Drilling and reaming holes, tapping
Holes in various products are drilled with drills installed in flanges in drilling machines, drills, rotors. In plumbing, twist drills are most often used, since they are easy to drill and give a clean hole of more accurate dimensions.
Twist drills are available in standard diameters with a sharpening angle (tip angle) of mostly 116 in. A drill with this sharpening angle is suitable for drilling in both hard and soft materials.
There are data on the sharpening of drills for metals of different hardness, however, changing the sharpening angle makes it necessary to change the shape of the grooves for removing chips. Therefore, it is undesirable to change the sharpening angle in twist drills, as this leads to rapid tool wear.
The drills are sharpened on special machines or manually on an emery wheel. The correctness of sharpening is checked using a special template. In a well sharpened drill, the cutting edges must be exactly the same length and located at the same angle to the drill axis. The middle of the bridge should be on the axis of the drill and form an angle of 55 in with the cutting edge.
The clearance angle of the template is checked, however, it should be equal to 6 in the outer surface of the drill and increase towards its axis up to 20 °. If these rules of sharpening are not followed, the drill will beat, go to the side, it is bad to take chips and quickly heat up, and the resulting hole will be incorrect.
Drills (left. Spiral, right. Perforated)
In the absence of twist drills of the required diameter or length, feather drills can be used. They are easy to make yourself from a bar of carbon tool steel. For this, a bar of the required dimensions is heated and flattened at one end in the form of a blade.
This end is hardened and then sharpened on an emery wheel so that cutting edges are formed at the tip of the drill at the desired sharpening angle. For drilling steel, the sharpening angle is taken equal to 120 in. For brass. 90 c. For 80 V aluminum.
To drill the hole, the selected drill is inserted into the failed drill chuck and slightly clamped. Then check that the drill does NOT hit during rotation, and clamp it in the chuck as much as possible.
Before starting drilling, it is necessary to deepen each center of the marked holes by re-punching, and then fix the product in a vice on a workbench so that it does NOT bend or move during the drilling process.
The drill, first you need to set perpendicular to the surface of the product, then, slowly and carefully drilling a small depression, check whether the drill coincides with the center of the punching.
If it has moved away from the center, then it is necessary to make a deeper punching or cut two or three radial grooves from the center of the recess with a cross-cutter in the direction where the drill should be fed. In this case, the drill will take large chips where the grooves are applied and move to the desired direction.
If this time it turns out to be eccentric, then it is necessary to make a new punching, drill a hole with a thin drill, and then with a drill of the required diameter. The pressure on the drill should be such that it produces uniform chips. When the drill comes out of the metal, it is necessary to reduce the pressure, since at this moment the drill picks up large chips and can break.
When drilling deep holes, remove the drill more often and free it from jammed chips. In addition, to reduce the heating of the drill, it is necessary to apply drops of lubricant into the hole with a brush. This will result in a cleaner and more accurate hole.
When drilling steel, ductile iron, red copper and brass, use mineral oil or soapy water, and when drilling aluminum, soapy water and kerosene. Gray cast iron and bronze are dry drilled.
A large hole is drilled in two passes. First, the hole is drilled with a small-diameter drill, and then with a drill of the required diameter. This method is due to the fact that drills with a smaller diameter are easier to install at the drilling point. In addition, the hole is more correct and more accurate.
You should be especially careful when using an electric drill with thin and long drills. In such cases, the worker must take a comfortable and stable position. The drill must be directed so that the drill coincides with the axis of the future hole.
It is advisable to finish drilling once, and do not remove the drill from the hole and DO NOT deflect the drill to the side, since the slightest tilt of the drill will break the drill. In this case, the feed is needed very low, and if the drill is in a vertical position, then the drill feed is carried out by the weight of the drill’s own weight.
When drilling large and shaped holes in sheet metal, a number of small holes are pre-drilled equally near the second so that they almost reach the marking mowing line. The gaps between these holes are cut with a cross cutter, and irregularities are cut with a file. Holes in cylindrical parts are drilled on a stand with cut out recesses.
Reaming is called the reaming workflow. Reaming of holes is performed when assembling parts, when a slightly larger hole is required or greater accuracy and purity of its finish, for example, for calibrating the bore of bushings.
In plumbing, manual cylindrical and conical reamers are used. Manual reamers have a large intake (working) part, and their tail has a square for putting on the wrench.
Tapered reamers are used for cleaning and straightening tapered holes. It is also convenient to use conical reamers to expand holes in sheet material, in the chassis of blocks. Reamers are made in a set, three pieces per set (rough, transitional and finishing) or two (transitional and finishing).
Expansion of holes on a cone for countersunk heads of screws, screws and rivets is made by conical countersink.
During manual work, the reamer should be rotated with a knob, for which leave it in the square hole of the knob.
Before using the reamer, you must check all its cutters by touch and, if any burrs are found, remove them. To obtain a hole of exact dimensions, the hole is pre-drilled with a drill, the diameter of which is 0.2 less than the required hole diameter. 0.4 mm, which provides a stock of material for deployment.
The product is clamped in a vice so that the hole is in a vertical position. Then the transitional sweep is left with the lower part in the hole and rotate it with a knob towards the direction of the sharp teeth. To obtain a hole of more accurate dimensions, a finishing one is used after a transitional sweep. It is necessary to rotate the reamer with pressure, drive it through the hole. You cannot rotate the sweep in the opposite direction.
In the repair business, threads are cut mainly by hand. Taps are used for cutting internal threads, and dies and screw boards for cutting external threads.
According to the method of application, taps are divided into manual (locksmith) and machine.
Hand taps are produced in sets. The set includes three taps: rough (first), middle (second) and finishing (third). All three taps are made so that the thickness of the chips cut by each tap is more or less the same. The third tap is used last for finishing and calibrating threads.
It is very important to select the correct drill diameter for drilling holes for threads.
For threading in soft metals such as copper or aluminum, the diameter of the hole must be taken a little larger, since when cutting, such metals are squeezed out, causing the taps to jam and galling.
The thread is cut as follows: the product is clamped in a vice, and the end of the first taps is inserted into the hole as accurately as possible and pressed on it with a knob.
At the beginning of work, the crank is taken with the right hand, grasping the tap with the thumb, middle and forefinger, and with slight pressure slowly rotate the tap clockwise, keeping its vertical position. As soon as the tap begins to pick up the chips, they switch to rotation with both hands. Having made one turn to the right, make half a turn to the left, etc. After passing the hole with the first tap, replace it with the second, and then the third.
With a thread length of up to 5 mm, only the first and third taps are bypassed, and for cutting less accurate threads, it is enough to use the first two taps. When cutting deep holes, unscrew the tap more often and clean it with a brush from chips, and lubricate the cutting area with two or three drops of oil. Holes in bronze and sir cast iron cut dry.
Dies and screw boards are used for cutting external threads. Dies are round (split and continuous). They are also called Lerka. For work, the die is inserted into a special Klupp with clamping screws.
Threading with round dies and screw boards is done in the same way as taps. When cutting with dies, it is important that the diameter of the rod is slightly less than the outer diameter of the cutting of the dies.
The cutting bolt is fixed in a vice and slightly rounded from above with a file for better grip with a die. Having lubricated the bolt with oil, put on a die on top and, pressing hard on it, at the same time turn Klupp to the right. As soon as the die picks up the chips, the Klupp is rotated in the same way as when working with a tap, i.E. After each full rotation, half a turn is made back. The thread is cut in one to two passes.
Equipment and accessories for drilling
A hole drilling tool has been developed for each stage. At the preparatory stage, the following tools are used to accurately mark the location of the future hole. For this, use: a core, a special template or a conductor. The core is a well-sharpened rod made of durable tool steel. With its help, a depression is made on the surface of the workpiece, at the point where it is planned to drill. Getting into this recess, the drill does NOT slide on the surface and accurate drilling is performed.
To increase productivity in enterprises with mass production, special templates are made. They allow marking the locations of future holes in the same type of workpieces. Special templates are used for drilling on cylindrical surfaces. They are made from a steel strip bent at a right angle. A small hole is drilled on one of the surfaces, which will later allow the core to mark the cylindrical surface.
To obtain increased accuracy of marking, observance of the vertical position of the drill and observance of the specified distance, a tool called a jig is used between the holes. In addition, it is used when drilling thin-walled products for which strong mechanical impact is NOT possible (for example, a hammer blow on a core).
In addition to THESE products, tools and devices are used that allow drilling with a drill when it is rigidly fixed. For this purpose I use:
- Guide latch;
- Holding rack;
- Guide to guide the drill.
The first two fixtures are made for a specific design of the Electric drill. The jig allows you to accurately guide the drill to the place of the future hole. It is successfully used for sizes, and not exceeding 20 millimeters. Therefore, when making large-diameter holes with the help of a jig, pre-boring is performed.
All these problems are easily solved when using drilling or turning machines. Drilling machines are divided into three categories:
They are classified according to the following criteria:
- Table design;
- Level of automation;
- The number of spindles available;
- Degree of accuracy;
- Availability of additional features.
The first category of machines allows you to solve almost the entire range of tasks for the production of holes. A serious limitation is the permissible distance that the chuck can move with the drill fixed. This circumstance does not allow drilling to a great depth. In this case, specialized machines are used. To increase labor productivity and increase the number of manufactured parts of the same type, special units are designed. They are capable of performing a list of required operations with high precision and speed.
By design, these machines are available with one or more spindles. The design of the table is diverse: ordinary, floating, lifting and others. The level of automation is determined by the way the drilling operations are performed. The simplest machines are manual and mechanical. advanced are automatic and numerical control machines.
In addition to drilling machines, various lathes are used to solve THESE tasks.
On a lathe, you can perform the entire list of operations related to obtaining holes: directly drilling itself, drilling with subsequent reaming or countersinking.
Drilling holes in metal and wood
The production of many metal parts involves the creation of various types of holes in the structure. They can be through or deaf. Holes are drilled when carrying out plumbing work. These operations allow you to get holes of different diameters and required depths. The technology of drilling holes in metal is brought in line with the flow chart. The drawing indicates the dimensions of the hole, the size of the tolerance, design features (for example, a constant or variable diameter, chamfering from one or both edges, and so on).
To obtain accurate and high-quality holes, it is necessary to observe the modes and technologies of all operations. Drilling metal assumes compliance with the following modes:
- Selection of the required diameter and type of drill;
- Cutting speed and depth;
- Feed speed and accuracy (drill or workpiece)
- The angle of contact of the cutting surface with the workpiece;
- Heating temperatures of the workpiece and drill (providing cooling, if necessary).
Fulfillment of all modes allows obtaining a hole in the metal that meets the conditions of the design documentation. Correctly selected mode improves machining accuracy and extends tool life. Special tables have been developed for the selection of drilling modes for metal products. They include precise parameters for cutting data. For example, knowing the steel grade and the diameter of the drill used, you can use the conversion table data to set the cutting speed. This will allow you to fine-tune the spindle speed of the machine used. To do this, use a conversion table, which is applied to a special plate and fixed on the front panel of each machine.
In SEPARATE cases, pre-drilling is used. It prepares the rough hole for further processing (milling or reaming). If the workpiece is thick enough or you need to get a deep hole, use a phased manufacturing mode.
Hole types and drilling methods
In the theory of metalworking, all holes are divided according to the following criteria:
- Geometrical dimensions and depth;
- Degree of processing.
According to their purpose, they are subdivided: for fastening two or more elements, subsequent threading, insertion of SEPARATE structural elements.
On the second basis, the following types are considered:
- Deaf (including deep)
- Large diameter.
A special place is occupied by holes, which are prepared for cutting internal threads. In this case, drilling and reaming of the holes is carried out taking into account the future diameter of the screwed in element with an external thread. For each of the holes, choose their own drilling methods.
Since drilling is a process of mechanical cutting of metal, therefore, in order to obtain the desired result, the necessary processing methods should be selected. For the production of through holes in parts, it is necessary to think over a system of their fastening, which will NOT allow damaging the surface behind the part. It is most advisable to apply pressure or clamps.
For the production of blind or half holes, an exact stop of the drill should be provided, which will provide the required size. Drilling large holes requires special equipment. If you need to get holes of different diameters, you should choose the Required set of Drills or use machines with numerical control. They will allow you to automatically change the drill to a tool with a given diameter.
The process involves the successive removal of a layer of metal in a circle of a given diameter using a cutting tool. Drilling in metal combines two types of movement. rotary and translational. To obtain the required hole dimensions in metal blanks, it is necessary to accurately maintain the following parameters of the technological process:
- Cutting tool rotation speed;
- Speed of horizontal or vertical movement (depending on the relative position of the workpiece and the drill).
A hole in the metal is obtained with the specified parameters only if the preparatory and basic operation is correctly performed, as well as the selection of the necessary equipment and cutting tools. Pre-drilling is often performed to obtain the required accuracy. It’s called rough. The operation is performed with a reduced accuracy class. Next, the finishing operation is carried out using high-precision machines and tools for metal blanks.
In all cases, various types of drills are used to obtain the required hole. On drilling machines, the chuck with the fixed drill rotates and is brought to the surface of the workpiece. On metal cutting machines, the drill is fixed in the tailstock of the machine, and the workpiece rotates. The second method allows you to get a higher accuracy of the hole and the walls of the resulting hole.
Depending on the tasks for both methods, the following types of drills are used:
- Spiral (the most common type of this tool)
- With soldered plates on the cutting edge;
- Feather (used for drilling holes in workpieces from any wood species).
Twist drills exert pressure on the metal surface with their transverse edges. This process accounts for more than 65% of the effort in rotational and translational movement. At this point, there is a significant increase in temperature, both of the surface of the workpiece and the leading edge of the drill. Therefore, it is necessary to correctly observe the thermal regime during the drilling process.
To speed up the cutting process in twist drills, so-called double sharpening is used. It allows you to work more efficiently on the hardest metal grades, including cast iron. Such sharpening leads to an increase in the chip width, the value of the main angle decreases, and the durability and durability of the drill increases.
Centering hole technology involves the use of Special Centering Drills. They are made of tool steel and have a double-sided combination design.
Application of plates with increased strength to the cutting edge of the drill allows them to be used for drilling in cast iron, metal of increased hardness, dense building structures (from concrete, stone, ceramic granite, and so on).
Pen drills differ in the cutting edge design. It is made in the form of plates. They are usually used for making holes in wood blanks. Sometimes special nib drills are used to make holes in hard forgings and some types of casting.
When carrying out work, professionals advise Pay attention to the following features. They are divided into three categories:
- Preliminary (preparatory) stage;
- Stage of work;
- Safety compliance.
At the first stage it is necessary:
The preliminary stage should end with a check of the reliability of the drill and workpiece fastening. If a drill retainer is used, check its reliability.
Hole drilling operations Must be carried out in strict sequence with the drawn up flow chart or technical process. Particular attention should be paid to:
- The drill must be brought to the place of the future hole only after it has entered the specified rotation speed;
- Remove the drill only during its rotation (preferably at minimum speed, if there is a possibility of changing the rotation speed)
- Observe the cutting process (for example, if the cutting edge does NOT perform the drilling operation, therefore the drill material is softer than the workpiece material)
- To drill NOT through holes, a fixer or a mark must be provided to determine the depth of the passage in the material;
- When working on machines equipped with CNC, it is necessary to control the sequence of operations.
An important element when carrying out drilling work is compliance with safety measures. It assumes compliance with the following rules:
- Ensuring the reliability of fastening all structural elements;
- Organization of the conditions for the removal of the formed shavings;
- Compliance with the temperature regime (preventing overheating of the drill and workpiece)
- The use of special clothing and protective equipment (hands, eyes, open areas of the body);
- There should be no hanging elements on the clothes;
- Long hair Must be tucked into the headgear (this will prevent it from being wound around the rotating parts of the machine).
The use of professional advice will allow you to perform a high-quality drilling operation and get holes of a high degree of accuracy at the places indicated in the design documentation.
Internal threading technology
As mentioned above, before starting work, you need to drill a hole, the diameter of which must exactly fit the thread of a certain size. It should be borne in mind: if the diameters of the holes intended for cutting metric threads are chosen incorrectly, this can lead not only to poor performance, but also to breakage of the taps.
Taking into account the fact that the tap, while forming the threaded grooves, not only cuts the metal, but also pushes it, the diameter of the drill for making the thread should be slightly less than its nominal diameter. For example, a drill for threading M3 should have a diameter of 2.5 mm, for M4. 3.3 mm, for M5 you should choose a drill with a diameter of 4.2 mm, for M6 threads. 5 mm, M8. 6.7 mm, M10. 8.5 mm, and for M12. 10.2.
Table 1. Main diameters of holes for metric threads
Table 2. Diameters of holes for inch threads
All diameters of drills for GOST threads are given in Special tables. In such tables, the diameters of the drills for making threads with both standard and reduced pitch are indicated, while it should be borne in mind that holes of different diameters are drilled for THESE purposes. In addition, if the thread is cut in products made of brittle metals (such as cast iron), the diameter of the threaded drill obtained from the table must be reduced by one tenth of a millimeter.
The diameters of drills for metric threads can be calculated independently. Here is the diameter of the thread that you want to cut, you need to subtract the value of its pitch. The thread pitch itself, the size of which is used when performing such calculations, can be found from the Special lookup tables. In order to determine what diameter the hole must be made with a drill in the event that a three-way taps will be used for threading, you must use the following formula:
Din = Dm x 0.8, where:
Din. this is the diameter of the hole to be made with the drill,
Dm. diameter of the taps with which the drilled element will be processed.
Tapping scheme for internal threading
The gates, in which the thread taps are inserted, can be of the simplest design or equipped with a ratchet. Working with such devices with tools fixed in them should be very careful. To obtain a high-quality and clean thread, the rotation of the taps clockwise, made half a turn, must be alternated with turning it one-fourth of a turn against the thread.
Threads will cut much more easily if lubricant is used during this procedure. The role of such a lubricant when cutting threads in steel products can be played by drying oil, and when processing aluminum alloys. alcohol, turpentine or kerosene. If such technical fluids are on hand, regular machine oil can be used to lubricate taps and threads (however, it has less effect than the substances listed above).
The strength of fastening the parts to each other is ensured by screwing the carrier of the external thread into the internal one of the second product. It is important that their parameters are kept in accordance with the standards, then such a connection will NOT be broken during operation and will provide the necessary tightness. After there are norms for the implementation of the thread and its SEPARATE elements.
Before cutting, a hole is made inside the part for a thread, the diameter of which should NOT exceed its internal diameter. This is done using drills for metal, the dimensions of which are given in the reference tables.
Manual or automatic cutting methods provide results in different accuracy and roughness classes. So, the main tool remains taps, which is a rod with cutting edges.
- Manual, for metric (M1-M68), inch. ¼-2 “. Pipe. 1 / 8-2”;
- Machine-manual. attachments for drilling and other machines, used for the same sizes as manual;
- Wrenches, which allow you to cut a through version for thin parts, with a nominal size of 2-33 mm.
- A set of tap rods is used for cutting metric threads:
- Rough, having an elongated intake part, consisting of 6-8 turns, and marked with one line at the base of the shank;
- Medium. with an intake part of an average length of 3.5-5 turns, and marking in the form of two dashes;
- Finishing has an intake part of only 2-3 turns, without risks.
Tolerance control of metric thread location
With manual cutting, if the pitch exceeds 3 mm, then 3 taps are used. If the step of the product is less than 3 mm, two are enough: rough and final.
The taps used for small metric threads (M1-M6) have 3 flutes for chip evacuation and a reinforced shank. In the design of the rest there are 4 grooves, and the shank is through.
The diameters of all three metric rods increase from rough to finish. The last threaded rod must have a diameter equal to its nominal.
The taps are attached to special devices. a tool holder (if it is small) or a knob. They are used to screw the cutting rod into the hole.
Holes are prepared for cutting using drills, countersinking and lathes. It is formed by drilling, and countersinking and boring increase its width and improve the surface quality. Fixtures are used for cylindrical and conical shapes.
The drill is a metal rod consisting of a cylindrical shank and a helical cutting edge. Their main geometric parameters include:
- The angle of helical lift, usually 27 °;
- Taper angle, which can be 118 ° or 135 °.
Countersinks for cylindrical shapes are called counterbores. They are metal rods with two cutters twisted into a spiral and a fixed guide pin to insert the countersink into the cavity.
Varieties and parameters of thread
The parameters by which the thread is divided into different types are:
- Diameter units (metric, inch, etc.);
- Number of thread starts (one-, two- or three-way)
- The shape in which the profile elements are made (triangular, rectangular, round, trapezoidal)
- Direction of lifting the turns (right or left)
- Location on the product (external or internal)
- Surface shape (cylindrical or conical)
- Purpose (fastening, fastening and sealing, running).
Metric thread options
Depending on the above parameters, the following types of thread are distinguished:
- Cylindrical, which is designated by the letters MJ;
- Metric and conical, denoted respectively M and MK;
- Pipe, for which the letters G and R are used;
- With a round profile, named after Edison and marked with the letter E;
- Trapezoidal, denoted by Tr;
- Round, used for the installation of sanitary fittings. Kr;
- Resistant and resistant reinforced, marked as S and S45 respectively;
- Inch thread, which can also be cylindrical and conical. BSW, UTS, NPT;
- Used to join pipes installed in oil wells.
Thread types according to GOST
A manual tap can be used to cut by observing the following steps:
- Drill an opening for the thread of the corresponding diameter and depth;
- To carry out its countersinking;
- Fix the tap in the holder or wrench;
- Set it perpendicular to the working cavity in which cutting will be carried out;
- Screw the tap with light pressure clockwise into the hole prepared in advance for threading;
- Turn the tap back every half-turn to cut the chips.
To cool and lubricate surfaces during the cutting process, it is important to use lubricants: machine oil, drying oil, kerosene, and the like. Incorrectly selected lubricant can lead to poor quality cutting results.
Before proceeding with threading, it is necessary to determine the diameter of the preparation hole and drill it. To facilitate this task, the Corresponding GOST was developed, which contains tables that allow you to accurately determine the diameter of the hole for the thread. This information makes it easy to select the drill size.
To cut a metric type thread on the inner walls of a hole made with a drill, a tap is used. a screw-shaped tool with cutting grooves, made in the form of a rod, which can have a cylindrical or conical shape. On its lateral surface there are special grooves located along its axis and dividing the working part into separate segments, which are called a comb. Sharp edges The comb are the working surfaces Taps.
Tap: design and parameters
In order for the internal thread turns to be clean and neat, and its geometric parameters correspond to the required values, it must be cut gradually, by gradually removing thin layers of metal from the surface to be treated. That is why, for this purpose, either taps are used, the working part of which is divided along the length into sections with different geometric parameters, or sets of such tools. Single taps, the working part of which has the same geometric parameters along its entire length, are needed in cases where it is necessary to restore the parameters of an existing thread.
The minimum set, with the help of which it is possible to perform the machining of the holes for the thread with sufficient quality, is a set consisting of two taps. a rough and a finishing one. The first cuts off a thin layer of metal from the walls of the hole for cutting metric threads and forms a shallow groove on them, the second Not only deepens the formed groove, but also cleans it.
Varieties of thread taps and their differences
Minimum set of taps
Combined two-way taps or sets of two tools are used for tapping small holes (up to 3 mm). For larger metric holes, use a 3-pass combination tool or a set of 3 taps.
To manipulate the tap, a special device is used. a knob. The main parameter of such devices, which can have a different design, is the size of the bore, which must exactly match the size of the tool shank.
Some varieties of taps
When using a set of three taps, differing in both their design and geometric parameters, the sequence of their use should be strictly observed. They can be distinguished from each other both by the special risks applied to the shanks and by their design features.
- The tap, with which the hole for the metric thread is machined first, has the smallest diameter among all the tools in the set and cutting with teeth, the top of which is heavily cut.
- The second tap has a shorter nose and longer flanges. Its working diameter Occupies an intermediate value between the diameter of the rest of the tools from the set.
- The third tap, with which the hole for tapping metric threads is processed last, is characterized by full ridges of the cutting teeth and a diameter, which must exactly match the size of the formed thread.
Set of three taps
Taps are mainly used for tapping metric type threads. Significantly less often than metric taps are used, designed for processing the inner walls of pipes. In accordance with their purpose, they are called pipe, and they can be distinguished by the letter G, which is present in their marking.
Types of thread
Threads according to the measurement system are divided into metric, expressed in millimeters, and inch, measured in the appropriate units. Both of THESE types can be performed in both cylindrical and conical shapes.
They can have profiles of various shapes: triangular, trapezoidal, round; divided by application: for fasteners, plumbing elements, pipe and others.
The diameters of the preparatory holes for threading depend on its type: metric, inch or pipe, this is normalized by the relevant documents.
Holes in pipe connections, expressed in inches, are prescribed in GOST 21348-75 for cylindrical shape and GOST 21350-75 for conical shape. The data is valid when copper and nickel-free steel alloys are used. Cutting is carried out inside auxiliary parts, into which pipes will be screwed. shale, clamps and others.
In GOST 19257-73, the diameters of holes for cutting metric threads are given, where the tables show the size series of nominal diameters and pitches, as well as the parameters of holes for metric threads, taking into account the values of the maximum deviations.
Thread types according to GOST
The data given in the table GOST19257-73 confirm the calculation given above, in which the parameters of holes for metric types are calculated from the nominal diameter and the pitch.
GOST 6111-52 standardizes the diameters of the holes for the inch tapered thread. The document indicates two diameters with a divergence on a taper and one without reaming, as well as drilling depths, all values, except for the nominal value, are expressed in millimeters.
The following thread parameters are distinguished:
- Diameters (internal, external, and so on);
- Profile shape, height and angle;
- Step and entry;
The condition for connecting the parts to each other is complete coincidence of the indicators of the external and internal threads. If any of them is performed without observing the requirements, then the fastening will be unreliable.
Fastening can be bolted or studded, which, in addition to the main parts, include nuts and washers. Holes are formed in the parts to be fastened before joining, and then cutting is carried out.
In the case of through execution, the hole diameter should be 5-10% larger than the size of the bolt or stud, then the condition is met:
Where d is the nominal diameter of the bolt or stud, mm.
To determine the size of the hole of the second part, the calculation is carried out as follows: the step size (P) is subtracted from the value of the nominal diameter (d). the result obtained is the desired value:
The calculation results are clearly shown in the table of thread hole diameters, compiled according to GOST 19257-73, for sizes 1-1.8 mm with small and basic steps.
|Nominal diameter, mm||Step, mm||Hole size, mm|
An important parameter is the drilling depth, which is calculated from the sum of such indicators:
- Screw-in depth;
- Stock of external thread of the screwed-in part;
- Its undercuts;
In this case, the last 3 parameters are reference, and the first is calculated through the factors of accounting for the material of the product, which are equal for products from:
- Steel, brass, bronze, titanium. 1;
- Gray and high-strength cast irons. 1.25;
- Light alloys. 2.
Internal thread on barrel coupling
Thus, the screw-in depth is the product of the material accounting factor and the nominal diameter, and is expressed in millimeters.
Drilling holes for tapping
Despite the fact that internal threading is not a complex technological operation, there are some peculiarities of preparation for this procedure. So, you should accurately determine the dimensions of the preparatory hole for threading, and also choose the right tool for which special tables of diameters of drills for thread are used. For each type of thread, use the Corresponding Tool and calculate the diameter of the preparation hole.
Thread diameter and bore must be in accordance with standards, otherwise the grooves will come out too small and the threaded connection will be unreliable
Drill size selection
The drill diameter for a hole for a metric thread is determined in the same way by formula (2), taking into account its main parameters.
It should be noted that when cutting in plastic materials, such as steel or brass, an increase in turns occurs, therefore it is necessary to choose a drill diameter larger for the thread than for brittle materials such as cast iron or bronze.
In practice, the dimensions of the drills are usually slightly smaller than the required hole. So, table 2 shows the ratio of the nominal and outer thread diameters, pitch, hole diameters and drills for it for cutting metric threads.
Table 2. Correlation of basic parameters of metric threads with normal pitch and diameters of holes and drills
|Nominal diameter, mm||Outside diameter, mm||Step, mm||Largest hole diameter, mm||Drill diameter, mm|
As you can see from the table, there is a certain dimensional limit, which is calculated taking into account the tolerances for the thread.
The size of the drill is then significantly smaller than the hole. So, for example, for a M6 thread, the outer diameter of which is 5.88 mm, and its largest hole value does not have to exceed 5.153 mm, it is worth using a 5 mm drill.
The hole for the M8 thread with an outer diameter of 7.87 mm will be only 6.912 mm, which means that the drill for it will be 6.8 mm.
The quality of the thread depends on many factors when cutting it: from the choice of the tool to the correctly calculated and prepared hole. Too small it will lead to increased roughness and even breakage of the taps. Large forces applied to the taps. contribute to non-compliance with tolerances and, as a result, the dimensions are not kept.
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Drill and thread size charts: metric, inch
Internal threading is usually NOT difficult. But there are some peculiarities of using the tool and selection of holes for cutting metric threads.
Types of thread
They differ in their main characteristics:
- System of calculating the diameter (inch, metric, others);
- Number of calls (two-, three- or one-way)
- Profile shape (rectangular, trapezoidal, triangular, round)
- Direction of rotation of the screw (left or right)
- Placement on parts (internal or external)
- Part shape (cone or cylinder)
- Purpose (running, fastening and sealing or fastening).
According to the listed characteristics, the following types are distinguished:
- Cylindrical (MJ)
- Metric and conical (M, MK)
- Pipe (G, R);
- Edison’s round (E)
- Trapezoidal (Tr)
- Round for plumbing fixtures (Kp)
- Persistent (S, S45)
- Inch, including cylindrical and conical (BSW, UTS, NPT)
- Oil country.
Before you start cutting, you should make a hole in the workpiece with the help of the Drill. The diameter of the hole from the drill must match the internal thread size. When the size of the made Drill hole is selected incorrectly, the tool may break or the grooves will be of poor quality.
For example, when cutting M5 (groove diameter is 5 mm), you should choose a drill for a 4.2 mm hole. To cut M4, the drill diameter should be 3.3 millimeters, and before working with the M6 tap, a hole is pre-drilled with a 5 mm drill. This indicator is calculated taking into account the thread pitch. The step can be calculated mathematically, but in practice they resort to correspondence tables, where for M5 taps the step is 0.8, for M4 this indicator is 0.7, for M6. 1. Subtract the step indicator from the diameter and get the required drill diameter. When working with brittle metals such as cast iron, the drill diameter should be reduced by 0.1 mm compared to the recommended size in the table.
The formula for calculating the hole diameter when working with three-way taps:
K = Dm 0.8;
Here: Dm. diameter Taps.
Table 1. Correspondence of thread diameters and preparation holes
Before starting work, the tap is inserted into a square shank. a knob. The gates can be conventional or with a ratchet. The thread is done carefully, the first pass is made with a tap number 1 to the end. Particular attention must be paid to the direction of movement: only clockwise, while it is necessary to apply some effort. It is carried out as follows: 1 \ 2 of a turn along the way alternates with 1 \ 4 of a turn against the screw stroke to break the chips.
|Thread in inches||Outer D, mm||Diameter, mm||Step, mm|
|3 \ 16 “||4.762||3.47||1,058|
|5 \ 16 “||7,938||6.13||1.411|
|7 \ 16 “||11,112||8.79||1,814|
|3 \ 8 “||9.525||7.49||1.588|
Table 2. Bore diameters for inch threads
Internal threading tools
To make internal cuts, you need a tap. a screw-shaped tool with sharp flutes. The rod can be in the form of a cone or a cylinder. The grooves run along and break the thread into sections called a comb. The edges of the Combs are the working surfaces.
Single taps are also found on the market, they are more often used to fix broken threads. To cut a new one, they buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing. The first cuts a shallow groove, the second cleans and deepens it. There are also three-pass instruments. Thin, up to 3 millimeters, taps are sold in two, wider ones in three. Three-way taps are inserted into the vertical. The Vorotkovy device is different, but their size must match the size of the cutter.
In a set, tools are distinguished by the risks applied to the tail end. If you look closely, you can see the shape differences:
- The first tap with strongly cut tops of the teeth, the outer diameter is slightly smaller than the second tools in the set;
- A second tap with a shorter intake segment, longer flanges. Its diameter is slightly larger than in the first;
- The third tap has full ridges of teeth, and its diameter must match the dimensions of the future thread.
Taps are divided into pipe (marked “G”) for threading inside the pipe and metric. the more common.
Homemade tap for aluminum alloys
To create internal threads in brass or light alloy parts, you can use a homemade tool and drills from a regular set. Calibrated steel wire will do. With the help of a die, an external thread is cut on it, after which the workpiece is hardened. After hardening, it is necessary to release the part to the color of ripe straw. The cutting edges are sharpened with a bar or sharpener, after clamping the part in a collet chuck.
In how the internal thread is cut: