To improve the quality of their work, craftsmen often make a machine for drill sharpening with your own hands. When using drills, you need to pay attention to their sharpness and absence of damage - the quality of drilling depends on this. Previously, sharpening was done by hand, but today you can buy a special machine or make it yourself according to individual parameters.
Features of the drilling process that affect the sharpness of drills
Drilling is ubiquitous in home and industrial settings. In this process, the cutting edges create indentations in the surface as they rotate. Their power is enough to affect most materials, and even metal. The presence of a spiral channel removes work waste and dust, so you can drill without stopping. But these particles wear out 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 squeaking sound is detected. As a result, not only the quality of drilling deteriorates, but also the heating of the tool increases, which can damage it. If the drill is heavily worn, the deterioration in sharpness can be felt even by touching it.
Types of sharpening:
- 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 so as not to damage the surface.
- Conical - used for large drills. They need to be held with both hands, since if you press on the part, it may slip off.
- Finishing is The final stage, which levels out single irregularities and polishes the surface.
Most often, spiral alloy drills with reinforcing tips are used. There are also flat models, For large holes. Regardless of the parameters and diameter, they require sharpening to prevent wear.
What will you need to assemble a drill sharpening machine?
Not only the grinding is responsible for the cutting ability of the drill, but also the angle of the blades - 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 sanding, which is also used in specialized equipment or when manual sharpening. Machines can be industrial or household, which determines their dimensions and power. Many masters create own equipment for sharpening - this is a cheap solution, often as good as the production model.
It is best performed on special machines. Modern market offers big choice such devices, but their parameters do not always meet expectations or the cost is too high. In this case, you can make the machine yourself; this requires only basic technical skills. Despite the lower power home machine, it has a number of advantages compared to industrial devices:
- use of single-phase electricity flow at 220V;
- individual performance tuning;
- mobility of equipment when installing limited functionality;
- high performance for the required type of drills;
- ease of repair and low assembly costs.
The right approach to creating a machine will allow you to obtain an effective sharpening apparatus. To assemble it you need a toggle switch, a plug, a grinding wheel, a fairly strong motor, a set of wires, a stand and an axle. It is important to observe safety precautions, so it is better to cover the machine in protective housing, leaving only the turning circle and the axis visible. To operate the device, they use both a constant power supply and a battery for greater mobility.
Assembling parts into a single device and installing safety elements
It is necessary to provide a surface for mounting the machine. A metal table is suitable for this, on which marks are made for the bolts. Next you need to take a granular disk, which is attached to the electric motor of the future machine. If the diameters of the shaft and disk do not match, they must be aligned using available tools. If there is a match, the washer is placed on the shaft, after which the disk and, again, the washer. The shaft must first be threaded. Next, install the fastening nut, and put the anti-sway attachment on the circle.
You can add a bushing if the shaft has a smaller diameter for the stone. A hole is made in it, with which it is attached to the shaft, since the bushing will improve fixation and will rotate together with the disk. If you cannot choose the right electric motor, you can use a motor with washing machine. Wires can also be installed from it if they have three contacts in suitable condition. Next, the winding is connected to the phase line of two buttons responsible for turning the machine on and off. Thus, the device will be triggered by simple commands buttons
The electric motor does not pose any danger open form, but he should provide protection. The motor can be hidden in a metal casing so that dust does not accumulate and moisture does not penetrate. Since a lot of chips are released when sharpening drills, this creates a danger. Need to build protective screen made of glass that will protect your eyes. Of course, you can use glasses, but metal particles may fly into your face. It is also advisable to make a protective casing. A tire is suitable for this, part of which will cover one third of the sharpening disc.
Sharpening parts on a homemade machine
If you can’t get an electric motor, you can get by with a simple drill. It is not necessary to buy a new device; an old device in which the engine operates will also work. To create a machine, you need to fix it on the surface, and install a universal disk (can be replaced with a grinding wheel) or bushing in the chuck. When you turn on the drill, it will be suitable for working on drill bits. 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 corresponds to the center of the drill.
Before you start sharpening, you need to check the reliability of the disk and protective elements. It will take half an hour for a high-quality result. Each drill material has its own sharpening characteristics and rotation direction, which must be studied before work. IN table machine a sharpener (abrasive disc or emery) of the coarsest format is installed. This will correct the main damage. After this, you need to switch to a fine abrasive that will grind the surface. It is important to maintain one sharpening angle, although the drill moves out in the process. If this is missed, there is a risk of dismounting and injury.
It is important to avoid overheating of drills. This destroys their plates, so you need to periodically immerse them in water (this cannot be done if the drill is already hot). Otherwise, simple skill is enough to sharpen drills. Following the procedure and safety rules will allow you to quickly sharpen drills on a homemade machine and do without expensive equipment.
Dull drill bits may 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 device for sharpening drills.
Step 1: Comparison of sharp and dull drill bits
The left side is blunt. This can be seen by the light reflection 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 your right hand at an angle of 59° relative to the drill sharpener. When the drill touches the sharpener, you need to move the shank further down to the left, while at the same time turning the drill around its axis clockwise. I've never succeeded in doing this.
I bought the sharpening tool you see in the photo almost thirty years ago. Such simple devices for sharpening drill bits are still sold at almost the same price.
Step 3: Set the degree
The guide on the stand can be installed in seven positions. My drills have a cutting edge angle profile of 59°, 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 set 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 must be equal to the radius (the distance between the green lines).
Step 6: Width and Angle of Cutting Edge
Pay attention to the angle of the red line. If you took the drill too far in the previous step, the cutting edge will move closer to the tip. The edge was too wide and the profile too flat. Because of this, it will slide along the surface of the metal and it will be difficult for you to drill. You can reduce the offset a little, but only a little, otherwise you may accidentally damage the sharpening tool tip on the stand's sharpening wheel.
Step 7: Ideal Cutting Edge Angle
Ideally, the edge should be as small as possible. It will be the lower point between the beveled edges of the drill grooves, indicated in the photo by a yellow line, this drill will cut metal very well.
Step 8: Clamp
Once you have the stem aligned, tighten the mounting screw.
Step 9: Set the length
Set the sharpening guide to the length of the drill. The end should be in the moving tray and not hanging in the air. Loosen the metal painted nut. Adjust the black nut. Tighten the painted metal nut.
Step 10: Setting the Height
The shank should be at right angles to the grinding wheel. For sharpening I use a radial cutting machine. The tip must be aligned with the center of the axis grinding wheel.
Step 11: Attach 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 will overheat and you will remove too much metal.
The base of the sharpening guide should be at right angles to the grinding wheel (green line). A top part turn the guide so that the tip points slightly to the left of center (the angle between the green and yellow lines). Move the machine forward until the drill bit touches the surface of the grinding wheel. Fix the machine on the table.
Step 12: Get Ready to Sharpen
Turn the tip to the right. Turn on the grinding wheel.
Step 13: Sharpening
Slide the tail of the guide to the right (red arrow) until the drill bit touches the whetstone. Yellow wavy lines represent sparks. When the drill is in this position, it will actually be sharpened.
Step 14: Rotate the Bat
Continue moving the tail of the guide to the right until the drill bit clears the edge of the stone. To sharpen the other side, you need to turn it around its axis half a turn.
First turn off the machine. Then loosen the fastener 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 it out of the mount. Check the width of the cross cutting edge. If you are unhappy with the quality of the sharpening, change the stem and repeat the process.
Step 15: Sharpened Drill
The photo shows good sharpening. The cutting edges are not worn or rounded, they are sharp and crisp. The length and angle of the transverse cutting edge are also quite good.
Step 16: Fine Drills
This sharpening tool is good for 3 mm and larger. If it is thinner, it will no longer be possible to sharpen it using this device.
To sharpen thin ones, do special block from a wooden block approximately 10 cm long. Please note that the angle between the red lines is 77°.
Step 17: 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 cutout 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 it to a block
Place the drill bit into the cut on the block. Place the block in the vise so that the shank is above the grip and the grip extends slightly beyond the beveled side of the block. Turn so that one of the cutting edges aligns with the guide edge of the triangular cutout. Secure with a clamp. Drop a little oil onto the sharpening stone. Slide along the beveled side of the device, thereby sharpening the drill.
When the sharpening stone stops removing metal, turn the drill half a turn and sharpen the other edge. Check homemade sharpening You can use a magnifying glass if necessary.
When working with hard workpieces, the working surface of the drill wears out quickly. A dull drill becomes very hot and loses strength. This occurs due to the “releasing” of the metal. The tool must be sharpened periodically. However, this applies not only to drills.
Drills are inexpensive devices. In any case, those models that are used in household. However, it is wasteful to buy a new tip every time it becomes dull.
There are factory-made sharpening devices, 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 into a resinous workpiece. Pobedite tips cannot be sharpened with stones. All that remains is to sharpen the drill for metal. Many experienced locksmiths carry out this procedure without any equipment.
However, the accuracy of the work leaves much to be desired, and not everyone has an eye home handyman developed so professionally. In any case, minimal mechanization is necessary.
How to make a homemade device for sharpening drills?
First of all, you need 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:
| 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 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, the same drill can be used for different workpieces; you just need to change the angle of the top of the working area.
If you only have to drill into wood, then you don’t have to worry about the sharpness of the drill, since the drill can serve well 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 bit. You can easily feel the difference when you take a completely new drill. Having started to cut into the metal rather quickly, with every minute the drill will plunge into the metal more and more slowly, and you will have to press on it more and more. The rate of dulling of a drill depends, in particular, on revolutions, feed rate, cooling and other factors, but no matter how hard you try, the time it takes for a drill to become unsatisfactory 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, 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, dullness begins at the corner and then spreads to the entire cutting edge. Its curve is clearly visible. Then the back edge wears off. Strokes and marks appear on it, coming from the cutting edge. As they 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 becomes wrinkled when worn.
At the beginning of dulling, 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 proceed faster.
To make it easier to control the geometry of the drill, the main thing that should be done is the template described below. With its help, even if sharpening is carried out without tools, you can always check where else the metal needs to be removed, and, in the end, get what you should get (it’s impossible that it won’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 and pressure constant for each section.
Sharpening twist drills
The drill is sharpened along its rear edges. It is very important that both blades (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 back angle (see below for which angle).There are special machines or devices for sharpening. If possible, it is better to sharpen drills using specialized equipment. But in a home workshop, such an opportunity, as a rule, does not exist. Drills have to be sharpened by hand using an ordinary sharpener.
Depending on what shape the back surface is given, there are different types sharpening: single-plane, double-plane, conical, cylindrical, screw.
With single-plane sharpening, the back surface of the pen is made in the form of a plane. The clearance angle for such sharpening should be 28-30°. With single-plane sharpening, there is a high risk of chipping the cutting edges. This method, which is the easiest to do with manual sharpening, is recommended for drills with a diameter of up to 3 mm.
Universal drills with a diameter greater than 3 mm are usually subjected to conical sharpening. In order to understand the features of such sharpening, let’s consider a diagram of conical sharpening on a drill machine with a 2φ angle of 118°. The figure below shows a grinding wheel and a drill pressed against its end with the cutting edge and back surface.
Let's imagine a cone, the generatrix of which is directed along the cutting edge and end grinding wheel, and the apex is 1.9 times the diameter of the drill. The apex angle is 26°. The drill axis 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 a cone along the end of a 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 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 the 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 this mixture will provide a conical back face and a back angle of 12-14°. The larger the offset value, the larger the relief angle will be. It should be remembered 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 sharpening conditions manually. The drill intended for sharpening is taken by the working part with the left hand, possibly closer to the intake cone, and by the tail with the right hand.
The cutting edge and rear surface of the drill are 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, rock it, creating a conical surface on the back edge of the pen. Then repeat the same procedure for the second feather.
When sharpening, it is advisable to repeat as accurately as possible the shape of the back surface that was after 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. The cutting edge of the drill is pressed against the end of the grinding wheel and with a smooth movement of the right hand, without lifting the drill from the stone, rotate 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 purpose, special bushings are often used when sharpening.
As a result of this sharpening, a tapered surface will be formed 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, therefore, the heating will be greater.
Due to friction with the grinding wheel, the tool heats up during sharpening. This causes the hardened part of the tool to temper. The metal softens and loses its hardness. Inept 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 carbide drills. Do not use oil for cooling when sharpening. If for any reason the tool is sharpened dry, then:
- a small layer of metal is removed in one pass;
- the rotation speed of the abrasive wheel should be as low as possible;
- The drill should never become so hot that the hand cannot tolerate it.
Practice shows that tool sharpening should be carried out against the movement of the grinding wheel. Then the cutting edge is more durable, and it is less likely to crumple or break off.
For sharpening, grinding wheels made of electrocorundum (grades 24A, 25A, 91A, 92A) with a grain size of 25-40, hardness M3-CM2, on ceramic bonds are used.
In production, sharpening is usually followed by finishing. Finishing makes the surface smoother and removes small nicks. A polished drill is more resistant to wear than a drill after sharpening. If you have the opportunity to do some fine-tuning, take it.
For finishing, grinding wheels made of green silicon carbide grade 63C, grit 5-6, hardness M3-SM1 on a bakelite bond, or wheels made of CBN LO, grit 6-8 on a bakelite bond, are used.
One of the main conditions correct sharpening drill - maintaining its axisymmetricity. Both cutting edges must be straight and have identical lengths and identical apex angles (and point angles) relative to the drill axis.
The correctness of sharpening is checked with a special template.
a - template; b - checking the apex angle and cutting edge lengths; c - sharpening angle; g - 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 is, of course, made of steel. The template is used to check the angle at the apex, the length of the cutting edges, and the angle between the jumper and the cutting edge. Instead of the back angle, which is very difficult to measure, the tip angle is measured using a template. It is advisable to make a template before using a new drill in order to transfer the required angles from the last one.
The uneven length of the cutting edges and their inclination to the axis of the drill also lead to unequal load. The drill will fail faster due to 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 parts of the drill will cause it to run out during the cutting process and, as a result, an increase in the diameter of the resulting hole.
The easiest way to check the correct sharpening is test drilling. If the drill feathers are sharpened unequally, then the less loaded one will have less chips from the corresponding groove. Sometimes chips protrude through only one groove. 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 it is sewn (nailed, glued) at an angle of 30-32° (depending on the angle 2φ, see below, 30° for 2φ=120°, 32° for 2φ=116°) ) wooden slats with a side edge beveled at an angle of 25-30° (for single-plane sharpening). This rack orients the holder with the drill being sharpened at the desired angle relative to the grinding wheel. The holder is made from a rectangular wooden block, one of the sides 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 sharpening of the front angle of the drill within the required limits (25-30°). On the other sidewall of the holder, mark and drill through holes perpendicular to the plane of this sidewall for each drill of one diameter or another. The length of the holder is chosen so that it is comfortable to hold when sharpening drills.
You cannot install the device on a regular pad (armrest), so you will have to come up with some kind of table or shelf for it; you can move the sharpening machine to a table where there will be room for this device. Place a holder with a drill inserted into it to be sharpened, close to the rail, on the base. Turn the drill in the holder socket so that the sharpened edge is oriented horizontally. With your left hand, hold the drill near the edge to be sharpened, and with your right hand, hold the drill shank. While pressing the holder against the beveled strip, move the drill to the emery wheel and sharpen one edge. Then turn the drill and process the second edge in the same way.
It can be done even simpler:
Sharpening angles and other characteristics of the drill
A twist drill is a rod that has two helical grooves to facilitate the release of chips. Thanks to the grooves on the drill, two screw feathers are formed, or, as they are otherwise called, teeth.A twist drill consists of a working part, a neck, a shank and a claw.
A - with a conical shank; B - s cylindrical shank; a - working cutting part; b - neck; in - width of the pen; g - foot; d - leash; e - screw flute; f - feather; z - shank; and - jumper; L - total length; L 0 - length of the “working cutting part”; D - diameter; ω - angle of inclination of the “chip screw groove”; 2φ - apex angle; f - width of the spiral ribbon; ψ is 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 to guide during cutting and is a spare part when resharpening the drill. On the feathers of the guide part along the helical line there are cylindrical chamfers-ribbons. The ribbon serves to guide the drill in the hole, as well as to reduce friction of the drill on the walls of the hole. It shouldn't be wide. Thus, the width of the drill strip with a diameter of 1.5 mm is 0.46 mm, and 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 neck.
The diameter of the drill, measured by the strips, 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 against the walls of the hole.
In order to understand the structure of the cutting part of the drill, we will consider the basic principles of operation of any cutting tool (including the drill). One of the most important requirements for a cutting tool is that the separated chips move freely from the cutting site. The surface of the tool along which the chips run is called the rake face. This face is deflected back at a certain angle from the vertical plane.
1 - wedge; 2 - object being processed; γ (gamma) - front angle; α (alpha) - rear angle; δ (delta) - cutting angle; β (beta) - sharpening angle.
Thanks to this angle, it is easier for the tool to cut into the metal and the chips flow more freely along the front edge. The angle between the front edge of the tool and a plane drawn 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 on the cutting surface. The angle between the rear edge of the tool and the cutting surface is called the clearance angle and is designated Greek letter α.
The angle between the front and back edges of the tool is called the point angle and is denoted by the Greek letter β.
The angle between the front 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 tip angle β and the relief angle α.
The rake and back angles are the angles that must be maintained when sharpening.
Now let’s find the edges and angles described above on the drill, which is not at all similar to the tool shown in the figure above. To do this, we cut the cutting part of the drill with plane AB, perpendicular to its cutting edge.
The cutting edge is the line of intersection of the front and rear edges of the tool. The rake angle γ of the drill is formed by a helical groove. The angle of inclination of the groove to the drill axis determines the size of the rake angle. The magnitude of the angles γ and α along the cutting edge is variable, as will be discussed below.
The drill has two cutting edges connected to each other by a bridge 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 edge of a twist drill is a complex helical surface. Facet is a conditional name, since the word “facet” implies a plane. The helical flute, the surface of which forms the leading edge, intersecting with the chamfer, 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 weakens as the inclination of the helical flute increases. Therefore, drills with small diameters having less strength, this angle is made smaller than that of drills large diameter. The angle of inclination of the helical flute also depends on the material of the drill. High speed steel drills can operate under more stressful conditions than carbon steel drills. Therefore, for them the angle ω may be larger.
The choice of inclination angle is influenced by the properties of the material being processed. The softer it is, the greater the angle of inclination can be. But this rule applies in production. At home, where one drill is used for processing different materials, the inclination angle 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 flute should create enough space to accommodate chips and allow them to be easily removed from the flute, but not weaken the drill too much. The width of the groove should be approximately equal to the width of the pen. The depth of the groove determines the thickness of the drill core. Strength depends on the thickness of the core. If the groove is made deeper, the chips will be better accommodated, 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 proportion 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 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, and therefore the rake angle decreases. The working conditions of the cutting edge near the center of the drill will be more difficult.
The rear angle, like the front angle, varies in size at different points of the cutting edge. At points located closer to the outer surface of the drill, it is smaller, at points located 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° at the center.
The bridge (transverse edge) is located in the center of the drill and connects both cutting edges. The angle of inclination of the jumper to the cutting edges ψ can be from 40 to 60°. Most drills have ψ=55°. The bridge is formed by the intersection of two back faces. Its length depends on the thickness of the drill core. As the thickness of the core increases towards the shank, the length of the bridge 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, metal. No wonder it was once called a scraping blade. By halving the length of the bridge, 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 tip angle of 2φ has a great influence on the operation of the drill. If the apex angle is small, the lower edge of the chip will touch the wall of the hole and there will be no conditions for proper chip formation.
The picture below shows a drill with a normal taper angle.
In this case, the edge of the chip fits well into the groove. Changing the tip angle changes the length of the cutting edge and therefore the load per unit length. As the tip angle increases, the load per unit length of the cutting edge increases, and the resistance to penetration of the drill into the metal in the feed direction increases. As the tip angle decreases, the force required to rotate the drill increases, as 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 high speed steel is 116-118° and is considered suitable for many materials. But in order to ensure best conditions work, it is changed as shown in the table.
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Having picked up correct drawing devices for sharpening drills, you can make homemade full-fledged equipment at home. Thanks to this device, the task of ensuring the desired geometric shape of the tool is significantly 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 maintained correctly, catching every degree by hand.
Features of using homemade sharpening devices
During the process of drilling holes in metal products, drills wear out quite a lot, which leads to their heating and loss of their properties. To avoid this phenomenon, measures are required to ensure 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 for high-quality sharpening without any significant financial costs.
Many experienced professionals 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, as this allows mechanization of this process. As a result of such work, maximum accuracy and quality of sharpening will be ensured.
The modern market offers different kinds equipment that allows high-quality restoration of geometry cutting tools, even if you have no experience in this matter. At the same time, there is no urgent need to purchase such products, since they can be made with your own hands according to the existing drawings of devices for sharpening drills.
Drawings of simple 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 into a reliable base, taking into account a certain angle. When selecting a bushing for such devices, you should pay attention to the correspondence of its internal diameter with the transverse size of the tools being sharpened. It is prohibited for the tools being processed to dangle in the sleeve, since even with a deviation of 1-2 degrees along the axis from the required values, the quality and accuracy of sharpening can significantly decrease.
Such homemade devices To sharpen drills, they must be equipped with clips. For their manufacture, copper or aluminum tubes are suitable, the internal diameter of which is equal to the typical size of the drilling tool used.
In some cases, the task can be simplified by setting this design wooden block, in which holes must be drilled with a diameter corresponding to the tool used. One of essential elements Such a product is considered to have a tool rest, which is necessary for:
- provision correct fixation drilling tool and the possibility of precise movement in relation to the surface of the abrasive stone;
- creating a stop point for the drill being sharpened.
Such products made from oak bars, which have holes of different sizes, are the most reliable. Thanks to them, high-quality and precise sharpening of tools is performed. The main problem that must be solved with a homemade machine 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. If you have the appropriate drawings and understand the operating principle of this equipment, you can make sharpening equipment yourself at home.
The structure consists of the following elements:
Promopore site
Fastening for drill and thrust screw
Bolts, nuts, pins, screws
Exist important rules that must be observed during the operation of such a device, namely, the tool being sharpened should not rotate around its axis. In case of even a slight rotation, sharpening must be done again.
The sharpened tool must be cooled in a natural way. After which you should check its restored geometric parameters. You can use a template for this. It should be taken into account 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 attention to this parameter if the drills have a small diameter.
Video “Device for sharpening drills according to drawing”
Drawing of a full-fledged device
A fairly simple way to make homemade sharpening equipment, which is practically no different from the factory product. To assemble it according to ready-made drawings it takes about 1.5-2 hours.
To make a device for sharpening drills with your own hands, you must provide the following: Supplies, equipment and tools:
- welding machine;
- electric drill;
- Bulgarians;
- standard locksmith kit tools;
- a corner, the size of the shelves is 30x30, and its length is 100-150 mm;
- metal plates having different thickness(3-5 mm);
- pins or a piece of steel rods, the diameter of which is 10-12 mm;
- washers, screws, bolts and nuts of various sizes.
First of all, the manufacturing of the bed is carried out, which will be the base in the sharpening device. To do this, use a steel plate onto which a steel rod (12 mm in diameter) is welded at an angle of 75 degrees. It will be the axis.
After that, a washer should be placed on the welded rod, which will act as a support bearing. The amount of angle and rotation of the bed when sharpening the drill will be insignificant, therefore, using a standard ball bearing no reason.
The bed where the sharpened tool will be placed is made from a prepared corner. The one side on the corner profile that faces the whetstone side needs to be ground at a 60 degree angle. On the stock, according to the drawing, a bracket is welded, through which the fixation will be carried out rotary unit devices. As a result, a structure will be made, the corners of which, in the case of a parallel position of the bed and frame, should be located to the surface of the abrasive stone in accordance with the angle of the drill being sharpened.
The sharpening machine, which is shown in the drawing, has fixed tilt angles, 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 device if 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 designs that can adjust the angles:
Video “Device made according to drawing”