For our M12 bolt, the inner diameter of the nut should be 12 mm minus the height of the tooth profile, that is, according to the reference books, 10.2 mm. For fine thread M 12 x1.25, the diameter will accordingly be less - 10.4 mm.
It is worth noting that something similar applies to the bolt or, as it is called in reference books, to the rod. Again, for the M 12 thread, the diameter of the rod should be slightly less than 11.7 mm, but for the M 12 X 1.25 thread - 11.9 mm. If you do not observe the dimensional tolerances for the thread for both the nut and the bolt, the thread will be of poor quality, loosened on one side, and on the other, if the tolerance is larger, it will simply break.
Rigging and threading tools
Do not be intimidated by the word "rig" because, in fact, this is a device where it is attached cutting tool: taps and die (stick). The old name of the plate is given in brackets, but you can still find it. The equipment includes a wrench of a rather simple design where a tap is inserted for threading in nuts and another type of device where a die for threading a bolt is attached.
Tooling and cutting tools for threading
The taps, as well as the dies, are made of high carbon cast iron, so they are fragile and afraid of heavy stress. Threading in nuts is mainly carried out by two taps: N 1 and N 2. The first has an incomplete thread for preliminary penetration, followed by the second tap.
Tapping taps
As a result, the thread is complete and of high quality, which means it will firmly hold the connection with the nut. Another type of tap is used, called "machine", which combines two tap numbers.
Die holder and die set
It would seem convenient, but this type of tap is long and inconvenient to work with. Used for long thread cutting. As for the dies, they have one number.
Another type of tooling, without which the threading process is almost impossible, is a medium-sized locksmith vice. Probably, nobody needs to explain what it is. The only thing to remember is that the vise must be securely fastened.
Thread cutting techniques
Immediately it is necessary to make a reservation that in the rod at the end and in the hole for the thread in the nut, any chamfers must be removed in an accessible way... Chamfers are necessary for accurate entry without skewing the cutting tool, that is, the tap and the die. Next, we clamp the object for threading into the knob, clamp the rod or workpiece under the nut from the vice and proceed to threading.
Die cutting
This is done without the use of excessive forces and always with a lubricant, which is ideal for sulfo-fresol. However, if one is not available, you can use an emulsion (solution of mineral oil in water) or just vegetable oils.
By the way, if you decide to cut the thread of a stainless steel or copper bolt, there is no better lubricant than ordinary fat, which has been proven more than once in practice.
When cutting a thread, you need to feel the tap or die: if they begin to spring a little, that is, strongly resist, you need to turn them out and clean them of chips. If this is neglected, the cutting tool may crack corny and you will have to prepare again a new rod or blank for the nut.
And finally: if you do not have the opportunity to order blanks for a bolt or nut from a turner, purchase (rolled metal in the form of a circle), which can be from five to 20 mm in diameter, and you don’t need any more, because it is almost impossible to manually cut large-diameter threads.
The operation of machining with the removal of chips, as a result of which external or internal helical grooves with a given profile and dimensions are formed on cylindrical or conical surfaces, is called tapping.
Threading on screws, bolts, nuts and other parts is carried out mainly on machine tools. When assembling and repair work a locksmith in some cases has to cut threads by hand or using pneumatic or electric machines - thread cutters.
The main elements of any thread, as noted in Ch. 3, are the profile, pitch, depth, outer, middle and inner diameters.
According to the shape of the profile, the threads are divided into triangular, rectangular, trapezoidal, thrust and round (Fig. 4.14).
The type or profile of the thread is selected according to GOST, depending on the purpose.
Fig. 4.14. Profiles and thread elements:
a - triangular;
b - rectangular;
c - trapezoidal;
g - persistent;
d - round;
d is the outer diameter of the thread;
dcp - average thread diameter;
d1 is the inner diameter of the thread.
In mechanical engineering, three systems of threads are adopted: metric, in which the pitch and diameter are measured in millimeters; inch, having a different profile shape and characterized by the number of threads per inch of its length and diameter in inches;
pipe thread, which has a profile like an inch, but smaller in pitch.
In the practice of plumbing, it is often necessary to determine the dimensions of the thread elements on the finished part. The outer diameter is measured using a caliper or micrometer, and the thread pitch is measured using a millimeter or inch thread gauge (a set of templates with threads of various sizes).
Taps are used for tapping holes, and dies for external threads.
A tap is a cutting tool, which is a hardened screw, on which several longitudinal straight or helical grooves are cut, forming cutting edges (Fig. 4.15). The tap has a working part and a square-ended shank.
Fig. 4.15. Tap and its elements:
but - general form:
1 - cutting pen;
2 - cutting edge;
3 - square;
4 - shank;
5 - groove;
b - cross section:
1 - front surface;
2 - cutting edge;
3 - back (backing) surface;
4 - groove;
5 - cutting pen.
The shank of the tap serves to fix the tool in the chuck or wrench during operation. Hand taps have a square end.
Working part - the cut part of the tap that makes thread cutting; it is subdivided into intake and calibrating parts.
The intake (cutting) part of the tap is the front tapered part, which first enters the hole being cut and performs the main cutting work.
The calibrating part protects and calibrates the hole to be cut.
Longitudinal grooves are used to form the cutting edges of the tap and chip out. The threaded portions of the tap, limited by the grooves, are called cutting blades.
According to the method of application, taps are divided into manual and machine. Hand taps are used for manual threading. They are usually produced in sets of two or three. A set of three taps includes roughing, medium and finishing (or 1, 2, 3), and a set of two taps includes roughing and finishing. They are used in the same order for threading.
The taps are conventionally designated by risks (grooves): for the roughing one on the shank, one circular risk, for the middle one - two, for the finishing one - three. It also indicates the type of thread and its size.
Is of great importance right choice diameters of holes for threading. The choice of drill diameters for this type and thread size is made according to special tables. However, with sufficient accuracy for practice, the drill diameter can be determined by the formula
Dw = dр - 2h
where Dw - drill diameter, mm; dр - outer diameter of the thread, mm; h is the height of the thread profile, mm.
Tapping with hand taps is done using a wrench that fits over the square ends of the shanks. There are gates various designs with fixed and adjustable tap holes.
The tool used to cut external threads is called a die. The die is a hardened steel nut with flutes forming cutting edges (fig. 4.16).
Fig. 4.16. Die and its elements:
a - general view;
b - geometric parameters of the plate.
1 - calibrating part;
2 - intake part;
3 - chip groove.
Dies are round (sometimes they are called lers), sliding (kluppovye) and special for cutting pipes.
To work with round dies, wrenches (handle holders) are used, which are a frame with two handles, into the hole of which a die is placed and is kept from turning by means of three locking screws, the conical ends of which enter the recesses on the side surface of the dies.
Sliding die holders are an oblique frame with two handles. Half-plates are inserted into the frame hole. Half dies are installed to the required size using a special pressure screw.
For tapping, the following techniques are performed. The part is fixed in a vise, the rough tap is lubricated and in a vertical position (without skewing) is inserted into the cut hole. Putting the knob on the tap and lightly pressing it against the part with your left hand, gently turn the knob clockwise with your right hand (when cutting the left thread - counterclockwise) until the tap cuts into the metal and its position in the hole becomes stable. Then the crank is taken with both hands and smoothly rotated (Fig. 4.17, a). After one or two full revolutions, the return movement of the tap breaks the chips by about a quarter of a turn, this greatly facilitates the cutting process. After finishing cutting, turn the tap out of the hole (by turning the knob in the opposite direction) or pass it through.
The second and third taps are lubricated and inserted into the hole without a wrench. After the tap is correctly installed on the thread, put on the wrench and continue threading.
When slicing deep holes it is necessary to completely unscrew the tap 2-3 times during the cutting process and clear it of chips, since an excess of it in the grooves can cause the tap to break or break the thread.
Before cutting the external thread with dies, turned to required diameter the rod is fixed in a vice. At the very end of the rod, a small chamfer is removed at an angle of 45 ° (Fig. 4.17.6). The rod should have a clean surface, as cutting threads on scale or rust will wear out the dies a lot.
Fig. 4.17. Techniques for cutting threads with hand taps (a) and dies (b, c).
To obtain the correct thread, the diameter of the rod is usually made 0.2-0.4 mm less than the required thread diameter.
On the end of the rod, fixed in a vice so that its end protrudes from the jaws 15-20 mm more than the length of the section to be cut., Impose a die fixed in the knob and, with slight pressure, begin to cut the thread, turning the knob with short clockwise movements (Fig. . 4.17, c). The first 1.0-1.5 threads are usually cut without lubrication, since the die captures dry metal more easily; then the rod is lubricated natural drying oil and continue to rotate the crank or screw-type tool one or two turns to the right and half a turn to the left to break the chips.
At the beginning of threading with dies, it is necessary to make some pressure on the die (during the working stroke), avoiding its distortion. During the cutting process, the pressure on both hands should be even.
Sliding dies in the die during cutting should be tightened only at the beginning of the pass; after passing along the entire length of the thread, the die screws are screwed on (or, as they say, "driven off"), then the dies are tightened again with a screw and the thread is passed through the second time.
If it is necessary to get an accurate and clean thread, cutting is done with two dies - rough and fine.
Mechanized threading is carried out hand drill or an electric threading machine, as well as on a drilling or threading machine. This work requires special attention and care, especially when using a drill and an electric or pneumatic machine.
Hand drills cut threads with a diameter of up to 6 mm, and the productivity in comparison with the work of the crank is tripled. The use of electric or pneumatic machines increases labor productivity by almost 5 times.
When threading with a drill or machines, the tap is clamped in the chuck and Special attention turns to ensure that there is no misalignment of the tap relative to the axis of the hole.