To improve the quality of their work, craftsmen often make a machine for sharpening drills do it yourself. When using drills, you need to pay attention to their sharpness and the absence of damage - the quality of drilling depends on this. Previously, sharpening was done manually, but today you can buy a special machine or make it on your own according to individual parameters.
Features of the drilling process that affect the sharpness of drills
Drilling is ubiquitous in home and industrial use. In this process, the cutting edges create depressions in the surface as they rotate. Their power is enough to act on most materials, and even metal. The spiral channel removes waste and dust, so drilling can be done without stopping. But these particles wear away the drill device, causing it to wear out. Periodic sharpening can prevent this.
The wear of the drill directly depends on the duration of its use.
Damage occurs most quickly when working with metal and wood. The problem can be noticed when a specific squeaky sound is detected. As a result, not only the quality of drilling deteriorates, but also the heating of the tool increases, which can disable it. If the drill is heavily worn, the deterioration in sharpness can be felt even by touching it.
Sharpening types:
- Single Plane - Used for large drills. This is a strong sharpening that can crush material, so you need to be careful. The part must be moved on a circular surface without shifting its position in order not to damage the surface.
- Conical - used for large drills. They must be held with both hands, as it can slip off when applied to the part.
- Launching is the final stage, which evens out single irregularities and grinds the surface.
The most commonly used spiral alloy drills with reinforcing solders. There are flat models, for large holes... Regardless of their parameters and diameter, they require sharpening to prevent wear.
What do you need to assemble a drill sharpener?
Not only the grinding is responsible for the cutting ability of the drill, but also the blade angle - the smaller it is, the better the drilling. Optimal angle 90 ° is considered, 100 ° is required for wood, and 30 ° is suitable for plastic. Sharpening improves the angle of the cutting edge and centers it. This is done with an emery coating, which is used in specialized equipment or when manual sharpening... The machines can be industrial or domestic, which determines their size and power. Many masters create own equipment for sharpening is a cheap solution, often no worse than a production model.
It is best performed on special machines. Modern market proposes big choice such devices, but not always their parameters correspond to expectations or the cost turns out to be too high. In this case, you can make a machine on your own, this requires only initial technical skills. Despite the lower power home machine, it has a number of advantages over industrial devices:
- use of a single-phase flow of electricity at 220V;
- individual performance tuning;
- equipment mobility when installing limited functionality;
- high performance for the required type of drills;
- ease of repair and low assembly costs.
The correct approach to creating a machine will allow you to get an effective sharpening device. To assemble it, you need a toggle switch, a plug, a grinding wheel, a sufficiently strong motor, a set of wires, a stand and an axle. It is important to observe safety precautions, therefore it is better to cover the machine in protective caseleaving only the milling circle and axis visible. For operation, the device uses both a constant power supply network and a battery - for greater mobility.
Assembly of parts into a single apparatus and arrangement of safety elements
It is necessary to provide a surface for fixing the machine. A metal table is suitable for this, on which marks are made for bolts. Next, you need to take a granular disc, which is attached to the electric motor of the future machine. If the diameters of the shaft and disc do not match, they must be aligned with the tools at hand. In case of coincidence, the washer is placed on the shaft, after which the disk and, again, the washer. A thread must first be made on the shaft. Next, a fastening nut is installed, and an anti-swing nozzle is put on the circle.
You can add a bushing if the shaft has a smaller diameter than a stone. A hole is made in it, with which it is attached to the shaft, since the bushing will improve the fixation and will rotate with the disc. If you cannot find the correct motor, you can use a motor with washing machine... Wires can also be installed from it if they have three contacts in a suitable state. Next, the winding is connected to the phase line of the two buttons, which are responsible for turning the machine on and off. Thus, the device will be triggered by simple commands buttons.
The electric motor is not dangerous in open form, but he should provide protection. The motor can be hidden in a metal case, so that dust and moisture do not accumulate in it. Since a lot of chips are generated when sharpening drills, this is a hazard. Need to build protective shield made of glass that will protect your eyes. Of course, glasses can be used, but metal particles can fly off into the face. It is also desirable to make a protective cover. For this, a tire is suitable, part of which will cover the grinding disc by a third.
We sharpen parts on a homemade machine
If there is no way to get an electric motor, you can get by with a simple drill. It is not necessary to buy a new device, the old device in which the engine is functioning will do. To create a machine, it must be fixed on the surface, and a universal disk (can be replaced with a grinding wheel) or a sleeve must be installed in the chuck. When turned on, the drill will be suitable for working on drills. To achieve best efficiency, you need to approach the sharpening process correctly. Since drills have two threads, it is important to maintain the same dimensions when machining them so that the axis of rotation matches the center of the drill.
Before starting sharpening, you need to check the reliability of the fastening of the disc and protective elements. It will take from half an hour for a quality result. Each drill material has its own sharpening characteristics and direction of rotation, which must be studied before work. IN bench machine a sharpener (abrasive disc or emery) of the coarsest format is installed. This will compensate for major damage. After that, you need to switch to a fine abrasive, which will grind the surface. It is important to stick to one sharpening angle, although the drill will slide out in the process. If this is missed, there is a risk of dismount and injury.
It is important to avoid overheating of the drills. This destroys their plates, so you need to periodically lower them in water (this cannot be done if the drill is already hot). For the rest, simple skill is enough for sharpening drills. Compliance with the procedure and safety rules will allow you to quickly sharpen drills on a home-made machine and do without expensive equipment.
Blunt drills can break during operation and injure you. It is much better and easier to work with sharp ones. In this manual you will find drawings and a drill sharpener.
Step 1: Compare a sharp and blunt drill
The left is blunt. This can be seen from the highlight on the cutting edge between the two grooves. The photo on the right shows a sharp cutting edge.
Step 2: sharpening tool
Experienced people know how to sharpen drills with their own hands. In theory, the shank should be held in the right hand at a 59 ° angle relative to the sharpening tool. When the drill touches the sharpener, slide the shank further down to the left while rotating the drill clockwise around its axis. I have never succeeded.
The sharpening tool you see in the photo I bought almost thirty years ago. Such simple fixtures for sharpening drills are still sold at almost the same price.
Step 3: set the degree
The rack rail can be adjusted in seven positions. My drills have a 59 ° cutting edge angle profile, you need to set this degree on the guide. Tighten the wing nut.
Step 4: align the edge
The sharpening tool has a small pointed tip and the edge of the groove needs to be flush against it. The tip can be lowered or raised to bring it to the edge of the groove.
Step 5: offset amount
First you need to set the offset (the distance between the yellow lines), it should be equal to the radius (the distance between the green lines).
Step 6: Width and angle of the cutting edge
Notice the angle of the red line. If you moved the drill too far in the previous step, the cutting edge will move closer to the tip. The hem is too wide and the profile is flat. Because of this, it will slide on the surface of the metal and it will be difficult for you to drill. You can reduce the offset a little, but not much, otherwise you could accidentally ruin the tip of the sharpening tool on the stand's grinding wheel.
Step 7: Ideal cutting edge angle
Ideally, the edge should be as small as possible. It will be the bottom point between the beveled edges of the grooves of the drill, shown in the photo with a yellow line, this drill will cut metal very well.
Step 8: Clamp
After you position the stem, tighten the mounting screw.
Step 9: set the length
Set the sharpening guide to the length of the drill. The end should be in a mobile tray and not suspended in the air. Loosen the metal painted nut. Adjust the black nut. Tighten the painted metal nut.
Step 10: adjust the height
The shank must be at right angles to the grinding wheel. For sharpening, I use a radial cut-off machine. The tip must be aligned with the center of the axis grinding wheel.
Step 11: fix the machine to the table
The bit should only lightly touch the grinding wheel. If you press too hard, it will be very difficult to sharpen it. It will overheat and you will remove too much metal.
The base of the sharpening guide must be at right angles to the sharpening wheel (green line). AND upper part turn the guide so that the point looks slightly to the left of the center (the angle between the green and yellow lines). Move the machine forward so that the drill touches the surface of the grinding wheel. Fix the machine to the table.
Step 12: get ready to sharpen
Turn the tip to the right. Turn on the grinding wheel.
Step 13: sharpen
Move the tail of the guide to the right (red arrow) so that the drill touches the grindstone. The yellow wavy lines represent sparks. When the drill is in this position, in fact, sharpening will take place.
Step 14: turn the bit
Continue sliding the tail of the guide to the right until the drill is past the edge of the rock. To sharpen on the other side, you need to rotate it around its axis by half a turn.
Turn off the machine first. Then loosen the mount and turn it half a turn. The edge of the groove should be flush with the sharpening tip. Repeat the previous two steps.
Turn off the machine. Pull out of the mount. Check the width of the transverse cutting edge. If you are not happy with the quality of your sharpening, change the stem and repeat the process.
Step 15: sharpened drill
The photo shows good sharpening... The cutting edges are not frayed or rounded; they are sharp and crisp. The length and angle of the lateral cutting edge are also quite good.
Step 16: thin drills
Such a sharpening tool is good for 3 mm or more. If it is thinner, it will no longer be possible to sharpen it with this device.
For sharpening thin ones, do special unit made of a block of wood about 10 cm long. Please note that the angle between the red lines is 77 °.
Step 17: the angle between the edges of the wood block
Side view of the block. The angle between the red lines is 59 °.
Step 18: guide line
A triangular cut is visible on the upper plane of the bar. This cut goes along the entire upper edge of the block and serves as a bed. The angle between the red lines is also 59 °. The edges of the triangular cut are used to align the cutting edges. You can check the edges by eye.
Step 19: attach to the bar
Place the drill bit in the cut on the block. Place the block in a vise so that the shank is over the jaw and the jaw extends slightly beyond the beveled side of the block. Rotate to align one of the cutting edges with the leading edge of the triangular notch. Secure with a clamp. Put some oil on the whetstone. Slide along the beveled side of the device to sharpen the drill.
When the whetstone stops stripping metal, turn the drill half a turn and sharpen the other edge. Check homemade sharpening you can use a magnifying glass if needed.
When working with hard workpieces, the working surface of the drill wears out quickly. A blunt drill will become very hot and lose strength. This is due to the "letting go" of the metal. The tool must be sharpened periodically. However, this applies not only to drills.
Drills are inexpensive fixtures. In any case, the models used in household... However, it is wasteful to buy a new tip every time it is dull.
There are factory-made sharpeners, but this violates the concept of economical use of household tools.
Wood drills practically do not blunt, except that the tool can be "driven" at high speeds in a resinous workpiece. Pobeditovye tips and stone are not sharpened. Remains sharpening the drill for metal. Many experienced locksmiths carry out this procedure, without any devices.
However, the accuracy of the work leaves much to be desired, and not everyone has an eye home master developed so professionally. In any case, minimal mechanization is needed.
How to make a homemade drill sharpener?
First of all, you need to acquire a means of control. No matter how you sharpen the drill, a template is needed 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 angles table:
| Processed 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 its alloys | 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, the same drill can be used for different workpieces, you just need to change the angle of the work area vertex.
If you only have to drill wood, then you don't need 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. The difference is easy to feel with a brand new drill. Having started to cut into metal quite briskly, with every minute the drill will sink into the metal more and more slowly, and you will have to press on it more and more. The bluntness rate of the drill depends in particular on the revolutions, feed rate, cooling and other factors, however, no matter how hard you try, the operating time of the drill to unsatisfactory performance is measured in minutes. If the volume 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 are dull.
At the periphery of the drill, the cutting speed is maximum, and therefore 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, bluntness starts from the corner, then extends to the entire cutting edge. Its rounding is clearly visible. Then the back edge is rubbed off. Strokes appear on it, risks coming from the cutting edge. With wear, the marks 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 crumples when worn.
At the beginning of bluntness, the drill makes a sharp squeaking 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 can't 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 pressure force constant.
Sharpening of twist drills
The drill is sharpened along its rear edges. It is very important that both feathers (teeth) of the drill are sharpened exactly the same. It is very difficult to do this manually. It is also not easy to manually create the required back face shape and the specified clearance angle (see below for what angle).There are special machines or devices for sharpening. If possible, it is better to sharpen the drills on specialized equipment. But in a home workshop, such an opportunity, as a rule, does not exist. The drills have to be sharpened by hand on an ordinary sharpener.
Depending on the shape of the back surface, there are different types sharpening: single-plane, two-plane, conical, cylindrical, screw.
With single-plane sharpening, the back surface of the feather is made in the form of a plane. The clearance angle for this 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 for manual sharpening, is recommended for drills up to 3 mm in diameter.
Universal drills with a diameter greater than 3 mm are usually tapered. In order to understand the features of such sharpening, consider a conical sharpening scheme on a drill machine with a 2φ angle of 118 °. The figure below shows a grinding wheel and a drill pressed against its end by the cutting edge and back surface.
Imagine a cone whose generatrix is \u200b\u200bdirected along the cutting edge and end grinding wheel, and the tip is 1.9 times from the drill diameter. The apex angle is 26 °. The axis of the drill intersects with the axis of the 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 edge of the drill. If the axis of the drill and the axis of the imaginary taper are in the same plane, then the clearance angle will be zero. To create a clearance angle, you need to offset the axis of the drill in relation to the axis of the imaginary taper. In practice, this offset will be 1/15 of the drill diameter. Swinging the drill along the axis of an imaginary taper with this mixing will provide a tapered flank and a clearance angle of 12-14 °. The larger the offset, the larger the clearance angle will be. It will be recalled that the clearance 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 of sharpening by hand. The drill intended for sharpening is taken with the left hand by the working part, possibly closer to the intake cone, and by the tail with the right hand.
The cutting edge and the rear surface of the drill are pressed against the end of the grinding wheel and, starting from the cutting edge, with smooth movements right handwithout lifting the drill from the stone, shake it, creating a tapered surface on the back edge of the feather. Then repeat the same procedure for the second pen.
When sharpening, it is advisable to repeat as accurately as possible the shape of the rear surface that was after the factory sharpening, so as not to lose the required rear 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 by the tail. With the cutting edge, the drill is pressed against the end of the grinding wheel and with a smooth movement of the right hand, without tearing 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 of the grinding wheel when rotating the drill. For this, special bushings are often used when sharpening.
As a result of this sharpening, a tapered surface will be obtained on the back surfaces of both feathers, but the clearance angle will not be formed. During operation, the friction of the rear surface against the walls of the hole and, therefore, 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. Inexperienced sharpening renders the tool blade 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 solid 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 the hand cannot tolerate it.
Practice shows that the sharpening of the tool should be carried out against the movement of the grinding wheel. Then the cutting edge is more durable, less often creasing and breaking.
For sharpening, use grinding wheels made of electrocorundum (grades 24A, 25A, 91A, 92A) with a grain size of 25-40, hardness M3-CM2, on ceramic bonds.
In production, sharpening is usually followed by fine-tuning. Lapping makes the surface smoother, removes small dents. A refined drill is more resistant to wear than a sharpened drill. If you have the opportunity to perform fine-tuning, 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 wheels from Elbor LO, grain size 6-8 on a bakelite bond are used.
One of the main conditions correct sharpening drills - maintaining its axisymmetry. Both cutting edges must be straight and of the same length, the same nose angles (and taper angles) in relation to the drill axis.
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 - the angle of sharpening; d - angle between the web and the cutting edge.
It is made independently from a sheet of copper, aluminum or steel with a thickness of approximately 1 mm. The most durable template is of course steel. The template is used to check the angle at the top, the length of the cutting edges, the angle between the bridge and the cutting edge. Instead of the clearance angle, which is very difficult to measure, the taper angle is measured with a template. It is advisable to make a template before using a new drill in order to transfer the desired corners from the last.
The uneven length of the cutting edges and their inclination to the axis of the drill lead to unequal loads. The drill will fail faster due to intense wear on the overloaded cutting edge.
a - the wedges of the cutting edges are not the same, the middle of the bridge 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 bridge coincides with the drill axis.
An uneven load on a part of the drill will cause its runout during cutting and, as a result, an increase in the diameter of the resulting hole.
The easiest way to check for correct sharpening is with trial drilling. If the nibs of the drill are sharpened unevenly, then the less loaded will have less chips from the corresponding groove. Sometimes the chips only protrude through one flute. The hole diameter can 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 \u003d 120 °, 32 ° for 2φ \u003d 116 °) is sewn (nailed, glued ) wooden lath with beveled at an angle of 25-30 ° (for single-plane sharpening) side edge. This rail orients at the desired angle the holder with the sharpened drill relative to the grinding wheel. The holder is made of a rectangular wooden bar, one of the sides of which is cut off 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 provides sharpening of the front corner of the drill 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 a given diameter. The length of the holder is chosen such that it is convenient to hold it when sharpening the drills.
You cannot install a device on an ordinary thrust bearing (armrest), so you have to come up with some kind of table or shelf for it, you can transfer the sharpening machine to the table where there will be a place for this device. On the base, place the holder with the drill inserted into it to be sharpened close to the rail. Turn the drill in the holder seat so that the sharpened edge is oriented horizontally. Use your left hand to hold the drill at the edge to be sharpened, and hold the drill shank with your right hand. Pressing the tool holder against the beveled bar, slide the drill over the emery wheel and sharpen one edge. Then unfold the drill and cut the second edge the same way.
You can make it 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 are formed, or, as they are otherwise called, teeth.The twist drill consists of a working part, a neck, a shank and a foot.
A - with a tapered shank; B - c cylindrical shank; a - working cutting part; b - neck; в - feather width; g - foot; d - leash; e - flute screw shaving; g - feather; h - shank; and - jumper; L is the total length; L 0 - the length of the "working cutting part"; D is the diameter; ω is the angle of inclination of the "screw chip groove"; 2φ - apex angle; f is the width of the spiral ribbon; ψ is the angle of inclination of the bulkhead.
The working part is divided into a cutting and a guide. 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 part for regrinding the drill. On the feathers of the guide part along a helical line, there are cylindrical chamfers-ribbons. The tape is used to guide the drill in the hole and to reduce the friction of the drill against the hole wall. It doesn't have to be wide. So, the width of the tape of the drill 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. The drills can be made with or without a neck.
Drill diameter measured by strips is not the same along drill length. At the intake cone, it is slightly larger than at the shank. This reduces friction of the ribbons against the hole walls.
In order to understand the structure of the cutting part of the drill, let us 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 chips to be separated freely move away from the cutting site. The surface of the tool on which the chips run down is called the leading edge. This face is tilted back at an angle from the vertical plane.
1 - wedge; 2 - processed item; γ (gamma) - front angle; α (alpha) - posterior angle; δ (delta) - cutting angle; β (beta) - taper angle.
Thanks to this angle for the tool, it is easier to plunge into the metal and chips come off more freely along the front edge. The angle between the leading edge of the tool and a plane perpendicular to the cutting surface is called the rake 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 against the cutting surface. The angle between the back face of the tool and the cutting surface is called the clearance angle and is denoted greek letter α.
The angle between the front and back faces of the tool is called the taper angle and is denoted by the Greek letter β.
The angle between the leading edge 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 clearance angle α.
Rake and clearance angles are the angles that must be observed when sharpening.
Now we will find the faces and corners described above on the drill, which does not at all look like the tool shown in the picture above. To do this, we will cut the cutting part of the drill with the AB plane, which is perpendicular to its cutting edge.
The cutting edge is the intersection of the leading and trailing edges of the tool. 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 angles γ and α along the cutting edge are variable, which will be discussed below.
The drill has two cutting edges connected by a bridge located at an angle ψ to the cutting edges.
Having got a general idea about the geometry of the cutting part of the drill, let's talk in more detail about its elements. The front face of a twist drill is a complex helical surface. Face is a conditional name, since the word "face" implies a plane. A helical groove, the surface of which forms a leading edge, intersects with the intake cone, creates straight cutting edges.
The angle of inclination of the helical groove to the drill axis is denoted by the Greek letter ω. The larger this angle, the larger the rake angle and the easier the chip exit. But the drill becomes weaker as the slope of the helical flute increases. Therefore, for drills with a small diameter, having lower strength, this angle is made smaller than that of drills large diameter... The angle of inclination of the helical groove 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 processed material. The softer it is, the greater the angle of inclination can be. But this rule is applicable in production. At home, where one drill is used for processing different materials, the angle of inclination is usually related to the drill diameter and varies from 19 to 28 ° for drills with a diameter of 0.25 to 10 mm.
The shape of the groove should provide sufficient space for the chips and allow the chips to be easily evacuated from the groove without weakening the drill too much. The groove width should be approximately the same as the feather width. The groove depth determines the thickness of the drill core. Strength depends on the thickness of the core. Making the groove deeper will allow the chips to fit better, but the drill will be weakened. 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 leading 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 near the center of the drill will be more difficult.
The clearance angle, as well as the clearance 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, it is larger. The clearance angle is formed when sharpening the intake cone and is approximately 8-12 ° at the periphery of the drill, and 20-25 ° in the center.
A bridge (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 \u003d 55 °. The bridge is formed by the intersection of the two back edges. Its length depends on the thickness of the drill core. As the thickness of the core increases towards the shank, the length of the web increases with each sharpening. During the drilling process, the transverse edge only interferes with 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 reducing the length of the web by half, the feed force can be reduced by 25%. However, reducing the web length by reducing the core thickness will weaken the drill.
The 2φ point angle has a great influence on drill performance. If the tip angle is small, the bottom edge of the chips 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.
In this case, the chip edge fits well into the groove. Changing the nose angle changes the length of the cutting edge and hence the load per unit length. With an increase in the angle at the tip, the load per unit length of the cutting edge increases, while the resistance to penetration of the drill into the metal in the feed direction increases. With a decrease in the nose angle, the force required to rotate the drill increases, since the conditions for chip formation deteriorate 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 the heat from the cutting edges is better removed.
Typically the tip angle (2φ) of standard universal drills in carbon steel, chrome steel 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.
When using the content of this site, you need to put active links to this site, visible to users and search robots.
Having picked up correct drawing tools for sharpening drills, you can make homemade full-fledged equipment at home. Thanks to such a device, the task of ensuring the required geometric shape of the tool is greatly simplified.
When using it, there is no need to worry not only about the rotation of potentially dangerous sharpening stones, but also about the sharpening angles, which must be properly maintained, fishing each degree by hand.
Features of using homemade sharpening devices
While drilling holes in metal products, drills wear out quite a lot, which leads to their heating and loss of their properties. To avoid such a phenomenon, measures are required to ensure the regular restoration of their geometric parameters. This can be done using special equipment for sharpening drilling tools. The creation of such a simple device can be done independently, which will allow high-quality sharpening without any significant financial costs.
Many experienced specialists practically do not use sharpening devices, since they are absolutely confident in their experience and eye, which allows them to sharpen drills correctly. But in practice, the use of such devices is extremely necessary, since it allows the mechanization of this process. As a result of such work, the maximum accuracy and quality of the sharpening will be ensured.
The modern market offers different kinds equipment that allows you to carry out the restoration of geometry in a quality manner cutting tools, even in the absence of experience in this matter. At the same time, there is no urgent need to purchase such products, since they can be made by hand according to the existing drawings of tools for sharpening drills.
Drawings of the simplest devices
The simplest devices for sharpening can be bushings, inner diameter which corresponds to the transverse dimensions of the drills. The sleeve is rigidly fixed to a secure base, taking into account a certain angle. When selecting a sleeve for such devices, you should pay attention to the correspondence of its inner diameter with the transverse dimension of the tools being sharpened. It is forbidden for the machined tools to dangle in the bushing, since, even with a deviation of 1-2 degrees along the axis from the required values, the quality and accuracy of sharpening may significantly decrease.
Such homemade gadgets for sharpening drills must be equipped with clips. For their manufacture, copper or aluminum tubes are suitable, the inner diameter of which is equal to the typical size of the drilling tool used.
In some cases, the task can be simplified by setting to this design wooden blockin which holes are to be drilled, with a diameter corresponding to the tool used. One of essential elements such a product is considered the presence of a handcuff, which is necessary for:
- securing correct fixation drilling tool and the ability to accurately move in relation to the surface of the abrasive stone;
- creating a stop point for the drill to be ground.
Such products made of oak bars, in which holes of different sizes are provided, are the most reliable. Thanks to them, high-quality and accurate sharpening of tools is carried out. The main task that must be solved with a homemade machine tool or similar device is correct orientation cutting part of the processed tools to obtain the accuracy of the required sharpening angle.
For the manufacture of homemade machine for sharpening drills, a number of different design variations of such equipment can be used. With the appropriate drawings and understanding of the principle of operation of this equipment, you can make grinding equipment yourself at home.
The structure consists of the following elements:
Promotional site
Mount for drill and stop screw
Bolts, nuts, pins, screws
Exist important rules, which must be observed during the operation of such a device, namely, the sharpened tool should not rotate around its axis. In the event of even a slight turn, sharpening must be done again.
The sharpened tool must be cooled in a natural way... After that, check its restored geometric parameters. You can use a template for this. It should be borne in mind that each cutting edge of the drill may differ from each other by no more than a tenth of a mm. Wherein, special attention it is worth paying this parameter if the drills have a small diameter.
Video "Attachment for sharpening drills according to the drawing"
A drawing of a complete fixture
Quite a simple way to make homemade sharpening equipment, which is practically no different from a factory product. It takes about 1.5-2 hours to assemble it according to the finished drawings.
To make do-it-yourself tools for sharpening drills, it is necessary to provide for the following supplies, equipment and tools:
- welding machine;
- electric drill;
- grinders;
- standard locksmith set tools;
- a corner, the size of the shelves of which is 30x30, and its length is 100-150 mm;
- metal plates having different thickness (3-5 mm);
- studs or pieces of steel rods, the diameter of which is 10-12 mm;
- washers, screws, bolts and nuts of various sizes.
First of all, the bed is made, which will be the base in the grinding device. For this, a steel plate is used, onto which a steel bar (12 mm in diameter) is welded at an angle of 75 degrees. It will be the axis.
After that, a washer should be put on the welded rod, which will be a thrust bearing. The value of the angle, the rotation of the bed when sharpening the drill will be insignificant, therefore, in using the standard ball bearing no reason.
The stock where the sharpened tool will be placed is made from a prepared corner. One side on the corner profile that faces the side of the grindstone must be grinded at a 60 degree angle. On the bed, according to the drawing, a bracket is welded, through which fixation will be performed swivel unit devices. As a result of this, a structure will be produced, the corners of which, in the case of a parallel position of the bed and the bed, should be located to the surface of the abrasive stone in accordance with the angle of the drill to be sharpened.
The sharpening machine, which is shown in the drawing, has fixed angles of inclination, but for greater possibilities it is desirable to provide the ability to adjust the angles. In such cases, there will be a greater chance of using the fixture when it is necessary to restore the instruments, with different angles sharpening, for example, if it is necessary to sharpen drills for metal, concrete, etc.
To create a more functional unit, you can use drawings of other structures that have the ability to adjust the angles:
Video "Device made from the drawing"