TO category:
Milling work
Milling keyways on shafts
Keyed connections are very common in mechanical engineering. They can be with prismatic, segmental, wedge and other key sections. The working drawings of the shaft must contain dimensions for a shaft with a feather key and for a shaft with a segment key.
Keyways are divided into through, open (with exit) and closed. Milling keyways is a very responsible operation. The nature of the fit of the parts mating to the shaft depends on the accuracy of the keyway. Milled keyways are subject to rigid technical requirements. The width of the keyway must be made according to the 2nd or 3rd accuracy class: the depth of the keyway must be made according to the 5th accuracy class; The length of the groove for the key is according to the 8th accuracy class. Failure to comply with these requirements when milling keyways entails labor-intensive fitting work during assembly - sawing down keys or other mating parts.
In addition to the above requirements, with regard to the accuracy of the keyway, there is also a requirement regarding the accuracy of its location and surface roughness. The side faces of the keyway must be located symmetrically relative to the plane passing through the shaft axis; The surface roughness of the side walls should be within the 5th roughness class, and sometimes higher.
By comparing the tolerances on cutters with the tolerances on the size of the keyway, one can be convinced of the difficulty of making a groove of the required accuracy on machines using measuring tools. Let's take as an example a groove with a width of 12psh
Practice shows that for machining a keyway, a groove that fits within the tolerance field of the PN must be carefully selected. cutters and make test passes. In serial and mass production, they tend to replace keyed connections with splined ones whenever possible.
Disc groove cutters (ST SEV 573-77) are intended for milling shallow grooves. They have teeth only on the cylindrical part.
Groove cutters backed according to GOST 8543-71 are also intended for processing grooves. They are sharpened only on the front surface. The advantage of these cutters is that they do not lose their width after regrinding. They are available in diameters from 50 to 100 mm, from 4 to 16 mm.
Key cutters in accordance with GOST 9140-78 are used for milling keyways and are manufactured with a cylindrical and conical shank. Key cutters have two cutting teeth with end cutting
common edges that perform the main cutting work. The cutting edges of the cutter are not directed outward, like a drill, but into the body of the tool. Such cutters can work with axial feed (like a drill) and with longitudinal feed. Resharpening of cutters is carried out along the end teeth, as a result of which the diameter of the cutter remains practically unchanged. This is very important for machining grooves.
Milling cutters with a cylindrical shank are manufactured for diameters from 2 to 20 mm, with a conical shank - from 16 to 40 mm. Currently, tool factories produce solid carbide key cutters with a diameter of 3, 4, 6, 8 and 10 mm with a helical flute angle of 20° from VK8 alloy. These cutters are mainly used for machining hardened steels and difficult-to-cut materials. The use of these cutters allows you to increase labor productivity by 2-3 times and increase the roughness class of the processed surface.
Shank cutters for slots for segment keys in accordance with GOST 6648-68* are intended for milling all slots for segment keys with a diameter of 4-5 mm.
Mounted cutters for grooves for segmental keys in accordance with GOST 6648-68* are intended for milling all grooves for segmental keys with a diameter of 55-80 mm.
Securing workpieces. Shaft blanks for milling keyways and flats into them are conveniently secured in prisms. For short workpieces, one prism is sufficient. For longer shaft lengths, the workpiece is mounted on two prisms. The correct positioning of the prism on the machine table is ensured by a tenon at the base of the prism, which fits into the groove of the table, as shown in the figure on the right. The shafts are secured with clamps. To avoid shaft deflection when fastening, it is necessary to ensure that the clamps rest on the shaft above the prisms. A thin copper or brass gasket should be placed under the clamps so as not to damage the final processed cylindrical surface of the shaft. In Fig. Figure 4 shows a vice for securing shafts. The vice can be fixed on the table either in the position shown in the figure, or it can be rotated 90°. They are therefore suitable for securing shafts on both horizontal and vertical milling machines. The shaft is mounted with a cylindrical surface on a prism and, when the handwheel rotates, it is clamped with jaws that rotate around the fingers. The prism can be installed in a vice on the other side of the larger diameter shaft. The stop is used to set the shaft along its length.
Rice. 1. Shaft with keyways
Rice. 2. Layout of tolerance fields for keyway and cutter
Rice. 3. Securing the shaft on the oisms
Rice. 4. Vise for securing shafts
In Fig. Figure 5 shows a magnetic prism with a permanent magnet. The prism body consists of two parts, between which a barium oxide magnet is placed. To secure the roller, simply turn the switch handle 90°. The clamping force is quite sufficient for milling keyways, flats, etc. on the rollers. Simultaneously with securing the part, the prism is attracted to the supporting surface of the machine table.
Milling through keyways. Keyways are milled after finishing the cylindrical surface. Through and open grooves with a groove exiting around a circle, the radius of which is equal to the radius of the cutter, are processed with disk cutters. The excess of the groove width compared to the width of the cutter is 0.1 mm or more. After sharpening disk slot cutters, the width of the cutter is slightly reduced, so the use of cutters is possible only up to certain limits, after which they are used for other work when the width size is not so important.
In Fig. Figure 6 shows the installation of the workpiece and cutter when milling a through keyway. When installing a cutter on a mandrel, it is necessary to ensure that the cutter has minimal runout at the end. The workpiece is secured in a machine vice with copper or brass jaws.
With a correctly installed vice, the accuracy of installing the shaft fixed in it does not need to be checked. The cutter should be installed so that it is located symmetrically relative to the diametrical plane passing through the shaft axis. To fulfill this condition, use the following technique. After securing the cutter and checking its runout with an indicator, the cutter is first installed in the diametrical plane of the shaft. Precise installation is carried out with a square and caliper.
To install the cutter, it is necessary to place it in the transverse direction at size S from the side of one of the ends of the shaft protruding above the vice. Check this size with a caliper. Then place a square on the other side of the shaft, as shown in Fig. 7 dotted line, and check size S again.
Rice. 5. Magnetic prism for securing shafts
simultaneously slowly lift the table until it touches the cutter and move it in the longitudinal direction. Having established the moment of contact of the cutter with the shaft, move the table away from under the cutter. Turn off the machine and rotate the vertical feed handle to raise the table to the depth of the keyway.
Milling closed keyways. Milling of closed keyways can be done on horizontal milling machines. To secure the shaft, use special self-centering vices or prisms. Since the milling installation according to Fig. 9, but differs from the installation in Fig. 9, b only by the location of the spindle, we will analyze only the order of milling the keyway on a horizontal milling machine.
Rice. 9. Milling closed keyways
Another way to install (“bullseye”) a keyed or end mill in the diametral plane of the cutter is as follows. The shaft is positioned as accurately as possible (by eye) relative to the cutter and the rotating cutter is slowly brought into contact with the shaft being processed until a barely noticeable trace of the cutter appears on the surface of the shaft. If this mark is obtained in the form of a complete circle, then this means that the cutter is located in the diametrical plane of the shaft. If the mark has the shape of an incomplete circle, then it is necessary to move the table.
Setting to groove depth. The shaft being processed, the diametral plane of which coincides with the axis of the cutter, is brought into contact with the cutter. In this position of the table, note the indication of the dial of the transverse or vertical feed screw, then move or raise the table to cutting depth B.
Closed keyways that allow fit are milled in one of two ways:
a) manual cutting to a certain depth and longitudinal mechanical feed, then cutting again to the same depth and longitudinal feed, but in a different direction;
b) manual cutting to the full depth of the groove and further mechanical longitudinal feed. This method is used when milling with keyway cutters with a diameter of over 12-14 mm.
Rice. 10. Installation diagram of the end mill in diameter! shaft plane
The width of the keyway should be checked using a gauge according to the tolerance specified in the drawing.
Milling of open keyways with a groove exiting along a circle, the radius of which is equal to the radius of the cutter, is carried out using disk cutters. Grooves in which the groove is not allowed to exit along the radius of the circle are milled with end or key cutters.
Milling the grooves of segment keys is carried out using shank or mounted cutters for segment keys, the diameter of which must be equal to double the radius of the groove. The feed is carried out in a vertical direction, perpendicular to the shaft axis (Fig. 11).
Milling of shafts on key-milling machines. To obtain grooves that are precise in width, processing is carried out on special key-milling machines with pendulum feed, working with two-tooth key cutters. With this method, the cutter cuts 0.2-0.4 mm and mills the groove along the entire length, then again cuts to the same depth as in the previous case, and mills the groove again along the entire length, but in a different direction. This is where the name of the method comes from - “pendulum feed”.
Rice. 11. Milling keyways for segmental keys
Rice. 12. Scheme for milling keyways using the “pendulum feed” method
Rice. 13. Control of groove size using gauges
At the end of milling, the spindle automatically returns to its original position and the longitudinal feed of the milling head is turned off. This method is the most rational for the manufacture of keyed shafts in serial and mass production, as it produces an accurate groove that ensures interchangeability in the keyed connection. In addition, since the cutter works with end cutting edges, it is more durable, since it does not wear out along the periphery. The disadvantage of this method is that it takes significantly more time compared to milling in one or two passes.
Milling of grooves on automated key-milling machines with a non-measured tool is carried out with an oscillating (oscillating) movement of the tool. By adjusting the oscillation range from zero to the required value, it is possible to mill keyways with the required width accuracy.
When milling with oscillation, the width of the cutter is less than the width of the groove being machined. Thus, the MA-57 machine is intended for milling open keyways on electric motor shafts using three-sided disk cutters in automated production. The 6D92 machine is designed for milling closed keyways using non-dimensional end mills. The required groove width is achieved due to the fact that the cutter is given an oscillating movement in the direction perpendicular to the longitudinal feed. The machine can be built into an automatic line.
Control of the dimensions of grooves and grooves. Control of the dimensions of grooves and grooves can be done using both line measuring instruments (vernier calipers, caliper depth number) and gauges. Measuring and counting the dimensions of grooves using universal tools does not differ from measuring other linear dimensions (length, width, thickness, diameter). The width of the groove can be controlled by round and sheet limit plug gauges. In Fig. 13, a shows the control of the width of the groove, given the size of 20+cm mm. In this case, the pass side of the caliber has a size of 20.0 mm, and the non-pass side has a size of 20.1 mm.
The symmetry of the location of the keyway relative to the shaft axis is controlled by special templates and devices.
Shoulder and groove milling
TO category:
Milling work
Shoulder and groove milling
A ledge is a recess limited by two mutually perpendicular planes forming a step. The part may have one, two or more ledges. A groove is a recess in a part, limited by planes or shaped surfaces. Depending on the shape of the recess, the grooves are divided into rectangular, T-shaped and shaped. Grooves of any profile can be through, open or with an exit and closed.
Processing of shoulders and grooves is one of the operations performed on milling machines. Milled shoulders and grooves are subject to different technical requirements depending on the purpose, serial production, dimensional accuracy, location accuracy and surface roughness. All these requirements determine the processing method.
Milling of shoulders and grooves is carried out with disk end mills, as well as a set of disk cutters. In addition, shoulders can be milled with end mills.
Milling shoulders and grooves with disc cutters. Disc cutters are designed for processing planes, shoulders and grooves. Disc cutters are distinguished between solid and inserted teeth. Solid disk cutters are divided into slotted (ST SEV 573-77), grooved backed (GOST 8543-71), three-sided with straight teeth (GOST 3755-78), three-sided with multi-directional small and normal teeth. Milling cutters with insert teeth are made three-sided (GOST 1669-78). Disc groove cutters have teeth only on the cylindrical part; they are used for milling shallow grooves. The main type of disk cutters are three-sided. They have teeth on the cylindrical surface and on both ends. They are used for processing ledges and deeper grooves. They provide a higher roughness class for the side walls of a groove or shoulder. To improve cutting conditions, three-sided disk cutters are equipped with inclined teeth with alternately alternating groove directions, i.e. one tooth has a right-hand groove direction, and the other adjacent to it has a left-hand direction. Therefore, such cutters are called multidirectional: Thanks to the alternating inclination of the teeth, the axial components of the cutting force of the right and left teeth are mutually balanced. These cutters have teeth on both ends. The main disadvantage of three-sided disk cutters is the reduction in width after the first regrinding along the end. When using adjustable cutters, consisting of two halves of the same thickness with overlapping teeth in the socket, after regrinding it is possible to restore the original size. This is achieved by using spacers of appropriate thickness made of copper or brass foil, which are placed in the socket between the cutters.
Rice. 1. Ledges
Rice. 2. Types of grooves by shape
Rice. 3. Manholes: through, with exit and closed
Disc cutters with insert knives equipped with hard alloy plates are three-sided (GOST 5348-69) and two-sided. Three-sided disk cutters are used for milling grooves, and two-sided ones are used for milling shoulders and planes. The insertion knives are fastened into the body of both types of cutters using axial corrugations and a wedge with an angle of 5°. The advantage of this method of attaching insert knives is the ability to compensate for wear and the layer removed during regrinding. Restoring the size in diameter is achieved by rearranging the knives by one or more corrugations, and in width - by correspondingly extending the knives. Three-sided cutters have knives with alternately alternating inclination with an angle of 10°, for double-sided ones - in one direction with an inclination angle of 10° (for right-cutting and left-cutting cutters).
The use of three-sided disk cutters with carbide inserts gives the highest productivity when processing grooves and shoulders. A disk cutter “holds” the size better than an end cutter.
Selecting the type and size of disk cutters. The type and size of the disk cutter are selected depending on the size of the surfaces being processed and the material of the workpiece. For given processing conditions, the type of cutter, the material of the cutting part and the main dimensions - B, D, d and z - are selected. For milling easily processed materials and materials of average processing difficulty with a large milling depth, cutters with normal large teeth are used. When processing difficult-to-cut materials and milling with small depths of cut, it is recommended to use cutters with normal and fine teeth.
The diameter of the cutter should be chosen as small as possible, since the smaller the diameter of the cutter, the higher its rigidity and vibration resistance. In addition, as the diameter increases, its durability increases.
Rice. 4. Selecting the diameter of disk cutters
In Fig. 5, a, b shows a diagram of milling two shoulders on a part. Milling of shoulders with disk cutters, as mentioned above, is usually carried out with a double-sided disk cutter. However, in our case, we should choose a three-sided disk cutter, since we need to process one shoulder on each side of the part in turn.
Rice. 5. Milling a shoulder with a disk cutter
Setting up a machine for milling through rectangular grooves using disk cutters. When milling shoulders, the accuracy of the width of the shoulder does not depend on the width of the cutter. Only one condition must be met: the width of the cutter must be greater than the width of the shoulder (if possible, no more than 3-5 mm).
When milling rectangular grooves, the width of the disk cutter should be equal to the width of the groove being milled in the case when the runout of the end teeth is zero. If there is runout of the cutter teeth, the size of the groove milled by such a cutter will be correspondingly larger than the width of the cutter. This should be kept in mind, especially when machining grooves that are precise in width.
Setting the cutting depth can be carried out according to the markings. To clearly highlight the marking lines, the workpiece is pre-painted with a chalk solution and recesses (cores) are applied to the line drawn by a surface scriber using a center punch. Setting the cutting depth along the marking line is carried out with trial passes. At the same time, make sure that the cutter cuts the allowance only half of the recesses from the center punch.
When setting up a machine for processing grooves, it is very important to correctly position the cutter relative to the workpiece being processed. In the case when the workpiece is installed in a special device, its position relative to the cutter is determined by the device itself.
Precise installation of cutters to a given depth is carried out using special settings or dimensions provided in the device. In Fig. Figure 6 shows diagrams for installing cutters to size using settings. Dimension 1 is a hardened steel plate (Fig. 6, a) or a square (Fig. 6, b, c), fixed to the body of the device. A measuring probe 3-5 mm thick is placed between the set and the cutting edge of the cutter tooth to avoid contact of the cutter tooth with the hardened surface of the set. If the processing of the same surface is carried out in two passes (roughing and finishing), then probes of different thicknesses are used to install cutters of the same size.
Milling shoulders and grooves with a set of disc cutters. When processing a batch of identical parts, simultaneous milling of two shoulders, two or more grooves can be carried out by a set of cutters. To obtain the required distance between the shoulders and grooves, a corresponding set of mounting rings is placed on the mandrel between the cutters.
When processing workpieces with a set of cutters, one cutter is installed according to the dimensions, since the relative position of the set on the mandrel is achieved by selecting mounting rings. When installing cutters to a given size, they resort to using special installation templates. For precise installation of cutters, plane-parallel end blocks and indicator stops are used. In Fig. Figure 7 shows a diagram of the arrangement of indicator stops on a horizontal milling machine for precise installation of cutters during transverse and vertical movements of the table. Using such a device, you can raise and lower the table by a given amount with accelerated movement, without fear of making a mistake in the count.
The feasibility of processing shoulders and grooves with a set of cutters can be established based on the total time spent (calculation time) per part for the compared options for processing grooves.
Milling shoulders and grooves with end mills. Shoulders and grooves can be machined with end mills on vertical and horizontal milling machines. End mills (GOST 17026-71*) are designed for processing planes, shoulders and grooves. They are manufactured with cylindrical and conical shanks. End mills are manufactured with normal and large teeth. Mills with normal teeth are used for semi-finishing and finishing machining of shoulders and grooves. Mills with large teeth are used for roughing.
Roughing end mills with backed teeth (GOST 4675-71) are intended for rough processing of workpieces obtained by casting and forging.
Carbide end mills (GOST 20533-75-20539-75) are manufactured in two types: equipped with carbide crowns for diameters 10-20 mm and screw plates (for diameters 16-50 mm).
Rice. 6. Application of installations for milling cutters
Currently, tool factories produce solid carbide end mills with a diameter of 3-10 mm and end mills with a solid carbide working part soldered into a steel conical shank. The diameter of the cutters is 14-18 mm, the number of teeth is three. The use of carbide cutters is especially effective when processing grooves and shoulders in workpieces made of hardened and difficult-to-cut steels.
The accuracy of grooves in width when processing them with measuring tools, such as disk and end mills, largely depends on the accuracy of the cutters used, as well as on the accuracy, rigidity of the milling machines and on the runout of the cutter after fastening in the spindle. The disadvantage of a measuring tool is the loss of its nominal size due to wear and after regrinding. For end mills, after the first regrinding along a cylindrical surface, the diameter size is distorted, and they turn out to be unsuitable for obtaining the exact width of the groove.
You can get the exact size of the groove width by processing it in two passes: roughing and finishing. During finishing, the cutter will only calibrate the groove in width, maintaining its size for a long period of time.
Recently, chucks have appeared for securing end mills, allowing the installation of a cutter with adjustable eccentricity, i.e., adjustable runout. In Fig. 8 shows a collet chuck used at the Leningrad Machine Tool Association named after. Y. M. Sverdlova. The hole in the chuck body is bored eccentrically by 0.3 mm relative to its shank. A sleeve for collets is inserted into this hole with the same eccentricity relative to the inner diameter. The bushing is attached to the body with two bolts. When the sleeve is turned with a nut and the bolts are slightly loosened, a conditional increase in the diameter of the cutter occurs (one division per limbg corresponds to an increase in the diameter of the cutter by 0.04 mm).
When machining grooves with an end mill, the chips must be directed upward along the helical groove so that they do not spoil the machined surface or cause breakage of the cutter tooth. This is possible in the case when the direction of the helical groove coincides with the direction of rotation of the cutter, i.e., when they are in the same direction. However, the axial component of the cutting force Px will be directed downward to push the cutter out of the spindle socket. Therefore, when machining grooves, the cutter must be fastened more securely than when machining an open plane with an end mill. The direction of rotation of the cutter and helical groove, as in the case of machining with face and cylindrical cutters, should be opposite, since in this case the axial component of the cutting force will be directed towards the spindle socket and tend to tighten the mandrel with the cutter into the spindle socket.
Rice. 8. Chuck for milling measuring grooves with standard cutters
Rice. 9. Milling an inclined plane in a vice
Rice. 10. Milling the recess of the body part
Other types of work performed by end mills. In addition to processing shoulders and grooves, end mills are used to perform other work on vertical and horizontal milling machines.
End mills are used for processing open planes: vertical, horizontal and inclined. In Fig. Figure 9 shows milling of an inclined plane in a universal vice. The techniques for processing planes with end mills are no different from the techniques for processing shoulders and grooves. End mills can be used to process various recesses (sockets). In Fig. Figure 10 shows the milling of a cavity using an end mill. Milling of recesses in the workpiece is carried out according to the markings. It is more convenient to first make preliminary milling of the recess contour (without reaching the marking lines), and then final milling of the contour.
In cases where it is necessary to mill a window rather than a recess, it is necessary to place an appropriate backing under the workpiece so as not to damage the vice when the end mill comes out.
Milling shoulders with an end mill. Shoulders can be milled on both vertical and horizontal milling machines. The processing of parts with symmetrically located shoulders can be carried out by securing the workpieces in two-position rotary tables. After milling the first shoulder, the fixture is rotated 180° and placed in the second position to mill the second shoulder.
Milling special slots
Parts with special grooves are widely used in mechanical engineering. Let's look at the two most common grooves ,
the method of processing them and the tools necessary when performing milling work.
Milling dovetail slots
The dovetail groove serves mainly as a guide for the moving elements of machines - these are consoles, table slides, lathe slide guides, milling machine shackles... The main tool for obtaining such a groove is an end angle cutter named after the dovetail groove type. tail". Dovetail cutters 
are made single-angled (the cutting edge, as a rule, is only on 
conical part of the cutter) or two-angle (cutting edge on two adjacent sides). Double angle cutters distribute the load more evenly, so they run smoother and are more durable. Dovetail cutters are made from high-speed steels R6M5, R9 and hard alloys VK8, T5K10 and T15K6.
Milling a dovetail groove is the final operation of milling a part; therefore, the selection of tools and proper fastening of the workpiece are very important. The workpiece is aligned directly in a machine vice or, if the part is large, on the table of a milling machine using a height gauge, squares and indicators regarding the feed direction.
The groove is processed in two stages:
The first is to mill a rectangular groove using an end mill or, if conditions permit, a three-sided milling cutter.
The second - an angular cutter (“dovetail”) is used to process the sides one by one.
Taking into account the difficult cutting conditions, the tool feed must be slightly reduced - to approximately 40% of normal working conditions (for a given material, width of the material being cut, coolant supply, etc.).
Measurements are made using a caliper tool, angular dimensions are made with a universal goniometer (the cutter itself), templates from the base surface of the part, two calibrated cylindrical rollers according to special formulas.
When milling a dovetail groove, you need to pay attention to the following problems that may arise:
The depth of the groove and the angles of inclination of the sides are not the same along the entire length - the reason is inaccurate alignment of the part in the horizontal plane;
The angle of inclination of the sides does not correspond to the specified value - incorrect calculation of the cutter angle, wear of the cutter due to a mismatch between the processing mode and the tool material;
Different groove widths along the entire length - displacement of the machine table in the guide consoles;
Surface roughness - working with an incorrectly sharpened tool, inappropriate feed.
Breakage of the cutter - due to the heavy load when processing this groove on the mating cutting edges, the top of the cutter breaks - it is necessary to first round it, make it with a small radius.
Milling T-slots
T-slots are used mainly in mechanical engineering for fastening parts. They are widely used in tables of machine tools for various purposes (grinding, drilling, milling, planing, etc.). They are used to place the heads of fastening bolts in them, as well as to align the fixture on the machine table. T-slots are characterized by their overall depth, the thickness between the slot and the table top, and the width of the narrow top and wide bottom. Grooves of this type are regulated by the standard. Each size corresponds to strictly defined other sizes, because... For them, special bolts, fastening devices, and equipment are manufactured on an industrial scale.
To make a T-slot you need:
End mill with a diameter equal to the narrow width of the groove or a smaller diameter in multiple passes;
- when producing several grooves, it is more convenient to work with a three-sided cutter with a thickness equal to the narrow part of the T-shaped groove. The groove is obtained more accurately and the processing speed is higher than with an end mill, and the scrap rate is lower;
Special T-shaped end mill. The cutter for T-slots consists of a working part with the elements and geometry of disk slot cutters, conical
o or a cylindrical shank and a smooth cylindrical ground neck, the diameter of which is usually selected equal to the width of the narrow part of the groove (it can be smaller). The working part of the cutter can have multi-directional teeth and is mademade from high-speed steels R6M5, R18 or equipped with carbide inserts VK8, T5K10, T15K6, etc.;
Dovetail cutter or countersink for internal and external chamfering.
The sequence of milling a T-slot is similar to the milling of type slots
“dovetail”. Initially, a rectangular groove is milled with a width equal to or less than the narrow part of the groove and a depth equal to the depth of the groove.
Next, select a cutter for T-slots. Depending on the size of the groove, a decision is made about passing with one cutter or several, because When the depth and width of the groove are large, the working tool experiences heavy loads; select one or more cutters with the same height of the working part and, if desired,
elno, with the appropriate neck size. Thus, a more gentle processing mode is achieved, because the thickness of the cut layer in the workpiece decreases. When working you need to pay attention Special attention to remove chips, because in closedIn the groove, this becomes very important and it is necessary to provide a mandatory supply of coolant (cutting fluid) to remove excess heat in order to avoid overheating of the working cutter. The feed speed for this type of work must be reduced as much as possible.
The final operation involves removing external and internal chamfers. In this case, single-angle or double-angle end mills are used. Dl
For an external chamfer - it is possible to use countersinks, for an internal chamfer - dovetail cutters. The main condition is that the diameter of the corner cutter must be larger than the size of the narrow part of the T-shaped groove to obtain a more even chamfer and greaterlabor productivity.
Measuring and controlling the dimensions of the T-shaped groove is carried out using calipers, height gauges, bore gauges, indicators, and also special templates.
When milling T-slots, the following types of defects can occur:
- the height of the groove along the entire length of the part is not the same - - the workpiece is not aligned when installed in a horizontal plane;- the width of the inner part of the groove at the end is less than the size at the beginning of the workpiece - untimely removal of chips, resulting in increased tool wear;
- the width of the narrow part exceeds the specified size - incorrect sharpening of the tool, runout of the cutting part of the cutter, insufficient rigidity (play) of the machine table.
Good luck to everyone and success!
Devices for hand router. Serial models of such devices are quite expensive, but you can save on their purchase and make devices for equipping a wood router with your own hands.
Various types of attachments can turn a hand router into a truly universal tool.
The main task that milling tools solve is to ensure that the tool is positioned in relation to the surface being machined in the required spatial position. Some of the most commonly used milling machine attachments come standard with milling machines. Those models that have a highly specialized purpose are purchased separately or made by hand. At the same time, many devices for a wood router have such a design that making them yourself does not present any special problems. For homemade devices for a hand router, you don’t even need drawings - their drawings will be enough.
Among the accessories for a wood router that you can make yourself, there are a number of popular models. Let's take a closer look at them.
Rip fence for straight and curved cuts
It is possible to ensure the stability of the router when processing narrow surfaces without special devices. This problem is solved using two boards, which are attached to both sides of the workpiece in such a way as to form one plane with the surface on which the groove is made. When using this technological technique, the router itself is positioned using a parallel stop.
In mechanical engineering, flat parts are often found that have ledges on one, two, three and even four sides. As an example in Fig. 194, and shows a prism for installing cylindrical parts during milling, which has two ledges.
Shoulder and groove milling
A ledge closed on both sides is called a groove. The grooves may have rectangular shape- then they are called rectangular, or shaped - then they are called shaped. In Fig. 194, b shows a part with a rectangular groove, and in Fig. 194, in - a fork having a shaped groove.
Mills for processing ledges and grooves. Milling of shoulders and rectangular slots is carried out either with disk cutters on horizontal milling machines, or with end mills on vertical milling machines.
Narrow cylindrical cutters are called disk cutters. Disc cutters can be made with pointed and backed teeth (Fig. 195, a and b).
Disc cutters that have teeth on the cylindrical and on one of the two end surfaces are called double-sided
(Fig. 195, b), and those having teeth on both end surfaces are called three-sided (Fig. 195, d). Double-sided and three-sided disc cutters are made with pointed teeth.
To increase productivity, three-sided disc cutters are manufactured with large multi-directional teeth. In Fig. 195, d shows a cutter in which the teeth are alternately oriented in different directions, forming end cutting edges through the tooth.
This shape of the teeth, like the set teeth of circular and rip saws for wood, allows you to remove a larger amount of chips and better divert them.
In Fig. 196 shows end mills proposed by the innovators of the Leningrad Kirov plant E.F. Savich, I.D. Leonov and V.Ya. Karasev. A state standard has been issued for these cutters (GOST 8237-57). Compared to previously manufactured cutters, the number of teeth in them has been reduced, the angle of inclination of the screw teeth has been increased to 30-45°, the height of the tooth has been increased and an uneven circumferential pitch of the teeth has been introduced. The back of the teeth of these cutters is made curved according to Fig. 51, v.
Milling cutters of this design provide increased productivity and cleanliness of the machined surface and eliminate vibration. End mills are made of two types: with a cylindrical shank (Fig. 196, a and b) and with a conical shank (Fig. 196, vig). Each of these types is manufactured in two versions: with a normal tooth (Fig. 196, abc) and with a large tooth (Fig. 196, b and d). The cutting part of end mills is made of high-speed steel.
End mills with large teeth are used for work with high feeds at large milling depths; cutters with normal teeth - for ordinary work.
Mills with a cylindrical shank are made with a diameter from 3 to 20 mm, with a conical shank - with a diameter from 16 to 50 mm.
Shoulder milling. Let's consider an example of milling two shoulders in a block on a horizontal milling machine (Fig. 197, left) to obtain a stepped key.
Choosing a cutter. Milling ledges on a horizontal milling machine is usually done with a double-sided disk cutter, but in this example it is necessary to work with a three-sided cutter, since it is necessary to alternately process one ledge on each side of the block.
For milling the shoulder, we will choose a three-sided cutter with multi-directional teeth with a diameter of 75 mm, a width of 10 mm, a hole diameter for the mandrel of 27 mm and a number of teeth of 18.
The processing will be carried out on a horizontal milling machine with the workpiece secured in a machine vice.
Preparing for work. We install, align and strengthen the vice on the machine table using a method known to us, after which we install the part in the vice at the required height (Fig. 198). We check the correct position (horizontalness) with a thickness gauge according to the marking marks, after which we firmly clamp the vice. The jaws of the vice must be covered with pads made of soft metal (brass, copper, aluminum) so as not to spoil the processed edges of the block.
We attach the disk cutter to the mandrel in the same way as a cylindrical cutter, maintaining the cleanliness of the mandrel, cutter and rings.
Setting up the machine for milling mode. We select the cutting mode when milling shoulders with high-speed disk cutters according to the table. 212 of the “Young Milling Machine Operator’s Handbook.”
Given: cutter diameter Z) = 75 mm, milling width B = 5 mm, cutting depth = 12 mm, surface finish V 5; According to the table, we select the cutting speed when feeding per tooth S3y6 = 0.05 mm/tooth.
The selected cutting speed a = 21.7 m/min corresponds to 92 rpm of the cutter and a feed of 83 mm/min. Then set the gearbox dial to 95 rpm and the feedbox dial to 75 mm/min.
Thus, we will mill the shoulder using a three-sided disk cutter 75x10x27 mm with multi-directional teeth (cutter material - high-speed steel P9 or P18) with a cutting depth of 12 mm, a milling width of 5 mm, a longitudinal feed of 75 mm/min or 0.04 mm/tooth and cutting speed of 22 m/min, we use cooling - emulsion.
Milling process. Milling each shoulder consists of the following basic techniques:
1) turn on the spindle rotation with the button;
take the chips, turn on the mechanical longitudinal feed (Fig. 199, a).
After processing the first shoulder, move the table to a distance equal to the width of the shoulder (17 mm) plus the width of the cutter (10 mm), i.e., 27 mm, and mill on the other side, observing all the described working techniques (Fig. 199.6) ;
4) upon completion of processing the part, without removing it from the vice, use a caliper to measure the depth and width of the ledge on each side according to the dimensions of the drawing with a tolerance of ±0.2 mm. If the dimensions of the part correspond to the drawing and the processing surface is clean, as required by the V5 mark on the drawing, we remove the part from the vice and hand it over to the master for inspection.
Milling through rectangular grooves. When milling through rectangular grooves, three-sided disk cutters are used, similar to the one shown in Fig. 195, g. The width of the cutter must correspond to the drawing size of the milled groove with permissible deviations, which is only true in cases where the installed cutter does not have an end runout. If the cutter beats, then the width of the milled groove will be greater than the width of the cutter, or, as they say, the cutter will break the groove, which can lead to defects.
That's why a three-sided cutter is selected based on a width slightly smaller than the width of the groove being milled.
Since three-sided disk cutters are made with pointed teeth, after subsequent regrinding of the end teeth, the width of the cutter is reduced. Consequently, this cutter after sharpening will no longer be suitable for milling a rectangular groove in the next batch of parts. To maintain the required width of three-sided disk cutters after regrinding, they are made composite with teeth overlapping each other (Fig. 195, e), which allows you to adjust their size. Gaskets made of steel or copper foil are inserted into the socket of such a composite cutter.
The process of milling rectangular slots, i.e., installing the cutter, securing the part, as well as milling techniques, do not differ from the shoulder milling examples described above.
Cutting modes when milling grooves with three-sided disk cutters made of high-speed steel are selected according to table. 213 of the “Young Milling Machine Operator’s Handbook.”
Milling closed grooves. In Fig. 200 shows a drawing of a 15 mm thick plank in which it is necessary to mill a closed groove 16 mm wide and 32 mm long.
Such processing should be carried out with an end mill on a vertical milling machine.
Preparing for work. We will choose for processing vertically milling machine 6N12. To mill a groove with a width of £=16 mm, we take an end mill with a diameter of 16 mm with a tapered shank; such a cutter has a number of teeth z = 5.
The part enters the milling machine with a marked groove. Since the groove needs to be machined in the middle of the part, the part can be secured at the level of the jaws of the vice, but the parallel pads must be positioned so that the end mill can have an exit between them (Fig. 201).
After installing the part, the cutter is secured in the machine spindle.
Setting up the machine for milling mode. We select the cutting mode for milling grooves with high-speed end mills according to the table. 211 of the “Young Milling Machine Operator’s Handbook.”
Let's take the feed s3y6 - = 0.01 mm/tooth. With cutter diameter D -16 mm, groove width B = 16 mm, number of teeth 2 = 5, feed s3y6 = = 0.01 mm/tooth, according to the table we find o = 43.3 m/min, or i = 860 rpm , and 5 =
43 mm/min. Let's set the machine speed dial to 750 rpm and calculate the resulting cutting speed using formula (1):
Let's set the dial of the machine's feed box to a minute feed of 37.5 mm/min and calculate the resulting feed per tooth using formula (5):
Thus, we will mill the groove with an end mill D = 16 mm from high-speed steel P9 at a longitudinal feed of 37.5 mm/min, or 0.01 mm/tooth, and a cutting speed of 37.8 m/min; We use cooling - emulsion.
Milling process. In Fig. 202 shows the process of milling a groove in a plank. Usually, after installing the cutter in its original position, a small manual vertical feed is first given so that the cutter cuts to a depth of 4-5 mm. After this, the mechanical longitudinal feed is turned on, giving, as indicated by the arrow, forward and backward movement to the table with the fixed part and after each double stroke manually lifting the table by 4-5 mm until the groove is milled to its entire depth.
When milling closed slots, the cutter is in the most difficult conditions during cutting to depth, so the manual feed during cutting should be small.
The ledges in the stepped key according to Fig. 197 can also be milled on a vertical milling machine using an end mill with a diameter of 20 mm. Think about how to structure the operation. The cutting modes must be taken according to the table. 211 of the “Young Milling Operator’s Handbook” for feed per tooth = 0.03 mm/tooth.