How to determine which tap is needed. How to choose the right drill for the tap? Thread cutting technology

Making an internal thread is usually not difficult. But some features of using a tool and selecting holes for cutting metric threads exist.

Thread types

They differ in the main characteristics:

• diameter calculation system (inch, metric, others);
• number of visits (two-, three- or single-pass);
• profile shape (rectangular, trapezoidal, triangular, round);
• direction of rotation of the screw (left or right);
• placement on the part (internal or external);
• the shape of the part (cone or cylinder);
• purpose (running, fastening-sealing or fastening).

According to the listed signs, the following types are distinguished:

• cylindrical (MJ);
• metric and conical (M, MK);
• pipe (G, R);
• Edison round (E);
• trapezoidal (Tr);
• round for plumbing fixtures (Kp);
• thrust (S, S45);
• inch, including cylindrical and conical (BSW, UTS, NPT);
• oil grade.

Tools for making internal threads

To make an internal thread, you need a tap - a helical tool with sharp grooves. The rod may be in the form of a cone or a cylinder. The grooves run along and break the thread into sections called combs. It is the edges of the combs that are the working surfaces.

To make the groove clean, the metal is removed gradually, in layers. This requires one very long tool or set.

Single taps are also found on sale, they are more often used to fix stripped threads. To cut a new one, they buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing work. The first cuts a shallow groove, the second cleans and deepens it. There are also three-pass tools. Thin, up to 3 millimeters taps are sold in twos, wider taps in threes. Three-way taps are inserted into the collars. The device of the knobs is different, but their size must match the size of the cutter.

In the set, the tools are distinguished by the risks applied on the tail end. If you look closely, you can notice the differences in shape:

• the first tap with heavily cut tooth tips, the outer diameter is slightly smaller than the other tools in the set;
• second tap with shorter pick segment, longer combs. Its diameter is slightly larger than that of 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 taps (marked with a “G”) for threading inside a pipe and metric taps - more common.

The quality directly depends on the properties of the tap: it must be made of good metal and sharp. Lubrication is used to extend the life of the tool and improve the quality of the thread. It usually takes 3-5 attempts to acquire a stable slicing skill.

cutting process

Before you start cutting, you should use drills to make a hole in the workpiece. The diameter of the hole from the drill must match the internal size of the thread. When the size of the hole made by the drills is not chosen correctly, you can break the tool or the grooves will turn out to be of poor quality.

During cutting, part of the metal does not fall out with chips, but is pressed through the working surfaces of the tap, forming a groove profile on the workpiece. Given this feature, the size of the drill with which the hole for the thread is made is selected slightly less than the nominal diameter of the future thread.

For example, when cutting M5 (groove diameter is 5 mm), you should choose a drill for a hole of 4.2 mm. For cutting M4, the diameter of the drill should be 3.3 millimeters, and before working with the M6 ​​tap, a hole is first made 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 the M5 tap the step is 0.8, for M4 this figure is 0.7, for M6 - 1. Subtract the step indicator from the diameter and get the desired drill diameter. When working with brittle metals, such as cast iron, the drill diameter should be reduced by 0.1 mm compared to the size recommended in the table.

The formula for calculating the hole diameter when working with three-pass taps:

Up to \u003d Dm * 0.8;

where: Dm is the diameter of the tap.

Table 1 Correspondence of thread diameters and preparatory holes

Before starting work, the tap is inserted into a square shank - a crank. Collars can be regular or with a ratchet. The carving is done carefully, the first pass is made with tap No. 1 to the end. Particular attention must be paid to the direction of movement: only clockwise, while some effort is necessary. It is carried out as follows: 1/2 turn in the direction alternates with 1/4 turn against the screw to break the chips.

Table 2. Hole diameters for inch threads

A couple of drops of lubricant make it much easier to work on blind threaded holes. Although engine oil is sometimes used as a lubricant, drying oil is optimal for working with steel. With aluminum alloys, it is preferable to use kerosene, alcohol or turpentine. Technical oil can also be used, but with less effect.

Homemade tap for aluminum alloys

To create internal threads in brass or alloy parts, you can use a homemade tool and drills from the usual set. Suitable calibrated steel wire. 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.

Video on how to cut an internal thread:

To cut an internal thread on a part, you must first drill a hole. Its size is not equal to the diameter of the thread, but should be slightly smaller. You can find the diameter of the drill for a thread in a special table, but for this you also need to know the type of thread.

main parameters

• diameter (D);
• step (P) - the distance from one turn to another.

They are determined by GOST 1973257-73. A large step is considered normal, but several smaller ones correspond to it. A small pitch is used when applied to thin-walled products (thin-walled pipes). They also make a small turn if the applied thread is a way to adjust any parameters. Also, a small step between the 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 threaded hole in each case is different. All of them are spelled out in GOSTs, 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.

fixtures

For threading with your own hands, small devices are used:

All these devices are made of alloys, which are characterized by increased strength and resistance to abrasion. Grooves and grooves are applied to their surface, 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 - knobs and die holders - fixed there with screws. Clamping the threading tool in the holder, put it on / insert it into the place where you want to make a detachable connection. By scrolling the device, turns are formed. It depends on how correctly the device is set at the beginning of work whether the turns “lie down” evenly. Therefore, make the first turns trying to keep the structure even, avoiding shifts and distortions. After a few turns have been made, the process will become easier.

You can cut threads of small or medium diameter manually. Complex types (two- and three-way) or working with large diameters by hand is not possible - too much effort is required. For these purposes, special mechanized equipment is used - on lathes with taps and dies attached to them.

How to cut correctly

You can thread almost any metal and their alloys - steel, copper, aluminum, cast iron, bronze, brass, etc. It is not recommended to make it on a red-hot iron - it is too rigid, it will crumble during operation and it will not be possible to achieve high-quality turns, which means that the connection will be unreliable.

Tool for the job

Training

It is necessary 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 available, soaked soap can be used. You can also use other lubricants:

You can often hear advice to use machine or mineral oil or even lard when threading. They work well, but experts say that it is better not to do this - the chips will stick to a viscous substance, which will lead to rapid wear of the tap or die.

Slicing process

When cutting an external thread, the die is placed strictly perpendicular to the surface of the pipe or rod. During operation, it should not wag, otherwise the turns will turn out to be uneven and the connection will be ugly and unreliable. The first turns are especially important. It depends on how they “lie down” whether the connection will then be skewed.

By applying an internal thread, the part is fixed motionless. If it is a small piece, it can be clamped in a vise. If the plate is large, ensure its immobility by 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 a little effort, little by little, they begin to twist in a given direction. As soon as you feel that the resistance has increased, unscrew the tap back and clean it of chips. After cleaning, the process continues.

The process of slicing in a photo

When threading in a blind hole, its depth should be slightly more than required - this excess should include the tip of the tap. If this is structurally impossible, the tip is cut off from the tap. At the same time, it is not suitable for further operation, but there is no other way out.

In order for the turns to turn out to be of high quality, two taps or dies are used - roughing and finishing. The first pass is a rough pass, the second is a finish pass. There are also combined threading devices. They allow you to do everything in one pass.

One more practical advice: so that the chips do not fall into the working area, when cutting, make one full turn clockwise, then half a turn counterclockwise. After that, the tool is returned to the place where it stopped and again make one revolution. So continue to the required length.

Tapping drill diameter selection tables

When making an internal thread, a hole is pre-drilled under it. It is not equal to the diameter of the thread, since during 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 applying, it is necessary to select the diameter of the drill for the thread. This can be done in tables. They are for each type of thread, but we will give the most popular ones - metric, inch, pipe.

Once again, we draw your attention to the fact that the diameter of the drill for threading is given for large (standard threads).

Table of rod diameters for external thread

When working in external thread the situation is very similar - part of the metal is squeezed out, not 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.

Everyone Have a good mood! Have you ever thought about the question - what kind of miracle of technology is a tap? That's what we'll talk about. Today I will try to consider the main types and design elements of taps. After reading this post to the end, you can say with confidence that the topic has been studied.

Tap - what kind of Christmas tree is this?

Tap- This is a cutting tool that allows you to easily get a fairly accurate thread in the hole. I didn't call it the Christmas tree for nothing. After all, it has teeth and if you look at a certain angle, it looks like.

Have you ever wondered how to correctly emphasize the tap or the tap? There is an answer - if you are talking about a tool for forming a threaded surface, then this is an option with an emphasis on the letter "and". And if you are talking about a person or a marking device, then speak with an emphasis on the letter “e”.

Well, that's sorted out, and now meet His Majesty.

The main parts of the design of the tap.

The tap does not have the main part, like its other counterparts, it happened to be so by the way. And he himself is made of the following elements:

Taps are ideal for tapping holes of various diameters. The tool that I showed in the photo above is its classic performance.

Do not forget that we live in the 21st century and mechanical engineering is constantly being improved and you will meet many interesting specimens. I will only talk about the most famous and popular examples of this threading tool.

Types and purpose of taps depending on the design.

1. With helical flutes.

Such a tap has proven itself when working with the use of coolant (lubricating coolant). See the curved grooves it has? When the tool is immersed in the body of the part, coolants no longer enter the cutting zone, which negatively affects both the durability of the tap and the quality of the thread. And when the grooves have a characteristic bend, then the output of chips and the ingress of coolant into the cutting zone increases many times.

Modern taps are all made in this design. After all, this design is optimal for the process of threading in metal.

A short video about the company's tap Walter with helical grooves:

2. Tap with staggered teeth.

Yes, Kramnik Vladimir Borisovich would be very surprised. After all, he is one of the best chess players in the world, and he probably never heard of this kind of chess. Okay I'm kidding. In such a tool, not all the teeth are located like cells on the board (through one). The intake part of this tap has a classic look, but the calibrating teeth are located through one.

For example, you can see that the tap located in the figure has 4 sides (feathers) and each has teeth. Here are the calibrating teeth on each of the bottoms shifted relative to each other. It is difficult to explain on the fingers so let's look at this picture.

Here you can see how the teeth are displaced, which the red arrow points to relative to the teeth indicated by the blue arrow. I think everything is clear about the staggered arrangement of the calibrating teeth. If not, write in the comments and discuss.

3. Machine-manual tap for threads from 3 to 10 mm.

Such a tap differs from the usual one by a more “steep” intake sector of turns. This allows you to cut threads as an ordinary locksmith manually and on machines of a drilling or turning group. Unlike its usual counterpart, a machine-hand tap can withstand decent loads and cutting forces.

4. Tap-broaching.

Such a broach for threading must be handled with great care. As shown in the figure, to obtain a threaded hole, such a tap must be fixed on the tool holder lathe. There are special devices for this, so you don’t need to invent anything. Although from practice I will say that I have seen SO many different homemade products ... I advise you to use only official equipment to perform various machining operations.

A little distracted. The figure above shows a diagram of threading with a broach tap.

1. Draw tap.
2. Shank grip.
3. Toolholder.
4. Workpiece.

The process is simple - pull the tap at the working feed, the spindle rotates as shown in the figure, a thread is obtained in the hole. The quality of the resulting surfaces with this cutting method is not very good. This tap is used very rarely (at least at our enterprise). See what it looks like in real life in this video.

4. Taps for threads Ø up to 2.5 mm.

Because of its size, it looks like matches from a box. They have a sharpening angle of the intake part of 75 degrees. They are widely used in mechanical engineering and not only. This is due to the fact that a hole diameter of up to 2.5 mm will not allow threading with anything else. It is better to choose imported products such as Guhring.

5. Combined tap drill.

You will not see the picture here, because it is at the very top of this article. The tap drill is a fresh breath of progress and a new look at the machining of threads. When the drill successfully passes through a layer of metal sheet, the spindle speed decreases and the threaded part of this hybrid comes into play. As you can see, a tap is not only threading, but also drilling. Yes, I tell everything, it's better to see once than hear a hundred times. Watching video

Here we have considered the main types of taps. I think the answer to the question is already being clarified in your heads - What kind of "Christmas tree" is this? Well, we're moving on.

Allowance and cutting pattern when working with a tap.

Any tool has a cutting pattern. Which is very clear from this photo.

Allowance distribution scheme.

As shown in the figure, the roughing tool removes 75 percent of the allowance, and only 25 percent remains for the finishing one. This is necessary to obtain a better thread in the part.

Cutting pattern.

The draft accounts for the lion's share of the allowance to be removed, but it does not form a profile. To form the thread profile, a special finishing tool is used, depending on the selected thread type.

Tap sizes. GOST

You will find all sizes in GOSTs which you can download at the end of the article. On many sites, for example, I see built-in tables. And I always ask myself WHY? If you are going to design a tap, then GOST will help you. GOSTs were developed for this, so that people like you and me could look there and get the necessary information.

Especially for you, my favorite readers of the engineer's blog, I have created a compilation of the most current and scanned in excellent quality GOSTs. The assembly contains 16 documents for different types of taps. Free download for you. For the link to appear, you do not need to register or send your phone number, I know that you are not a robot. Just share this article in social networks. Download, enjoy!

And this is where we end. Today you learned that a tap is a tool for obtaining sufficiently accurate and high-quality threads in metal structures and details. I think the post was helpful to you. I will be glad to see YOUR COMMENTS.

Bye everyone! And see you soon.

Andrew was with you!

2017-06-15

Which tap to choose if the master is faced with the task of drilling holes with internal threads to restore studs, nuts, broken bolts and similar work? We suggest following the recommendations - take into account the parameters described below.

Image #1:

1. Thread standard.

Today they produce dies with two standards: metric and inch. The most common are metric products, the cutting edges of which have a conical blade type.

2. Thread profile.

The profile on the last turns of the triangular blades allows you to wrap nuts on the restored thread.

3. The principle of cutting.

The use of hand-type taps is possible in plumbing. When working with tough alloys (for example, based on titanium), it is better to use machine-type tools.

4. Type of die.

Distribution received dies of split, solid and sliding types. Solid products create threads best quality because they have a high level of rigidity. Sliding ones are used in sets, as they can be used to make threads of various sizes.

Types of taps and their purpose

The purpose of the taps varies, so for each type of work you need your own tool. Let's talk about the main varieties.

Image #2:

1. Manual / machine. Choose the option that is designed for the appropriate type of work. At the same time, pay attention to the device of the product (screw, straight, with shortened grooves).
2. Wrench. Single tool for straight through threads. It is longer than the machine-manual one and has a sharp lead, similar to the first number of the complete tap.
3. With cut thread. The tool is suitable for processing sheets and cutting holes in plate metal.
4. Locksmith. Designed for manual cutting of holes. Supplied in sets consisting of three tools (roughing, finishing, medium). Work begins with a draft, the hole is corrected with a middle one and polished with a finishing element.
5. Conical. Suitable for threading through holes. The intake part of the products has an incomplete thread, and the calibrating part has a full thread.
6. Flat. Suitable for making pre-threads. They have large intake cones.
7. Royal. Used for cleaning threads. The main difference from other types is the presence of a spiral on the right side.
8. Beskanavochnye. Suitable for long-term work with high productivity. The product has a short base of the receiving cone without longitudinal grooves, which reduces the likelihood of breakage.
9. Combined. These are products made up of two parts (roughing and finishing, connected by a neck). The combination tool reduces the time to complete the work. For example, you can buy a tap drill that is suitable for drilling and tapping at the same time.
10. Special. Products are highly specialized. This type includes mounted, ship and tandem taps.

How to choose a drill for a tap?

How to choose a tap drill if you need to cut a thread of a certain size? In order not to be mistaken, remember the principle of creating holes. The fact is that when threading, the metal is removed along with the chips, leaving through the cutting edges of the tool. Therefore, the diameters of the rods are chosen not according to the nominal diameter of the thread, but slightly less. The table below will help guide you.

For cast iron and highly brittle metals, the drill diameter is reduced by 0.1 mm from the table value. For high-quality inch threads, pay attention to the required pitch and hole diameter (see table below).

Table #2:

How to choose a thread tap

• diameter measuring system (inch, metric);
• number of tool passes (one, two, three);
• profile shape (rectangular, trapezoidal, triangular);
• the side in which the screw rotates (left, right);
• thread placement on the part (inside, outside);
• the shape of the part (cone-shaped, cylindrical).

If single products are mainly used to fix a broken thread, then kits are taken to create a new one. In them, the types of taps for threading are defined as rough, medium and finishing.

Image #3:

The first is designed for cutting a rough thread, the second for deepening it, the third for bringing it to the final (finishing) form. To distinguish one product from the rest in the set, pay attention to the shape of the marks on the tail parts.

• The first tap has cut tooth tips and is smaller in outer diameter than the rest of the tools in the set.
• The second, with short tooth segments, has elongated ridges. The diameter of the middle tap is slightly larger than the fine tap.
• The third has a full comb of teeth and matches in diameter with the dimensions of the future thread.

When calculating the future diameter of the hole, the formula is useful:

Table #3:

Important points for choosing and working with taps

1. If you decide to buy taps in a set, use them in the desired sequence, from rough to finish. Otherwise, damage to the thread and breakage of the tool may occur.
2. Use the crank after you start working with the finishing tool. Usually, increased resistance indicates that it is necessary to use an additional device.
3. Take a square to check the perpendicularity of the stroke of the tap relative to the surface of the workpiece.
4. Choose the correct coolant. At the same time, please note that blanks made of bronze and cast iron are cut without lubrication. Steel and brass go well with linseed oil, aluminum - with kerosene, copper - with turpentine.