In the process of building radio-controlled models, especially ships, you almost always have to cut threads, since a fairly 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-handed or left-handed, has a diameter and a pitch; on the right, the screw line rises counterclockwise, and on the left, clockwise. It follows that the name corresponds to the direction in which the product is twisted. A metric thread is designated by the letter “M”, followed by a number indicating its diameter, and the value after the “x” sign indicates the pitch, if it is not specified, then the main 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 can be universal or complete, which represent a set of two or three tools, which are used alternately: first for roughing, and then for finishing.
With a universal tap, all the work is done in one pass. First, a hole is drilled in the place where the internal threading is necessary. Its diameter is selected according to the table.
If the hole is drilled larger, the connection will not have a full profile and will not be of good quality. If the diameter is smaller, the tap will be difficult to move and this can lead to jamming and breakage, especially in hard materials. After drilling, the square shank is securely fixed in the driver and, well lubricated, for example, with grease, is inserted into the hole. Then, smoothly rotating the knob, making two turns forward and half a turn back, cuts are made. Every 4-5 revolutions, the tap is removed, chips are removed from it, and after lubrication, the actions are repeated.
Sometimes you need to re-thread or re-thread a rod, stud, bolt or shaft. A die is used for this. Unlike tapping in a hole, on a rod all the work 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 grease, a die is installed, clamped into a knob. Then the knob rotates with smooth movements, and after every half turn it is advisable to turn the tool back a little to remove chips. Good lubrication ensures ease of movement and prevents premature dulling of the working surfaces of the tool.
To cut threads on shafts, this “device” is used.
It works as a guide, since it is quite difficult to accurately install 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 “device”. The tool under M2 is fixed in the thick part. During operation, the thin part is put on the shaft and then cutting is carried out. This guide allows the die to move strictly in the center of the shaft. Such a part is made on a lathe, individually for each section of the shaft.
The question of how to cut a thread with a tap arises in cases where a pre-made hole needs to be prepared to accommodate a bolt, screw, stud or any other type of threaded fastener. In such situations, it is the tap that is the main tool that allows you to quickly and accurately cut an internal thread with the required geometric parameters.
Types and areas of application of taps
Internal thread cutting can be done manually or using various types of machines (drilling, lathe, etc.). The working tools that perform the main work of cutting internal threads are machine-hand or machine taps.
Taps are divided into different types depending on a number of parameters. The following principles for classifying taps are generally accepted.
- According to the method of rotation, a distinction is made between machine-manual and machine taps, with the help of which internal threads are cut. Machine-hand taps equipped with a square shank are used in conjunction with a special device with two handles (this is the so-called tap holder). With the help of such a device, the tap is rotated and cuts the thread. Thread cutting with a machine tap is carried out on metal-cutting machines of various types, in the chuck of which such a tool is fixed.
- Based on the method by which internal threads are cut, a distinction is made between universal (through) taps and complete taps. The working part of the former is divided into several sections, each of which differs from the others in its geometric parameters. The section of the working part that first begins to interact with the surface being processed performs rough processing, the second - intermediate, and the third, located closer to the shank - finishing. Cutting threads with complete taps requires the use of several tools. So, if a set consists of three taps, then the first of them is intended for roughing, the second for intermediate, and the third for finishing. As a rule, a set of taps for cutting threads of a certain diameter includes three tools, but in some cases, when products made of particularly hard material are processed, sets consisting of five tools can be used.
- Based on the type of hole on the inner surface of which it is necessary to cut a thread, taps for through and blind holes are distinguished. A tool for processing through holes is characterized by an elongated conical tip (approach), which smoothly passes into the working part. Universal type taps most often have this design. The process of cutting internal threads in blind holes is carried out using taps, the conical tip of which is cut off and performs the function of a simple milling cutter. This design of the tap allows it to cut threads to the full depth of a blind hole. To cut a thread of this type, as a rule, a set of taps is used, driven manually using a wrench.
- According to the design of the working part, taps can have straight, helical or shortened chip removal grooves. It should be borne in mind that taps with grooves of various types can be used for cutting threads in products made of relatively soft materials - carbon, low-alloy steel alloys, etc. If threads need to be cut in parts made of very hard or viscous materials (stainless, heat-resistant steels, etc.), then for these purposes taps are used, the cutting elements of which are arranged in a checkerboard pattern.
Taps are usually used for cutting metric threads, but there are tools that can be used to cut pipe and inch internal threads. In addition, taps also differ in the shape of their working surface, which can be cylindrical or conical.
Preparing to cut internal threads
In order for the process of cutting internal threads using a tap to not cause any particular difficulties and result in a high-quality result, it is necessary to properly prepare for this technological operation. All methods of cutting threads using a tap assume that a hole with the appropriate diameter has already been made in the workpiece. If the internal thread that needs to be cut has a standard size, then a special table with data in accordance with GOST can be used to determine the diameter of the preparation hole.
Table 1. Diameters of holes drilled for standard metric threads
If the thread that needs to be cut does not belong to the standard category, you can calculate the diameter of the hole to make it using a universal formula. First of all, it is necessary to study the marking of the tap, which must indicate the type of thread being cut, its diameter and pitch, measured in millimeters (for metric). Then, to determine the cross-sectional size of the hole that needs to be drilled for the thread, it is enough to subtract the pitch from its diameter. For example, if a tool marked M6x0.75 is used to cut a non-standard internal thread, then the diameter of the preparation hole is calculated as follows: 6 – 0.75 = 5.25 mm.
For standard threads belonging to the inch category, there is also a table that allows you to choose the right drill with which to carry out the preparatory work.
Table 2. Diameters of holes drilled for inch threads
An important question to obtain a high-quality result is not only the question of what is used to cut the thread, but also what drill to use to make the preparation hole. When choosing a drill, you need to pay attention to the parameters and quality of its sharpening, as well as to ensure that it rotates in the chuck of the equipment used without runout.
The sharpening angle of the cutting part is selected depending on the hardness of the material that needs to be drilled. The higher the hardness of the material, the greater the sharpening angle of the drill should be, but this value should not exceed 140°.
How to cut threads correctly? First you need to select tools and consumables:
- an electric drill or drilling machine capable of operating at low speeds;
- a drill whose diameter is calculated or selected using reference tables;
- a drill or countersink, with the help of which a chamfer will be removed from the edge of the prepared hole;
- a set of taps of the appropriate size;
- manual holder for taps (drives);
- bench vice (if the product in which the thread needs to be cut needs to be fixed);
- core;
- hammer;
- machine oil or other composition, which during the processing process must be used to lubricate both the tap and the thread section being cut by it;
- rags.
Features of the technology
When cutting internal threads with a tap, the following algorithm is used.
- In the place on the surface of the workpiece where the hole for threading will be drilled, it is necessary to form a recess for a more accurate entry of the drill, using a core and a regular hammer. The drill is fixed in the chuck of an electric drill or drilling machine, on which low rotation speeds of the tool are set. Before starting drilling, the cutting part of the drill must be treated with a lubricating compound: a lubricated tool enters more easily into the structure of the material being processed and creates less friction in the processing area. You can lubricate the drill with a piece of ordinary lard or grease, and when processing viscous materials, machine oil is used for these purposes.
- If it is necessary to cut threads in small parts, they should first be fixed using a bench vice. When starting drilling, the tool fixed in the equipment chuck must be positioned strictly perpendicular to the surface of the workpiece. You should lubricate the tap regularly and ensure that it does not warp and moves strictly in the given direction.
- At the entrance to the hole, as mentioned above, it is necessary to remove the chamfer, the depth of which should be 0.5–1 mm (depending on the diameter of the hole). For this purpose, you can use a larger diameter drill or countersink, installing them in the chuck of drilling equipment.
- The process of cutting internal threads begins with tap No. 1, which is the first to be installed in the driver. We should not forget about the lubricant, which must be applied to the tap for threading. The position of the tap relative to the hole being machined must be set at the very beginning of the work, since later, when the tool is already inside the hole, this will not be possible. When cutting a thread with a tap, you must adhere to the following rule: 2 turns of the tap are made in the direction of cutting the thread, 1 - against the direction. When the tap makes one revolution back, chips are thrown off its cutting part and the load on it is reduced. Thread cutting with a die is performed using a similar technique.
- After cutting the thread with tap No. 1, tool No. 2 is installed in the driver, and after it – No. 3. They are processed according to the method described above. When cutting threads with taps and dies, you need to feel when the tool begins to rotate with force. As soon as such a moment occurs, you should turn the knob in the opposite direction to throw the chips off the cutting part of the tool.
To cut an internal thread on a part, you must first drill a hole. Its size is not equal to the thread diameter, but should be slightly smaller. You can find the diameter of the drill for the thread in a special table, but to do this you also need to know the type of thread.
Main settings
- diameter (D);
- pitch (P) - the distance from one turn to another.
They are determined by GOST 1973257-73. A large step is considered normal, but it corresponds to several smaller ones. A small pitch is used when applying to thin-walled products (pipes with a thin wall). They also make a small turn if the applied thread is a way to adjust any parameters. Also, a small step between turns is made to increase the tightness of the connection and to overcome the phenomenon of self-unscrewing of the part. In other cases, a standard (large) step is cut.
There are many types of threads, since each has its own formation characteristics; the diameter of the hole for the thread is different in each case. All of them are prescribed in GOST standards, but most often they use triangular metric and conical metric threads. We will talk about them further.
We usually see triangular threads on bolts and other similar fasteners, conical threads on most plumbing products that require a detachable connection.
Adaptations
To apply carvings with your own hands, use small devices:
All these devices are made of alloys characterized by increased strength and abrasion resistance. Grooves and grooves are applied to their surfaces, with the help of which their mirror image is obtained on the workpiece.
Any tap or die is marked - they have an inscription indicating the type of thread that this device cuts - diameter and pitch. They are inserted into holders - collars and die holders - and secured there with screws. Having clamped the thread cutting device in the holder, it is put on/inserted into the place where you want to make a detachable connection. By turning the device, turns are formed. How correctly the device is positioned at the beginning of work determines whether the turns will “lay down” evenly. Therefore, make the first revolutions, trying to keep the structure level, avoiding shifts and distortions. After a few turns, the process will become easier.
You can cut small or medium diameter threads by hand. Complex types (two- and three-way) or working with large diameters by hand are impossible - too much effort is required. For these purposes, special mechanized equipment is used - lathes with taps and dies attached to them.
How to cut correctly
Threads can be applied to almost any metals and their alloys - steel, copper, aluminum, cast iron, bronze, brass, etc. It is not recommended to do it on hot iron - it is too hard, it will crumble during operation and it will not be possible to achieve high-quality turns, which means the connection will be unreliable.
Tool for the job
Preparation
You need to work on clean metal - remove rust, sand and other contaminants. Then the place where the thread will be applied must be lubricated (except for cast iron and bronze - they must be worked “dry”). There is a special emulsion for lubrication, but if it is not there, you can use soaked soap. You can also use other lubricants:
You can often hear advice to use machine or mineral oil or even lard when cutting threads. They work well, but experts say that it is better not to do this - the chips will stick to the viscous substance, which will lead to rapid wear of the tap or die.
Slicing process
When cutting external threads, the die is placed strictly perpendicular to the surface of the pipe or rod. During operation, it should not wiggle, otherwise the turns will turn out uneven and the connection will be ugly and unreliable. The first turns are especially important. How they “lay down” determines whether the connection will then be skewed.
By applying the internal thread, the part is fixed motionless. If it is a small piece, you can clamp it in a vice. If the plate is large, ensure its immobility using available methods, for example, by fixing it with bars. M
The tap is inserted into the hole so that its axis is parallel to the axis of the hole. With little effort, little by little, they begin to twist in the given direction. As soon as you feel that the resistance has increased, unscrew the tap back and clear it of chips. After cleaning, the process continues.
Photo cutting process
When cutting a thread in a blind hole, its depth should be slightly greater than required - this excess should include the tip of the tap. If this is structurally impossible, the tip of the tap is cut off. At the same time, it is not suitable for further use, but there is no other way out.
In order for the turns to be of high quality, two taps or dies are used - rough and finishing. The first pass is done as a rough pass, the second as a finishing pass. There are also combined devices for applying threads. They allow you to do everything in one pass.
Another practical tip: to prevent chips from getting into the working area, when cutting, make one full turn clockwise, then half a turn counterclockwise. After this, return the tool to the place where you stopped and make one revolution again. Continue this way until the required length.
Tables for selecting the diameter of a drill for threading
When making an internal thread, a hole is pre-drilled for it. It is not equal to the diameter of the thread, since when cutting, part of the material is not removed in the form of chips, but is squeezed out, increasing the size of the protrusions. Therefore, before application, it is necessary to select the diameter of the drill bit for the thread. This can be done using tables. They are available for every type of thread, but here are the most popular ones - metric, inch, pipe.
| Metric thread | Inch thread | Pipe thread | |||||
|---|---|---|---|---|---|---|---|
| Thread diameter, inches | Thread pitch, mm | Drill diameter, mm | Thread diameter, inches | Thread pitch, mm | Drill diameter, mm | Thread diameter, inches | Threaded hole diameter, mm |
| M1 | 0.25 | 0,75 | 3/16 | 1.058 | 3.6 | 1/8 | 8,8 |
| M1.4 | 0,3 | 1,1 | 1/4 | 1.270 | 5.0 | 1/4 | 11,7 |
| M1.7 | 0,35 | 1,3 | 5/16 | 1.411 | 6.4 | 3/8 | 15,2 |
| M2 | 0,4 | 1,6 | 3/8 | 1.588 | 7.8 | 1/2 | 18,6 |
| M2.6 | 0,4 | 2,2 | 7/16 | 1.814 | 9.2 | 3/4 | 24,3 |
| M3 | 0,5 | 2,5 | 1/2 | 2,117 | 10,4 | 1 | 30,5 |
| M3.5 | 0,6 | 2,8 | 9/16 | 2,117 | 11,8 | - | - |
| M4 | 0,7 | 3,3 | 5/8 | 2,309 | 13,3 | 11/4 | 39,2 |
| M5 | 0,8 | 4,2 | 3/4 | 2,540 | 16,3 | 13/8 | 41,6 |
| M6 | 1,0 | 5,0 | 7/8 | 2,822 | 19,1 | 11/2 | 45,1 |
| M8 | 1,25 | 6,75 | 1 | 3,175 | 21,3 | - | - |
| M10 | 1,5 | 8,5 | 11/8 | 3,629 | 24,6 | - | - |
| M12 | 1,75 | 10,25 | 11/4 | 3,629 | 27,6 | - | - |
| M14 | 2,0 | 11,5 | 13/8 | 4,233 | 30,1 | - | - |
| M16 | 2,0 | 13,5 | - | - | - | - | - |
| M18 | 2,5 | 15,25 | 11/2 | 4,33 | 33,2 | - | - |
| M20 | 2,5 | 17,25 | 15/8 | 6,080 | 35,2 | - | - |
| M22 | 2,6 | 19 | 13/4 | 5,080 | 34,0 | - | - |
| M24 | 3,0 | 20,5 | 17/8 | 5,644 | 41,1 | - | - |
Once again, please note that the diameter of the drill bit for the thread is given for large (standard thread).
Table of rod diameters for external threads
When working with external threads, the situation is very similar - part of the metal is extruded rather than cut off. Therefore, the diameter of the rod or pipe on which the thread is applied should be slightly smaller. How accurate - see the table below.
| Thread diameter, mm | 5,0 | 6 | 8 | 10 | 12 | 16 | 20 | 24 |
|---|---|---|---|---|---|---|---|---|
| Rod diameter, mm | 4,92 | 5,92 | 7,9 | 9,9 | 11,88 | 15,88 | 19,86 | 23,86 |
The joining of structural parts occurs through bolts, screws and studs, which in turn have special external and internal threads. This kind of connection is called detachable. Bolts, screws and studs are cylindrical rods with screw threads. The thread cutting process is carried out mechanically and manually, on machines with special tools.
Processing methods
Internal thread applied with taps external- with dies. Taps are shaped like a screw, with a groove along the screw part that will allow the chips to slide off during the process. The geometric shape of the dies resembles a nut. Capable of cutting threads with a diameter of up to 52 mm. There are round, square, hexagonal and prismatic.Features of internal thread cutting
A thread is a reliable way to connect two parts; this indicator increases significantly if the thread is internal. Cutting taps– removal of metal material using cutting edges with different pitches. The operation is performed in one pass. Depending on the intended purpose, swords are divided into: metalworking (metric and inch threads), nut, master and die. By type of thread - left-handed for creating left-handed threads and, accordingly, right-handed.tap processing method
The internal thread is applied with a tap, which is made of carbon or high-alloy steel. The tool consists of a shank attached to a cup chuck and a working area - a cutting part with longitudinal and helical grooves. The intake part - the upper part of the cone, carries out thread cutting work. Calibrating part – calibrates the direction of the process. General operating rules:- It is not recommended to immediately apply threads to products made by casting or stamping. It is necessary to pre-drill the hole, thereby removing carbon deposits and scale;
- on drilling machines, the tap must be secured in reversible chucks to prevent the possibility of breakage;
- mandatory chamfering in those places where work is planned.
cutting method on a lathe
The main problem with using taps is chip removal in holes 6 mm and over 16 mm. Due to the limited space, chip removal is difficult, which can cause tool failure. On lathe-type machines, threads are applied using a boring cutter and carbide inserts with a full or partial profile.Features of external thread cutting
Threads are grooves of various geometric shapes, cut with special tools - dies, thread cutters, taps and grinding wheels. The thread is applied either manually or using a lathe and cutter.cutting method with a die and tap
A tap is a screw with straight and helical grooves, designed for cutting internal threads. The manual cutting method requires 3 taps: rough, for applying the initial thread, medium and finishing. The machine cutting method is carried out on lathes and milling machines. The dies are similar in shape and appearance to a nut; on the inside of the tool there are conical cutting teeth for cutting external threads. They are divided into round, square and hexagonal shapes. According to the design - solid, split and sliding. To ensure smooth passage of the die through the part, it is necessary to remove the chamfer.turning method
In production, threads are cut using a lathe and a special tool - a thread cutter. For each product, an individual indicator of the helical pitch is established; it is determined by measuring the distance between adjacent turns. The part is placed in a lathe, and as the workpiece rotates, the cutter moves along all axes, creating a helical surface. Based on their design features, thread cutters are divided into: prismatic, rod and round/disc. The thread profiles used are triangular, rectangular, trapezoidal, thrust and round geometric shapes.
Features of pipe threading
In pipe threading, 3 types are used: on a lathe, using a die or a pipe die. In practice, the most common thread is the triangular type:- inch, with measurement calculations in inches. The thread has high strength due to the large pitch and large profile. Used for water pipes;
- metric, measured in millimeters, used for pipe fasteners.
On lathes, the process is structured as follows: the pipe is fixed in the spindle, then all excess is removed with a cutting cutter, the appropriate pitch is selected and the thread is applied.