Drill: types, characteristics and recommendations for selection

A drill is a common cutting tool that is used not only to produce through holes by drilling, but also to increase the size of existing ones.

Technically, the products are attachments for hand drills, hammer drills and various machines.

Drilling itself involves removing material through the rotational movement of a sharp cutting edge.

The instrument is divided into a huge number of types according to its shape and purpose.

Drill characteristics

The main characteristic of any drill is its strength, which should exceed this indicator for the material being processed.

The tool, depending on the conditions of use, has different sizes and shapes.

The sharpening angle of the cutting part, color, etc. also differ.

Each product has a shank, the type of which must match the chuck of a drill, screwdriver or machine.

Material

For the manufacture of drills, alloys with different characteristics are used.

In this case, the so-called “high-speed” steel grades P18, P9, P9K15 are used.

If the diameter of the drill exceeds 8 mm, a welding method is used in its manufacture, for example: carbon steel for the shank, high-speed steel for the working part.

For materials with high hardness (mainly metal), cobalt drills are usually used.

Their peculiarity is that the working part is made from high-speed steel R6M5K5, VK6M with the addition of cobalt.

NOTE

After the letter “K” in the marking there is always a number that indicates the amount of cobalt in the parts.

Carbide Pobedit drills are used for drilling concrete, stone and brick.

The tip of such a tool is tipped with pobedite, an alloy of tungsten (90%) and cobalt (10%), developed in the USSR. There are more than ten modern modifications of this alloy.

IMPORTANT!

The pobedite tip does not cut the material, but crumbles it, so it is not suitable for working with metal, plastic and wood.

In addition to tungsten and cobalt, chromium, molybdenum, and vanadium are found in the alloys, and their percentage is indicated in the marking.

Coating

To extend the life of drills, their body has one of the following coatings:

• Oxide film – significantly increases resistance to overheating from friction.

Also protects the product from rust.

The service life naturally increases.

• Diamond coating is the most durable coating available.

It is mainly used on those products that are used when working with extremely hard materials, including stone and porcelain stoneware.

• Titanium coating is a general name indicating that the material contains a chemical compound of titanium - TiN (titanium nitride), TiAIN (titanium aluminum nitride), TiCN (titanium carbonitride).

Coloring

The color of the drill is very important.

It indicates the coating used or processing method:

• Gray is the native color of steel.

Indicates the absence of any processing.

The cheapest and most short-lived products are gray in color.

• Black is the color of steel that has been exposed to superheated steam during finishing.

Black products are much more durable than the previous option.

• Yellow is the color of steel that has been tempered (processing of metal to relieve its internal stress).

It speaks of the high hardness of steel, and its brittleness is greatly reduced by tempering.

• Golden – the color of titanium nitride. Bright golden tools are very durable, and they also have reduced friction against the workpiece.

Dimensions and weight

Manufacturers of cutting tools offer an impressive range of drills of every possible “caliber”, depending on the design and purpose.

Let's look at the most common spiral products according to GOST:

• Short: 20 – 131 mm in length, 0.3 – 20 mm in diameter (GOST 4010-77);
• Extended: 19 – 205 mm in length, 0.3 – 20 mm in diameter (GOST 10902-77);
• Long: 56 – 254 mm in length, 1 – 20 mm in diameter (GOST 886-77).

As for the exact weight, it depends not only on the design of the products, their sizes, but also on the material of manufacture.

The weight of ordinary twist drills usually ranges from several units to several tens of grams.

Processing accuracy

For twist drills there is such a characteristic as accuracy class:

• A - increased accuracy (10 - 13 qualifications);
• B1 – normal accuracy (up to 14 qualifications);
• B – normal accuracy (up to 15 qualifications).

Quality is a characteristic of accuracy that determines the tolerance values.

Differences between a smooth conical and a stepped drill

Before we find out the scope and advantages of cone devices, let’s look at their varieties. Smoothing elements in the form of a cone drill thin sheet steel, gradually increasing the size of the hole. To drill a hole of the required diameter with such a drill, you need to periodically stop and take measurements. Some manufacturers of smooth-bore cone drills eliminate this drawback by applying digital markings.

Stepped elements allow you to drill a hole with greater accuracy due to the presence of degrees. When drilling, there is a smooth transition through the steps, and as a result, the operator can easily track what diameter the hole has. It should be noted that cone drills are quite expensive. Their price ranges from 2 thousand rubles or more. It all depends on the material of manufacture, as well as the size of the holes being drilled. Many people may think that cone devices are completely useless equipment from China until they test the cutting tool in action. Craftsmen openly declare that if frequent drilling of thin-sheet materials is necessary, it is recommended to use conical cutting attachments.

Types of drills

Products are divided into several groups according to design and purpose.

This allows you to quickly select a tool for specific tasks.

BY FORM

Based on the shape of the drill, it is quite easy to determine what material it can be used for:

Spiral

Classic instrument.

The working part has two teeth, which are twisted in a spiral.

The tool, biting into the material, pushes the chips to the surface with its grooves.

The shape of the tip depends entirely on the material for which the tool is intended.

As a rule, the diameter of products does not exceed 80 mm.

Screw

A modernized previous version, which has a more advanced form of grooves that remove chips.

Another difference is that such products are longer.

Feather

The product is flat in shape, the cutting part is made in the shape of a sharp peak, the outlines of which turn into a wider blade.

Other names are flat cutting drill, which is dictated by its shape, feather drill.

Builders call it perka.

Used where you need to get a deep and at the same time wide hole.

Ring

For those cases when you need to drill a hole with a large diameter without preliminary preparation.

More commonly known as a crown.

The shape of the tool resembles a hollow cylinder, and on the axis of rotation there is a centering twist drill.

The part that cuts the material is made either in the form of teeth, carbide tipped, or has a coating of diamond chips.

Conical (tapered)

Its shape resembles a cone with a sharp tip.

Suitable for working with metal whose thickness does not exceed 0.5 cm.

Just one tool can make holes of different sizes.

It all depends on the initial and final diameter of the cone, as well as on the immersion depth.

On the opposite sides of the drill there are special grooves with sharpened edges.

Stepped

A type of cone version.

The cone is divided into steps with increasing diameter, which have their own size.

The tool is convenient in that it allows you to monitor the diameter of the hole being formed during operation.

Spear-shaped

The shape resembles the tip of a spear, hence the name.

Used when working with hard, but at the same time fragile materials, such as glass and tiles.

Ballerina (ballerina)

Circular drill, which is used when working with wood and tiles.

It all depends on the installed cutting part.

Designed in such a way that the output is a perfectly smooth hole of large diameter.

The tool has a cross-shaped shape with cutters, the distance to which from the center can be adjusted.

This sets the diameter of the required hole.

The central part is a spiral drill, around which the cutters rotate.

Single cut drills

The cutting edges are located on one side relative to the axis of the tool itself.

In turn, they are divided into cannon type (the front end of the rod-shaped form is half cut off, which forms an outlet channel for chips)

and rifle-type (a compressed tube with a cavity through which coolant is supplied, and a groove angle of up to 120 degrees).

Tubular

Similar to crowns, but with a longer working part.

Forstner designs

An improved version of the spiral tool, but with additional cutters.

Zhirov's designs

A subtype of screw tool that has three cones on the cutting part, which is why its length is increased.

The design is also supplemented with a jumper with a groove, which is sharpened by a third of the cutting edge.

Designs by Yudovin and Masarnovsky

A tool with a large groove angle and a special shape, which distinguishes it from other types.

Countersinking

A monolithic cylinder having several cutting edges forming a cone.

Used for countersinking holes for screw heads.

BY PURPOSE

The instrument is divided according to its purpose, which is the reason for its special shape in each specific case.

The following drills are used in construction, at home and in production:

Universal

As the name implies, they cope with most materials.

They have a special sharpening, which received the corresponding name - universal.

On wood

These include spiral and feather, ring and screw.

Forstner drills and ballerina drills work well on wood, among others.

For metal

Conical, crown, stepped, as well as classic spiral.

On concrete

Crowned with carbide tipped, impact spiral and screw.

They have different shanks for hammer drill chucks.

For ceramics

Crowns, spear-shaped and ballerina.

The first ones are produced without teeth.

The cutting function is performed by a special diamond coating.

When working on glass, these are the types that are used.

For plastic

Special spiral options and crowns that can pass through material without breaking it.

There is a specialized tool that is used strictly to perform a specific task:

For deep drilling

Spiral tool with through channels.

Their purpose is to supply coolant directly to the cutting part.

This includes rifle and cannon subspecies.

Single-sided cutting

A tool whose main purpose is to create precise holes.

Subtype - ejector drills designed for drilling machines.

As the name implies, the cutting edges are offset to one side of the axis around which the tool rotates.

Centering

A specific tool capable of making only center holes in parts, but nothing more.

Differences in the operation of an extra-long drill from a regular drill

Long drills are designed for drilling precision holes. Working with such equipment has some differences from working with a conventional short tool. What features can be noted:

1. Extra-long metal cutters are subject to more heat than ordinary ones. This is due to the large contact area of ​​the tool with the channel walls and poor heat transfer due to the closed space. Therefore, it is necessary to organize forced cooling during drilling.
2. An elongated drill has increased bending strength, but if you drill continuously, passing a channel at a time, then the probability of the drill breaking due to the metal shavings formed in the channel is very high. It is important to remove these chips from time to time by returning the tool back.
3. Fast and continuous feed of the cutter can also cause destruction of the tool, so you need to go forward with short feeds.
4. It is difficult to use an extra-long metal drill with a conventional electric drill: it is impossible to hold the tool perfectly level. The hole may turn out to be of poor quality, parallelism will not be maintained, and the probability of breaking the equipment is high. All this can be avoided by drilling using a special machine.
5. To drill hard alloys, it is necessary to work at low shaft rotation speeds. This will prevent the cutting edge from overheating and becoming damaged.
6. Sharpening of cutters for metal must be done using special equipment, strictly observing the angle. It is better to use a template for this.

For each specific drill there is technical documentation, which indicates the optimal operating modes of the equipment. These requirements must be adhered to during operation of the product.

How to choose a drill

When choosing a good drill for your home, you should focus on the color of the product, its size, and manufacturer.

As for shanks, one of the following options occurs:

• Cylindrical (for drills);
• Conical (Morse shank);
• SDS type (for rotary hammers);
• Triangular (for hand drills), tetrahedral, hexagonal (hex for screwdrivers and drills).

When choosing a drill for professional activities, the following will be useful:

• Marking is a combination of letters and numbers indicating such parameters as diameter, steel hardness, impurities in the alloy, place of production and its technology.

NOTE

The marking is placed on products whose diameter is more than 2 mm.

• Sharpening angle – differs for different materials and is the angle between the cutting edges.

The ease of drilling and speed depend on it.

How to sharpen metal drills correctly

As the cutting edge of the drill becomes dull, it becomes necessary to sharpen it. This can be understood by the following signs: a characteristic squeal, rapid heating of the equipment, longer drilling, decreased accuracy, dullness is felt when touching the edge. To ensure quality work, it is recommended to take into account the following recommendations from experienced craftsmen.

An easy way to sharpen a drill

1. Before sharpening, make sure that the sharpening tool/machine is in good working order and that it is in a stable position.
2. Prepare a container with cold water to cool the metal.
3. When passing the drill along the grinding wheel, you need to press the equipment tightly. Sharpening should begin from the back of the edge.
4. When heating a metal, cool it in prepared water to avoid overheating.
5. The sharpening angle is applied depending on the metal alloy used in the production of the drill.

The entire cutting surface, including the side passages, must be sharpened.

What you need to know about drills

Morse taper type shanks are usually found on tools intended for installation in industrial machine tool chucks.

Since these shanks are available in sizes from KM0 to KM7, and the machine chuck is designed to work with one option, special sets of adapters are produced.

In addition to monolithic drills, drills with removable tips (feather drills) are produced.

As a rule, they are installed on universal CNC drilling machines.

The tips are made of various shapes from hard alloys or powder steel.

Important!

Drills coated with titanium nitride (TiN) cannot be sharpened.

Otherwise, all its strength indicators come to naught.

Drill manufacturers

Modern, time-tested manufacturers:

• Bosch is one of the top three brands in the world for construction tools;
• Ruko – good value for money;
• Bison is a manufacturer with a good pricing policy and tool durability;
• Haisser – powerful tools for industrial needs.

Particular attention is paid to Soviet-made drills, as the most reliable and durable.

Today it is difficult to find such a tool, however, every professional knows that a tool marked “Made in the USSR” is always preferable.