Homemade device for sharpening small diameter drills. Do-it-yourself drill sharpener drawings Homemade drill sharpener

Drilling metal or wood is a job that you do regularly. A high-quality nozzle does not require sharpening for a long time, but there are some errors in which blunting occurs ahead of time:

The use of a drill that does not match the material being processed. This does not necessarily mean drilling reinforced concrete with a wood drill, although in this case you will instantly turn the cutting tool into a bar with a rounded end. There are specially made drill bits for drilling various types of metal and hard plastics. In case of discrepancy - the cutting edge quickly becomes unusable;
Wrong sharpening angle. This value must also correspond to the type of material in which the hole is made;
Overheat. The most common reason. When working with durable material, we want to quickly finish drilling, and we often forget about such trifles as cooling the work area. If it is not possible to ensure the supply of coolant to the tool, it is necessary to take breaks to cool the cutting edge. You can dip a hot drill into a container of water.

The mechanism of hot blunting is simple: The hot edge is “released”, that is, it loses its hardness. Cutting properties deteriorate, resulting in increased friction. Heating increases more strongly, and the process is aggravated in an arithmetic progression.

As a result, we may lose a good and possibly expensive tool. If there is a grinder for drills at hand, the problem is solved on the spot, if not, you have to invent your own methods of sharpening.

Manual sharpening without tools

Locksmiths with extensive experience sharpen drills with their hands, using only a sharpener with a handy tool. But not all home masters can boast of such skills.

In addition, in this way it is possible to restore the sharpness only to products large diameter. Then it is easier to control the angle. The most popular size (3-5 mm) cannot be sharpened in this way. Even a template won't help here.

Masters who regularly conduct drilling work- you will be interested in a variety of sharpening machines for drills offered in power tool stores.

However, such devices (despite the obvious ease of use) are quite expensive. So the “home-made” run to the store for another Chinese tip. But home craftsmen with experience still use a tool from the times of the USSR, which corresponds to GOSTs in terms of strength and durability.

The secret is simple - many locksmiths of the old school have in stock homemade machine for sharpening.

IMPORTANT! For most household chores, you can get by with simple sharpening tools. Especially if the word "machine" scares you.

The simplest devices for dressing the cutting edge of the drill

To understand the process, take a look at constituent parts tip.

Then, by turning the bed, a plane (more precisely, a cone) of the backing is formed.

Sharpening is checked on the template and evaluated visually. All planes comply with the standard.

A guide is welded to the lower (rear) part of the corner bed to stop the drill shank. The emphasis itself is welded from the coupling and the corner.

Fixation is made with a screw. The stop is set to the limit value of the edge to be ground, and due to this, both cutting elements of the drill are ground symmetrically.

The sharpening of the working edge is made against the rotation of the emery wheel. In this case, the resulting burr is automatically removed by the running surface of the emery. For sharpening, two or three swings of the bed along the radius of the backing cone are sufficient.

This type of drill is sharpened along the outer surface of the emery stone, if necessary, use the lateral (radial) plane - the device can be turned to any angle.

The drill grinder is attached to the workbench with a clamp. You can fix the base permanently - but in this case, the possibility of fine adjustment will be lost.

Drills for metal are always hardened, but products can become dull over time. Naturally, this is not a reason to throw them out. If desired, you can sharpen the drill with your own hands, using professional equipment or homemade devices.

The main types of sharpening

Experienced craftsmen know that sharpening a drill for metal can be different. depending on diameter and application.

Single plane sharpening is designed for drills with a maximum diameter of 3 mm. In the process of doing the work, it is possible to “chunk” the edge, so you need to be very careful. To properly sharpen the product, it should be applied to the circle and moved parallel to the surface.
The tapered procedure is for larger metal cutting tools. In this case, the tool must be held with both hands, making sequential sharpening.
Finishing is performed after the end of sharpening. Thanks to this procedure, it is possible to grind the cutting edge and eliminate even the smallest notches.

To sharpen the drill with your own hands correctly, you must use the appropriate machines. Similar devices are divided into 2 groups.

If you are interested in the question of how to sharpen a drill for metal, then be sure to purchase the appropriate machine. For home use, an inexpensive model with medium power is suitable. It will allow you to sharpen small drills for metal.

Naturally, when buying pay attention to the noise level, as well as the design of the model. The best option will become a simple machine, because to choose for it the right details it will be easy.

It is necessary to buy such devices only in specialized places, since the kit provides for the presence of a technical passport. Moreover, you will be given a warranty card.

Use of machines at home

As mentioned earlier, at home it is advisable to use household machines. With their help, it is possible to sharpen various types of drills. It is important to remember that for some varieties you will have to buy the appropriate circles.

To sharpen the drill yourself, you should give preference to a machine equipped with a universal chuck. It allows you to clamp elements of various diameters.

The kit often comes with:

keys;
collets;
spare parts;
lamp for the working area.

The equipment from Drill Doctor and GS is the most popular. Similar products are designed for sharpening drill diameter in 2–13 mm and 14–34 mm. Unfortunately, this equipment does not allow you to sharpen drills that are too thin. For this purpose, you will have to purchase a special machine.

All equipment for sharpening drills at home, has a number of advantages:

the ability to work from the mains;
high performance;
ease of use;
functionality;
sharpening accuracy;
affordable price;
compact dimensions;
light weight;
convenient control system, thanks to which you can adjust the intensity of sharpening and its speed.

Homemade sharpeners

If you do not have the appropriate machine, then you can sharpen using other devices. It is about an electric drill or homemade equipment, created according to the drawing. It is best to give preference to the second option, otherwise you can ruin a lot of drills before you master the correct sharpening.

You can create a suitable fixture with your own hands even from wood. So, a bar with holes corresponding to the diameter of the drills is fixed on a horizontal surface. The mentioned holes are made at a slight inclination to obtain the required sharpening angle.

Some masters prefer an electric drill equipped with the appropriate nozzles. Naturally, a small range of similar items, which complicates the sharpening with your own hands. As a rule, a stone and a leash are included with the nozzles. If you plan to sharpen drills using a specific drill, the leash should be shortened immediately.

If you wish, you can independently make a similar nozzle for a drill, guided by the recommendations given in the corresponding video. Such devices must be equipped with fasteners for fixing the drill.

Features of the sharpening process

If you first decided to sharpen a part with your own hands, do the work in a strict sequence.

First of all, the back surface is processed. So, the drill is pressed tightly and constantly monitored so that the sharpening angle remains the same. As a result of processing, the tip of the drill will resemble a regular cone.
Next comes the turn of the cutting part.
The last stage involves finishing the back surface. In this case, it is necessary to make sure that the size of the jumper is no more than 0.4 mm. Naturally, for a large drill for metal, this parameter should be slightly larger.

If something doesn't work out right the first time, don't despair. It is best to start practicing with tools that are unlikely to be needed. The main thing is to learn how to press and maintain the angle correctly. In this case, it is necessary to take into account the fact that the side parts of the drill, and not the tip, are responsible for drilling. Accordingly, the edges must be sharpened.

It is important to remember that in the process of sharpening small particles are formed. Because of the heat, they scatter in the form of sparks. It is for this reason that safety precautions must be followed. We are talking about the use of goggles and gloves. Also, when sharpening, make sure that the drill is securely fixed. Otherwise, it may accidentally slip out of your hands.

If you decide to use the appropriate machine for sharpening, be sure to prepare workplace. In particular, it is about good lighting. Also need wear protective gloves and goggles.

To properly sharpen the drill with your own hands, you need use a suitable device. It can be a household or industrial machine, as well as an electric drill with a special nozzle. If you have not tried to sharpen a drill before, first check out the corresponding video.

Do you need the drills to always be sharpened, and you can’t find a special machine during the day with fire even in specialized stores? And make a machine for sharpening drills with your own hands. You can easily assemble a simple structure if you have at least a little experience in working with basic tools.

Homemade machine

A drill sharpener can be of great value in household just like with this device you can independently sharpen drills of any diameter and type. In addition to the manufacture of a special unit, you will need an electric motor with a grindstone.

Main materials:

Metal plate with holes - 1 pc.;
Bolt or stud 70x15 mm long;
Set of washers;
Corner - 30x30 or 40x40;
Plates - 3-4 mm thick;
Cotter pin - 30x1.5 mm;
Clamps.

In addition to materials, you will need tools for their machining and connection, in particular electric welding and a grinder.

Tools:

Electric welding.
Drill.
Bulgarian.
Hammer with percussion tips.
Special clips 2 pcs.
Spanners.
Pliers.

Manufacturing process:

1. Making the mounting plate

The mounting plate is made of a metal lining with holes about 3-4 mm thick. On the one hand, the part is cut off by 3 centimeters, while during cutting it is required to save the finished hole. The cut off part will be needed for the manufacture of the next part of the grinding device, and a large element for lining during the installation of the product on the table.

2. Corner for fixing the drill

The element is designed to fix the drill during sharpening. It is made by cutting off a part of a regular corner 30x30 or 40x40. The total length varies between 60-90 mm, while the extreme part is cut at an angle of 60 degrees to give the sharpened plane the desired level.

3. Fixing bracket

The cut off part with a hole from the plate is connected to another metal plate, while the elements are superimposed on each other and welded to the corner by electric welding. For welding, a mounting cutout should be cut on the plates in order to butt-fit the parts and scald them.

In the connected parts, a hole is drilled along the diameter of the bolt or stud, and the parts themselves are carefully scalded on all sides to stiffen.

4. Bolt welding

A bolt or stud is designed to fix the corner. The element is welded at an angle of 75 degrees to the main plate. During scalding, the lower plane should be taken into account, if necessary, remove the slag in order to prevent the product from being skewed.

5. Fastening the washer to the bolt

The washer on the bolt is installed at a level of 25 mm from the upper extreme part. The approximate diameter is 30 mm. The element is welded using electric welding in the desired design position, observing all levels along the plane.

6. Hole in the stud

In the absence of a hole for installing a cotter pin in a bolt (stud), it is required to make it using a drill and a drill of the required diameter. Due to this technical element, the fixing angle will be fastened. The diameter may be different, but the main condition is reliable fixation.

7. Drill stop

It is made of a metal bar and a special vise clamp. The rod is welded to the fixing angle from below. The clamping mechanism is mounted on a bar, while on the device a special bowl-stop for the drill should be equipped from the corner.

The system is mounted on a grinding table and fixed with additional clamps.

Video: how to make a tool for sharpening drills.

Drill grinder

This method is available to anyone. For this you will need a drill. Perhaps not immediately from the store counter, but already obsolete and not used by you. She will act as an engine.

It must be fixed on the bed, insert a sleeve or a grinding wheel ready for installation or a universal fine-grained disk into the chuck. All. Turning on the drill, you get a rotating abrasive, which is a pleasure to sharpen the drill.

A very simple sharpening solution. However, do not forget about the devices for sharpening the drill, which fixes the element to be sharpened relative to the sharpener.

The quality and accuracy of drilling depends on the sharpness of the working tool. In addition, unlike a table knife, the drill must be sharpened correctly. Experienced locksmiths can level the cutting edge on a regular grinder, just holding the drill in their hands (at least in their words). But this method requires skill and years of experience. Even if you have a steady hand and an excellent eye - without understanding the process, you will simply ruin the instrument.

A few basic sharpening rules (for example, spiral drills for metal):

For a better perception of the material, let's remember the device of the drill.

You can not press the tip to the emery for more than 2-3 seconds in one go. The metal is heated and the so-called "release" occurs, that is, the deprivation of hardening. Accordingly, the required hardness of the metal is lost. The first sign is the presence of temperature tarnishes on the edge.
For drills with a diameter of up to 4 mm: at each touch of the emery plane, the drill is held in one position: rotation around its axis is unacceptable. For a larger diameter, the sharpening geometry is somewhat different.
On spiral drills, only the back surface of the cutting part is sharpened.
The cutting edge should be directed towards the rotation of the sharpener (with mechanical sharpening).
The main angle (in the illustration - 2φ) depends on the type of material being processed.

Which drills to sharpen and how often?

Feather and other special wood drills do not restore at home, and they do not get dull so quickly. Pobedite tips for concrete are not sharpened in principle. The most popular tool remains - twist drills for metal. Of course, they are also used for processing wood (plastic, rubber and even stone), but this is not the topic.

Spiral drill. The cutting edge has small size, therefore, during operation, it quickly heats up from friction (there is no dispersion area). The main reason for blunting is overheating. At correct use wear is not as intense. Characteristic features of a blunt drill:

A creak is heard during operation.
Instead of curled chips, sawdust comes out of the hole.
Instant heating of the tool without advance in depth.

Important: Do not work with a blunt drill, wear from overheating will only progress.

So, it's time to sharpen the tool. You do not want to spoil the drill, and you want to mechanize the process.

At your service are mini sharpening machines:

All devices are divided into two types: nozzles or stops for universal tool, And independent devices narrow specialization. Consider the most popular of them, from simple to complex:

This is just a device for those who have a steady hand and a diamond eye. In fact, it only allows you to hold the drill in a given position without fear of injuring your fingers. The control of the angle is visual, according to the position of the "wings" relative to any landmark. There are few advantages: instant readiness for work, compactness and price. The disadvantages are obvious: manual control of the process does not add accuracy.

In fact, this element is not a special tool for drills. It simply allows you to fix the tool at a certain angle. The accuracy will be higher than in the previous version. Most stops allow you to set the angle of inclination, and even have a marking scale. And yet you have to rely on the firmness of the hands.

There are also more advanced stands: with interchangeable elements and adjustment of not only the angle, but also the height. Devices are mounted not on the body of the emery, but on the workbench: which makes them more versatile.

In fact, such an emphasis can be adapted to any electric grindstone. An additional bonus - with the help of such a stand you can sharpen knives, cutters, screwdrivers, chisels, etc.

Semi-professional guides for all types of drills

This is a fairly advanced tool that allows you to control sharpening characteristics to the nearest micron. All linear parameters are securely fixed, the values are set according to the markup. The drill is fixed in the chute, accidental displacement or rotation around its axis is excluded.

For sharpening, the possibility of both linear movement and movement of the edge along the arc path (for conical sharpening of large diameter drills) is provided. Linear movement (along the axis) can be controlled by the master, or a limit stop can be set.

From the point of view of the quality of processing, there are practically no shortcomings in the device. But for correct sharpening the operator must know the parameters of the drill. That is, there is no automation: therefore, the tool belongs to the category of professional.

As a development of the line - a guide with its own sharpening unit. There is no need to set the emphasis on the workbench and change the discs. In fact - you have a semi-automatic desktop machine for sharpening.

Important note: All of the listed accessories are designed to work with standard electric sharpeners. Therefore, before starting the processing of drills, it is advisable to install a special emery disc.

They are a specialized power tool for a single task: sharpening twist drills.

Even a person who is far from technology can use the machine (although why does he need sharp drills?). The operator is only required to determine the diameter of the drill and plunge it into the appropriate hole. It is convenient to work, errors are practically excluded. However, all drills are sharpened “one size fits all”. The price paid for ease of use is the lack of flexibility in settings. For home use – the best choice: especially if there is an additional attachment for sharpening knives and scissors.

There are versions for masters. The drill is installed taking into account the sharpening parameters, the process can be controlled by the operator.

The angle of sharpening, the method of processing the edge (linear or conical), the depth of metal removal are selected. The drill is located not in a common holder, but in an individual cartridge.

Industrial sharpening equipment for a metalworking shop

With intensive use of drilling machines, a separate post is required to restore the tool's performance. Professional stands for sharpening drills of any diameter save time and effort, but the cost of such equipment is too high for home use.

The information obtained will help you choose a sharpening device, without extra financial costs. In addition, there are interchangeable nozzles for hand-held power tools (for example, a drill). But that's a topic for another article.

If you only have to drill wood, then you don’t have to think about the sharpness of the drill, since the drill can regularly serve for months and years without sharpening. But when it comes to drilling metal, the sharpness of the drill becomes very important, in other words, you can only drill through metal with a sharp drill. It's easy to feel the difference with a brand new drill. Having started to crash into the metal quite quickly, every minute the drill will plunge into the metal more and more slowly, and you will have to put pressure on it more and more. The rate of drill blunting depends in particular on revolutions, feed rate, cooling and other factors, however, no matter how hard you try, the time it takes for a drill to work to unsatisfactory performance is measured in minutes. If the amount of work is significant, it will be expensive to constantly buy new drills, so it is better to learn how to sharpen them. Although it is still worth having several drills of the same diameter (3-10, depending on the diameter and, accordingly, the price) in order to return to sharpening only when all the drills have become dull.

At the periphery of the drill, the cutting speed is maximum, and, consequently, the heating of the cutting edges is maximum. At the same time, heat removal from the corner of the cutting edge is very difficult. Therefore, blunting starts from the corner, then spreads to the entire cutting edge. Its rounding is clearly visible. Then the back edge is abraded. Strokes appear on it, risks coming from the cutting edge. With wear, the risks merge into a continuous strip along the cutting edge, wider at the periphery and tapering towards the center of the drill. The transverse cutting edge collapses when worn.

At the beginning of blunting, the drill makes a sharp creaking sound. If the drill is not sharpened in time, the amount of heat generated will increase and the wear process will go faster.

To make it easier to control the geometry of the drill, the main thing to do is the template described below. With its help, even if sharpening is performed without fixtures, you can always check where else you need to remove the metal, and, in the end, get what you should get (it cannot be that it doesn’t work, even if you have to grind off half the length of the drill) . To maintain symmetry, try to keep the sharpening time of each section and the pressing force constant.

Sharpening twist drills

The drill is sharpened along its back edges. It is very important that both feathers (teeth) of the drill are sharpened exactly the same. Doing this manually is very difficult. It is also not easy to manually create the required shape of the back face and the specified clearance angle (see below for which angle).

For sharpening, there are special machines or devices. If possible, it is better to sharpen drills on specialized equipment. But in a home workshop, such an opportunity, as a rule, does not happen. Drills have to be sharpened by hand on an ordinary sharpener.

Depending on what shape the back surface is given, there are different types sharpening: single-plane, two-plane, conical, cylindrical, screw.

With single-plane sharpening, the back surface of the pen is made in the form of a plane. The back angle with such sharpening should be 28-30 °. With single-plane sharpening, there is a high risk of chipping of the cutting edges. This method, which is the easiest to manual sharpening, recommended for drills up to 3 mm in diameter.

Universal drills with a diameter greater than 3 mm are usually subjected to conical sharpening. In order to understand the features of such sharpening, consider the scheme of conical sharpening on a drill machine with an angle of 2φ of 118 °. The figure below shows a grinding wheel and a drill pressed against its end with a cutting edge and a back surface.

Imagine a cone, the generatrix of which is directed along the cutting edge and end grinding wheel, and the top is separated from the diameter of the drill by 1.9 of its value. The vertex angle is 26°. The axis of the drill intersects with the axis of an imaginary cone at an angle of 45°. If you rotate the drill around the axis of an imaginary cone (as if rolling the cone along the end of the grinding wheel), then a conical surface is formed on the back face of the drill. If the axis of the drill and the axis of the imaginary cone are in the same plane, then the clearance angle will be zero. To form a back angle, you need to shift the axis of the drill relative to the axis of an imaginary cone. In practice, this offset will be equal to 1/15 of the drill diameter. Swinging the drill along the axis of an imaginary cone with such a mixture will provide a conical back face and a clearance angle of 12-14 °. The larger the offset value, the larger the relief angle will be. It should be recalled that the relief angle along the cutting edge changes and increases towards the center of the drill.

It is clear that it is very difficult to fulfill all these conditions for sharpening manually. The drill intended for sharpening is taken with the left hand by the working part, possibly closer to the intake cone, and with the right hand by the tail.

With the cutting edge and back surface, the drill is pressed against the end of the grinding wheel and, starting from the cutting edge, with smooth movements right hand, without lifting the drill from the stone, shake it, creating a conical surface on the back face of the pen. Then repeat the same procedure for the second pen.

When sharpening, it is desirable to repeat as accurately as possible the shape of the back surface that was after the factory sharpening, so as not to lose the required back angles.

Another sharpening method, widely used by home craftsmen, is as follows. As in the previous case, the drill is taken with the left hand by the working part as close as possible to the intake cone, and with the right hand by the tail. With a cutting edge, the drill is pressed against the end of the grinding wheel and with a smooth movement of the right hand, without taking the drill off the stone, turn it around its axis, sharpening the back surface. It is very important to maintain the desired angle of inclination to the end face of the grinding wheel when rotating the drill. For this, special bushings are often used when sharpening.

As a result of such sharpening, a tapered surface will be obtained on the back surfaces of both feathers, but a relief angle will not be formed. During operation, the friction of the rear surface against the walls of the hole and, consequently, the heating will be greater.

Due to friction on the grinding wheel, the tool heats up during sharpening. This causes tempering of the hardened part of the tool. The metal softens, loses its hardness. Inept sharpening causes the blade of the tool to become unusable. Therefore, sharpening should be carried out with repeated cooling of the drill in water or in a water-soda solution. This requirement does not apply to carbide drills. Do not use oil for cooling when sharpening. If, for whatever reason, the tool is sharpened dry, then:

a small layer of metal is removed in one pass;
rotational speed abrasive wheel should be as low as possible;
the drill should never be heated to such an extent that it cannot be tolerated by the hand.

Practice shows that tool sharpening should be carried out against the movement of the grinding wheel. Then the cutting edge is more durable, less likely to crush and break off.

For sharpening, grinding wheels made of electrocorundum (grades 24A, 25A, 91A, 92A) with a grain size of 25-40, a hardness of M3-CM2, on ceramic bonds are used.

In production, sharpening is usually followed by finishing. Finishing makes the surface smoother, removes small notches. A drill that has been honed is more resistant to wear than a drill that has been sharpened. If you have the opportunity to refine, use it.

For finishing, grinding wheels made of green silicon carbide grade 63C with a grain size of 5-6, hardness M3-CM1 on a bakelite bond or ELBOR LO wheels, a grain size of 6-8 on a bakelite bond are used.

One of the main conditions for the correct sharpening of the drill is to maintain its axisymmetry. Both cutting edges must be straight and have an identical length, identical angles at the top (and taper angles) with respect to the axis of the drill.

The correctness of sharpening is checked with a special template.

a - template; b - checking the angle at the top and the lengths of the cutting edges; in - pointing angle; d - the angle between the jumper and the cutting edge.

It is made independently from a sheet of copper, aluminum or steel approximately 1 mm thick. The most durable template, of course, is made of steel. The template checks the angle at the top, the length of the cutting edges, the angle between the jumper and the cutting edge. Instead of the back angle, which is very difficult to measure, the taper angle is measured with a template. It is advisable to make a template before starting to use a new drill in order to transfer the desired angles from the latter.

The uneven length of the cutting edges and their inclination to the axis of the drill also lead to an unequal load. The drill will fail faster due to the intense wear of the overloaded cutting edge.

a - the wedges of the cutting edges are not the same, the middle of the jumper does not coincide with the axis of the drill; b - cutting edges are sharpened under different angles to the axis of the drill, the middle of the jumper coincides with the axis of the drill.

An uneven load on the parts of the drill will cause it to beat during the cutting process and, as a result, an increase in the diameter of the resulting hole.

The easiest way to check the correctness of sharpening is test drilling. If the drill bits are not sharpened equally, then the less loaded one will have less chips from the corresponding groove. Sometimes chips protrude through only one flute. The hole diameter may be exaggerated compared to the drill diameter.

The device consists of a fixed base and a removable holder with holes for drills of different diameters.

1 - rail; 2 - drill; 3 - emery wheel; 4 - base; 5 - holder.

The base is made of a planed board 30-40 mm thick, to which at an angle of 30-32° (depending on the angle 2φ, see below, 30° for 2φ=120°, 32° for 2φ=116°) is sewn (nailed, glued ) wooden lath with a beveled at an angle of 25-30 ° (for single-plane sharpening) side edge. This rail and orients under right angle holder with a sharpened drill relative to the grinding wheel. The holder is made of rectangular wooden block, one of the sidewalls of which is planed at an angle of 60-65 ° (depending on the angle of the side face of the rail). With this sidewall, the holder is pressed against the rail on the base board, which ensures that the front angle of the drill is sharpened within the required limits (25-30 °). On the other sidewall, the holders are marked and drilled perpendicular to the plane of this sidewall. through holes for each drill of one or another diameter. The length of the holder is chosen so that it is convenient to hold it when sharpening drills.

You can’t install a device on a regular thrust bearing (armrest), so you have to come up with some kind of table or shelf for it, you can move it grinding machine on the table where there will be a place for this device. On the base, place a holder with a drill inserted into it to be sharpened close to the rail. Rotate the drill in the socket of the holder so that the edge to be sharpened is oriented horizontally. With your left hand, hold the drill at the edge to be sharpened, with your right hand, the drill shank. Pressing the holder against the beveled rail, bring the drill to the emery wheel and sharpen one edge. Then unfold the drill and process the second edge in the same way.

You can do it even easier:

Sharpening angles and other characteristics of the drill

A twist drill is a rod that has two helical grooves to facilitate the exit of chips. Thanks to the grooves on the drill, two helical feathers, or, as they are otherwise called, teeth, are formed.

The twist drill consists of a working part, a neck, a shank and a foot.

A - with a conical shank; B - from cylindrical shank; a - working cutting part; b - neck; c - pen width; g - foot; d - leash; e - helical chip groove; g - feather; h - shank; and - jumper; L - total length; L 0 - the length of the "working cutting part"; D - diameter; ω - the angle of inclination of the "groove chip screw"; 2φ - angle at the top; f is the width of the spiral ribbon; ψ - the angle of inclination of the jumper.

The working part is divided into cutting and guiding. All cutting elements of the drill are located on the cutting part - the intake cone. The guide part serves as a guide during cutting and is a spare when regrinding the drill. Cylindrical chamfer-ribbons are located on the feathers of the guide part along the helical line. Ribbon serves to guide the drill in the hole, as well as to reduce the friction of the drill against the walls of the hole. It doesn't have to be wide. So, the width of the drill bit with a diameter of 1.5 mm is 0.46 mm, with a diameter of 50 mm - 3.35 mm. The drill shank and foot are used to secure the drill in the machine spindle or chuck. Drills can be made with or without a collar.

The diameter of the drill, measured by the ribbons, is not the same along the length of the drill. At the intake cone, it is slightly larger than at the shank. This reduces the friction of the ribbons on the walls of the hole.

In order to understand the device of the cutting part of the drill, consider the basic principles of operation of any cutting tool (including drills). One of the most important requirements for cutting tool is that the chip to be separated freely moves away from the place of cutting. The surface of the tool along which the chips run is called the front face. This face is tilted back at some angle from the vertical plane.

1 - wedge; 2 - processed object; γ (gamma) - front angle; α (alpha) - back angle; δ (delta) - cutting angle; β (beta) - taper angle.

Thanks to this angle, it is easier for the tool to plunge into the metal and the chips come off more freely along the front edge. The angle between the front face of the tool and a plane drawn perpendicular to the cutting surface is called the front angle and is denoted by the Greek beech γ.

The surface of the tool facing the part is called the back face. It is deflected at a certain angle from the surface of the workpiece to reduce the friction of the tool on the cutting surface. The angle between the back face of the tool and the cutting surface is called the clearance angle and is denoted by the Greek letter α.

The angle between the front and back faces of the tool is called the angle of taper and is denoted by the Greek letter β.

The angle between the front face of the tool and the cutting surface is called the cutting angle and is denoted by the Greek letter δ. This angle is the sum of the taper angle β and the relief angle α.

The front and back angles are the angles that must be observed when sharpening.

Now let's find the edges and corners described above on the drill, which is not at all like the tool shown in the figure above. To do this, we cut the cutting part of the drill with the plane AB, perpendicular to its cutting edge.

The cutting edge is the line where the front and back edges of the tool intersect. The rake angle γ at the drill forms a helical groove. The angle of the groove to the drill axis determines the rake angle. The value of the angles γ and α along the cutting edge is variable, which will be discussed below.

The drill has two cutting edges interconnected by a jumper located at an angle ψ to the cutting edges.

Having received a general idea of the geometry of the cutting part of the drill, let's talk in more detail about its elements. front face twist drill is a complex helical surface. Edge is a conventional name, since the word "edge" suggests a plane. The helical groove, the surface of which forms the front face, intersecting with the intake cone, creates straight cutting edges.

The angle of inclination of the helical groove to the axis of the drill is denoted by the Greek letter ω. The larger this angle, the larger the rake angle and the easier the chip flow. But the drill with an increase in the inclination of the helical groove is weakened. Therefore, for drills with a small diameter, which have less strength, this angle is made smaller than for drills with a large diameter. The helix angle also depends on the material of the drill. HSS drills can work in more stressful conditions than carbon steel drills. Therefore, for them, the angle ω can be larger.

The choice of the angle of inclination is influenced by the properties of the material being processed. The softer it is, the greater the angle of inclination. But this rule applies in production. At home, where one drill is used for processing different materials, the angle of inclination is usually related to the diameter of the drill and varies from 19 to 28° for drills with a diameter of 0.25 to 10 mm.

The shape of the flute should create enough room for the chips to be easily evacuated from the flute without weakening the drill too much. The groove width should be approximately equal to the nib width. The depth of the flute determines the thickness of the core of the drill. Strength depends on the thickness of the core. If the groove is made deeper, the chips will be better placed, but the drill will be loose. Therefore, the thickness of the core is chosen depending on the diameter of the drill. In small diameter drills, the core thickness is a larger fraction of the drill diameter than in large diameter drills. So, for drills with a diameter of 0.8-1 mm, the core width is 0.21-0.22 mm, and for drills with a diameter of 10 mm, the core width is 1.5 mm. In order to increase the strength of the drill, the thickness of the core is increased towards the shank.

The front edge of the drill is not re-sharpened.

The design of the helical grooves is such that as they approach from the edge of the drill to the center, their angle of inclination decreases, which means that the rake angle also decreases. The working conditions of the cutting edge at the center of the drill will be more difficult.

The rear angle, as well as the front angle, varies in magnitude at different points of the cutting edge. At points closer to outer surface drill, it is smaller, at points located closer to the center, more. The back angle is formed when sharpening the intake cone and is approximately 8-12 ° on the periphery of the drill, and 20-25 ° in the center.

The jumper (transverse edge) is located in the center of the drill and connects both cutting edges. The angle of inclination of the bridge to the cutting edges ψ can be from 40 to 60°. Most drills have ψ=55°. The jumper is formed by the intersection of two back faces. Its length depends on the thickness of the core of the drill. Since the thickness of the core increases towards the shank, the length of the web increases with each sharpening. In the process of drilling, the transverse edge only prevents the penetration of the drill into the metal. It does not cut, but scrapes or, rather, crushes the metal. No wonder it was once called the scraping blade. By cutting the web length in half, the feed force can be reduced by 25%. However, reducing the length of the bridge by reducing the thickness of the core will weaken the drill.

The angle at the top 2φ has a great influence on the operation of the drill. If the angle at the top is small, the chips with their lower edge will touch the wall of the hole and there will be no conditions for proper chip formation.

The figure below shows a drill with a normal taper angle.

The edge of the chip in this case fits well into the groove. Changing the corner angle changes the length of the cutting edge and, consequently, the load per unit of its length. With an increase in the angle at the top, the load per unit length of the cutting edge increases, while the resistance to the penetration of the drill into the metal in the feed direction increases. With a decrease in the angle at the top, the force required to rotate the drill increases, since the conditions for chip formation worsen and friction increases. But at the same time, the load per unit length of the cutting edge decreases, the thickness of the cut chips becomes smaller, and heat is better removed from the cutting edges.

Typically, the point angle (2φ) of standard universal drills made of carbon, chromium and HSS is 116-118° and is considered suitable for many materials. But in order to provide best conditions work, it is changed as shown in the table.