Center drill. Accurate work guarantee

Center drills belong to the series professional tools, since they are used in most cases in the industrial field. The main difference between these devices and conventional ones is their accuracy of the drilled hole. How centering drills are arranged and where they are used, you will find out right now.

Design features

Externally, this tool is a small drill of short dimensions with a very thick base. Moreover, its diameter can be 2-3 times the width of the working tip of the mechanism. Thanks to this design, the center drill (GOST confirmation of this) has a very high rigidity, therefore, when drilling a hole, it is almost impossible to bend it or deform it in any other way.

How does this tool work?

First, a small tip drills a hole of small diameter. It, as a rule, is formed after several rotations of the instrument (no more than 2-3 seconds). After that, that very small hole is expanded by the cutting edge of the thick conical part of the drill. It should be noted that during the operation of this mechanism, the exact perpendicularity of the recess relative to the material being processed and its surface is ensured.

Application

The center drill is used for drilling both metal and wooden surfaces. However, "according to the passport", that is, for its intended purpose, this tool should only be used for processing steel materials. However, this did not prevent our builders from using it as a countersink for wood, for example, when it is necessary to deepen the hole for the incoming screw head. Due to their heat-resistant and high-strength design, they absolutely do not fail after processing such objects and materials.

As for their intended purpose, these tools are widely used for drilling holes on milling, drilling and turning machines. In addition, center drills can also be used in household. Radio amateurs also like to use such devices. Such drills are more necessary than ever for making holes in A, since the devices used have high rigidity(this is due not only to their composition, but also to the special geometry that we talked about a little earlier), it is very easy and convenient to work with them.

Material

The composition of these devices most often includes tool steel of the R6M5 series. In addition, center drills can be made from HSS. But tools made of steel of the P9 series, which has a high content of tungsten, are especially valued in the production. Due to this, the product becomes even more durable and reliable.

Price

The cost of centering drills directly depends on their dimension. So, for example, the smallest 1-millimeter devices cost about 15 rubles per unit. The largest drills with a diameter of 6.3 mm cost about a hundred rubles.

In everyday life, you often have to drill holes in metal products. The operation is simple: I fixed the workpiece, marked the place for the hole, punched it, prepared a drill of the required diameter, turned on the drill or bench-drilling machine. Everything! But this sequence of actions is good for drilling one or two holes. With mass drilling in this way, a lot of time and effort will be required. It is for this purpose that experienced home craftsmen have a center drill in their tool arsenal.

How does it look and work?

First, let's remember the device and the principle of operation conventional drill. Its conical part, based on a conical recess previously drilled in the workpiece, enters it, and relying on the cone generatrices, makes a gradual penetration into the thickness of the metal. Chip sampling is carried out by the feather part of the drill, and by bringing it out with the help of spirally arranged grooves. If there is no basting for the hole, then the support for the conical part is also lost, as a result of which the drill slides and can even cause injury to an inexperienced user. Therefore, the preliminary centering of the hole with special requirements for the accuracy of its location is mandatory.

The center drill, designed for mass production of holes, eliminates the need for punching places for subsequent drilling. To this end, it has a special design, which was developed in accordance with the requirements of GOST 14952-75. Initially, the tool was intended as a tool for CNC milling machines, but it turned out to be very useful in the production of mass drilling operations in metal.

There are the following constructive varieties of the tool in question:

1. Drills that can simultaneously countersink the initial taper. The angle of such a cone is standardized and is 60°, while the center drill itself can be made with or without a safety cone.
2. Drills with a 75° lead-in cone that do not have a separate safety cone (due to the increased surface of the supporting zone).
3. Drills for making holes, the generatrix of which has a complex, arcuate shape.

Such a tool is produced in the size range of 0.5 ... 10 mm. Center drills with a large diameter do not have clear advantages over conventional countersinks, but will require (with hand power tools) increased drilling effort. On the other hand, mass drilling transitions are most often in demand in the manufacture of circuit boards for radio engineering devices, where the hole diameters fit well into 0.5 ... 1.0 mm.

GOST 14952 provides for two ranges of finished hole roughness. Examples of designations for such a tool are given in the above standard.

Design and technological requirements

The center drill includes three zones:

• actually centering, which has a smaller diameter, and therefore is easier to penetrate into the metal;
• the main one, which samples the material with a simultaneous increase in the quality of the generatrix;
• support, which ensures the centering of the tool, when it is deepened into the workpiece.

The transition from one part of the drill to the next is carried out very smoothly, along a parabolic curve, which eliminates the occurrence of stress concentrators during power supply. Distinctive feature of all versions of center drills is their relatively small length. This, on the one hand, facilitates the installation of the drill into the landing part, and, on the other hand, increases the rigidity of the tooling, which is essential when machining steels with increased hardness. In addition, center drills are always double-sided, and therefore the total tool life increases. The shank of such a drill is unified in diameter with the seats of metal-cutting equipment and electric drill chucks.

The main operational requirement for center drills for metal is high hardness, therefore, for their manufacture, high-speed steels of grades R6M5, R9K6 and R18 according to GOST 19265 are used. The presence of a large amount of tungsten and cobalt, as well as the presence of vanadium in the chemical composition, gives the tool high resistance with significant friction forces . Therefore, such drills can process not only steel, but even mineral ceramics - oxide-carbide alloys such as B3, VOK 60, etc.

For less critical tasks, in particular, when drilling wood, it is permissible to use center drills made from cold-formed chromium steels of the 9XC type according to GOST 5950. But they are not used to obtain holes in steel blanks, due to the fact that the temperatures reached in the working tempering temperatures are reached in the zone, and the tool quickly fails.

Tool life can be increased if coolant (emulsol, sulfofresol, etc.) is applied to the machining zone during drilling.

How to determine the quality of a center drill?

There are a number of checks for center drills:

1. Rockwell hardness test. According to GOST 14952-75, the hardness of the working part must fit into the range of 63 ... 66 HRC (lower values ​​usually correspond to larger diameter drills). At higher values, brittleness increases and the tendency of high-speed steel to break increases. Reduced hardness will reduce tool life.
2. Check for accuracy with a micrometer. Tolerances diameters should not exceed 0.05 mm for equipment with a diameter of up to 0.8 mm inclusive, 0.1 mm - with diameters up to 2.5 mm, 0.12 mm - up to 5 mm and 0.15 mm - with diameters over 5 mm .
3. Checking the accuracy of the manufacture of feathers of the main part. It must be uniform throughout the entire screw part, and the permissible deviations cannot exceed 0.07 mm for diameters up to 3.15 mm, and 0.1 mm for diameters over 3.15 mm.
4. Visual check, which consists in the fact that there should be no traces of discoloration (change in the main color), scratches and other defects on the working surfaces. To assess the quality, an ordinary measuring magnifier is sufficient.
5. Wear check. It is performed at home, during trial processing of products made of steel 45 with a hardness of at least 44 ... 48 HRC. After drilling, there should be no traces of chipping of the working edges on the tool.

The status and reputation of the center drill manufacturer is also important. In our country, the most reliable are the tools that are manufactured by Dormer. The size range of such equipment from Dormer includes products with a diameter of the centering part of 1.0 ... 6.3 mm, the main part of 3.15 ... 16.0 mm and lengths of 31.5 ... 71.0 mm. Products are suitable for use on machine tools. Center drill price domestic production is in the range from 50 to 200 rubles. a piece.

Drilling holes, especially in hard materials is usually associated with a number of difficulties. First, the drill slides over the surface, often after the core has been applied. Secondly, it is not always possible to achieve strict perpendicularity to the longitudinal axis of a conventional tool. And this is a big minus if increased requirements are imposed on the quality of processing the base.

The use of a special centering drill eliminates all such problems, including the gradual accumulation of probable inaccuracies associated with drilling errors. What CAs are, how they are better than traditional samples, when it is advisable to use them is the topic of the proposed article.

Specifications for combined center drills are prescribed in. The document indicates the standard sizes of products (Appendix 1), marking features, product requirements (Tables 5 - 7).

Center drills belong to the "professional" category of tools and are used mainly in enterprises or in repair shops with machine tools (turning,).

Types of center drills combined

1. A, B - for centering holes 600. The first version - without a safety cone, the second - with it.
2. C - Same as Type A but for 750 holes.
3. R - for center holes with an arcuate generatrix.

For each type of CA, 2 versions are provided: d is less than or equal to 0.8; d ˃ 0.8 (mm). What is the reason for this? The tool of the first option provides the minimum roughness of the walls at the drilling site, the second - a little more. In other words, the difference is in the quality of the metal sample.

You can get acquainted with all the symbols in more detail according to Table No. 2 GOST.

Center drill cost

It mainly depends on the diameter and version. Variation in prices, taking into account a large assortment, significant. For example, a 0.9 mm type A drill costs about 28 rubles. A larger analogue (PC B 5) will cost 412 rubles. If we talk about products that are most often used in everyday life, then their cost lies in the range of 23 - 486 rubles / unit.

The specifics of using the CA at home

It is believed that mainly center drills are used by those who are engaged in independent design. For example, the manufacture of printed circuit boards. Given their miniature size, the density of the proposed layout of radio components, the accuracy of drilling holes for their legs becomes special meaning. And this is true, but only in part.

The center drill will become indispensable assistant if there is a problem with twisting fastener(screw, screw, self-tapping screw). This happens quite often, especially if any product is operated outdoors. In such cases, they say "got stuck." But if you drill a little with the help of the CA, the head of the fastener, then it will easily give in to a screwdriver. Checked.

A center drill will bring no less benefit to those who like to do carpentry at home.

Making holes, chamfers in the manufacture of, for example, furniture items also requires maximum precision. Otherwise, distortions of structural parts will be revealed during assembly.

Group G23

INTERSTATE STANDARD

COMBINED CENTERING DRILLS Specifications

Combined cntre drills. Specifications

MKS 25.100.30 OKP 39 1242

Introduction date 01.01.77

The limitation of the validity period has been removed but protocol No. 7-95 of the Interstate Council for Standardization, Metrology and Certification (IUS 11-95)

This standard applies to combined center drills for processing center holes in accordance with GOST 14034-74.

(Revised edition, Rev. No. I, 3).

1. TYPES AND DIMENSIONS

1.1. Combined center drills must be manufactured in four types:

A - drills for centering holes 60 "without safety cone;

В - drills for center holes 60 1 with safety cone 120“;

С - drills for center holes 75“ without safety cone;

R - drills for center holes with an arcuate generatrix. Each type of drill must be produced in two versions.

1.2. The dimensions of the drills must correspond to those indicated in Fig. 1-4 and in table. 1-4.

Reprint prohibited

Edition with Amendments No. I, 2, 3, approved in November 1981, December 1986, May 1990

(IUS 1-82. 3-87. 8-90).

Example symbol type A drills with a diameter d = 1.0 mm, version 1:

The same, execution 2:

An example of a symbol for a drill type B. with a diameter of */= 1.0 mm. execution I:

Same. execution 2:

For d = 0.8 mm For d St. 0.8 mm

G1 r and m s ch a n and i. (Excluded, Him. No. 2).

An example of a symbol for a type C drill, diameter d - 1.0 mm, version 1:

Same. execution 2:

For d up to 0.8 mm For d St. 0.8 mm

An example of a symbol for a drill type R. with a diameter of J = 1.0 mm, version 1:

The same, execution 2:

1.1. 1.2.

1.3. Structural dimensions and geometric parameters drills are specified in the appendix.

2. TECHNICAL REQUIREMENTS

2.1. Drills must be made of high speed steel - according to GOST 19265-73.

2.2. The hardness of the working part of the centering drills must be: for drills with a diameter of up to 3.15 mm - 63 ... 65 HRC;

for drills with a diameter of over 3.15 mm - 63 ... 66 HRC>.

The hardness of the working part of drills made of high-speed steel with a vanadium content of 3% or more and cobalt of 5% or more should be higher by 1-2 HRC units.

2.3. The parameters of the surface roughness of drills according to GOST 2789-73 should not exceed the values ​​\u200b\u200bspecified in Table. five.

2.2, 2.3. (Revised edition, Rev. No. 2).

2.4. Cracks, nicks, black spots and tint colors are not allowed on the surfaces of the centering sweeps (with the exception of grooves, where tint colors are allowed at the point where the circle exits).

2.5. Limit deviations the dimensions of the combined drills should not exceed:

drilling part diameter. . . to 12;

diameter of the clamping cylindrical part... . h9; taper angles 60" and 75". . . minus 30";

taper angle 120"... ±1*.

G1 r and m s h a n and s. The dimensions of the nominal diameters of the drilling part must be measured at the beginning of the cutting part.

(Revised edition, Rev. No. 3).

2.6. Drills of types L. V and C should have a reduction in diameter on the drilling part towards the shank (reverse taper) within 0.05-0.10 mm per 10 mm of length.

(Revised edition, Rev. No. 2).

2.7. The thickening of the core of combined drills in the direction of the shank by 5 mm in length should be:

for drills up to Ø 3.15 mm....................... 0.40 mm

» » St. 3.15 mm............. 0.25 mm

2.S. The radial run-out tolerance of the auxiliary edges of the drilling part relative to the axis of the clamping part must be no more than:

for drills up to Ø 3.15 mm....................... 0.03 mm

» * * St. 3.15 mm ........................ 0.04 mm

2.9. End runout tolerance, checked in the middle of the cutting edges, should be no more than:

for svsrl diameter up to 6.0 mm....................... 0.10 mm

» » St. 6.0 mm to 10.0 mm... ., ...........0.13 mm

» * » St. 10.0 mm........................ 0.15 mm

For drills with a diameter of up to 6 mm, instead of the tolerance of the end runout of the drilling part, it is allowed to check:

the difference of half the angle at the top of the drill, which should not be more than GZO ";

symmetry tolerance in the radial expression of the transverse edge relative to the axis of the clamping part of the drill:

for svsrl diameter up to 3.15 mm » * » St. 3.15mm

0.05 mm 0.10 mm

(Revised edition, Rev. No. 2).

2.10. The difference in the widths of the feathers on one drill should be no more than:

for svsrl diameter up to 3.15 mm....................... 0.07 mm

* * » St. 3.15 mm........................ 0.10 mm

2.11. The values ​​of the mean time to failure and 95% failure-free operating time of drills made of steel R6M5 version 2 under the test conditions specified in Sec. 4, must be at least those given in table. 6.

G1 r and m with h and and and with. For drills of execution 1, the correction factor for the average and established periods of resistance is 1.3.

(Revised edition, Rev. No. 3).

2.12. The criterion for failure of centering drills with a diameter of up to 3.15 mm is breakage, and from 4 mm and above - the achievement of wear hi along the back surface in accordance with Table. 7.

2.11, 2.12. (Introduced additionally,

2.13. Each drill must be clearly marked with:

diameter of the drilling part;

trademark of the manufacturer;

drill designation (last four digits);

stai brand.

Notes:

1. On drills with a diameter of D msnss 10 mm, the designation of the drill is not allowed to be marked.

2. It is allowed not to mark steel grades R6M5, R6AM5.

3. It is allowed to mark the letters HSS instead of designating the grade of high-speed steel, for steel grades containing cobalt, the letters HSS C 0, while the grade was indicated only on labels.

2.14. Packaging, marking of transport and consumer containers - according to GOST 18088-83.

2.13. 2.14. (Introduced additionally. Amendment No. 3).

3. ACCEPTANCE RULES

3.1. Drill acceptance rules - according to GOST 23726-79.

(Revised edition, Rev. No. I).

3.2. Periodic tests, including the mean time to failure, should be carried out once every three years on at least five drills.

A 95% uptime test should be performed once a year on at least five drills.

(Changed edition, Rev. No. 1, 2, 3).

3.3-3.7. (Deleted, Rev. No. 1).

4. TEST METHODS

4.1. Drill tests should be carried out on drilling, centering and turning machines using auxiliary tool, which must comply with the standards of accuracy and rigidity established for them.

4.2. Drills should be tested on samples of steel grade 45 according to GOST 1050-88 with a hardness of 187-207 HB.

4.3. Drills of type B are subjected to resistance tests, as well as type A, R or C with diameters of 0.5; 1.6; 2.0; 2.5; 4.0; 10.0 mm in the modes indicated in Table. 8.

The combination center drill is used to create in workpieces from different types cast iron, unalloyed, alloyed steel and cermet alloys based on bronze and iron centering holes.

1

Such a drill is usually referred to as a tool professional level due to the fact that it is mainly used by various industrial enterprises and large private workshops equipped with milling and turning machines. This tool guarantees the absolute perpendicularity of the drilled hole in the workpieces relative to their surface.

No other type of drill or other device can provide such high quality and hole accuracy.

In addition, when using this product for drilling, the probability of accumulation of errors and inaccuracies is reduced to zero (many others cannot boast of this). According to GOST, a center drill, a drawing of which can be found in the same State Standard 14952, approved in 1975, is produced with a diameter of 0.5 to 10 mm. There are four types of CAs:

• A and B: for 60 degree holes with and without safety cone, respectively;
• C: for holes 75 degrees (cone-fuse is not provided in them);
• R: for holes with an arc-shaped generatrix.

Depending on the requirements put forward to the roughness of the machined surface, all these types of tools are produced in two versions. Products of the first execution provide a smaller hole roughness, the second - a large one. You can distinguish them from each other by marking. For example, if we see a drill with the inscription 2317-0001 in front of us, we can understand that its diameter is 1 mm, and it is made in the second version. Approximately the same designation 2317-0101 tells us about the first version of the tool of the same diameter. Both of these drills belong to group A.

Drills with a diameter of 1 mm of group B are marked as follows - 2317-00-12 (second version) and 2317-0113 (first version), groups C - 2317-0022 and 2317-0124, groups R - 2317-0027 and 2317-0129 . All of them are manufactured with such geometric dimensions and design parameters that are recommended by the previously mentioned GOST.

2

For the production of the described tool, it is used, which is capable of providing the following indicators of their hardness working area(HRC):

• 63–66 for CA with a diameter of more than 3.15 mm;
• 63–65 for CA less than 3.15 mm.

At the same time, drills that are produced from steel with a content of five percent cobalt and three percent vanadium must have even greater hardness (at least 1 HRC).

Permissible deviations of centering tool diameters for tool diameters:

• from 5 mm: +0.15 mm;
• 2.5-5mm: +0.12mm;
• 0.8-2.5mm: +0.10mm;
• up to 0.8 mm: +0.05 mm.

On the surface of the drilling tool there should be no black spots, cracks, discoloration and nicks. The criterion for failure of a drill with a diameter of more than 4 mm is its wear, up to 4 mm - breakage.

On one CA, the difference in the width of the tool feathers should be no more than:

• 0.1 mm for drills 3.15 mm and larger;
• 0.07 mm for drills up to 3.15 mm.

3

The tool performance test is performed on samples of steel 45, which have a hardness of 187 to 207 HB, on turning, centering and drilling machines. It is mandatory to use additional tool with well-defined indicators of rigidity and accuracy.

After verification finished products on her cutting edges blemishes are not allowed. In other words, after testing, it should be possible to use the tool for its intended purpose. Appearance drills are evaluated visually, hardness - by State standard 9013–59.

Under the visual assessment of the quality of the instrument is understood its thorough inspection using a magnifying glass with 2-4 times magnification. And the parameters of the drills are determined using special means and control principles with the following error:

• 25% of the tolerance value for the examined parameter when controlling the location of surfaces and shape;
• 35% of the tolerance value when setting the angle index.

The evaluation of the linear dimensions of the product is carried out according to the requirements and the recommended scheme set out in GOST 8.051-81.

The surface roughness of the tools is evaluated by comparing it with standard tools or with the roughness indicators specified in the 1975 State Standard 9378.

described by us drilling tool It is used not only at industrial enterprises, but also by home craftsmen. It is most commonly used by radio amateurs, allowing them to drill into printed circuit boards holes of various sizes. It is much more convenient to work with such a drill than with a conventional one, since the centering tool is many times more rigid in its characteristics.

It is clear that at home a person does not need the entire range of CAs. Large diameters remain absolutely unclaimed. As a rule, amateurs use drills with a diameter of 0.6, 0.5 and 0.8 mm. It is not difficult to buy them now, there are both domestic products and more popular imported ones on sale (they will be discussed below).

Also, drills with small diameters can be useful in a situation where some "stubborn" screw or screw in a particular design categorically does not want to get out. It is not difficult to solve such a problem if you use a center drilling tool. With it, you need to drill the head of the "shrew" fastener. Believe me, after this simple operation, he will easily succumb to your efforts.

The described technique is best suited for screws and screws for a Phillips screwdriver (in which the head has a recess in the center, which makes it possible to determine the direction of movement of the drill as accurately as possible). However, you can drill and connections for a flat screwdriver. But they should be pre-drilled before drilling.

5

Russian home craftsmen with great pleasure use the Dormer 0.5 mm center drill (or tools with a large diameter), which allows you to easily drill stainless steel and products made from it. Such a tool is made of high-speed high-quality steel. And then he is exposed special kind heat treatment that provides finished product increased hardness.

Drills under the Dormer brand retain a given hardness at elevated metal processing temperatures, which is facilitated by cobalt, which is part of the steel for the manufacture of products. It is also important that the company's products are distinguished by unique wear resistance. Also, experts note the high accuracy of the location of the hole, obtained due to the ability of Dormer products to self-center.