Milling grooves is a responsible procedure; the accuracy and correctness of its implementation directly affects the reliability and quality of joints in various mechanical devices where dowels are used.
1 Types of keyways and requirements for their processing
Keyed connections can be found in most different devices. Most often they are used in the mechanical engineering industry. Keys for such connections are wedge, segmental and prismatic; products with other types of sections are less common.
Keyways are usually divided into the following types:
- with exit (in other words - open);
- end-to-end;
- closed.
Any of these grooves must be milled as accurately as possible, since the reliability of the fit of the products mating to the shaft on the key depends on the quality of the operation performed. The accuracy of the grooves after processing should have the following indicators:
- Accuracy class 8 – length;
- 5th grade – depth;
- 3 or 2 class – width.
The quality of accuracy must be strictly observed. Otherwise, after milling you will have to perform labor-intensive and very complex work on fitting, in particular, filing of mating structural elements or dowels themselves.
Regulatory documents put forward strict requirements for the accuracy of the location of the keyway, as well as the amount of roughness of its surface.
The roughness quality of the walls (sides) of the groove cannot be lower than the fifth class, and its faces must be placed absolutely symmetrically with respect to the plane passing through the axis of the shaft.
2 Keyway cutters
To ensure the required quality of accuracy of various grooves, they are processed using different types slot cutters:
- Backed according to State Standard 8543. They can have a cross-section of 4–15 and 50–100 mm. After regrinding, such a tool does not change in width. Backed cutters are sharpened exclusively on the front surface.
- Disc according to standard 573. Their teeth are located on the cylindrical part. Disc cutting tools are recommended for processing shallow grooves.
- With cylindrical and conical shank. They come in cross-sections of 16–40 mm (conical) and 2–20 mm (cylindrical). For the manufacture of such cutters, hard alloys are usually used (for example, VK8). The tool has a 20-degree flute angle. A carbide cutting device makes it possible to mill shoulders and grooves from materials that are difficult to machine and hardened steels. Such a tool increases the quality of accuracy and surface roughness several times, and also significantly increases productivity.
- Mounted for segment-type keys according to State Standard 6648. Mills that allow processing of any types of slots for segment keys with a cross-section from 55 to 80 mm. The same standard also describes the tail tool for such keys. With their help, products with a cross section of no more than 5 mm are milled.
The main tool for processing grooves are special key cutters produced according to Gosstandart 9140. They have two teeth with cutting end edges and have a conical or cylindrical shank. They are ideal for machining a keyway, since the working edges of these cutters are directed into the tool body, and not outward.
Key cutters work with both longitudinal and axial feed (as in), they guarantee the necessary quality of the roughness of the shoulders and grooves after processing. Regrinding of such a tool is carried out along the teeth located in the end part of the cutter, due to which its initial cross-section remains almost unchanged.
3 Features of processing key shoulders and grooves
Milling of keyed connection elements is carried out on shafts. For convenient fastening of shaft blanks, a prism is used - special device, facilitating the processing process. If the shaft is long, use two prisms; if it is short, one is enough.
The prismatic device for the ledges and grooves must be positioned as accurately as possible. This is achieved due to the presence of a spike at its base, which is inserted into the groove of the desktop. Clamps are used to secure the shafts. They rest directly on the shaft, which eliminates the possibility of the latter bending. Usually a brass or copper (small in thickness) plate is placed under the clamps. It protects the finished surface of the product from damage.
The shafts are fastened in a conventional vice, which is mounted on the table so that it can be rotated 90 degrees. Due to the possibility of rotation, the vice can be easily installed on vertical and horizontal milling units.
The shaft is fixed on the prism with jaws (it is clamped using a handwheel) rotating around the fingers. The described device for processing shoulders and keyways has a stop in its design. It allows you to mount the shaft along its length.
Most often, prisms with a permanent magnet (barium oxide) are used. The prismatic body is made of two parts. A magnet is installed between these halves. As you can see, the device for milling shoulders and keyed joints is made quite simply, but at the same time guarantees efficient processing products.
4 How are closed slots milled?
Grooving closed type carried out on horizontal milling units. For work, the device described above is used, which is equipped with prisms or a self-centering vice. The shafts are installed on them in a standard manner.
In addition, there is another option for installing shafts. Experts call it “bull’s-eye editing.” In this case, the shaft is placed in relation to the working tool (end or key cutter for shoulders and grooves) by eye. Then the cutting device is launched and carefully brought to the shaft until they interact.
When the cutter and shaft come into contact, a faint trace of the working tool remains on the latter. When the trace appears in the form of an incomplete circle, the table needs to be slightly shifted. If the worker sees a complete circle in front of him, no additional actions need to be performed; milling can begin.
Closed grooves, which are subsequently slightly adjusted, are processed according to two different schemes:
- By inserting a cutter (manual operation) to the entire depth of the ledge and mechanical feed in the longitudinal direction.
- By manual cutting of the tool to a given depth and mechanical longitudinal feed in one direction, and then another plunge and feed, but in the opposite direction.
The first method of processing shoulders and grooves is used for cutters with a cross section of 12–14 mm. In other cases, the second scheme is recommended.
5 Subtleties of processing open and through grooves and ledges
Such elements are milled only after all work on their cylindrical surface is completely completed. Disc tools are used in situations where the radii of the cutter and groove are the same.
Please note that the operation of cutters is allowed up to a certain point. With each new sharpening of the tool, its width becomes smaller by a certain amount. After several such operations, the cutters become unsuitable for working with grooves; they can be used to perform other operations that do not place high demands on the geometric parameters of the width.
The previously discussed device is suitable for processing ledges and grooves of through and open type. It is important here to ensure correct installation cutting tool onto a mandrel. Installation must be done so that the runout of the cutter along the end is as small as possible. The workpiece is fixed in a vice with pads (brass, copper) on the jaws.
The accuracy of the cutter installation is checked with a caliper and a square. The process looks like this:
- the tool is placed transversely from the end of the shaft, which protrudes from the vice, at a predetermined distance;
- using a caliper, check the correctness of the set distance;
- A square is installed at the other end of the shaft and the test is performed again.
The coincidence of the measurement results indicates that the cutter is mounted correctly.
Let us add that segment keys are processed with special cutters (mounted or shank). The double radius of the grooves of these keys determines the diameter of the tool that can be used for milling. When performing such work, the feed is performed vertically (relative to the shaft axis - in a perpendicular direction).
6 Key and milling units for processing shafts
If the grooves must have the most precise width, they should be processed on special keying machines. They work with a keyed two-tooth cutting tool, and the feed on such units is carried out according to a pendulum scheme.
Key-milling machine equipment ensures processing of the groove along its entire length when cutting the working tool to a depth of 0.2 to 0.4 millimeters. Moreover, milling is carried out twice (plunging and feeding in one direction, then the same operations in the opposite direction).
The described machines are optimal for mass and serial production of key shafts. They operate in automatic mode - after processing the product, the feed of the headstock in the longitudinal direction is automatically turned off and the spindle unit moves to the initial position.
In addition, these units guarantee high accuracy the resulting groove, and the milling cutter wears out almost completely along the periphery, since milling is carried out with its end parts. The disadvantage of using this technology is its duration. Standard machining of grooves in two or one pass is several times faster.
The dimensions of the grooves when using key-milling equipment are controlled either by gauges or by a measuring line tool. Round plugs are used as gauges. Measurements using a depth gauge and calipers are carried out as standard (the cross-section, width, length, and thickness of the groove are set).
On modern enterprises Two keying machines are actively used: 6D92 - for processing closed grooves with an end non-dimensional tool, and MA-57 - for milling open grooves with a three-sided tool. These units are usually integrated into automated production lines.
Typically a lathe is used for boring, tapping, reaming, countersinking and drilling, but their capabilities don't end there. I propose to consider a way to use it to drill out a keyway on the bushing. For this I use a 1K62 screw-cutting lathe.
Set of tools
To perform the work, in addition to the machine, you will need:
- boring cutter;
- slotting cutter;
- oil for lubrication.
Any boring cutter can be used, of course, within the capabilities of the sleeve diameter. As for the slotting tool, its cross-section is selected to match the required width of the keyway. Lubricating oil is only required if you have to work with hard metal. For soft steels, provided that high-quality cutters are used, it is not necessary, since chamfer boring and chiselling does not cause critical overheating, which can accelerate the abrasion of the cutting edge of the tool.
Preparatory stage
The bushing is installed in a three-jaw chuck. Before performing chiselling, you must first prepare its internal and external chamfer with a boring cutter. They are made only on the side from which the slotting tool will enter. This is a simple process, familiar even to an amateur turner, and therefore does not require separate consideration.
After preparing the chamfers on the machine, you need to put minimum speed to prevent spindle spin. On many machines, the jaw chuck can give play under load, so in this case it is necessary to install a spacer. To do this, place a bolt and nut of suitable height under it. When unscrewing it, the length of the stop increases, so it is pressed tightly against the cartridge, thereby eliminating the rolling.
The slotting cutter is lightly clamped in the tool holder. It aligns the bushing in the center, after which it is necessary to make fine adjustments. To do this, it is inserted into the bushing, moving longitudinally with the caliper along the slide. The resulting scratch should run along the bushing hole from one edge to the other. There should not be a section without a scratch in the cut line. If it exists, then this indicates the presence of a distortion. When the cutter is positioned correctly, it must be clamped very tightly, since the load during chiselling is much higher than during standard turning work.
Chiseling process
Since the sleeve has its own radius inside, before starting to measure the depth of the groove, it is necessary to cut it off in order to obtain a flat area, which will be the zero reference point. To do this, using a caliper, I move the cutter inside the bushing along the longitudinal slide, removing the finest metal shavings. After it returns to its original position, I bring the cutting edge closer along the transverse slide to the body of the sleeve by 0.1 mm. Again I make a longitudinal movement along the carriage. I repeat the process until the gutter loses its radius. As soon as he leaves, this will be the zero point for the countdown.
Now I start chiseling the keyway. In my case, its depth should be 2.6 mm. Using 0.1mm increments, it would take 26 cuts of the cutter to achieve this depth.
After deepening the groove by 2.6 mm, without changing the settings on the dial, you need to make a few more repeated movements of the cutter to clean the plane of small burrs. Next, the sleeve is removed from the cartridge. Its second end is quite rough, but this is easily solved. The boring cutter is again installed in the tool holder, and neat chamfers are removed. After this, the sleeve can be used for its intended purpose.
Chiseling on lathe a lengthy, although not complicated, process. In my case, the longitudinal movement of the caliper is motorized, so everything is done relatively quickly. It is also possible to make a groove on budget machines with manual drive, but in this case it will take much more time.
In a home workshop, without special machines and devices, it is possible to make, perhaps, only the so-called “collective farm” keyway: this is when a joint hole is drilled with an electric drill in a gear or pulley mounted on a shaft with the center on the circumference of the joining of the parts. Then a cylindrical key is inserted into this hole. But such a connection of parts is unreliable - after all, it is not for nothing that it is not in any GOST.
To produce “GOST” keyways in parts, I developed a manual table machine(or, one might say, a device), which I have been using for several years now. I think that such a machine can be useful, like me, for home craftsmen, amateur designers, and in a school workshop.
This vertical planing machine-device with a manual drive is similar in design to a drilling machine, and in its operating principle - to a slotting machine.
The entire structure is assembled on a base measuring 350x350x20 mm. It (the base) is also a work table on which there is a stand with all the components necessary for cutting pavements and a support with a three-jaw lathe chuck. The thickness of the base of my machine is 20 mm. At first it was particle board(as in the photo), but then I replaced it with a steel one with the same dimensions - the machine became more massive, but also more stable.
Here I will make an explanation: there are other differences in the drawings from the image of the machine in the photographs. The fact is that during operation it became clear that some components and parts would have been better done a little differently. And these improvements are reflected in the drawings.
1—base (steel plate s20); 2 — stand (steel, circle d40); 3 — support flange (steel); 4 — fastening the flange to the base (M12 screw, 3 pcs.); 5—holder (steel); 6 — holder stopper (M12 screw); 7 — lever rod axis (half of an M12 stud with a nut, 2 pcs.); 8—lever rod (steel strip 30×8, 2 pcs.); 9 — articulated connection of the rod with the lever (M12 bolt, 2 pcs.); 10 — lever (steel strip 30×8, 2 pcs.); 11—compression spring; 12 — console; 13 — slider (M12 screw); 14—clamp (M12 screw); 15—mounting the lever on the axle (M12 mount, 2 pcs.); 16 — handle axis (steel, circle 18); 17 — handle (pipe d30x18.5); 18 — mandrel-tool holder (steel, circle d64); 19 — cutter; 20 — stopper (M10 screw); 21—three-cam scroll chuck: 22 - caliper
Near one edge of the base, a stand is fixed by means of a flange - a steel rod with a diameter of 40 mm and a height of 450 mm. A longitudinal groove is cut along the entire rack, and on one of the youngsters there is a groove for joining to the flange. Now it became clear to me that it would be nice to make the rack higher - up to 500 mm - there is often a need when you need to make a groove in long (or high) parts (for example, hubs), and then the console lift is not enough. The flange is a large stepped washer with a central hole for the stand and three evenly spaced holes with a diameter of 12.5 mm for attaching to the base plate. Correspondingly located, but only M12 threaded holes are made in the base table. The stand with its machined end is inserted into the central hole of the flange, and the parts are connected by welding, and after that the flange is screwed to the base.
A holder and a console with a compression spring between them are slidingly mounted on the stand.
The holder is a rectangular parallelepiped with a small height relative to its dimensions in plan, with a central hole for the stand and three M12 threaded holes - two counter blind side ones and one through one at one of the ends. Of course, the definitions of “end” and “side” of such a geometric body are identical, but, I hope, are clear from the drawing. The holder locking screw is screwed into the end hole, and the studs, which serve as the axes of the lever rods, are screwed into the side holes.
The console is a more complicated part. It consists of two hollow cylinders (rack-mount and mandrel), connected to each other by a steel bridge square pipe dimensions 60x60x2.5 by welding. The body of each cylinder has an M12 threaded hole: in the rack cylinder there is a locking screw for preventing rotation, and in the mandrel cylinder there is a locking screw. In addition, a pair of M12 “half-pins” are welded to the rack cylinder in the middle on opposite sides (you can also use screws with the same thread) - they serve as axes for the tool feed levers.
1—rack cylinder (circle d80); 2—jumper (pipe 60x60x2.5); 3—mandrel cylinder (pipe 80×64); 4—lever axis (M12 pin, cut in half, 2 pcs.)
We must try to perform this operation as accurately as possible, so that later during operation the levers do not warp, the holes in them do not break, and the axes themselves do not wear out. Therefore, before welding them, it is worth doing some technological operations. First, on the rack cylinder it is necessary to mill (or grind off with a file) a pair of diametrically opposite flats measuring 20x20 mm. Holes with a diameter of 4 mm are drilled in the center of the flats on each side. They are then drilled out to a diameter of 6 mm in one installation using a drill of the required length. Axial holes of the same diameter are made in both “half-pins” (screws). After this, a straight piece of wire of the same diameter is inserted into the holes of the cylinder. “Half-pins” are placed on the protruding ends and first grabbed, and after aligning the positions, they are finally welded to the cylinder. At the end of the operation, a piece of wire is knocked out.
Holder on stand required height It is secured with a locking screw and serves as a support for the entire tool feed mechanism: a console with a mandrel with a cutting tool fixed in it and a system of levers for its longitudinal feed. The console is lifted and held in the upper position by a spring. The console is kept from rotating on the stand by a fixing screw, the end of which, sharpened to fit the appropriate profile, slides in the longitudinal groove of the stand. The rubbing surfaces of parts are coated before work. thin layer(like a firearm) grease.
A mandrel is a part with which a tool or its holder is secured in the console. In my case, the mandrel and tool holder are made of 45 steel as one piece in the shape of a stepped cylinder with a diametrical hole for the cutter near the free thinner end. Here, an M10 threaded hole is drilled in the end - through it, the cutter is secured in the hole of the tool holder with a corresponding screw. On a cylinder of larger diameter, a flat is milled - an M12 fixing screw rests against it, which does not allow the mandrel to rotate when torque from the cutter occurs. The same screw keeps the mandrel from falling out of the console cylinder. But his effort from squeezing the mandrel out of the cylinder during the working stroke may not be enough: for this purpose, a shoulder is left on the mandrel.
Levers and rods are made of steel strip with a cross-section of 30×8 mm. The levers are mounted on the axles of the console's mandrel cylinder, and the rods are mounted on the axis of the holder. Both of them are hingedly fastened together with axle bolts.
Between the upper (free) ends of the levers, the handle axis is inserted and secured - a cylindrical rod with a diameter of 18 mm with an M12 thread on the end grooves. The handle itself, made in the form of a sleeve with a diameter of 30×18 mm, is loosely placed on a lubricated axle. The surface of the bushing is pre-rolled.
A special story about the machine support. Outwardly, it looks like a machine vice. And the workpieces for processing are fixed in a three-jaw chuck from a lathe mounted on the upper movable platform of the support metal cutting machine. Using the caliper, the workpiece is fed relative to the cutting tool to the cutting depth. Looking ahead, I note that the cutting depth in one pass is very small - only 0.2 - 0.3 mm.
The support consists of a welded body and a movable table. Although there are several body elements to be welded (5 pieces), they are very simple - almost all (except for the racks) are in the form of rectangular parallelepipeds. The racks are made of equal-flange rolled steel angle 40×40 with a half-cut vertical flange. By the way, the traverses of the body and the cross member of the movable table are holders (bodies) from broken turning cutting tools. Who has it in stock? milling machine, he can easily manufacture the body and platform as one part from a massive blank.
1—hull stand (40×40 corner with a trimmed vertical shelf, 2 pcs.); 2—body platform (steel, sheet s7); 3—front traverse (cutter holder); 4—rear crossbar (cutter holder); 5—movable table (steel, sheet B7); 6—cross member of the movable table (cutter holder); 7-way screw M12; 8—left tie, right not shown (screw M12.2 pcs.); 9—flywheel with handle; 10—cotter pin d3; 11—overlay ( steel sheet sЗ); 12—fastening the lining to the body (M4 screw, 2 pcs.)
Preliminary supply of workpieces to cutting tool can be done “manually” by loosening the screws securing its body to the base table and moving the entire support in the grooves (oblong holes).
The platform is moved from the flywheel handle using a lead screw with a conventional M12 thread. There is no matrix nut, as such, in the mechanism. The corresponding threaded hole, along with a pair of guide holes, is made in the cross member under the platform. The guides themselves are a pair of standard long M12 screws. It must be said that the caliper table can be moved up to 60 mm, although for cutting grooves and splines, as a rule, more than 10 mm is not required.
As noted earlier, the depth of cut (feed) when operating the machine is small. To speed up the production of “GOST” keyways, you can use the technology given at the beginning of the article for drilling semicircular “collective farm” grooves, and then use a slotting machine to refine them to a rectangular section.
G. SPIRYAKOV. Chelyabinsk
Keyways (grooves) on shafts are made for prismatic and segment keys. Keyways for parallel keys can be closed on both sides (blind), closed on one side and through.
Keyways are made in various ways depending on the configuration of the slot and shaft and the tool used. They are performed on general-purpose horizontal milling or vertical milling machines or on special machines.
Through keyways and open on one side are made by milling with disk cutters (Fig. 22, A).
Rice. 22. Methods for milling shaft keyways: A– disk cutter with longitudinal feed; b– end mill with longitudinal feed; V– end mill with pendulum feed; G– disk cutter with vertical feed
The groove is milled in one or two passes. This method is the most productive and provides sufficient accuracy of the groove width, but its use is limited by the configuration of the grooves: closed grooves with rounded ends cannot be made in this way. Such grooves are made using end mills with longitudinal feed in one or several passes (Fig. 22, b).
Milling with an end mill in one pass is carried out in such a way that first the cutter, with a vertical feed, passes to the full depth of the groove, then the longitudinal feed is switched on, with which the keyway is milled to its full length. This method requires a powerful machine, strong attachment of the cutter and abundant cooling with emulsion. Due to the fact that the cutter operates mainly as a peripheral part, the diameter of which decreases from resharpening to resharpening, as the number of resharpenings increases, the processing accuracy (across the groove width) deteriorates.
To obtain grooves that are precise in width, special key-milling machines with “pendulum feed” are used, working with double-spiral end mills with frontal cutting edges. With this method, the cutter cuts to a depth of 0.1–0.3 mm and mills the groove along its entire length, then again cuts to the same depth as in the previous case and mills the groove along its entire length, but in the opposite direction (Fig. 22, V). This is where the name “pendulum feed” comes from.
This method is the most rational for the production of keyways in serial and mass production, since the precision of the groove ensures interchangeability in the keyway connection. In addition, since the cutter works with the frontal part, it will be longer lasting, since the frontal part of the cutter wears out, and not the peripheral part of the cutter. The disadvantage of this method is low productivity. It follows from this that the pendulum feed method should be used when making grooves that require interchangeability, and the single-pass milling method should be used in cases where it is possible to fit the keys along the groove.
Keyways for segment keys are made by milling using disk cutters (Fig. 22, G). Through keyways of shafts can be processed on planing machines (long grooves - on longitudinal planing machines, and short grooves - on transverse planing machines).
Keyways in the holes of gear bushings, pulleys and other parts fitted onto a shaft with a key are processed in individual and small-scale production on slotting machines, and in large-scale and mass production on broaching machines.
