Sharpening and manufacturing of worm cutters. Sharpening of milling cutters for metal: end, worm X third-party disk mills sharpening

Today, a fairly large number of mills of various sizes are produced. They can be classified according to their functional and constructive qualities.

End mill sharpening is performed using special devices for such tools. In some cases, sharpening can be done manually.

Milling cutters have a relatively large length and roughness of the teeth for cutting. In the process of sharpening, you will need to take care of the movement of the base of the circle along the edge. In this case, it will be necessary to sharpen shaped milling cutters that have a backed angle. You should know that sharpening is quite difficult. To preserve the design profile and facilitate the sharpening process, the backed cloves will need to be sharpened exclusively on the front base. Sharp teeth, which have a flat or curved shape, must be sharpened exclusively on the rear base. Cutting and cutting mills can be sharpened on the front and rear bases of the cloves.

Geometry of cutter teeth

The geometry of the cutter teeth: a - sharpened tooth, b - backed tooth.

To sharpen correctly, you need to know the geometry of the cutter teeth. According to the design of the teeth, mills with backed and sharp teeth are distinguished. In the latter, the part of the rear base that abuts the cutting edge is a plane. The sharp-pointed teeth in most cases are sharpened on the rear base, but they can also be sharpened on the front base of the tooth.

The backed teeth, which come complete with end mills, have a rear base made in a spiral of Archimedes. It is quite difficult to process a shaped base technologically, therefore it is possible to sharpen milling cutters with backed teeth only on the front base.

Regardless of the number of teeth in the cutter, each of them can be considered as a separate tooth, which is characterized by typical parameters for the tooth - the angles of the front and rear parts, the size of the sharpening area, as well as the angle of inclination of the teeth.

The sharpening platform is an element of the rear base of the clove, which is subjected to grinding during the process of grinding on the rear base. On this basis, maximum wear of the teeth will occur. Its size affects the magnitude of the friction force between the tool and the workpiece being processed, therefore, the base must be maintained in a specific range.

Scheme of sharpening of prefabricated mills on a universal grinding machine.

The main rake angle is the angle between the tangent to the front base and the axis base. It can be measured in a plane that will pass through a given point perpendicular to the main edge for cutting.

Main trailing angle - the angle between the tangent to the rear base at a given point of the main edge for cutting and tangent to the plane of rotation of this point. This angle helps reduce friction between the tool and the workpiece.

With the help of an auxiliary rear angle, a large clearance between the milled base and the tooth body can be characterized. You need to sharpen the tool at an additional angle for a specific amount of tool damage and increase the sharpening area. The purpose of this action is to reduce friction between the tooth and the workpiece being milled. You should be aware that not all tools of this type have this angle.

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How to sharpen end mills for wood processing?

The shape of the teeth can be straight or screw. The inclination of the teeth of the tool can be described as the angle between the expanded edge of the screw type and the axial part of the tool.

The values \u200b\u200bof the tooth angles will depend on the type of tool, the grade of alloy and steel from which it is made, as well as the type of material for which the tool is intended to be milled.

During milling of viscous materials, the main rake angle must be selected in the range of 15-20 ° or more. Hard metal tools for milling steels have an angle of 0 ° or -5 °. The rear angle varies in a wide range.

Elements to be used:

1. Diamond beam.
2. Table.
3. Water or solution with soap.
4. Solvent.
5. Abrasive paper.
6. Hardwood plank or steel strip.
7. Abrasive wheel.

It is possible to sharpen shaped end mills without special devices for sharpening, on the front base, with a small diamond beam. The beam needs to be installed on the extreme part of the table. If the tool has a large recess, then the tool needs to be fixed along the table.

Temperature resistance table of various materials, ° C.

When sharpening, the beam will need to be moistened with clean water or a solution with soap. After sharpening, the tool will need to be washed and dried.

In the process of sharpening the front base, the edge will become sharper, but the diameter of the tool will decrease slightly.

If a bearing is installed on the tool, then it is first necessary to dismantle it, and then sharpen it. An attempt to save time in this case may result in a damaged bearing and a milling cutter.

Be sure to clean the cutter of excess resin from the trees. For this, it is best to use a solvent.

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In the process of sharpening tools, it will be necessary to use bars of different grain sizes.Granularity will depend on the thickness of the removed layer of material and the desired cleanliness of the base. Before sharpening, you will need to make sure that the beam has a suitable shape.

Figure 1. Forms of grinding wheels.

If the cutter teeth are made of relatively soft material, abrasive paper can be used instead of the timber, which adheres to a flat base. As a base, you can use a plank of solid wood or a steel strip.

End mills for milling wood are sharpened on a special device with a low speed of rotation of the circle. In this case, you will need to use a suitable abrasive wheel.

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Sharpening wheels

Sharpening modular milling cutters can be done in circles of white or ordinary electrocorundum, diamond and others. For example, using electrocorundum wheels, you can qualitatively sharpen mills for working with metal and wood, which are made of tool or other steel of standard performance. Elbor circles have the ability to sharpen high-performance steel structures. Silicon carbide and diamond wheels are used for sharpening hard metal cutters.

By increasing the temperature, the hardness of such a device is reduced. A temperature of 1000 ° C can reduce hardness by almost 2 times. At a temperature of 1300 ° C, this figure will decrease by about 6 times.

Figure 2. Sharpening of the end mill: a - the main cutting edge, b - the auxiliary cutting edge, c - installation diagram of the cutter for sharpening the teeth of the auxiliary cutting edge.

The use of water to lower the temperature in most cases leads to the appearance of rust on the workpieces and corners of the machine. To eliminate corrosion, soap and some electrolytes must be added to the water, which can form films for protection. When grinding, almost always use a solution with soap or soda. If fine grinding is carried out, then a low-concentration emulsion should be used.

In order to increase the grinding quality with an abrasive wheel and reduce significant damage, it is recommended to select the maximum grain size, which can provide the required grade of cleanliness of the base of the mill used.

The peripheral speed of a circle during sharpening of teeth made of solid metals should be approximately 15-18 m / s. For example, in the process of using a circle with a diameter of 12.5 cm, the engine speed should be approximately 1600-2700 rpm. If it is necessary to sharpen more brittle materials, the actions must be performed at a lower speed. In the process of using tools made of hard metals, the use of hard mode leads to the appearance of high stresses and cracks, and in some cases to damage to the edges for cutting. The wear of the circle in this case will increase.

The shape of the circle for sharpening the rear corner of the teeth on the basis of a cylindrical shape should be cup or plate. To sharpen the front corner you need to use a circle dish-shaped or flat.

Existing shapes of grinding wheels can be seen in (Fig. 1).

The cutting tool dies sooner or later. If it is disposable, then there is only one way out - to a landfill. But the cutting edge of expensive appliances is most often restored. in this article we will tell you about how to give them a "second youth".

Different cutting tools require a differentiated sharpening approach. Today we’ll talk about restoring chisels, planers, wood mills and metal drills.

Sharpening chisels and planers

It’s not so difficult to bring a chisel or planer knife into working condition. Their sharpening procedure consists of only two stages. When working on tool sharpening, you will need a regular grinding machine. A chisel or planer knife for soft wood is sharpened at an angle of 250 °. For hard rocks - 350 °. When sharpening, you must constantly maintain a given angle, which is not so simple. Simplify the task can special tools for sharpening chisels, allowing you to work in the range from 25 to 35 °. To avoid overheating, periodically cool the instrument in water.

Do not immediately grind the edge of the iron until the cutting part appears. When bringing its thickness to half a millimeter with a square, check that the axis is perpendicular to the cutting edge. Final sharpening is best done manually or on a low-speed water-cooled grinder, bringing the tool to the required sharpness of the cutting edge.

When sharpening a round chisel with an outer edge, the tool moves along the bar from edge to edge along the entire length of the stone, describing the “eight”. A burr on the inside of the groove, which necessarily forms during sharpening, is removed using a shaped grindstone. The final sharpening of the cutting edge is made with sandpaper of various degrees of graininess.

Wood sharpening

For sharpening shaped end mills, the presence of special devices is optional. It is enough to have a diamond block laid on the edge of the table or workbench. The mill is sharpened by holding the front surface of the bar, previously cleaned of residual tar, dirt and dust with a solvent.

If there is a guide bearing, it must be dismantled before grinding. An attempt to save a couple of minutes will result in, if not its deformation, but, quite possibly, a damaged mill. In the process of sharpening, the whetstone is slightly wetted with water, and after completion of work it is wiped dry. As the front surface is ground, the edge of the cutter will sharpen and its diameter will slightly decrease.

When sharpening the tool, bars of various grain sizes should be used, depending on the desired end result and the cleanliness of the surface to be treated. When sharpening the incisors to maintain symmetry, a multiple number of movements are made with equal pressure. Depending on the material the cutter is made of, abrasive paper mounted on a strip of steel or a wooden lath can be used instead of a bar.

If at your disposal there is a grinding machine with a low speed of rotation, then installing the appropriate abrasive wheel can reduce manual labor to naught.

Sharpening a drill for metal

Over time, the drills get dull and many just throw them away, buying new ones. However, almost always a drill can be given a “second chance” and extend its life. To do this, it is enough to treat the dull surface on the grinding wheel.

Before starting work, stock up on a container of water in which the drill will be dipped from time to time to avoid overheating. Sharpening is carried out sequentially and begins with the processing of the rear surface, which is neatly but firmly pressed to the surface of the grinding wheel until the formation of the correct cone.

After that, its cutting part is sharpened and final refinement of the rear surface is carried out. During sharpening, you must constantly monitor the jumper on the tip of the drill. For drills with a diameter of 8 mm and less, it should not exceed a size of 0.4 mm. For large samples, the size of the jumper varies from 1-1.5 mm. Keep in mind that drilling does not produce the tip, but the side lobes of the drill!

Electric Sharpener

Structurally, electric sharpeners are extremely simple.

They consist of an induction motor, grinding wheels and shrouds. Moving the conversation to the plane of choosing a specific manufacturer and model, it should be noted that if you plan to buy the device for personal purposes, then the brand is not critical. Such equipment is included in the network for a short time and has a rather large resource. The price of a sharpener directly depends on its diameter.

The larger it is, the more expensive the device. Inspecting the electric sharpener before buying, try moving the shaft. If he not only rotates, but also “walks” - give up on him and choose further. Of course, it is best to include a sharpener in the network, but not every store will meet you on this issue.

Electric sharpeners or sharpening machines are divided into three groups:

1. High-speed sharpeners equipped with interchangeable holders for various types of tools.
2. Highly specialized machines designed for a specific tool (for example, drills).
3. Water cooled low speed machines.

If high-speed sharpeners are untwisted up to 3000 rpm, then such machines rotate as much as 150 revolutions and can sharpen any cutting tool. Low speed and water cooling are ideal conditions for a high-quality cutting edge.

Domestic and foreign manufacturers produce hundreds of types and thousands of sizes of all kinds of milling cutters, which are classified according to technological characteristics and design features.

Sharpening is carried out on specialized and universal machines for sharpening mills, less often manually.

Milling material

For the manufacture of milling cutters, various materials are used: carbon and alloyed tool steels, high-speed tool steels, hard alloys, cermets, elbor, diamonds.

Of tool steels, grades U7A, U8A, U9A, HG, XB5, 9XC, HVG, etc. are used.

High-speed tool steel for milling is divided into steel of normal productivity (P6M5, P9, P12, P18, etc.) and high. The latter category includes steels alloyed with cobalt, vanadium, tungsten and molybdenum (R6M3, R18F2K5, R9F2K10, R9F2K5, etc.).

The hard alloys from which the cutter teeth are made are produced in the form of inserts of standard sizes and shapes, fastened to the mill body with high-temperature soldering (for example, PSr-40 silver solder) or using threaded joints (prefabricated cutters). They consist of tungsten, titanium and tantalum carbides bonded by cobalt. Mills made of tungsten-cobalt alloys (VK2, VK3, VK6, VK6M, VK8, etc.) are used for machining cast iron, non-ferrous metals, non-metallic materials. Titanium-tungsten-cobalt alloys (T5K10, T15K6, T14K8, T30K4, etc.) are less durable than VK alloys, but they have higher wear resistance when machining parts from various types of steel. Three-carbide alloys consisting of tungsten, tantalum, titanium and cobalt carbides (TT7K12, etc.) are also mainly used for steel processing.

If the cutter has soldered platinum cutters, then this does not mean that they are made of hard alloy. They, for example, can be from high-speed steel.

  According to the design of the teeth, cutters with pointed (pointed) and backed teeth are distinguished. For spiky teeth, the portion of the rear surface of width f adjacent to the cutting edge is a plane. Spiky teeth are sharpened on the back surface. Although, if necessary, their sharpening is possible on the front surface of the tooth.

The geometry of the cutter teeth: a - sharpened tooth, b - backed tooth

At the backed teeth, which are equipped with shaped cutters, the back surface is made in an Archimedean spiral. Since the machining of the contoured surface is very difficult technologically, the grinding of milling cutters with backed teeth is carried out along the front surface.

Regardless of how many teeth there are on the cutter, each of them can be considered as a separate cutter, characterized by the standard parameters for each cutter - front (γ) and rear (α) angles, the size of the ground to be ground (f), the angle of inclination of the teeth (λ) .

Pad f  represents a part of the posterior surface of the tooth that undergoes grinding when sharpening along the posterior surface. The main wear of the teeth occurs along this surface, its size affects the magnitude of the friction force between the cutter and the workpiece, therefore, it must be maintained in a certain range.

Main rake angle γ  - the angle between the tangent to the front surface and the axial plane. It is measured in the plane that passes through this point perpendicular to the main cutting edge.

Main rear angle α  - the angle between the tangent to the rear surface at the considered point of the main cutting edge and the tangent to the circle of rotation of this point. The function of the angle α includes the reduction of friction between the cutter and the workpiece.

Auxiliary rear angle α 1  characterizes the increased clearance between the treated surface and the tooth body. The need for sharpening mills at the auxiliary angle arises with a certain amount of wear on the milling cutter and increasing the area f. Its goal is to reduce friction between the tooth and the material being processed. Not all cutters have this angle.

Depending on the shape and direction of the cutting edge, the teeth can be straight or helical. The inclination of the cutter teeth is characterized by angle λ  between the unfolded helical edge and the axis of the cutter.

The values \u200b\u200bof the angles depend on the type of cutter, the grade of alloy or steel from which it is made, and the type of material for which it is intended.

When processing viscous materials, the main rake angle is selected in the range of 10-20 ° or more. For carbide milling steels, it is close to zero or even negative. The rear angle can also vary widely.

  Shaped end mills can be sharpened without a special tool for sharpening mills, on the front surface, with a thin diamond bar. The block either lies on the edge of the table, or, if the cutter has a deep notch, is fixed as shown in the photo below. The mill is driven along a fixed bar.

During sharpening, the whetstone is wetted with clean or soapy water. After sharpening, it is washed and dried.

As the front surface is ground, the edge will sharpen and the cutter diameter will decrease slightly.

If there is a guide bearing on the mill, it must first be removed (if possible) and only then sharpened. An attempt to save a minute will end with a ruined bearing and a damaged mill. Still need to clean the cutter from the remnants of wood resin, using a solvent.

As when sharpening any other tool, you need to use bars of different grain sizes, depending on the thickness of the material to be removed and the required surface cleanliness. Before sharpening, you need to make sure that the bar has the correct shape.

Sharpening each cutter, to maintain symmetry, you need to try to make the same number of sharpening movements and with the same pressure.

If the material of the cutter cutters is soft enough, instead of a bar, you can use abrasive paper glued to a flat surface (solid wood rail or a strip of steel).

Wood end mills can also be sharpened on a grinder with a low speed of rotation of the wheel, using the appropriate abrasive wheel.

Sharpening wheels

  Depending on the material from which the cutters are made, they can be sharpened in circles made of white or normal electrocorundum, circles made of elbor (CBN), green silicon carbide or diamond (PCD). For example, electrocorundum wheels can provide high-quality sharpening of mills for wood or metal made only of tool or high-speed steel of normal productivity, while elboric wheels can sharpen mills of high-speed steel, diamond wheels and circles of green silicon carbide - cutters made of hard alloys.

When using abrasive wheels (especially diamond), it is desirable to cool them with coolant.

One of the significant disadvantages of diamond is the relatively low temperature stability - at a temperature of about 900 ° C, the diamond burns.

With increasing temperature, the microhardness of abrasive materials decreases. Raising the temperature to 1000 ° C reduces the microhardness by almost 2-2.5 times compared with microhardness at room temperature. An increase in temperature to 1300 ° C causes a decrease in hardness of abrasive materials by almost 4-6 times.

The use of water for cooling can lead to rust on parts and components of the machine. To eliminate corrosion, soap and certain electrolytes are added to the water (sodium carbonate, soda ash, trisodium phosphate, sodium nitrite, sodium silicate, etc.), which form protective films. In conventional grinding, soap and soda solutions are most often used, and in fine grinding, with low-concentration emulsions.

To increase grinding performance with abrasive wheels and reduce specific wear, it is necessary to choose the highest grit, which provides the required class of surface cleanliness of the tool to be sharpened.

To select the grain size of the abrasive, in accordance with the stage of sharpening, you can use the table in the article about bars for sharpening.

The peripheral speed of the circle when grinding carbide teeth should be about 10-18 m / s. This means that when using a circle with a diameter of 125 mm, the engine speed should be about 1500-2700 rpm. Sharpening of more brittle alloys is performed at a lower speed from this range. When sharpening carbide tools, the use of hard conditions leads to the formation of increased stresses and cracks, and sometimes to chipping of the cutting edges, while the wear of the wheel increases.

The shape of the circle for sharpening the rear corner of the teeth on the cylindrical surface is cup (cup or cup) or plate (1T, 2T, 3T), and the front corner is plate or flat.

Milling Sharpening Machine

  Given the most difficult cases - spiral teeth, the machine for sharpening mills should provide rotational and translational movement of the sharpened milling cutter. The figure below shows the machine for sharpening end mills E-90 DAREX.

The essence of sharpening the end mill is that when it is longitudinally moved relative to the circle, it simultaneously synchronizes its rotation around its axis. Due to this, the sharpened edge is always in contact with the circle at the same height (the same sharpening angle is ensured). Synchronization of translational and rotational movements is achieved with the help of a copier needle, which abuts against a depression on the front surface of the tooth. Pressing the sharpened tooth to the needle and smoothly shifting the cutter in the axial direction, the operator in one motion makes the tooth sharpened for its entire length.

Side tooth sharpening. In a simplified form, the sharpening of helical teeth looks like this. The cutter is installed in a grip.

The copier needle is installed in the position at which it is in the highest position, and its tip touches the outer edge of the groove of the end mill.

The cutter is installed in the initial (extended) position, in which the needle is located near the shank, resting against the groove of the tooth.

The grinding wheel with the side shift handle moves to a position in which its outer edge coincides with the needle.

The engine turns on, and with the direct feed handle, the circle is slowly brought to the mill until sparking begins. Then, using the feed scale, the thickness of the removed metal is established (usually 25-50 microns).

Sharpening the tooth for its entire length is carried out by retracting the spindle with the cutter until the latter comes off the needle. In this case, you must ensure that the cutter is constantly in contact with the needle. This ensures the rotation of the cutter, necessary so that the sharpened edge is in contact with the circle at the same mutual position.

To ensure clean processing, the cutter pass is repeated one more time without changing the thickness of the removed metal. On this, the processing of one tooth ends, and a similar operation is repeated for all other teeth. To sharpen all the teeth the same, you should not change the thickness of the removed metal, which was first set using the direct feed handle.

By changing the position of the needle so that its tip abuts at different points on the groove of the tooth (on the edge or middle, for example), you can change the angle α and α 1.

Saw sharpening. To sharpen the front teeth, the end mill must be set in a position in which the sharpened tooth would be located strictly horizontally. The E-90 sharpening system is equipped with a graduated ring, which makes it easy and simple to set the end teeth horizontally. If you use a machine for sharpening mills, not equipped with a similar mechanism, you can set the horizontality of the teeth using a square.

Sharpening a tooth set horizontally is done by moving the edge of the grinding wheel along the edge of the tooth. The angle of sharpening is adjusted by shifting the circle vertically or by tilting the spindle with the mill (if possible).

Sharpening quality control

  After sharpening, the cutter must be subjected to control. Visually with the naked eye or with the help of a magnifying glass, the presence of chips, scratches, cracks is checked, with the help of devices - beating of teeth, angle values, surface roughness.

Allowable deviations of the front and rear sharpening angle of all cutters is ± 1 °. Angles can be measured with a special angle meter 2URI or pendulum angle meter.

For standard cutters, the radial runout of two adjacent (σcm) and two opposite (σpr) teeth, as well as the end runout, are regulated. The permissible values \u200b\u200bof the radial and end beats of the cutter teeth are shown in the table below (for cutters that do not have end teeth, the allowable runout of the supporting ends is indicated).

Checking the quality of sharpening or fine-tuning is done by external inspection using a magnifier. Cutting edges of cutters should be free of nicks and potholes.

If there are notches on the surface of the tooth, then the protrusions will crumble during the operation of the cutter, and it will become dull very quickly. It is necessary to strive to make the tooth surface very smooth.

The presence of cracks on the plates of the hard alloy is determined using a magnifying glass, wetting the plate with kerosene. In this case, in the presence of cracks, kerosene acts.

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The mill can work productively only if it is used correctly. If the work is carried out with correctly assigned milling modes, the mill can process a large number of workpieces before it becomes noticeably dull. However, if you continue to work with a noticeably blunt cutter, the cutting force will increase sharply, which will cause an increase in friction, rapid further blunting and even breakage of the cutter teeth.
Sharpening a normally dull cutter requires relatively little time and slightly reduces the size of the tooth. Sharpening a very blunt cutter is a long, laborious operation, you have to remove a fairly large layer of metal, so the cutter does not need to be brought to a strong blunting.
Especially it is necessary to monitor the condition of the cutting edges and timely sharpening of expensive mills made of high speed steel and equipped with hard alloy plates.

Sharpening cylindrical cutters with pointed teeth

Cylindrical milling cutters with spiky teeth are sharpened on the posterior surface of the tooth with a cup circle (Fig. 332), and the specified rear angle & 3945; must be observed.

When sharpening, the cutter is put on a mandrel installed in the centers of the grinding machine. The axis of the cup circle is set at an angle of 1 - 2 ° to the axis of the cutter so that the circle touches the sharpened cutter with only one side (Fig. 332, c).
If the axes of the cup circle and the cutter to be ground are located in the same horizontal plane (Fig. 332, a), then the cutter tooth angle α will not work. To create a trailing angle, the cup circle is positioned below the axis of the sharpened cutter by an amount H  (Fig. 332, b), which is determined from a right triangle with side and angle α:

The angle α should be selected according to the table. 35.
The position of the cutter tooth during sharpening is fixed with a special emphasis (Fig. 332) in the form of an ordinary spring steel bar. The emphasis supporting the sharpened tooth should be installed very close to the cutting edge. It also serves as a direction for sharpening milling cutters with helical teeth.
When sharpening the back surface of cylindrical cutters with disk circles on a tooth, a concave chamfer is obtained, which weakens the tooth blade and accelerates their wear. When sharpening, cup circles give a flat bevel (ribbon), which ensures greater resistance of the cutters; For this reason, sharpening cutters with disk circles is not recommended.

End Mill Sharpening

Sharpening main cutting edge  the tooth of face mills is made on the back surface like grinding of cylindrical mills with pointed teeth (Fig. 333, a).

At sharpening the auxiliary cutting edge  tooth (Fig. 333, b), first, the cutter is installed so that its auxiliary cutting edge occupies a horizontal position. Then the axis of the cutter is rotated in the horizontal plane by the value of the auxiliary angle in terms of φ 1 and at the same time tilted in the vertical plane by the end rear angle α 1. Sharpening of the front surface on the auxiliary cutting edge is made by the lateral surface of the disk circle. The milling cutter is set so that the auxiliary cutting edge is turned upward, and the axis of the milling cutter is tilted in a vertical plane by the size of the rake angle of the auxiliary cutting edge.

End Mill Sharpening

main cutting edge  end mills (Fig. 334) is made like cylindrical mills with the end surface of the cup circle when installing the end mill in the centers.

Sharpening the back surface on auxiliary cutting edge  it is made like face mills with a cup circle. The cutter is fixed with a tapered shank in the socket of the cartridge.

Sharpening disk cutters

Sharpening the back surface on cylindrical edge  disk mills are made like cylindrical mills in a cup circle.
Sharpening the rear surface of the face teeth is similar to sharpening the teeth of the auxiliary cutting edge of the end mill. Sharpening of the front surface of the front teeth is made like end mills. Sharpened teeth are directed upward, and the axis of the cutter occupies the position:
a) vertical - when the cutter has simple teeth,
b) inclined - when the mill has multidirectional teeth, and the angle of inclination of the axis of the mill in the vertical plane is equal to the angle ω of the inclination of the cylindrical cutting edge.

Sharpening milling cutters

The teeth of the backed cutters are sharpened on the front surface. In fig. 335, and the installation diagram for sharpening a tooth with a front angle γ equal to zero (radial front surface) is given, and in Fig. 335, b - with a rake angle γ greater than zero. Value N  1 shift of the grinding wheel from the center of the cutter is determined by the formula:

The size of the layer removed during sharpening for all teeth should be the same in order to avoid the beating of the cutter. If one tooth is removed a smaller layer than the rest, it will be longer, will remove chips of a larger cross section and more likely to become dull. Sharpening of mills on the front surface is done in a dish-shaped circle.
When sharpening, make sure that the front surface is radial, as shown in Fig. 336, and (tooth 3 ) If the front surface has an undercut (tooth 1 ) or, conversely, a negative rake angle (tooth 2 ), the tooth profile will be distorted and cut the wrong contour in the workpiece. The position of the cutter tooth during sharpening is fixed with an emphasis, which should lie against the back surface of the sharpened tooth.

To ensure that the cutting edges have minimal runout after sharpening, it is recommended to sharpen with a copier having the same number of teeth as the sharpened mill (Fig. 336, b).

Sharpening of prefabricated cutters (milling heads)

The knife of a combined cutter has a greater number of sharpening elements. In addition to the rear corners, it is necessary to sharpen: the main angles of the corner edge in terms of φ and the transition edge φ 0, the auxiliary angle in the plan of φ 1 and the portion of the transition edge f  0. To ensure sharpening of each corner in terms of the cutter takes a position corresponding to this corner (Fig. 337). Sharpening can be done on special grinding or universal grinding machines.

When sharpening on special machines  cutter 1   inserted with your shank or worn mandrel into the head 2   in a horizontal position (Fig. 338). Head 2   can rotate about a vertical axis. The cutter can be rotated around its axis using the handwheel. 3 and fixed in position, using the stop. After sharpening one tooth, the transition to the next one is made by turning the cutter around its axis.

In fig. 339 shows the position when sharpening the cutter on a special grinding machine. First, the ends of the plates or knives (I) are compared, then the plates are aligned along the cylindrical edges (II). For the formation of rear angles, the head with the grinding wheel is tilted and fixed in this position (III); To obtain angles in the plan, the head with the mill rotates around the vertical axis (IV, V, VI). The complexity of such sharpening is high and ranges from 3 to 12 hours, depending on the degree of blunting (amount of removal), the number of teeth and the diameter of the cutter.

It should be noted that the wear of the grinding wheel during sharpening by the machine mechanism is not compensated. Therefore, from sharpening one element of the first tooth to sharpening the same element of the last tooth, a known wear of the grinding wheel accumulates. To eliminate the beating of the tooth elements that occurs during the wear of the grinding wheel, it is necessary to introduce an additional finishing pass, which increases the complexity of the operation.
On the universal grinding machine  the mill is ground at the centers (see. Fig. 337). Due to the fact that the mounting holes, i.e. the mounting base of the cutter, are not used in this installation, the error in the alignment of the sharpening of the cutter cutters increases.
Since precast mills are the main tool for high-speed cutting methods, the complexity of sharpening mills could be a serious brake when introducing high-speed milling. Therefore, in the process of mastering high-speed milling, the sharpening process was redesigned in order to reduce its complexity. For this, a method for sharpening prefabricated milling cutters with dismantled cutters and plates and their subsequent installation using a template was developed, tested and introduced.
Before sharpening, the insert knives are removed from the body and usually sharpened with a kit. In fig. 340 shows a special rotary device for this purpose, sharply reducing the complexity of sharpening. The device is installed in the centers of the universal grinding machine. After sharpening one element, the device with a fixed set of teeth is rotated by a given angle and proceed to sharpening another element.

After sharpening, the cutters are installed in the head housing, using various kinds of templates (Fig. 341, a - e). Checking the assembled milling head for runout should be done with an indicator template (Fig. 341, f).

Carbide Milling Finishing

When sharpening with a grinding wheel, the hard alloy plate heats up unevenly, as a result of which tiny cracks can appear on its surface. Cracks in the cutting process increase and can cause tooth chipping during operation.
One of the refinement goals is to remove the defective layer with cracks. The second task of finishing is to increase the cleanliness of the surface of the cutting edge, which is necessary to reduce friction and wear of the tooth, as well as (to increase the cleanliness of the processed surface. The third task of finishing is to eliminate blockages of the surface of the cutter teeth and give them a more correct geometry.
The finishing of the cutting surfaces is carried out on special finishing machines with cast-iron discs or manually with a slight pressure of the cast-iron donkey. The best lapping results are obtained at a lapping disk speed between 1.0-1.5 m / s. For finishing use a paste of boron carbide with a grain size of 170 - 230.
For manual adjustments, the correct position of the oselok in relation to the cutting edge and the correct movement of the oselok must be observed. First, the front and rear surfaces are finished, then they form lapping (bordering) chamfers: for this, the donkey plane is set at an angle of 45 ° to the front surface, and with a weak pressure, make several passes along the cutting edge. For the formation of a bordering chamfer, they spend 2-3 seconds. on every knife.
Boron carbide is a strong abrasive. Using a cast iron oselka with boron carbide paste, wear holes on the teeth can be removed without removing the milling cutter from the machine, which is very important for high-speed milling of small workpieces with short cutting periods.