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 conventional grinder by simply holding the drill in their hands (at least according to them). But this method requires skill and many 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 a small size, therefore, during operation, it quickly heats up from friction (there is no dispersion area). The main reason for blunting is overheating. With proper 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 a universal tool, and independent devices of a 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 proper 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 sharpening machine.
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 tools, 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 out, 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 of 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, the easiest to do with manual sharpening, is 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 the end of the grinding wheel, and the top is 1.9 times its size from the diameter of the drill. 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 face of the grinding wheel and, starting from the cutting edge, with smooth movements of the 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;
- the speed of rotation of the 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 - the cutting edges are sharpened at different angles to the drill axis, the middle of the jumper coincides with the drill axis.
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 ) a wooden lath with a side edge beveled at an angle of 25-30 ° (for single-plane sharpening). This rail also orients the holder with the drill being sharpened at the right angle relative to the grinding wheel. The holder is made of a rectangular wooden bar, one of the sidewalls of which is planed at an angle of 60-65 ° (depending on the angle of the side edge 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 mark and drill through holes perpendicular to the plane of this sidewall 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 fixture on a regular thrust bearing (armrest), so you have to come up with some kind of table or shelf for it, you can transfer the grinding machine to a table where there will be room for this fixture. 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 - with a 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 a cutting tool is that the chip to be separated is free to move away from the cutting point. 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. The front face of the 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 the same drill is used for 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 the outer surface of the drill, it is smaller, at points 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 the best working conditions, it is changed, as shown in the table.
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If we talk about those drills that are used by craftsmen at home, then their cost in stores is low. But even in this case, you should not use them as a consumable for a single use. After all, updating the drill to the best working condition will not be difficult if the master has the skill or special tools.
There are factory machines that are intended for sharpening, but this is a separate expense item, so most often craftsmen create such devices with their own hands.
Drills for metal create the most problems, and wooden blanks do not reduce the sharpness of the cutting edges so quickly.
To make a machine for restoring the sharpness of cutting elements, the necessary means of control (template), which is used to verify the tool.
Usually tools for ferrous metal, carbide bronze, steel or cast iron - with an edge angle of 115-125 degrees. The length of the other material, these parameters are different.
for soft bronze, red copper - 125, for brass alloys - 135;
for aluminum and soft aluminum alloys, granite, ceramics and wood - 135 degrees;
for magnesium and its alloys - 85 degrees;
for plastic, textolite and silumin - from 90 to 100 degrees.
Wizards, if necessary, make templates according to the above data. By the way, theoretically a single copy of the drill can be suitable for all these metals and other materials, if each time you sharpen different working surfaces.
An elementary handicraft fixture that is often used, bushings attached to the base. There are many drawings on the Internet for self-production. It should be noted that the tool must be well clamped, the accuracy depends on 1 degree.
If desired, you can make a significant size clip, using aluminum or copper tubes correlative with the typical characteristics of drills, or drill many holes in a soft metal blank. It is necessary that the sharpener has a comfortable hand rest to move the device and hold the stop.
This primitive sharpening machine is easy to install on a workbench or table.
Practical example of working with a drawing
The essence of the problem: there are drills, they need to be sharpened.
We will use one of the sharpening methods, close to the factory ones. Too lazy to catch hands. Better monkey way - put it and you're done. It took about 1 hour to make the fixture according to the finished drawing.
Some welding work on the template. A corner has been made. Put on the puck, it's just pressed on.
Let's try the first sharpenings, if everything is assembled correctly, we will refine and cultivate, make a quick adaptation.
After sharpening the drill, we carry out a test. Two casting chips are visible, which means that the sharpening was carried out correctly.
The only drawback is that one chip is longer than the other, which means they missed the length of the edges. It is necessary to make an emphasis, which will regulate the length, ensure the symmetry of the edges. To do this, we will make a thrust washer, which will be exposed and machined. Or we cut it so that it becomes possible to process shorter drills. 
When working with hard workpieces, the working surface of the drill wears out quickly. A dull drill gets very hot and loses its strength. This is due to the "release" of the metal. The tool needs to be sharpened periodically. However, this does not only apply to drills.
Drills are inexpensive devices. In any case, those models that are used in the household. However, buying a new tip every time it becomes dull is wasteful.
There are factory-made sharpeners, but this violates the concept of economical use of home tools.
Wood drills practically do not become dull, except that the tool can be “driven” at high speeds in a resinous workpiece. Pobedite tips for concrete and stone are not sharpened. It remains to sharpen the drill for metal. Many experienced locksmiths carry out this procedure with their own hands, without any tools.
However, the accuracy of the work leaves much to be desired, and not every home master's eye is developed so professionally. In any case, minimal mechanization is necessary.
IMPORTANT! Sharpening tips with a file, needle file and even sandpaper is pointless. To do this, you need an electric emery (grindstone).
How to make a homemade tool for sharpening drills?
First of all, it is necessary to acquire a means of control. No matter how you sharpen the drill, you need a template to check the accuracy of the work.
Conventional drills for working with ferrous metals have an edge angle of 115-120 degrees. If you have to work with different materials, check out the table of angles:
Workpiece material sharpening angle Steel, cast iron, carbide bronze 115-120 Brass alloys, soft bronze 125-135 Red copper 125 Aluminum and soft alloys based on it 135 Ceramics, granite 135 Wood of any species 135 Magnesium and alloys based on it 85 Silumin 90- 100 Plastic, textolite 90-100
Knowing these values, you can prepare several templates, and in accordance with them, sharpen yourself. In this case, you can use the same drill for different workpieces, you just need to change the angle of the top of the working area.
The simplest, but very effective tool for sharpening - bushings of different diameters, fixed on some kind of base.
Schematic drawing of the device in the illustration:
IMPORTANT! The tool in the sleeve should not hang out, an error of only one degree will reduce the quality of drilling.
It is best to make a whole clip of copper or aluminum tubes, for standard drill sizes. Or drill a sufficient number of holes in a bar of soft material. The main thing is to install a convenient hand-piece on your grinder, which will allow you to move the sharpening device at the right angle, and serve as a reliable stop.
Our grandfathers used this method. Only as a material for the manufacture of a grinding machine - a corner, an oak bar was used.
In principle, it was enough to place a table or workbench opposite the side surface of the emery - and the grinding machine is ready. At the same time, the quality and accuracy of processing was at a high level.
There are different drawings of sharpening devices.
You can use ready-made, or develop it yourself. The main thing is to understand the principle of working with a drill.
IMPORTANT! When working on a grinder, do not allow the drill to rotate around its axis.
If the tool turns at least a millimeter, it will be damaged, and you will have to grind a certain distance for re-processing.
After finishing sharpening, let the drill cool down and take measurements using a template. Both edges must be symmetrical to the nearest tenth of a millimeter. This is especially important for small diameter drills.
The diagram shows typical errors of self-sharpening:
The design of a grinding machine for twist drills for metal, made from improvised materials
As a basis, a household grinding machine with a proud inscription "made in Germany" is taken, which has all the signs of a product from the Middle Kingdom. Nevertheless, it works properly, there is no axle beating, it keeps the speed under load.
The terms of reference are as follows:
- the handpiece must be strictly on the same horizontal line (or above it) with the axis of rotation of the emery;
- the design is strong and reliable, ensuring the safety of work;
- there should be the possibility of both manual sharpening and semi-automatic - using a tool;
- the shape of the handpiece allows you to freely lower the drill shank to the required angle.
No scarce parts are required for the manufacture of the device. All the materials were actually lying underfoot in the shed. The processing of blanks was carried out by a grinder, the same upgraded sharpener, and welding.
Since the emphasis was supposed to be swinging (for semi-automatic mode), a loop connection was made. The holes of the tube, bracket and bolt are matched exactly to avoid backlash. The resulting device has two degrees of freedom.
The platform can be rotated along the vertical axis - changing the angle of sharpening the drill. This axle is fixed. Also, the handpiece can swing, leaning on a horizontal axis, providing the correct articulation during sharpening. This degree of freedom is not fixed.
For the base plate, metal 4 mm thick was chosen, the remaining structural elements - 3 mm. The strength is more than sufficient. The handpiece is rigidly connected to the body of the emery. Of course, it is unacceptable to attach it to the protective casing, so we fasten the bracket with the help of an additional metal “cheek”.
The actual guide plate for drills is screwed to the handpiece (more precisely, to the base plate). The plate is 5 mm thick, it has a triangular groove for fixing the drill during processing.
The angle of rotation of the structure is 90 degrees. This will ensure sharpening in any way, from the Leontiev method to pressing at one angle with the development of an acute edge angle due to the curvature of the emery.
The drill being machined is not only firmly held in the groove - it can be freely fed to the abrasive along the groove, without the slightest deviation of the sharpening angle.
Due to some excess of the plane of the base plate above the axis of rotation of the disk, the optimal shape of the sharpening of the back of the head of the working edge has been achieved.
Before starting work, we press the drill against the plate and set the cutting edge parallel to the plate. This completes the adjustment and you can feed the tool to the emery. Sharpening a drill requires certain skills, do everything slowly, carefully monitor the sharpening angle.
The accuracy of the work is the highest, the template is actually not required. It takes some time to install the fixture and adjust the angle, but you can quickly sharpen a couple of dozen drills without spending any effort.
If it is necessary to sharpen a drill with a carbide tip, the oscillating plate can be fixed at a fixed angle. To do this, you just need to put a couple of washers under the axle nut.
A few words about the emery wheel
Usually, for universal tasks, a white circle of electrocorundum is used in a home grinder. It sharpens knives, axes and shovels very well. With it, you can quickly process metal workpieces.
When sharpening carbide drills (and high-speed metal also requires a harder disk), a green silicon carbide abrasive wheel is used. Such circles are marked 64C.
Grit for household work is usually selected 25H.
When sharpening drills, a smaller fraction is required, it is better to work in the range 8H - 16H. It must be remembered that silicon carbide emery gets very hot during operation. Therefore, you can not keep the drill in contact with the abrasive for a long time. After 2-3 approaches, let the metal cool. Best of all, cool it with baking soda water.
IMPORTANT! The direction of rotation of the abrasive determines the quality of the edge. The working surface of the disk should run into the cut, that is, move from top to bottom.
The peripheral surface of the emery, as the main processing surface, must be perfectly flat. You can edit it with an elbor nozzle. For discs of small diameter, it is quite possible to get by with pliers in which the CBN cutter is held.
