Reaming holes. types and features of the operation
Deployment, which is a fairly common technological operation, is performed in cases where a previously prepared hole in a metal product must be brought to meet the required parameters. These parameters, in particular, include the shape and size of the hole, the roughness of the surface that forms it.
Connecting rod bore machining with a sliding reamer
The tool with which the deployment is performed manually or using a drilling machine is called “reamer”. Such a tool could be:
- manual and machine. depending on how it is used;
- cylindrical and conical. depending on its own configuration and shape of the hole being machined;
- tail and mounted. by the method of fixation;
- with a uniform and uneven arrangement of cutting teeth around its circumference for the formation of machined surfaces with varying degrees of roughness.
Types of metal reamers
The hand and machine tools used for deployment have certain differences in their design. Thus, a hand-held reamer is distinguished by elongated cutting edges on its working part and a square shank, with which the reamer is installed in the wrench. The design of the machine tool, which allows reaming of holes of considerable depth, has a shorter working part and a longer neck.
Drilling, countersinking and reaming with R-Tiger Electric Tapping arm
When choosing a reamer for hole machining, the following technical parameters are relevant:
- tool type (for rough or fine reaming, manual or machine);
- diameter (depending on the geometric parameters of the hole to be reamed).
As a rule, a rough reaming requires an allowance of one tenth to fifteen hundredths of a millimeter, and for a finishing one. from five hundredths to one tenth of a millimeter.
In order to understand in more detail how the deployment is carried out, you can consider the procedure for carrying out such a technological operation using a specific example. To obtain a hole with a diameter of 30 mm, first use a drill with a diameter of 15 mm, then ream the resulting hole to a diameter of 29.8 mm. It is processed with a rough reamer with a diameter of 29.95 mm, and then finishing is performed using a tool with a diameter of 30 mm, with which an allowance of 0.05 mm is removed.
Hole machining sequence
How high the accuracy of the hole obtained during reaming, as well as the degree of roughness of its surface, is significantly influenced not only by the geometric parameters of the tool used, but also by the type of cutting fluid used during processing. When reaming holes in steel parts, special emulsions mixed with mineral oil are used as such a liquid. When processing bronze and brass parts, mineral oils are not added to the coolant.
How Machine Deployment Works
You can use special tables to select the modes for performing machine deployment. In this case, the initial parameters are the diameter of the hole being formed, the grade of the material being processed, and the material from which the reamer is made. The main modes of reaming performed by a machine are the cutting speed and the frequency with which the equipment spindle should rotate.
The maximum cutting speed, as a rule, is used when processing normalized steels, the minimum. when reaming holes in viscous materials.
Conical hole machining
With the help of the technological operation of reaming, conical holes can also be processed, which previously had a cylindrical shape or were drilled with shoulders, for which drills of different diameters were used. Making a preliminary hole with shoulders in such cases allows you to leave a smaller allowance for further reaming.
The implementation of the deployment of tapered holes is practically no different from the technological scheme for processing cylindrical holes. To perform such a technological operation, as a rule, a roughing, intermediate and finishing tool is used.
Tapered hole machining sequence
A special taper gauge is used to check the results of this deployment. In this case, the check is carried out both along the plane of contact of the surfaces of the formed hole and the caliber, and along the depth of passage of the control tool.
Gauge tapered center holes (KKTsO)
Such a check is carried out according to the following scheme.
- Several pencil lines (usually 3-4) are applied to the side surface of the cone gauge along its axis, placing them at approximately the same distance from each other.
- Using slight pressure, the gauge is inserted into the tapered hole in the part.
- Then the gauge is turned 1/3 turn.
- Having taken out the caliber, they control the condition of the pencil lines applied to its surface.
The fact that the deployment operation was performed efficiently is evidenced by the uniform erasure of pencil lines on all sections of the lateral surface of the caliber.
Use of hand tools
Manual countersinking and deployment is carried out according to a similar scheme, which implies the following technological operations.
- Based on the parameters of the start and end hole, a tool is selected for performing a rough and fine reaming.
- The workpiece is securely fixed in a vice, if its dimensions allow it to be done. If it is significant in size, then it is not fixed before deployment.
- A tool for rough reaming is inserted into the hole in the part, which was previously obtained during the casting of the workpiece or its drilling.
- On the shank of the tool, which has a square cross-sectional shape, a wrench is put on.
- The outer surface of the reamer and the inner surface of the hole are lubricated with a special liquid.
- The reamer, using a wrench, begins to rotate in the direction of the location of its cutting edges. During the rotation of the tool, which should be performed slowly, without sudden movements, lubricant is constantly applied to its working surface. Rotating the reamer, it is necessary to carefully feed it in the direction of the processing, which ends after the metal layer left on the allowance is completely removed from the inner surface of the hole.
- After the rough reaming is completed, the tool is carefully removed, and it is not allowed to perform its reverse rotation.
- A finishing tool is placed in the hole machined with a rough reamer, on the square shank of which a knob is also inserted.
- The reamer for finishing is rotated clockwise, while this rotation is carried out very smoothly and accurately, constantly using lubricant. The amount of feed of the tool, in order to obtain a hole with the required parameters of the roughness of the inner surface, must be minimal.
- After finishing finishing, the reamer is removed from the hole and its geometric parameters are checked using a smooth limit plug gauge.
Manual deployment techniques
When reaming holes in workpieces made from different materials, you can use the following recommendations for choosing a coolant:
- steels belonging to the category of carbonaceous, structural and tool steels. water solution of soap, emulsion, sulfurized oil, mixture of oils;
- cast iron. can be processed without coolant or using kerosene;
- copper. emulsion;
- aluminum. emulsion, mixture of oils, pure kerosene, mixture of kerosene with turpentine oil, rapeseed oil.
- bronze. processed without using coolant.
Coolant compositions used for reaming holes in various materials
Some nuances of machine deployment
It is very important to properly prepare the hardware before machine deployment. Such preparation consists in the following.
- The taper of the tool shank and the bore in the machine spindle are thoroughly wiped.
- The reamer is inserted into the spindle in the same way as a taper shank drill.
- The workpiece is fixed on the equipment work table so that the axis of the hole exactly coincides with the axis of the tool used.
Machining a hole on a machine with a carbide reamer
The deployment process itself, for which a roughing and finishing tool is used, is performed in the following sequence:
- After completing drilling of the workpiece to be processed, the drill in the spindle of the drilling equipment is replaced with a rough reamer.
- Conducting a rough rollout.
- The roughing tool is replaced with a finishing one and the hole pattern is repeated.
- After final deployment, the tool is taken out of the processing area, the machine’s electric motor is turned off and the result of the work is checked using a plug gauge.
In some cases, for fine reaming, floating chucks or articulated mandrels can be used, in which the cutting tool is fixed.
Wood and metal processing
Reaming is the process of finishing the holes, which ensures the accuracy of the 7th-9th grade and the surface roughness of the 7th-8th grade. Deployment Tool. Sweeps.
The reaming of the holes is carried out on drilling and turning machines or manually. Reamers used for manual reaming are called manual, and for machine reaming. machine reamers. Machine reamers have a shorter working section.
According to the shape of the hole being machined, the reamers are subdivided into cylindrical and conical. Manual and machine reamers consist of three main parts: working, neck and shank.
The working part of the reamer, on which there are teeth located around the circumference, is in turn divided into a cutting, or intake, part, a calibrating cylindrical part and an inverse taper.
The cutting, or intake, part at the end has a guide cone (bevel at an angle of 45 °), the purpose of which is to remove the reaming allowance and protect the top of the cutting edges from nicks during reaming.
The cutting edges of the intake part form an angle at the top of 2F with the sweep axis (for manual sweeps 0.5. 1.5 °, and for machine sweeps 3-5 °).
The calibrating part is designed to calibrate the hole and the direction of the reamer during operation. Each tooth of the gauging part along the working part of the reamer ends with a groove, due to which the cutting edges are formed; in addition, the grooves serve to evacuate chips.
The back taper is on the gauge part closer to the shank. It serves to reduce the friction of the reamer on the hole surface and maintain the quality of the machined surface when the reamer leaves the hole.
For manual reamers, the value of the reverse cone is from 0.05 to 0.10 mm, and for machine reamers. from 0.04 to 0.3 mm.
The reamer neck is located behind the inverse taper and is intended for the exit of the cutter when milling (cutting) on the reamers of the teeth, as well as the grinding wheel when sharpening.
The hand reamer shank has a square for the driver. The shank of machine reamers with a diameter of 10-12 mm is cylindrical, more coiled reamers. conical.
Center holes are used to install the reamer during its manufacture, as well as when sharpening and regrinding teeth.
The cutting elements of the reamer are the teeth.
The teeth of the sweep are determined by the back angle (6-15 °; large values are taken for sweeps of large diameters), the angle of sharpening (3, the front angle y (for rough sweeps from 0 to 10 °. For fine sweeps. 0 °).
The angles of sharpening p and cutting 5 are determined depending on the angles a and Y.
Reamers are made with a uniform and uneven distribution of teeth around the circumference. When manually deploying, teeth with an uneven distribution of teeth around the circumference are used, for example, in a reamer having eight teeth, the angles between the teeth will be: 42, 44, 46 and 48 °. Such a distribution ensures that a cleaner surface is obtained in the hole, and most importantly, it limits the possibility of the formation of the so-called faceting, that is, the formation of holes is not cylindrical, but multifaceted.
If the sweep step were uniform, then at each turn of the sweep knob, the teeth would stop in the same place, which would inevitably lead to a waviness (faceted) surface.
Machine reamers are made with a uniform distribution of teeth around the circumference. The number of teeth of reamers is even: 6, 8, 10, etc. The more teeth, the higher the processing quality.
Manual and machine reamers are performed with straight (spur) and helical (spiral) grooves. According to the directions of the helical grooves, they are divided into right and left.
When working with a reamer with a spiral tooth, the surface is cleaner than when working with a straight tooth. However, the manufacture and especially sharpening of reamers with a spiral tooth is very difficult, and therefore such reamers are used only when reaming holes in which there are grooves or grooves.
Both conical and cylindrical reamers are made in sets of two or three pieces. In a set of two pieces, one is preliminary and the other is final. In a set of three pieces, the first reamer is rough or rough, the second is semi-finishing and the third is finishing, which gives the hole the final dimensions and the required roughness.
Conical reamers work in more severe conditions than cylindrical reamers, therefore, for conical reamers on straight teeth, transverse slots are made to remove chips not with the entire length of the tooth, which significantly reduces cutting forces. over, since the rough sweep removes a large allowance, it is made stepwise, in the form of individual teeth, which, during operation, crush the chips into small pieces. On the intermediate reamer, which removes significantly less chips, the slots are made smaller and the other profile. The fine reamer does not have any chip-chipping grooves.
Manual cylindrical reamers are used for reaming holes with a diameter of 3 to 60 mm. According to the degree of accuracy, they are divided by numbers: 1,2 and 3.
Machine reamers with a cylindrical shank are made of three types: I, II and III. Reamers are used to process holes of the 6th-8th grade. They are manufactured with a diameter of 3. 50 mm. The reamers are fixed in self-centering chucks of machine tools.
Machine reamers with a tapered shank of type II are made with a diameter of 10 to 18 mm and a shorter working part. This reamer is fixed directly in the spindle of the machine.
Machine shell reamers of type III are made with a diameter of 25. 50 mm. These reamers process the hole of the 5th-6th qualifications.
Machine reamers with a square head are made with a diameter of 10. 32 mm, are designed to process holes in 6-7 grades, are fixed in cartridges that allow swinging and self-centering of reamers in the holes.
Reamers with plug-in knives of type I (mounted) have the same purpose as the previous ones, and they are made with a diameter of 25-100 mm.
Machine reamers, equipped with T15K6 hard alloy plates, are used to process holes of large diameters with high speed and high accuracy.
In addition to the considered designs of reamers, other reamers are widely used, which increase the accuracy and quality of hole processing.
Sliding (adjustable) reamers are used when reaming holes with a diameter of 24 to 80 mm. They allow an increase in diameter of 0.25. 0.5 mm.
Adjustable sweeps are the most common. They consist of a housing that lasts a long time and are made of relatively inexpensive structural steels and simple shaped knives. Knives are made from thin plates, they consume a small amount of expensive metal. They can be rearranged or extended to a larger diameter, adjusting or sharpening to the desired size. When the knives are worn down and no longer provide a secure attachment, they are replaced with new ones.
To deploy through holes, expanding reamers are widely used (Fig. 246.6), in which the knives are fastened either with screws, or in precisely fitted grooves they are pressed to the bottom of the groove by the tapered grooves of the end nuts, or by screws that expand the body.
When working with a reamer on a machine, there are often cases when, with a rigidly fixed reamer, its axis does not coincide with the axis of the hole being machined, and therefore the reamed hole turns out to be of an irregular shape. This happens with a faulty machine: the spindle rotation axis does not coincide with the hole axis (spindle runout).
To improve the quality of processing and to avoid rejects when reaming the hole, swing mandrels are used.
The swinging mandrel is fixed in the machine spindle with a tapered shank. In the housing bore, the swinging part of the mandrel is fastened with a pin with a gap, which rests with a ball against the thrust bearing. Thanks to such a device, the swinging mandrel with a reamer can easily take a position coinciding with the axis of the reamer hole.
To obtain high accuracy of the hole, floating reamers are used, which are plates inserted into precisely machined grooves of a cylindrical mandrel. The outer edges of the plate are sharpened in the same way as the reamer tooth. To ensure regulation, the seams are made composite. When working with floating reamers, precise alignment of the hole to be machined and the machine spindle is not needed and, in addition, an accurate hole is obtained even when the spindle beats, since the plate with its ribbons is centered along the walls of the hole, moving in the slot of the mandrel in the transverse direction. The use of a rational design of reamers not only ensures high quality of work, but also significantly increases labor productivity.
In some engineering plants, when reaming the tapered holes, a restricting retaining ring is placed on the tapered part of the reamer, which eliminates the cost. time to measure.
To reduce the load on the sweep during operation, the length of its intake part is doubled. This eliminates the need for a second sweep and improves productivity and processing accuracy.
The combined tool for simultaneous drilling and countersinking of a hole is widely used.
Drill-countersink, drill-countersink, drill-reamer, countersink-reamer allow you to combine two operations and get a hole of a given shape, quality and roughness.
Drilling and reaming holes, tapping
Holes in various products are drilled with drills installed in drilling machines, drills, rotors. In plumbing, twist drills are most often used, since they are easy to drill and give a clean hole of more accurate dimensions.
Twist drills are available in standard diameters with a sharpening angle (tip angle) of mostly 116 degrees. A drill with this sharpening angle is suitable for drilling in both hard and soft materials.
There are data on the sharpening of drills for metals of different hardness, however, changing the sharpening angle makes it necessary to change the shape of the grooves for removing chips. Therefore, in twist drills, it is undesirable to change the sharpening angle, as this leads to rapid tool wear.
The drills are sharpened on special machines or manually on an emery wheel. The correctness of sharpening is checked using a special template. For a well sharpened drill, the cutting edges should be exactly the same length and at the same angle to the axis of the drill. The middle of the bridge should be on the axis of the drill and form an angle of 55 ° with the cutting edge.
The back angle of sharpening with a template is not checked, but it should be equal to 6 ° at the outer surface of the drill and increase towards its axis up to 20 °. If these sharpening rules are not followed, the drill will hit, go to the side, it is bad to take chips and quickly heat up, and the resulting hole will be incorrect.
Drills (left spiral, right pen)
In the absence of twist drills of the required diameter or length, feather drills can be used. They are easy to make yourself from a bar of carbon tool steel. For this, a bar of the required dimensions is heated and flattened at one end in the form of a spatula.
This end is hardened and then sharpened on an emery wheel so that cutting edges are formed at the tip of the drill at the desired sharpening angle. For drilling steel, the sharpening angle is taken equal to 120 °. for brass. 90 p. for aluminum 80 o.
To drill a hole, insert the selected drill until the drill chuck fails and clamp it slightly. Then check that the drill does not hit when rotating, and clamp it in the chuck as much as possible.
Before starting drilling, it is necessary to deepen each center of the outlined holes by re-punching, and then fix the product in a vice on a workbench so that it does not bend or move during the drilling process.
The drill, first you need to set perpendicular to the surface of the product, then, slowly and carefully drilling a small depression, check whether the drill coincides with the center of the punching.
If it has moved away from the center, then it is necessary to make a deeper punching or cut two or three radial grooves from the center of the recess with a cross-cutter in the direction where the drill should be fed. In this case, the drill will take large chips where the grooves are applied and move to the desired direction.
If this time it turns out to be eccentric, then it is necessary to make a new punching, drill a hole with a thin drill, and then with a drill of the required diameter. The pressure on the drill should be such that it delivers uniform chips. When the drill comes out of the metal, it is necessary to reduce the pressure, since at this moment the drill picks up large chips and can break.
When drilling deep holes, remove the drill more often and free it from jammed chips. In addition, to reduce the heating of the drill, it is necessary to apply drops of lubricant into the hole with a brush. This will result in a cleaner and more accurate hole.
When drilling steel, ductile iron, red copper and brass, use mineral oil or soapy water, and when drilling aluminum, soapy water and kerosene. Gray cast iron and bronze are dry drilled.
A large hole is drilled in two passes. First, the hole is drilled with a small-diameter drill, and then with a drill of the required diameter. This method is due to the fact that drills with a smaller diameter are easier to install at the drilling point. In addition, the hole is more correct and more accurate.
Particular care should be taken when using an electric drill with thin and long drills. In such cases, the worker needs to take a comfortable and stable position. The drill must be directed so that the axis of the drill coincides with the axis of the future hole.
It is advisable to finish drilling once, without removing the drill from the hole and not tilting the drill to the side, since the slightest tilt of the drill will break the drill. In this case, the feed is needed very small, and if the drill is in a vertical position, then the drill feed is carried out by the weight of the drill’s own weight.
When drilling large and shaped holes in sheet metal, a number of small holes are pre-drilled next to each other so that they almost reach the marking mowing line. The gaps between these holes are cut with a cross cutter, and the irregularities are cut with a file. Holes in cylindrical parts are drilled on a stand with a cut out recess.
Reaming is the process of machining holes by reaming. Reaming of holes is performed when assembling parts, when a slightly larger hole is required or greater accuracy and purity of its finish, for example, for calibrating the bore of bushings.
In plumbing, manual cylindrical and conical reamers are used. Manual reamers have a large intake (working) part, and their tail has a square for putting on the wrench.
Tapered reamers are used for stripping and straightening tapered holes. It is also convenient to use conical reamers to expand the holes in the sheet material, in the chassis of the blocks. Reamers are made in a set, three pieces per set (rough, transitional and finishing) or two each (transitional and finishing).
Expansion of holes on a cone for countersunk heads of screws, screws and rivets is made by conical countersink.
During manual work, the reamer should be rotated with a knob, for which leave it in the square hole of the knob.
Before using the reamer, it is necessary to check all its cutters by touch and, if any burrs are found, remove them. To obtain a hole of exact dimensions, the hole is pre-drilled with a drill, the diameter of which is 0.2 less than the required hole diameter. 0.4 mm, which provides a stock of material for deployment.
The product is clamped in a vice so that the hole is in a vertical position. Then the transitional reamer is left with the lower part in the hole and rotated with a knob towards the direction of the tip of the teeth. To obtain a hole of more accurate dimensions, a finishing one is used after a transitional sweep. It is necessary to rotate the reamer with pressure, run through the hole. You can not rotate the sweep in the opposite direction.
In the repair business, threads are cut mainly by hand. Taps are used for cutting internal threads, and dies and screw boards are used for cutting external threads.
According to the method of application, taps are divided into manual (locksmith) and machine.
Hand taps are produced in sets. The set includes three taps: rough (first), middle (second) and finishing (third). All three taps are made so that the thickness of the chips cut by each tap is more or less the same. The third tap is used last for finishing and calibrating threads.
It is very important to select the correct drill diameter for drilling holes for threads.
For threading in soft metals such as copper or aluminum, the diameter of the hole must be taken slightly larger, since when cutting, such metals are squeezed out, causing the tap to jam and gall the thread.
The thread is cut as follows: the product is clamped in a vice, and the end of the first tap is inserted into the hole as accurately as possible and pressed on it with a knob.
At the beginning of work, the crank is taken with the right hand, grasping the tap with the thumb, middle and forefinger, and with slight pressure slowly rotate the tap clockwise, keeping its vertical position. As soon as the tap begins to pick up the chips, they switch to rotation with both hands. Having made one turn to the right, make half a turn to the left, etc. Having passed the hole with the first tap, replace it with the second, and then with the third.
With a cutting length of up to 5 mm, only the first and third taps are dispensed with, and for cutting less accurate threads, it is enough to use the first two taps. When cutting deep holes, unscrew the tap more often and clean it with a brush from shavings, and lubricate the cutting area with two or three drops of oil. Holes in bronze and gray cast iron are dry cut.
Dies and screw boards are used for cutting external threads. Dies are round (split and continuous). They are also called lerks. For work, the die is inserted into a special die with clamping screws.
Threading with round dies and screw boards is performed in the same way as with taps. When cutting with dies, it is important that the diameter of the rod is slightly less than the outer diameter of the cutting of the dies.
The cutting bolt is fixed in a vice and slightly rounded from above with a file for better grip with the die. Having lubricated the bolt with oil, put on a die on top and, pressing strongly on it, at the same time turn the klupp to the right. As soon as the die takes the chips, the die is rotated in the same way as when working with a tap, that is, after each full turn, make half a turn back. The thread is cut in one to two passes.
Drilling, countersinking and reaming holes.
Drilling the process of forming a hole in a solid material is called a cutting tool. a drill. The processing accuracy does not exceed 11. 12 grades and surface roughness Rz = 25. 80 microns. Drilling is used to obtain irrelevant holes that serve to facilitate parts, holes for fastening bolts, rivets, studs, etc., holes intended for further processing: boring, countersinking, reaming, threading.
By reaming is an operation to increase the diameter of a previously drilled hole with a larger diameter drill. Usually it is performed when a hole with a diameter of more than 25 mm needs to be obtained in solid metal. The difference between the diameters of the first and second drill is approximately 10. 15mm.
|and. drilling; b. reaming; in. countersinking; r. boring; d. countersinking; e. deployment; f ironing; s. cutting of internal threads; and counter-milling (trimming) of ends; to. cutting discs (washers); l. internal groove groove Figure 7.1. Work performed on drilling machines|
The working part of the drill consists of a cutting and a guide part. The cutting part of the drill (Fig. 7.3, a) has two teeth with cutting edges 2 and 6 located at an angle of 2φ, two grooves 5 and 9 for chip exit, two rear surfaces 4 and 8, a transverse cutting edge (bridge) 1, inclined at an angle ψ = 55 0. The drill tooth has the shape of a wedge with the corresponding angles (Fig. 7.3, b). The rake angle γ of the drill at each point of the cutting edge is variable and decreases as it approaches the center of the drill. Clearance angle α increases from the periphery to the center of the drill.
|Figure 7.3 Parts and elements of twist drills with tapered and cylindrical shanks|
|and. feathers; b. spiral with a cylindrical shank; in. spiral with a tapered shank; r. centers; d. combination drill / countersink Figure 7.2 Different drill designs|
To increase the diameter of the hole obtained by drilling, casting or stamping, as well as to obtain conical and cylindrical recesses, cleaning the end surfaces of the bosses and hubs, the following technological operations are used: countersinking, countersinking and counterbore (Figure 7.4).
Countersinking is the process of machining pre-drilled, stamped, cast holes in order to give them a more regular geometric shape (eliminate deviations from roundness and other defects), achieve higher accuracy (9.11 grade) and reduce the surface roughness to Ra = 1, 25. 2.5 microns. This processing can be either final or intermediate (semi-finishing) before reaming, giving even more accurate holes (6.9 quality) and surface roughness up to Ra = 0.16. 1.25 microns. When processing precise holes with a diameter of less than 12 mm, instead of countersinking, immediately reaming is used.
|Figure 7.4 Structures and elements of countersinks|
Countersinking the process of processing with a special tool is called countersinking conical grooves and chamfers for the heads of bolts, screws, rivets. Unlike countersinks, countersinks have cutting teeth at the end and sometimes guide pins, with which the countersinks are introduced into the drilled hole, which ensures that the axis of the hole coincides with the recess formed by the countersink for the screw head. Fixing countersinks and countersinks on drilling machines is no different from fixing drills.
Deployment is the process of final finishing of holes, which provides high dimensional accuracy and surface roughness in the range of Ra = 1.25. 0.16 μm. The reaming of the holes is performed both on drilling and other metalworking machines, and manually during locksmith and fitter-assembly processing. Manual reamers (Figure 7.5, a). with straight and helical teeth, attachment, adjustable. equipped with a square end on the shank for rotating them with a wrench.
Fragment of the text of the work
the operation of obtaining blind and through holes in a solid material with drills of various types. Most often, twist drills are used for this purpose, which allow you to drill holes in the range of diameters from 0.25 to 80 mm (Fig.1.20, and). The accuracy of the drilled holes due to the low rigidity of the tool, significant axial cutting forces and imbalance of radial forces is not high and corresponds to 12-14 accuracy grades. The height of the roughness of the profile of the machined hole surface exceeds the values Rand 6.3 μm.
Using a drill, you can increase the diameter of an existing hole. This type of processing is called reaming (Fig. 1.20, b).
Countersinking. a method of processing a pre-drilled, stamped or cast hole with a countersink in order to achieve a more correct geometric shape of the hole, straightness of the axis, increase accuracy and reduce surface roughness (Fig.1.20, in). Countersinking provides 10–12 quality levels of hole machining accuracy and surface roughness by parameter Ra within the range of 1.25–12.5 microns. This technique can be used for finishing or semi-finishing a hole before reaming.
Deployment used to further improve the accuracy and reduce the roughness of the machined holes (Fig. 1.20, r). This method is referred to as finishing processing methods. Deployment provides the ability to obtain 6-9 quality levels of accuracy and the height of the irregularities of the profile of the processed surface by parameter Ra up to 0.32 μm.
Drilling, countersinking, reaming and tapping on a radial drilling machine
Hole cutting tools
Twist drill (fig. 1.21, and) consists of a working part ℓone, necks ℓ2, shank ℓ3and paws ℓfour. The working part of the drill is divided into cutting ℓfive, bearing main cutting edges of the tool 3, four, and on the guide part ℓ6. The drill has two cutting blades (feathers), the surfaces of which five and 6 are the helical surfaces of the chip grooves 7 and 8. Chips move along these surfaces, called front surfaces, during the drilling process.
and. twist drill with a tapered shank; b. tail countersink; in. tail machine sweep; r. tap
On the guide part of the drill along the helical groove there are two narrow bands one and 2, providing the direction of movement of the drill when cutting. The intersection of the drill feathers forms its apex in the form of a transverse cutting edge 9.
Shank ℓ3 required to install the drill in the machine spindle. Foot ℓfour, located at the end of the shank, serves as a stop when knocking the drill out of the spindle hole.
Countersink. By their design, countersinks are solid and prefabricated, mounted and tail-mounted. In fig. 1.21, b depicts a one-piece tail countersink. Its main elements are the working part ℓone, consisting in turn of cutting ℓfive and calibrating ℓ6 parts, neck ℓ2, shank ℓ3 and foot ℓfour.
A tail countersink, unlike a twist drill, has three or four cutting teeth with cutting edges located on the cutting part, and does not contain a transverse edge.
The increase in machining accuracy achieved by the countersink is provided by its greater rigidity and shallower cutting depth than a drill.
Sweep. a tool for finishing holes. The main difference between the sweep (Fig.1.21, in) from the countersink is that it has a greater number of cutting teeth (6–14), which, cutting off small layers of material, provide an increased quality of hole accuracy compared to processing with a countersink.
Reamers are subdivided into machine and manual. The latter are designed to handle holes manually. Machine reamers, according to the method of installation on the machine, are divided into tail and mounted, according to the design of the working part. into solid and prefabricated. The structural elements of the tail sweep are the working part ℓone, neck
Drilling, reaming, countersinking holes
Drilling is the most common method for making holes in solid material.
Cutting data for drilling
For drilling holes, twist drills made of tool steels, high-speed steels, and also from hard alloys are used.
For HSS drills, cutting speed v = 25-35 m / min, for tool steel drills v = 12-18 m / min, for carbide drills v = 50-70 m / min. In this case, large values of the cutting speed are taken with an increase in the diameter of the drill and a decrease in feed.
Standard drills have a 118 degree point angle, but 135 degree point angle drills are recommended for harder materials (and deeper holes).
Drills with taper shanks are installed directly into the taper hole of the tailstock quill, and if the sizes of the tapers do not match, then adapter sleeves are used. To mount drills with cylindrical shanks (up to 16 mm in diameter), drill chucks are used (Fig. 1), which are installed in the tailstock quill. The drill is fixed by cams 6, which can be brought together and spread by moving in the grooves of the body 2. At the ends of the cams there are rails that mesh with the thread on the inner surface of the ring 4. From the key 5, through the bevel gear, sleeve 3 with ring 4 is rotated. along the thread of which the cams 6 move up or down and at the same time in the radial direction. For installation in the tailstock quill, chucks are supplied with tapered shanks 1.
To reduce the friction of the tool against the walls of the hole, drilling is performed with a supply of cutting fluid (coolant), especially when processing steel and aluminum workpieces. Cast iron, brass and bronze workpieces can be drilled without cooling. Cooling during drilling lowers the temperature of the drill, which heats up from the heat of cutting and friction against the walls of the hole, reduces the friction of the drill against these walls and, finally, helps to remove chips. The use of coolant allows to increase the cutting speed by 1.4-1.5 times.
Drilling glass sinks and countersinks for drains with Electroplated and Sintered Core drills
The coolant used is an emulsion solution (for structural steels), compounded oils (for alloy steels), an emulsion solution and kerosene (for cast iron and aluminum alloys). If cooling is not provided on the machine, then a mixture of engine oil with kerosene is used as a coolant.
Tool safety during drilling
For the safety of the tool when drilling, you should work with the maximum allowable cutting speeds and with the minimum allowable feeds. When drilling for a pass at the moment the drill leaves the workpiece, it is necessary to sharply reduce the feed in order to avoid breakage of the drill.
Be especially careful when the hole to be machined is greater than the length of the drill bit. If the entire helical flute of the drill is in the hole, the drilling chips will not have an exit, will fill the flutes and the drill will break. In such cases, from time to time, remove the drill from the hole and remove chips from both the hole and the grooves of the drill.
With an incorrectly sharpened drill, an oblique hole with a large surface roughness is obtained. In addition, when working with an insufficiently sharpened (blunt) drill, burrs form at the exit part of the hole. The unequal length of the cutting edges and their asymmetric sharpening, the eccentric location of the bridge and the different width of the bands cause the drill to jam in the hole, which increases frictional forces and leads to tool breakage.
Improving drilling efficiency
To improve the efficiency of twist drills, the following methods are used:
- undercut of a transverse edge,
- vertex angle change,
- sharpening the ribbon,
- double sharpening,
- preliminary reaming of holes, etc.
Precision and surface roughness obtained by drilling
The hole diameter when drilling is slightly larger than the drill diameter. This is due to the fact that the drill moves away from the axis of the hole even with minor irregularities made when sharpening the drill and installing it on the machine, as well as with uneven hardness of the material being processed.
When drilling large holes, the feed force can be excessive and can be tiring for the worker. Sometimes, when working with such drills, the power of the machine may be insufficient. In such cases, the formation of holes is made sequentially by two drills of different diameters, the ratio of which should be such that the diameter of the first drill is greater than the length of the transverse edge of the second drill. Under this condition, the transverse edge of the second drill does not participate in cutting, as a result of which the force required for feeding is significantly reduced, and, which is very important, the drift of the drill to the side from the axis of the hole being machined decreases.
In practice, it is customary to take the diameter of the first drill equal to approximately half of the second, which ensures favorable conditions for drill wear and an even distribution of the feed force when both drills are in operation.
Reaming allows for more accurate holes and less drift of the drill from the axis of the part. Cutting conditions for reaming holes are the same as for drilling.
A countersink is a more productive tool compared to a twist drill for increasing the diameter of holes obtained by drilling, casting or punching.
Countersinks are made of high-speed steel, less often for severe cutting conditions, equipped with carbide plates.
Taper shank countersinks are used to machine holes with a diameter of 10 to 40 mm. In appearance, they are somewhat similar to twist drills, but they have three helical grooves and, therefore, three cutting edges, which increases the rigidity of their structure, allows them to increase cutting conditions compared to reaming, and, consequently, productivity.
Mounted countersinks. one-piece and equipped with carbide plates. are used for machining holes with a diameter of 32 to 80 mm. Such countersinks have four helical grooves and therefore four cutting edges. They are mounted in the tailstock quill of the machine with a mandrel, on which they are centered with a tapered hole. For large holes with a diameter of 50 to 100 mm, countersinks are manufactured with plug-in knives.
To prevent the countersink from turning during operation, two protrusions (keys) are made on the mandrel, which enter the corresponding slots of the countersink.
The diameter of the hole, machined with a countersink, which removes a small allowance and guided by three (or four) ribbons, is more accurate than when drilling. The absence of the counterbore drift away from the axis of the hole to be machined ensures the straightness of the latter better than when working with a drill. To reduce the offset of the countersink, especially when machining cast or pierced deep holes, before countersinking, bore them with a cutter to the diameter of the countersink to a depth approximately equal to half the length of the countersink.
A countersink is stronger than a drill, so the feed (per revolution of the workpiece) during countersinking can be higher than when drilling. At the same time, the countersink, in comparison with the drill, has a larger number of cutting edges, so the thickness of the chips removed by each of the edges is less than the thickness of the chips when drilling. Thanks to this, the surface of the hole processed with a countersink is cleaner. This allows the use of countersinks not only for roughing, but also for semi-finishing holes after a drill, roughing countersink or roughing cutter. before reaming and even for finishing holes.
Other articles on similar topics
Basic concepts of turning and lathes.
Steel grades AISI 409, 430, 439. analogues of domestic brands 08 × 13, 12 × 17 and 08 × 17T
Hydraulic guillotine shears, CNC guillotine shears for cutting and processing sheet materials.
Rules for applying designations of surface roughness in drawings