What tool is used for drilling. Countersinking and countersinking
If you need to hang something or connect parts, you often have to drill holes. It is important to choose the right drilling method and tool for this. In this article we look at different kinds of drilling tools.
Before you start Use quality tools, a sturdy step ladder or step stool, and reliable safety equipment such as sturdy shoes, safety glasses, work gloves a respirator mask. Always replace worn-out tools and use new dowels, screws, blades, drills, and blades
Ask yourself the following questions:
- What kind of material I have to work with? This question leads to a series of other questions:
- Do I need a drill or would I be better off using nails or glue??
- What kind of drill do I need?
- What kind of drill do I need??
- Will it be necessary to use dowels and, if so, what kind?
- What kind of screws or bolts will I need?
Tools for drilling and machining holes
The most common drilling tool is the twist drill.
Spiral drill bit (Fig. 2.1.2) consists of a working part /, a neck /// and a shank IV. The working part is differentiated between the cutting part and the guide or centering part.
In the guide part of the drill bit (fig.2.1.3) there are two grooves 1 and 6 to divert chips from the drilled hole, as well as two ribbons 3 and 8 to ensure the direction of the drill when cutting.
Cutting part of the drill bit has two main cutting edges 2 and 7,
transversal edge 4 and two back surfaces 5 и 9.
The angle at the tip of the drill bit 2φ, formed by the cutting edges, is chosen depending on the hardness and brittleness of the processed material. For medium-hard steel and cast iron the angle at the apex is-
a) usual, b) with hole for cooling fluid supply
for red copper. 125°, for aluminum, soft bronze, brass. 130-140°.
Angle of inclination of the helical groove ε Depending on the diameter of the drill bit take 18-30°.
Diameter of twist drill bits with cylindrical and conic shank varies from 0,25 to 80 mm. Drilling is possible in ∆3 to ∆5 surface finish classes and accuracy classes 4 to 6.
Countersinking and reaming are used for further processing of holes, obtained by drilling, casting or punching.
countersink drill bits for metal. Набор зенковок.
Countersinking gives holes in purity classes 3 through 7 and ∆ 5 through 6; reaming gives holes in purity classes 2-3 and ∆ 5 through 9.
The cutting tools for countersinking and reaming are countersinks and reamers.
Counterbore (Fig. 2.1.4) consists of the working part I, Flare neck IV, tapered shank V and foot VI. In the working part there is a cutting part II (fence) and calibrating III (guiding) part.
The cutting part of the countersink consists of a cut face part. core 3 and three or four cutting edges 2. Each of these, as in other tools, is formed by the intersection of the front 1 and back 4 surfaces. The main angle in plan φ is chosen within the range of 45-60°.
The countersinking area has three or four helical grooves and ribbons 5. The latter are countersink guiding elements; they provide greater precision in machining by preventing possible sideways deflection of the tool. Angle of inclination of helical grooves ε. 10-30°.
Countersinks are subdivided by the type of holes to be drilled into cylindrical, conical and combined (multistage). Beside solid countersinks up to 80 mm in diameter, countersinks (solid and with inserted blades up to 100 mm in diameter) and countersinks with brazed hard-alloy plates are used.
Reamer at (fig. 2.1.5,a) has the working part I, neck II and shank III. The working part includes the guide cone or intake part IV, the cutting part V, the calibrating part VI and the return cone VII.
The main work is performed by the cutting part, each tooth of which has a main cutting edge), the front 2 and the rear 3 surfaces (Fig. 2.1.5,6). On the front surface the chip to be cut comes down. Tooth reamer has a rake angle of γ and rear α(Fig. 2.1.5,в).
Cutting part for through hole machining has an angle equal to 0,5-1,5° for manual reamer, for mechanical reamer for steel processing. 12-15° and for cast iron. 3-5°. The main angle in the plan φ affects the axial thrust: the larger it is, the higher the axial thrust required.
Reamers are cylindrical and cone, manual and machine. Machine reamers have a much shorter working section than their manual counterparts. According to their design, reamers are divided into tail reamers and attachable, solid blades and with inserted blades, equipped with hard alloy blades.
Spiral drills, countersinks and reamers are made of different brands of carbon tool steels UYA and U12A, chromium and tungsten tool steels 9ÕÑ and Â1 for low speeds of processing, and of high-speed steel for high speeds of processing. Drills, countersinks, and reamers equipped with carbide inserts of BK and TK grades are also produced.
Monolithic carbide twist drills (BK15M, BK 10M, etc.).) of 1.5 to 5.5 mm diameter are designed for drilling in difficult to work materials. Durability of such drills is almost 20 times higher than that of HSSD drills.
a) drill-drill, b) drill-sink, c) drill-drill, d) countersink-drill, e) drill-sink-drill
Combination cutting tools (fig. 2.1.6) is used to increase productivity in machining holes in mass production. Replacement of several tools by one combined tool considerably reduces auxiliary time (for tool changes), improves machining quality, eliminates the danger of tool and hole axis mismatch, etc. д.
Drilling. bladed machining of holes with axial tools. The main cutting movement is rotary and the feed movement is rectilinear. Holes (through or blind) with rectilinear axis and cylindrical formations are machined by drilling. Drilling is the only type of cutting that can produce small (from 0.1 to 20mm) precise cylindrical and conical holes.
Surface Finishing Diagrams for Drilling
Drilling, reaming, countersinking, reaming, countersinking, countersinking, step hole machining and internal thread cutting are performed on the drilling machines (fig. 5.22).
By drilling (fig. 5.22, а) through and blind holes are obtained. Reboring (fig. 5.22, а) Increase the diameter of a previously drilled hole. countersinking (Fig. 5.22, б) also increase the diameter of a hole in a workpiece produced by casting or pressure methods. reaming (fig. 5.22, в). a finishing operation which provides high accuracy of the hole. Cylindrical and conical holes after countersinking or reaming are machined by reaming. The machining scheme of the exact conical hole includes the following transitions: drilling a cylindrical hole, countersinking with a stepped conical countersink, reaming with a conical reamer with chip splitting grooves, reaming with a smooth conical reamer. Countersinking (Fig. 5.22, г) machining cylindrical and tapered recesses for bolt and screw heads. To ensure perpendicularity and coaxiality of the machined surface to the main hole, the cutting tool (countersinking) is provided with a guiding cylinder. countersinking (fig. 5.22, д) machining end bearing flats for bolt heads, screws and nuts. Perpendicularity of the machined face surface to the main hole is ensured by the guiding cylinder of the cutting tool (forging). Complex stepped surfaces are machined with combined tools (Fig. 5.22, е).
- spiral: designed for making holes of medium diameters and lengths;
- feathering: for machining easily machinable materials;
- Gun and cannon: for manufacturing high-precision deep holes;
- ring-shaped: for making through holes of large diameters;
- centering: for making centering holes in workpieces for the purpose of their subsequent fastening and machining in the centers of machine tools;
- Combined: having two or more different diameters on the body of the same tool or tools with different purposes (e.g. drill countersinks);
- Ejector drills: with internal supply of cooling lubrication fluid (coolant) through special channels in drill bit body for effective cooling of cutting zone and chip evacuation.
а. spiral; б. feather; в. ring; d. centering; д. ejector
Drills can be either solid or prefabricated: the cutting part is either made entirely of tool material or in the form of cutting inserts that are somehow attached to the body of the tool.
Spiral drill bit (fig. 5.24) has a working part 9 and shank 7. The shank serves for fixation of the drill bit in the working tool of the machine and is made cylindrical or conical.
1. front surface; 2. the transverse edge; 3. main back surface; 4. ribbon; 5. screw groove; 6. foot; 7. shank; 8- guide part; 9- working part; 10. cutting part; 11. main cutting edge; a, y, f. cutting angles
Tapered shank is equipped with a foot 6, which prevents it from being knocked out of the machine tool spindle. Working part of drill bit is made of tool steel or with tungsten carbide inserts. It carries out the cutting process, shapes the surface of the machined hole, removes chips from the cutting zone and guides the drill during machining. It consists of a cutting 10 and guide 8 parts. The guide part has two helical grooves 5 necessary to divert chips from the cutting zone, and two ribbons 4, necessary for guiding the drill. The cutting part has two main cutting edges // formed by the front 1 and the main rear 3 surfaces. The main cutting edges are connected at angle 2cr by a cross cutting edge 2. Thickness and width of the cut layer, ratio between radial and axial components of cutting force and temperature in the cutting zone depend on the value of angle 2cr. As the angle 2f increases, the axial (Px) and reduces the main (P,) components of cutting force. The width of the cut layer decreases, which increases the temperature in the cutting zone. As the 2f angle changes, the values of the front and rear angles and the shape of the main cutting edges change. The recommended values of angle 2f are given in table. 5.1.
The geometrical parameters of the cutting part of the twist drill bit are shown in Fig. 5.25:
y. rake angle. formed between the tangent to the front surface at the considered point of the main cutting edge and the perpendicular to the cutting plane (has variable value of-
Medium-hard cast iron, hard bronze
The angle 2f is formed between the cutting plane and the main cutting edge);
a. posterior angle. formed between the cutting plane and the tangent to the auxiliary posterior surface at the considered point (the posterior angle, like the angle y, changes its values as it moves along the main cutting edge);
2cr. drill bit sharpening angle. formed between the projections of the two main cutting edges on the plane;
co. angle of inclination of screw groove. formed between the drill bit axis and tangent to the screw groove (affects the efficiency of chip removal from the cutting zone, the more co, the better the chip is removed);
Machines of drilling group
In individual and small-lot production vertical drilling machines. WSD (fig. 20a) are used. 20, а). On the base plate the column 8 is mounted, along the vertical guides of which the table 2 and the drilling head 4 move. Installation movements of the table are carried out manually with the help of a screw jack 1. On the upper plane of table 2 work pieces or workpieces are installed. Setting vertical movements of the drilling head are carried out manually due to a system of counterweights 7, attached to the drilling head by a cable, thrown over the unit 6. Rotary motion of the tool is transferred from the electric motor 5 through the gear box and spindle 3. The mechanisms of the main motion and the feed motion are located inside the drilling head.
CNC vertical drilling machines are widely used in individual and serial production. Their peculiarity is combination of easy machine readjustment for machining of different products with automatic or semiautomatic work cycle. The CNC vertical drilling machine is shown in Fig. 20, б. Skids 15 move along the vertical guides of bed 8, the table 2 moves along the horizontal guides. Table and slide movements are performed according to the numerical program that provides accurate movement of the workpiece relative to the cutting tool. Drilling head 4 with spindles 3. Mechanisms of main motion and feed motion are installed inside the drilling head. All movements (motions) of cutting tools are carried out according to the program.
When consecutive processing of several holes in massive or large-sized workpieces the use of vertical drilling tools
of the machine tools is extremely inconvenient, because it is almost impossible to exactly align the axis of rotation of the cutting tool with the axis of the machined hole. Therefore, radial drilling machines are used for such workpieces (fig. 20, c), at work on which the workpiece remains stationary, but the spindle with the tool moves relative to the workpiece and can be set at a required point of the horizontal plane.
Bollard 14 with vertical column is fixed on the base plate 9. On a column sleeve 13 is installed, which rotates relative to the column in the horizontal plane by 360 °. The traverse 10 fixed on a sleeve can move vertically relative to the column due to the screw mechanism 12. The traverse has horizontal guides on which the drilling head 4 moves. Drilling head mechanism consists of a spindle 3, speed box 11 and feed box. The workpiece is placed stationary on the table 2. angular displacement of the cross beam and radial displacement of the drilling head in the horizontal plane allow to install cutting tool precisely in relation to the axis of the work hole.
Reaming is carried out through holes which have been previously drilled into the workpiece. Components processed by this technological operation can have precision up to the sixth quality level, as well as a low roughness. up to Ra 0,63. Boring is divided into roughing and finishing, and can also be manual or machine.
Cylindrical manual reamers 24H8 0150
The recommendations that should be followed when performing this type of machining are as follows.
Depending on the type of production and the task at hand, metal drilling can be performed in different ways.
Boring by guided drilling and drilling by marking
In small series and individual production, holes are drilled directly over the markings. The holes are already marked (with the center of the future hole and the control circles marked on them) when they are delivered to the operator. Pre-drilling is carried out first. It is carried out with manual feed, the diameter of the pilot hole is approx. 0,25D. Then the spindle with the drill is retracted, the swarf is removed, and it is checked whether the pilot circle matches the circles indicated by the control circle. When a good match is found, metal drilling is continued and completed. If there is a deviation, a correction is necessary: in the direction in which the drill should be moved, a narrow chisel cuts a groove in which it must go to the right point. Then continue drilling until the desired result is achieved.
Drill collars are used in mass production to shorten set-up times and improve the accuracy of the drilling process. They are designed for workpiece fixation in the required position and exact guiding of cutting tool in accordance with the requirements of technological process. The workpiece is placed in the locating base and the workpiece is guided by conductor sleeves. The operator does not set up the machine and/or check the accuracy of the setting; he only sets up the workpiece, switches the machine on and off, then removes the finished workpiece and sets the next one. This reduces the time required to drill through the workpiece and increases the accuracy of machining. Drill collars are not used in individual production because it is uneconomical to produce a special device for drilling holes in several pieces.
Through-hole and blind holes
Holes that go through the entire pattern are called through holes, while those drilled to a certain depth are called blind holes. There are significant differences in their drilling processes. For example, when the drill bit leaves the workpiece on the opposite side it can jam, or it can break because of the sudden decrease in resistance of the workpiece material. Considering that operations on the drilling machine are usually performed with mechanical feed, it is necessary to switch to manual feed and reduce the feed rate to the lowest one.
There are three ways of drilling blind holes:
- On machines with automatic spindle feed cutoff the desired drilling depth is set when setting up the workpiece.
- A special chuck with an adjustable stop is used on the machines without automatic feed cutoff device by setting the stop sleeve relative to the housing to the required drilling depth (accuracy up to 0.5 mm).
- If great depth accuracy is not needed, it is marked with chalk directly on the drill.
Large diameter holes (from 25 mm and up) are usually drilled in two steps. First drill a hole with a reduced diameter (this should be about the same length as the second, larger drill bit’s cutting edge). The larger diameter drill will then be less stressed when cutting metal. Only holes obtained by drilling are suitable for reaming.
Manual drilling is carried out with hand-held, pneumatic or electric hand-held drills.
Drilling with a hand-held drill. Handheld drills are used when a small hole diameter is required in the absence of a drilling machine or in a bulky workpiece.
The complexity of manual drilling consists in the fact that the operator must simultaneously hold the drill in a certain position, to produce the appropriate pressure, aimed at the axis of the drilled hole, and the rotation of the crank to rotate the drill bit, periodically cooling it. Depending on the position of the axis of the hole to be drilled, the drill can be oriented horizontally, vertically or at an angle.
The drilling procedure with the drill horizontal is as follows:
- Before starting work with the hand drill, it is necessary to check the smoothness of movement by rotation of the handle and reliability of the bib fastening.
- After consulting the drawing, use marking tools to mark centers and circles, then bore them out.
- clamp the part in a vice so that the borders of the hole are higher than the jaws of the vice by more than half of the chuck diameter.
- Insert drill bit in chuck.
- The drill is set in the desired position by holding the stationary handle with the left hand and the rotation knob with the right hand, fig. 9.54.
- Bringing the tip of the drill bit to the center of the core cutter, guide the drill bit along the axis of the hole and perform test bore. Turn the drill handle smoothly, without jerking, without rocking the drill.
- If this check does not reveal any sideways movement of the drill bit, increase the pressure on the bib and finally drill the hole.
When the drill comes out of the workpiece, release the pressure and reduce the speed of the drill, in case of jamming, turn the knob back.
Fig. 9.54. Drilling with a hand-held drill for horizontal holes
Drilling of holes with vertical axis is performed in the same sequence as for horizontal drilling, but the holding techniques of the hand drill are different for horizontal and vertical drilling.
When drilling a part located on a high base, hold the drill with the left hand on the bib and the right hand on the rotary knob, Fig. 9.55а. Slightly press the bib and carry out a test bore. If the hole is positioned correctly, apply more pressure and continue drilling until the hole is complete. Sometimes the pressure is increased by pressing on the left hand with the chin.
Fig. 9.55. Techniques for drilling vertical holes with a hand drill: а. on a high base;
When drilling parts located on a low base, the drill is held with the right hand by the rotary knob and the left hand by the stationary knob, while the chest rests on the bib, Fig. 9.556. When drilling, the drill should be held rigidly vertically, without rocking, otherwise the drill could break or swing the drilling axis to the side.
Drilling with an electric drill. In the locksmith-assembly business, in order to facilitate the work of the worker and to increase productivity, various hand-held portable mechanized tools are used. These include electrified tools.
Electric drilling machines. electric drills, depending on the type of work performed, can be of the heavy, medium and light types. In addition, for drilling holes in hard-to-reach places, electric angle drills are produced, Fig. 9.56.
The drill has an electric motor in the casing, the armature of which has a small pinion on the axis, coupled with a large pinion attached to a rod. There is a drill chuck on the other end of the drill rod to hold the drill bit.
Fig. 9.56. Types of drills produced by industry
Countersink Selection- Everything you need to know (for aluminum)
Most modern power drills have a switch for the direction of rotation of the drill bit (reverse), Fig. 9.57.
Fig. 9.57. Portable electric drill
All modern electric drills have a switch with a lock button for long and continuous operation. The drill is ignited by depressing the switch in the handle. In the continuous duty mode, the locking button located on the side of the switch is also pressed so that it is in the recessed position. To stop the drill from continuous duty simply push the switch as far as it will go. The deadlocking pushbutton then automatically returns to its initial position (up).
Most power drills are equipped with an electronic speed regulator that enables infinitely variable speed adjustment. This is set at the push of a switch. The harder the pressure, the higher the RPM. The upper speed limit can be adjusted with a special thumb wheel 2 (Fig. 9.58) located on the switch 1. To increase the RPM upper limit, turn the thumbwheel toward the “G” indication; to decrease the RPM lower limit, turn it toward the “A” indication located on the thumbwheel.
This function makes it easy to precisely pre-drill a hole in the right place. For example, if you begin drilling at high RPM, the rapid rotation of the drill bit may cause the center of the hole to be offset from the center of the core point. 9 Via-
Fig. 9.58. Electronic RPM control
Pre-drilling is carried out at low speeds using the electronic control. After making sure that the hole is not offset, increase the RPM to the maximum recommended value for drilling in a given material.
Note. In order to achieve the longest regulator life, a low RPM should be used only at the beginning of the drill. Continuous work at low rpm can damage the regulator.
Features of drilling deep holes
Drilling is called deep drilling if the depth of the hole to be drilled exceeds five hole diameters. It is a very complex and time-consuming technological operation, and the main condition for its good performance is the effective cooling of the tool used, which usually takes place under pressure.
In order to perform quality and accurate deep hole drilling, it is very important to have the right tool direction at the beginning of machining. For this purpose a special conductor bushing is used or such procedure is carried out on the previously made hole of smaller diameter.
Because of the technical challenges involved, deep hole drilling must be carried out using special equipment
The drill bit used for deep hole drilling must not be rotated at full speed outside the workpiece itself: this can cause the cutting part to drift from the desired path. In addition, drilling deep holes with a long drill bit creates unfavorable conditions for chip removal from the machining area, which can also lead to tool misalignment.
Drilling Technology and Techniques
Before starting the drill, the drill bit is driven in rotation. The drill smoothly (without shock) led to a fixed workpiece and made alignment of the drill with the center of the hole and drill to a small depth (suprasdrilivayut). Then retract the tool, stop the drill, and check the accuracy of the overdrilled hole.
To avoid displacement of the drill recommended pre-drilling workpiece drill a small diameter of 2-5 mm. Due to this, the transverse edge of the drill bit does not work during final hole reaming, which reduces the movement of the drill bit relative to the axis of the hole on the workpiece during final drilling.
When drilling a hole greater in depth than its diameter, the drill bit is periodically removed from the hole in question, and the drill grooves and the workpiece hole are cleaned from accumulated swarf.
To reduce friction of the tool against the walls of the hole, drilling is performed with supply of cooling lubricant, especially when processing steel and aluminum workpieces. Cast iron, brass and bronze workpieces can be drilled without cooling. Application of coolant allows to increase cutting speed by 1,4-1,5 times. Emulsion solution (for structural steels), compound oils (for alloy steels), emulsion solution and kerosene (for cast iron and aluminium alloys) are used as coolant. If no cooling is provided on the machine, then a mixture of machine oil and kerosene is used as coolant, in which the drill bit is dipped or the drill bit is poured from an oil can.
During feed-through drilling, at the moment of drill exit from the workpiece, the feed rate must be rapidly reduced to prevent breakage of the drill bit. To keep the tool safe when drilling, work at the maximum permissible cutting speeds and the minimum permissible feeds. A properly sharpened drill bit has both cutting edges working and the chips coming off in two spiral grooves.
The size of the hole during drilling is larger than specified if the cutting edges of the drill have different lengths, although sharpened at the same angles; the cutting edges have different lengths and sharpened at different angles; the cutting edges have equal lengths, but sharpened at different angles. A drill bit that is not properly and sufficiently sharpened produces a tapered hole with a very rough surface. In addition, if an insufficiently sharpened (blunt) drill bit is used, burrs form at the outlet of the hole. Unequal length of the cutting edges and their asymmetrical sharpening, eccentric location of the bridge and different width of the ribbons cause pinching of the drill bit in the hole, which increases the frictional forces (as the drill bit goes deeper into the workpiece) and, consequently, leads to tool breakage.
The holes to be drilled are called deep if they are 5 times as deep as the hole diameter. When drilling deep holes use long twist drill bit with the usual geometric parameters, which is periodically removed from the workpiece to cool and remove chips accumulated in the grooves. For increased productivity drills with forced chip control are used.
The workpieces can be positioned and clamped on the drilling machine table in different ways. This depends on the size, configuration and weight of the workpiece, as well as the diameter of the hole to be machined, etc.
Small parts when drilling holes of up to 10 mm in diameter are usually clamped in a hand vise or held against rotation by pliers. When drilling holes of larger diameters, the workpiece must be clamped more securely, e.g., in a machine vice. Before installing the machine vise on the machine table, carefully free it from swarf, clean the surface of the table from dirt, wipe and oil the supporting planes. After alignment of the vice relative to the machine tool spindle fasten it to the table surface with machine screws inserted into the T-slots of the table. When drilling holes of small diameter the vice doesn’t have to be clamped.
The workpieces that do not fit between the jaws of the vice are clamped by clamping bars to the surface of the table or fixture.
When machining through holes, the possibility of the cutting tool exiting the hole without damaging the surface of the table or fixture, or the tool itself, must be taken into account.
When drilling, the drill axis must be perpendicular to the surface on which the hole is drilled. If this is not ensured, the hole axis will be at an angle and drill bit breakage is possible.
Before starting work clean machine table and bearing surfaces of fixture from shavings and other foreign objects.
Under the workpiece when drilling through holes (fig. 3, a) a wooden pad should be put under, and for precision parts. a steel ring or tile with a hole for the drill passage.
When drilling holes on a cylindrical or inclined surface as shown (Fig. 3, b, c), it is necessary to prepare the area A. This area can be milled or drilled perpendicular to the surface and only then the hole can be drilled. A distinction is made between guided boring and guided drilling.
Marked drilling. The center of the hole is tapped with a core cutter with an angle of sharpening approximately equal to the angle at the apex of the drill bit. The workpiece to be drilled is clamped so that the center of the hole and the tip of the drill coincide.
First, with a slight hand feed, drill the hole to a depth of about 1/4 of the drill bit diameter, and then inspect the resulting circle. If the obtained circle is not displaced relative to the center of the marking, then the drilling continues. If the center of the hole is displaced, the fitting tool with the semicircular blade cuts a groove from the center of the hole to the side where the center of the drill needs to be displaced. After that, the center of the hole is tapped again in the cut out groove and drilling begins. When drilling deep holes with spiral drill bit, periodically without stopping the machine, remove the drill bit from the hole and remove chips from the grooves.