What do you need to cut a thread?

What rod diameter should I choose for an external metric thread? — Homo habilis. Magazine for skilled people

Yuri Makarov Category: Workshop: June 26, 2014 25671

:  5 / 5

Christian Schnettelker, flickr.com CC BY

Screws, bolts and studs are the most common externally threaded components. Most often, they fall into the hands of a home craftsman ready-made. But it happens that you need to make some tricky bolt or non-standard pin. The blank for such a part is a rod, the diameter of which must correspond to the thread being cut.

The diameter of the rod for an external thread depends on the nominal diameter of the thread and the size of the thread pitch. All this information is usually indicated on the drawing of the part in the form of the designation M10 × 1.5. The letter “M” denotes a metric thread, the number after the letter is the nominal diameter, the number after the sign “x” is the thread pitch. When using the main (large) step, it may not be indicated. The main thread pitch is determined by the standard and is the most preferred.

When choosing the diameter of a rod for external threads, they are guided by the same principles as when choosing holes for internal threads. It has been established that the best thread quality is obtained if the diameter of the rod is slightly smaller than the nominal diameter of the thread being cut. When cutting, the metal is slightly squeezed out and the thread profile is complete.

If the diameter of the rod is much smaller than the required one, then the tops of the threads will be cut off; if it is larger, then the die simply will not screw onto the rod or will break during operation.

For each combination of diameter and thread pitch, there is an optimal rod diameter . The easiest way to determine this diameter is from the table, which shows the most common threads that a home craftsman may encounter. The main thread pitch for each nominal diameter is highlighted in bold in the table.

Thread	Thread pitch	Nominal rod diameter (maximum)
M2	0,4	1,93-1,95 (1,88)
0,25	1,95-1,97 (1,91)
M2.5	0,45	2,43-2,45 (2,37)
0,35	2,45-2,47 (2,39)
M3	0,5	2,89-2,94 (2,83)
0,35	2,93-2,95 (2,89)
M4	0,7	3,89-3,94 (3,81)
0,5	3,89-3,94 (3,83)
M5	0,8	4,88-4,94 (4,78)
0,5	4,89-4,94 (4,83)
M6	1	5,86-5,92 (5,76)
0,75	5,88-5,94 (5,79)
0,5	5,89-5,94 (5,83)
M8	1,25	7,84-7,90 (7,73)
1	7,86-7,92 (7,76)
0,75	7,88-7,94 (7,79)
0,5	7,89-7,94 (7,83)
M10	1,5	9,81-9,88 (9,69)
1	9,86-9,92 (9,76)
0,5	9,89-9,94 (9,83)
0,75	9,88-9,94 (9,79)
M12	1,75	11,80-11,86 (11,67)
1,5	11,81-11,88 (11,69)
1,25	11,84-11,90 (11,73)
1	11,86-11,92 (11,76)
0,75	11,88-11,94 (11,79)
0,5	11,89-11,94 (11,83)
M14	2	13,77-13,84 (13,64)
1,5	13,81-13,88 (13,69)
1	13,86-13,92 (13,76)
0,75	13,88-13,94 (13,79)
0,5	13,89-13,94 (13,83)
M16	2	15,77-15,84 (15,64)
1,5	15,81-15,88 (15,69)
1	15,86-15,92 (15,76)
0,75	15,88-15,94 (15,79)
0,5	15,89-15,94 (15,83)
M18	2	17,77-17,84 (17,64)
1,5	17,81-17,88 (17,69)
1	17,86-17,92 (17,76)
0,75	17,92-17,94 (17,86)
M20	2,5	19,76-19,84 (19,58)
1,5	19,81-19,88 (19,69)
1	19,86-19,92 (19,76)
0,75	19,88-19,94 (19,79)
0,5	19,89-19,94 (19,83)

The main tool for cutting external threads is a die. Most often, round continuous dies in the form of a hardened steel nut are used.

To form the cutting edges, the die threads are crossed by through longitudinal holes, which also provide chip exit. To facilitate entry, the outer threads of the thread have an incomplete profile. To rotate the die, use a die holder - a tool with a socket for the die and long handles. There are also split and sliding (clump) dies, but these are rare in the home workshop.

To reduce friction and obtain clean threads, a lubricant is used on steel rods - mineral oil or kerosene, and on copper rods - turpentine. At the end of the rod, to facilitate entry, a chamfer must be made with a width of at least the size of the thread pitch.

We recommend reading

Source: https://homo-habilis.ru/masterskaya/237-kakoj-diametr-sterzhnya-podobrat-pod-naruzhnuyu-metricheskuyu-rezbu

Table for selecting taps for thread cutting, and other secrets of manual cutting

Various methods are used to connect products to each other:

• welding;
• gluing;
• riveting;
• bolted;
• screw;
• hairpin.

If parts are connected with a bolt and nut, additional space is required. In addition, the thickness of the components does not always allow making a through hole.

In this case, a screw connection is used.

To screw in the screw, you need to cut the thread with a tap. The tool is a steel rod consisting of a working part and a shank and is designed for cutting internal threads. The working area has a slightly conical shape. It has teeth that consistently follow the shape of the thread. There are grooves for removing sawdust and shavings.

Specification of taps by thread cutting method

Pass-through (universal).
The thread is cut in one pass. The working part contains teeth for marking and final cutting. The device is well suited for soft metals. When working with durable material, more effort is required.

Complete.
For work, several nozzles (two or three) of the same thread size are used. When working with particularly hard metals, it is possible to use a set of five nozzles. The carving is created in several stages.

The beginning is laid with a marking tap, then a deeper cutting is carried out, and finally the final part, when the edges are finally formed.

It takes more time to complete the task, but the quality is significantly higher, and the likelihood of tool breakage is practically eliminated;

Application Specification

Machine.
Extended length shank. Designed for mounting in an electrical tool holder.

Machine - manual.
The shortened shank has flats with a square structure. Can be used both in an electric drill and manually. In the second case, a special wrench is used - a tap holder.

Specification by hole type

For through holes.
Such nozzles have an elongated approach (sharp tip of the working area), smoothly turning into the working diameter. Working with such a tap is not difficult; an electric drive can handle cutting. After the pass, the tool will simply come out on the opposite side of the workpiece.

For blind holes.
The tip of the working area is cut off like a milling cutter. This allows threads to be cut to almost the entire depth of the hole. You should work with extreme caution, since when reaching the bottom of a blind hole, a stuck tap may break. For this reason, hand cutting is practiced.

Specification by work area type

To work with various metals, the shape of the working area (teeth) can be straight, helical or with shortened grooves. The teeth themselves are arranged in one line or in a checkerboard pattern. Universal tap designs in soft and hard alloys cannot be used.

Popular: Construction pistols: features of choice

Therefore, if you want to cut threads correctly, use a tool that matches the type of metal and hole.

When cutting threads with taps and dies, it is necessary to accurately select the drill and cutting tool for the screw or stud used in the future.

Table of taps and drills for internal threads

The fact is that the through hole and thread diameter must comply with the standards. If the hole diameter is too large, the depth of the grooves will be too small and the threaded connection will be unreliable.

At the slightest load the thread will break. The other extreme is a narrow threaded hole. In this case, the tap will play the role of a drill, and its configuration is not suitable for this. There is a very high probability of tool failure.

After that, be sure to countersink and carefully cut the thread with a triple set of taps.

How to cut threads by hand correctly and without wasting a tool

1. Preparing the hole. We select a drill according to the table and carefully make a hole.

   It is better to drill on a machine. It is advisable to countersink the entrance of the hole. This will make both cutting and subsequent tightening of the screw easier.

   When making a blind threaded connection, measure the length of the non-working part of the tap, multiply this value by 2, and add to the depth of the hole. No matter how prepared the tap is for such holes, it will not be possible to cut a thread to the very bottom of the hole;

2. Slicing process. There is no need to rush when working with your hands. That is why manual cutting requires complete sets. To speed up the process, you should not start immediately from the next number.

   Otherwise, the thread will turn out rough, with burrs. Also, do not neglect the last number. A thread that is not cut to the final depth promises difficulties when tightening the screw, and even jamming.

   The tap sizes are also not designed for experimentation. If you have an M5 screw, then the tap should have the same marking. There are no half-measures; these are all the tricks of Chinese garage manufacturers.

   Moreover, this thread size does not exist in technical standards.

   The tap holder should be grasped firmly by both handles and equal forces should be applied to them. The golden rule of cutting: +360 degrees, – 180 degrees.

   This means that for one full turn along the thread, half a turn is made back to chip and remove chips. Don't be fooled by the feeling that the tap moves so easily. The temptation to spin quickly at the final stage is especially great. Internal thread cutting must occur at a uniform speed and force;

3. Cleaning and checking. The last step is to remove any remaining shavings and sawdust from the threaded hole. Through holes are cleaned with metal brushes.

Deaf - first cleaned with a hard brush, then blown with compressed air.

After that, a screw is screwed into the hole and the quality of the thread is checked. Twisting should happen easily, without effort. Fixing a screw connection using a “crooked” thread is unacceptable.

If something went wrong, or what to do with a broken tap

If the work is carried out incorrectly, the tap may break. Reasons leading to breakdown:

• tool misalignment;
• hole diameter mismatch;
• cutting speed too high;
• disregard for the rule +360 degrees, -180 degrees.

If you don’t know what preliminary hole needs to be made in the metal in order to cut a thread and not break the tap, download GOST 19257-73, it’s called “Holes for cutting metric threads.”

How to unscrew a broken tap

There are actually few ways.

1. Extractor. Classic extractors for broken bolts and studs will not help here.

   It is almost impossible to drill a hole in the tap due to its exceptional hardness. A special device is required.

   Special guides are inserted into the grooves of the stuck tap, pressed with a sleeve against the rod, and the tap is unscrewed with a regular wrench;

2. Spot welding. An L-shaped steel rod is welded to the tap. After tacking, the tip can be easily unscrewed;
3. Etching with acid compounds. If the tap breaks in non-ferrous metal, you can etch it with acid. The use of hydrochloric or sulfuric acid is dangerous to health, so it is necessary to use citric or oxalic acid. The solution is poured into the hole and heating is carried out. The tap corrodes intensely, and after some time it can be removed.

And in conclusion, video information on cutting internal threads with a tap.

Source: https://obinstrumente.ru/ruchnoj-instrument/tablica-po-podboru-metchikov.html

Is it possible to cut threads in cast iron? — Metals, equipment, instructions

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.

Manual cutting of internal threads is performed using metalworking taps complete with a wrench

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.

1. 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.
2. 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.
3. 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.
4. 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.

A good tap is made of high-quality tool steel, looks neat and has smoothly machined turns and grooves

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°.

When drilling blind holes, control the drilling depth

How to cut threads correctly? First you need to select tools and consumables:

1. an electric drill or drilling machine capable of operating at low speeds;
2. a drill whose diameter is calculated or selected using reference tables;
3. a drill or countersink, with the help of which a chamfer will be removed from the edge of the prepared hole;
4. a set of taps of the appropriate size;
5. manual holder for taps (drives);
6. bench vice (if the product in which the thread needs to be cut needs to be fixed);
7. core;
8. hammer;
9. 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;
10. rags.

Diagram of thread cutting with a tap

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.

  Is it possible to line a potbelly stove with bricks?

The harder the material being processed, the more abundantly the tap must be lubricated during the thread cutting process.

Before making internal threads with a tap or cutting threads with a die on external surfaces, you should thoroughly study these procedures and strictly follow the rules for their implementation. Only in this case can you count on the result satisfying you with its quality and accuracy.

Source: https://spb-metalloobrabotka.com/mozhno-li-narezat-rezbu-v-chugune/

Thread cutting methods

Thread cutting is required for the manufacture of fasteners or fasteners of various designs from blanks. This requires a minimum number of tools, the technology is easy to implement, and experience is not required. Strict adherence to the basic cutting rules will allow you to create high-quality threads.

Thread cutting machine

Basic cutting methods

Threading methods:

• cutters or combs;
• dies, taps;
• rolling with round or flat dies;
• on a milling machine using special cutters;
• grinding with special wheels.

To cut external threads, cutters, dies, cutters, circles are used, and internal threads are used with taps.

To obtain a part with an accurate internal or external thread, when cutting with the tool holder, it is necessary to make one revolution around the axis by 1800, and the second - in the opposite direction by 900. This rule will allow you to get rid of long chips that have accumulated in the die and reduce the amount of applied rotational force.

How to cut threads

To cut threads, you will need the following tools:

• tap, set of thread-cutting tools, dies;
• drilling machine with speed control;
• electric drill with low speed operating mode;
• a set of drills for creating holes in parts;
• vice for fixing the workpiece;

Machine-hand taps are designed for manual use or for mounting in a drill chuck. For machine use, the designs are distinguished by an extended shank. It will not be possible to install a tap holder for manual threading on it.

• hammer;
• core for creating marks for drilling holes;
• a lubricant that prevents the tool or workpiece from overheating during processing;
• rags to remove oil after work.

Dies and taps for cutting

How to correctly determine the hole diameter

Before cutting internal threads, it is necessary to make a hole in the workpiece in advance. Its dimensions must be selected strictly, since exceeding the optimal value will not allow you to create a strong bolt connection, and reducing it will increase the likelihood of damage to the tool during operation.

To determine the diameter of the hole for a standard thread, you will need to use reference books. To create non-standard threads, you need to make simple calculations: subtract the pitch size from the diameter.

How to cut threads

Thread cutting is quite simple, but requires special care when working and a precise sequence of actions. The choice of cutting method will determine the list of tools used and the features of preparing the part for processing.

You will need a technical reference book with data on the sizes of the tools used. The thread pitch can be found on the tap used.

Preparing for thread cutting

Cut the thread only after completing the preparatory work:

• in the directory they look for the necessary information on the diameters of cutting tools for further selection;
• collect the tools needed for work;
• use a core to mark the location of the hole for the internal thread, then drill it with a drill;
• for external cutting, prepare a workpiece of the required diameter on a milling machine and cut a chamfer;
• clean the surface of the workpiece from dirt and oil stains, then apply lubricant to it and the tool.

Thread cutting tool

Work order

Only after the preparatory work should you start processing the workpiece, since otherwise it will not be possible to cut the thread correctly. Step by step cutting is done like this:

1. It is necessary to firmly fix the workpiece in a vice to prevent rotational or translational movements deviating from the original position.
2. Depending on the type of thread, chamfer (external) or drill a through or blind hole using a drill. Drills with sharpening angles are used, depending on the hardness of the material, but not more than 1400.
3. The hole needs to be chamfered with a countersink. The depth should be in the range of 0.5-1 mm, selected based on the dimensions of the part and the thread diameter.
4. Cutting is performed with a tap or die. The cutting part must be lubricated.
5. Cleaning the surface from chips using brushes.

When cutting, you need to sequentially use tools numbered from 1 to 3, included in the kit.
To increase the speed of work, it is not allowed to use large numbers without using the previous ones. The last number is used to form the finishing turns, without which the screw may jam when screwed in. Thread cutting. Set of tools. Dies, lerks, runs, taps

Thread cutting methods Link to main publication

Source: https://metalloy.ru/obrabotka/rezba/narezka-rezby