How to place parts with curved contours. Basics of drawing and marking. Mark a part with straight contours by drawing parallel lines
Plumbing markings
TO category:
Marking
Plumbing markings
Marking is the process of transferring the shape and dimensions of a part or part of it from a drawing to a workpiece. The main purpose of marking is to indicate on the workpiece the places and boundaries of processing. The processing locations are indicated by the centers of the holes obtained by subsequent drilling or by bending lines. Processing boundaries separate the material that must be removed from the material that remains and forms the part. In addition, markings are used to check the dimensions of the workpiece and its suitability for the manufacture of a given part, as well as to control the correct installation of the workpiece on the machine.
Workpieces can be processed without marking, using jigs, stops and other devices. However, the costs of manufacturing such devices are recouped only in the production of serial and mass-produced parts.
Marking (which is essentially close to technical drawing) is performed using special tools and fixtures on the surfaces of workpieces. Marking marks, i.e. lines applied to the surface of the workpiece, indicate the boundaries of processing, and their intersections indicate the positions of the centers of the holes or the position of the centers of arcs of circles of mating surfaces. All subsequent processing of the workpiece is carried out according to the marking marks.
Marking can be mechanized or manual. Mechanized marking, performed on jig boring machines or other devices that ensure precise movements of the workpiece relative to the marking tool, is used for large, complex and expensive workpieces. Manual markings are performed by toolmakers.
There are surface and spatial markings. Surface marking is carried out on one surface of the workpiece, without linking its individual points and lines with points and lines lying on the other surface of this workpiece. The following methods are used: geometric constructions; according to a template or sample of a part; using devices; on the machine. The most common type of surface marking is planar, used in the manufacture of flat gauges, jig plates, die parts, etc.
Spatial marking is carried out by linking dimensions between points and lines lying on various surfaces blanks. The following methods are used: for one installation; with rotation and installation of the workpiece in several positions; combined. Spatial markings are used in the manufacture of parts of complex shapes.
Tools and devices for marking. According to their purpose, marking tools are divided into the following types:
1) for making marks and making indentations (scribers, surface planers, compasses, center punches);
2) for measuring and monitoring linear and angular quantities (metal rulers, calipers, squares, micrometers, precision squares, protractors, etc.);
3) combined, allowing you to take measurements and carry out risks (marking calipers, gage gauges, etc.).
Scribblers are used to apply marks on the surface of workpieces. Steel scribers are used to mark untreated or pre-processed surfaces of workpieces, brass scribers are used to mark ground and polished surfaces, and soft sharpened pencils are used to mark precise and finished surfaces of workpieces made of non-ferrous alloys.
Marking compasses correspond in design and purpose to drawing compasses and are used for drawing circles and dividing them into parts, transferring linear dimensions, etc.
Rice. 1. Marking tool: a - scriber, b - compass, c - center punch, d - square
The steel legs of scribers and compasses are made from steels U7 and U8 (the working ends are hardened to 52-56 HRC3) and from hard alloys VK.6 and VK8. The working ends of scribers and compasses are sharpened sharply. The thinner and harder the tips of these tools, the thinner the marks are and the more accurately the part will be made.
The center punch (Fig. 1, c) is used for making recesses (cores) on marking marks. This is necessary so that during processing the marking marks, even when erased, are noticeable. A center punch is a steel round rod made of alloy (7ХФ, 8ХФ) or carbon (У7А, У8А) steel. Its working part is hardened and sharpened at an angle of 609. The head of the punch, which is struck with a hammer, is made rounded or chamfered and also hardened.
The marking tool, used for spatial marking to make horizontal marks on the surface being marked and to check the position of the workpiece on the marking plate, is made in the form of a stand on which the scriber can be moved in height and secured in the required position. In the simplest planner in design, the scriber is set to the required height using a vertical scale ruler or using gauge blocks. In tool production, gauges are mainly used, and sometimes (if necessary) gauges of a special design (for example, a multi-thread gauge, which has several scribers on a stand, independently set in height to a given size). Combined surface gauges are also used, i.e. regular surface gauges equipped with additional various devices and tools (for example, a surface gauge with a center finder).
The square is used to draw lines, construct angles and check them.
Marking calipers are used to measure the dimensions of external and internal surfaces and for marking marks. It differs from a conventional caliper by the presence of sharply sharpened carbide tips on its jaws.
Devices used for marking and used for installation, alignment and securing of workpieces include adjustable wedges, prisms, linings, jacks, chucks, collets, rectangular magnetic plates, rotary tables, sine tables, dividing heads and many others.
To prepare workpiece surfaces for marking, use auxiliary materials. The workpieces are cleaned from dust, dirt, rust, scale and oil with steel brushes, files, sandpaper, wiping ends, napkins, brushes, etc. In order for the marking marks to be clearly visible during subsequent processing, the cleaned surface is usually painted smooth and thin layer. The paint should adhere well to the surface, dry quickly and be easily removed. Untreated or roughly processed surfaces of steel and cast iron workpieces are painted with chalk dissolved in water with the addition of wood glue and turpentine (or linseed oil and drier). Pre-treated surfaces are coated with a solution of copper sulfate. Treated surfaces large sizes and aluminum alloys are coated with a special marking varnish. For this purpose, you can use a solution of shellac in alcohol, colored with fuchsin. Small surfaces are painted using cross movements of the brush. Large surfaces are spray painted. The painted surface is dried.
Sequence of work during marking. Marking includes three stages: preparation of blanks for marking; actual marking and marking quality control.
The preparation of the workpiece for marking is carried out as follows:
1. Carefully study and check the drawing of the part.
2. Preliminarily inspect the workpiece, identify defects (cracks, scratches, cavities), control its dimensions (they must be sufficient to produce a part of the required quality, but not excessive).
3. Clean the workpiece from dirt, oil, and traces of corrosion; paint and dry those surfaces of the workpiece on which the marking will be made.
4. Select the base surfaces from which the dimensions will be taken and prepare them. If the edge of the workpiece is chosen as the base, it is pre-aligned; if there are two mutually perpendicular surfaces, they are processed at a right angle. The base lines are applied already during the marking process. The location of the bases should ensure that the part fits into the contour of the workpiece with the smallest and uniform allowance.
The actual marking is performed in the sequence determined by the marking method. When marking according to a template, the latter is installed on the workpiece, correctly oriented relative to the bases, and secured. The template should fit tightly to the workpiece along the entire contour. Then they trace the outline of the template on the workpiece with a scriber and unfasten the template.
Marking using the geometric construction method is carried out as follows. First, all horizontal and then all vertical marking marks are drawn (relative to the base); then make all the fillets, circles and connect them with straight or inclined lines.
When marking, the surface gauge stand is taken by the base and moved along the marking plate relative to the surface of the workpiece, without allowing skewing. The surface scriber touches the vertical surface of the workpiece and leaves a horizontal mark on it. The scriber should be located under acute angle to the direction of movement, and the pressure on it should be small and uniform. The marks are drawn parallel to the working surface of the marking plate. In order for the marks to be strictly linear and horizontal, the supporting surfaces of the surface planer and the marking plate must be processed with great precision. The quality of marking improves if a flat scriber is used in the surface planer.
Quality control of markings and cores is The final stage markings. The centers of the cores must be located exactly along the marking marks; the cores should not be too deep and differ in size from each other. On straight lines, cores are punched at distances of 10-20 mm, on curved ones - 5-10 mm. The distances between the cores are the same. As the size of the workpiece increases, the distance between the cores also increases. The points of intersection and intersection of marking marks must be cored. On the processed surfaces of precision products, marking marks are not punched.
Marking defects can lead to significant material losses. Its most common causes are: incorrect choice of bases and their poor preparation; errors when reading the drawing, when setting aside dimensions and in calculations; incorrect choice marking tools, devices, their malfunction; incorrect marking methods and techniques.
The widespread use of mechanized marking tools and devices improves the quality and productivity of marking. Therefore, mechanical, electrical and pneumatic punches, calipers and gage gauges with electronic indication, and mechanized devices for installing, aligning and securing workpieces should be widely used. The use of microcalculators for calculations significantly speeds up work and reduces the number of errors. It is necessary to create more universal and easy-to-use marking tools and devices. Where it is economically justified, coordinate machines, coordinate measuring machines should be used for marking, or marking should be eliminated altogether by processing workpieces on CNC machines.
When processing metal or forgings, some of their surfaces are left black, while a layer of metal of a certain thickness is removed from others so that the processed surfaces have the shape and dimensions indicated in the drawing. Therefore, before starting processing, it is necessary to mark the parts.
Marking called the operation of transferring the necessary contour dimensions from the drawing onto the plane of the material or workpiece in order to carry out the necessary plumbing processes for final production products. There are plane and spatial markings.
Planar marking– this is the application of contour dimensions on the plane of the material from which the part will be made. For example, marking the cut of air ducts from sheet material, marking flanges, gaskets.
Spatial marking - this is the application contour lines on the plane of workpieces mated at different angles. For example, applying the required contours to a voluminous part blank made with excessive allowances.
In order for the contour lines applied to the marked surfaces of the workpiece to be clearly visible, these surfaces must be pre-painted.
Unprocessed or roughly processed planes of cast parts of forgings are first cleaned of dirt, residual molding soil, sand, scale, burrs and tides are cut off, and then painted with chalk, quick-drying paint or varnished.
For painting, crushed chalk is dissolved in water (125g of chalk per 1 liter of water) until thick as milk, boiled, and then a little linseed oil is added so that the chalk does not crumble, and a drier, which speeds up the drying of the paint.
A solution of copper sulfate (three teaspoons of sulfate per glass of water) or lump copper sulfate paint cleanly processed surfaces. Liquid solutions Apply a thin layer to the surface of the workpiece with a brush. Rub lump vitriol on the surface of the workpiece moistened with water. Marking is done after the paint has dried.
When producing workpieces, an allowance for processing is provided in advance.
Allowance- this is an increase in the size of the workpiece compared to the contour lines (marks) drawn exactly according to the drawing.
The allowance should be the smallest in order to save material, reduce time spent on processing the part and increase worker productivity. Marking is necessary to ensure the correct dimensions of the workpiece and allowances.
Planar marking
Marking work in plumbing are an auxiliary technological operation consisting in transferring contour constructions according to the dimensions of the drawing to the workpiece.
Marking– this is an operation of applying lines (marks) to the surface of the workpiece, defining the contours of the part being manufactured, which is part of some technological operations.
Planar marking used when processing sheet material and rolled profiles, as well as parts on which marking marks are applied in one plane.
Planar marking consists of applying contour lines to a material or workpiece: parallel and perpendicular, circles, arcs, angles, various geometric shapes according to given dimensions or contours according to templates. Contour lines are applied in the form of solid marks.
In order for traces of the marks to remain until the end of processing, small depressions are applied to the marks using a punch, close to one another, or a control mark is applied next to the marking mark. Risks must be subtle and clear.
Spatial marking- This is the application of marks on the surfaces of the workpiece, interconnected by mutual arrangement.
Planar markings are made on the workpiece using a scriber. Marking accuracy is achieved up to 0.5mm. Marking marks with a scriber are carried out once.
The depth of the core recess is 0.5 mm. When performing a practical task, the scriber and marking compass can be kept on a mechanic's workbench.
At the end of the work, it is necessary to remove dust and scale from the marking plate using a sweeping brush. When performing a practical task, you need to press the ruler against the workpiece with three fingers of your left hand so that there is no gap between it and the workpiece. When marking long marks (more than 150mm), the distance between the recesses should be 25..30mm. When marking short marks (less than 150mm), the distance between the indentations should be 10..15mm. Before setting the compass to the size of the arc radius, the center of the future arc must be marked. To set the compass to the size, you need to set one leg of the compass with its tip at the tenth division of the ruler, and the second at a division that exceeds the specified one by 10 mm. Angles less than 90º are measured with a goniometer using a square. When marking planarly, parallel marks are applied using a ruler and a square. When marking a circle of a given diameter on a plate, you need to install a compass to a size that exceeds the radius of the circle by 8..10mm.
The following tools are used to mark, measure and check the correct manufacture of products: ruler, square, compass, vernier caliper, caliper, bore gauge, scale and pattern ruler, protractor, scriber, center punch, marking plate. Templates, patterns, and stencils are used as devices that speed up the marking process.
Scriber should be convenient for drawing clear lines on the surface to be marked and, at the same time, not spoil the working planes of the ruler or square. The scribe material is selected depending on the properties of the surfaces being marked. For example, a brass scriber leaves a clearly visible mark on the surface of steel. When marking parts from more soft materials It is advisable to use a pencil. Before marking, it is better to apply a thin layer of water-based paint to the surface.
Center punches are used to mark the centers of circles and holes on marked surfaces. Cores are made of solid steel. The length of the center punch is from 90 to 150mm and the diameter is from 8 to 13mm.
As percussion instrument When making core recesses, a mechanic's hammer is used, which should be light in weight. Depending on how deep the core hole should be, hammers weighing from 50 to 200 grams are used.
Protractor steel with a protractor is used for marking and checking angles in the manufacture of mating pipe assemblies, fittings and other parts of air ducts.
Marking compass used for drawing circles, arcs and various geometric constructions, as well as for transferring dimensions from a ruler to a marking blank or vice versa. There are rack and pinion calipers, calipers, calipers, inside calipers, and vernier calipers.
Marking boards installed on special stands and cabinets with drawers for storing marking tools and accessories. Marking boards small size placed on tables. The working surfaces of the marking plate should not have significant deviations from the plane.
Various geometric shapes are applied to the plane using the same marking tool: ruler, square, compass and protractor. To speed up and simplify planar marking templates made of sheet steel are used for identical products.
A template is placed on the workpiece or material and pressed tightly so that it does not move during marking. Along the contour of the template, lines are drawn with a scribe, indicating the contours of the workpiece.
Large parts are marked on the plate, and small parts are marked in a vice. If the product is hollow, for example a flange, then a wooden plug is hammered into the hole and a metal plate is fixed in the center of the plug, on which the center for the compass leg is marked with a center punch.
The flange is marked as follows. The surface of the workpiece is painted with chalk, the center is marked and circles are drawn with a compass: the outer contour, the contour of the hole and the center line along the centers of the holes for the bolts. Often the flanges are marked according to a template, and the holes are drilled according to the jig without marking.
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Drawing Basics
You already know that to make any product you need to know its structure, the shape and size of the parts, the material from which they are made, and how the parts are connected to each other. You can find out all this information from drawing, sketch or technical drawing.
Drawing
- This is a conventional image of a product, made according to certain rules using drawing tools.
The drawing shows several types of products. The views are performed based on how the product is viewed: from the front, from above or from the left (side).
The name of the product and parts, as well as information about the quantity and material of parts, is entered in a special table - specification.
Often the product is depicted enlarged or reduced in comparison with the original. But despite this, the dimensions shown in the drawing are actual.
The number that shows how many times the actual dimensions are reduced or increased is called scale
.
The scale cannot be arbitrary. For example, for increase
accepted scale 2:1
, 4:1
etc., for decreasing
-1:2
, 1:4
etc.
For example, if the drawing contains the inscription “ M 1:2
", then this means that the image is half the size of the actual one, and if " M 4:1
", then four times more.
Often used in production sketch
- an image of an object, made by hand according to the same rules as a drawing, but without observing the exact scale. When drawing up a sketch, the relationship between the parts of the object is maintained.
Technical drawing - visual image item, made by hand using the same lines as the drawing, indicating the dimensions and material from which the product is made. It is built approximately, by eye, maintaining the relationships between the individual parts of the object.
The number of views in the drawing (sketch) should be such as to give a complete picture of the shape of the object.
There are certain rules for sizing. For a rectangular part, dimensions are applied as shown in the figure above.
Size
(in millimeters) are placed above the dimension line from left to right and from bottom to top. The name of the units of measurement is not indicated.
Part thickness
denoted by a Latin letter S; the number to the right of this letter shows the thickness of the part in millimeters.
Certain rules also apply to the designation on the drawing. hole diameter
- it is designated by the symbol Ø
.
Circle radii
denoted by a Latin letter R; the number to the right of this letter shows the radius of the circle in millimeters.
Part outline
must be shown on the drawing (sketch) solid thick main lines(visible contour lines); dimension lines
- solid thin; invisible contour lines
- dashed; axial
- dash-dot etc. The table shows Various types lines used in drawings.
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Read the drawing, sketch, technical drawing - means determining the name of the product, the scale and images of the views, the dimensions of the product and individual parts, their names and quantity, shape, location, material, type of connection.
Technical documentation and means of harmonization
Technical documentation for the manufacture of a simple single-part, multi-part or complex product includes:
image
finished product, specification and brief information about function ( F), structures ( TO), technologies ( T) and finishing (aesthetics) ( E) of this object of labor - the first sheet;
scheme
possible options changes overall dimensions and configuration of the product or its parts. The proposed changes are based on various systems of correlation and division of forms - the second sheet;
parts drawings
complex configuration that are made according to templates - the third sheet (not for all products);
illustrative technological map
, containing information about the sequence of manufacturing parts or the product itself in the form of operational drawings and about the tools and devices used to perform this operation - subsequent sheets. Their content may be partially changed. These changes relate mainly to the use of special technological devices that make it possible to speed up the execution of individual operations (marking, sawing, drilling, etc.) and obtain more quality parts and products.
Development of the design of any product, to appearance which certain aesthetic requirements are presented, is associated with the use of certain patterns, techniques and means of composition. Ignoring at least one of them leads to a significant violation of the form, making the product inexpressive and ugly.
The most commonly used means of harmonization are: proportioning(finding the harmonic relationship of the sides of the product), subordination and division of form.
Proportionality- this is the proportionality of elements, the most rational relationship of parts between themselves and the whole, giving the object harmonious integrity and artistic completeness. Proportions establish the harmonic measure of parts and the whole using mathematical relationships.
A system of rectangles with proportional aspect ratios can be constructed using:
A) integer ratios from 1 to 6 (1:2, 1:3, 1:4, 1:5, 1:6, 2:3, 3:4, 3:5, 4:5, 5:6) (Fig. 1) ;
b) the so-called “ golden ratio
" Determined by formula a: в=в:(а+в). Any segment can be proportionally divided into two unequal parts in this regard (Fig. 2). Based on this relationship, the sides of the rectangle can be constructed or divided (Fig. 3);
V) proportional series, composed of roots natural numbers: √2, √3, √4" √5. You can construct a system of rectangles of this series as follows: on the side of the square “1” and its diagonal “√2” - a rectangle with an aspect ratio of 1: √2; on the diagonal of the latter there is a new rectangle with an aspect ratio of 1: √3; then a rectangle - 1: √4 (two squares) and 1: √5 (Fig. 4).
To find the harmonic aspect ratio, use the system subordination and division of form:
A) subordination it is used when another element is attached to one element, commensurate with the main part (Fig. 5);
b) dismemberment is used when it is necessary to break the main form into smaller elements (Fig. 6).
Below are options for changing the shape configuration of products and options for changing overall dimensions, which use the above harmonization rules.
Marking rectangular parts
Purpose and role of marking. The process of applying contour lines of a future workpiece to wood is called marking. Marking- one of the most important and labor-intensive operations, the implementation of which largely determines not only the quality of products, but also the cost of material and working time. Marking before sawing is called preliminary or marking of rough blanks.
In production, preliminary marking is carried out taking into account allowances for processing and drying. In training workshops, dried materials are processed, so allowances for shrinkage are not taken into account.
You should know that when processing dried workpieces, a surface with low roughness is obtained and high adhesive strength and finishing are achieved. Grinding allowances on one side the details of the planed surfaces are equal to 0.3 mm, and for parts whose surfaces are sawn, - no more than 0.8 mm. There are no allowances for planing fibreboards and plywood, since they are not planed.
Marking perform pencil using marking tools (measuring ruler, carpenter's square, surface planer, measuring rod, tape measure, caliper, etc.) in accordance with the drawing, sketch, technical drawing. General form Some marking tools are shown below.
Marking and measuring tools. As you already know, marking wood and wood materials perform various instruments, most of which are also used for measurements during the manufacturing process of parts: roulette- for measuring and marking lumber and timber; meter- for marking rough blanks; ruler- for measuring parts and workpieces; square- for measuring and drawing rectangular parts; erunok- for drawing and checking angles of 45° and 135° and when marking miter joints; fry- for drawing and checking various angles (the given angle is set using a protractor); thicknesser and bracket- for drawing parallel lines when processing edges or faces of workpieces; compass- for drawing arcs, circles and marking dimensions; calipers- to determine the diameter round holes; bore gauge- for measuring the diameter of holes.
From the accuracy of marking The quality of the product depends. Therefore, be careful when working. Try to mark in such a way that you get as many parts as possible from one workpiece.
Don't forget about allowance. Allowance
- layer of wood that is removed when processing the workpiece(when sawing, they usually give an allowance of up to 10 mm, when planing - up to 5 mm).
When marking a rectangular piece of plywood (Fig. A
) do this:
1. Choose base edge workpiece (if there is no such edge, then it should be cut along a previously applied ruler baseline).
2. A line is drawn along the square at right angles to the base edge (line) at a distance of approximately 10 mm from the end (Fig. b
)
3. From the drawn line along the ruler, mark the length of the part (Fig. V
).
4. A line is drawn along the square, limiting the length of the part (Fig. G
).
5. Using a ruler, mark the width of the part on both lines limiting the length of the part (Fig. d
).
6. Connect both obtained points (Fig. e
).
If the part is made from a board or block, then the markings are made from the most even and smooth faces and edges (if there are none, then the front faces and edges are first cut out). The front surfaces on the workpiece are marked with wavy lines.
Subsequent markup is done like this:
1. From the front edge, mark the width of the part and draw it with a pencil marking line(Fig. a).
2. The thicknesser rail is pulled out so that the distance from the tip of the pin to the block is equal to the thickness of the part (Fig. b).
3. Use a thickness gauge to mark the thickness of the part (Fig. c).
4. Mark the length of the part using a ruler and square (Fig. d).
Marking of a large number of identical parts or parts with a curved contour is carried out using special templates
. They are made in the form of plates having the same outline as the contour of the product.
You need to mark out the details with a simple and sharply sharpened pencil.
When marking, the template should be pressed tightly against the workpiece.
Wood product manufacturing process
In educational workshops they learn to make various products from lumber and plywood. Each of these products consists of individual parts joined together. Parts may have different shape. First they try to make flat rectangular parts. To do this, you need to choose the right workpiece (block, board, sheet of plywood), learn how to mark, plan, saw, and strip. After all the parts have been manufactured, the product is assembled and finished. Each of these stages of work is called operation .
Each operation is performed with a specific tool, often using devices . This is the name for devices that make work easier and make it better. Some devices help, for example, quickly and reliably fasten a part or workpiece, tools, others accurately mark and perform this or that operation without errors. It is also advisable to use devices when it is necessary to make a large number of identical parts. With one of the devices - a clamp carpentry workbench- you already know each other.
In the training workshop you will most often work on technological map , which indicates sequence of operations . Below is a technological map for making a kitchen board.
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Process charts used in production indicate all operations, their components, materials, equipment, tools, the time required to manufacture the product, and other necessary information. In school workshops they use simplified technological maps. They often use various graphic images of products (technical drawings, sketches, drawings).
The finished product will be of high quality if it meets the dimensions and requirements specified in the drawing.
To obtain a quality product, you must hold the tool correctly, maintain a working posture, perform all operations accurately, and constantly monitor yourself.
Not all machine parts have contours outlined by straight lines, like those discussed in previous chapters; many details represent flat surfaces, limited laterally curvilinear contours. In Fig. 222 shows parts with curved contours: wrench(Fig. 222, a), clamp (Fig. 222.6), cam for the automatic lathe (Fig. 222, c), engine connecting rod (Fig. 222, d).
The curvilinear contour shown in Fig. 222 parts consists of straight segments conjugated with curves or circular arcs various diameters, and can be obtained by milling on a conventional vertical milling or special copy milling machine.
Milling curved contours on a vertical milling machine it can be carried out: by marking by combining manual feeds, by marking using a round turntable and by copier.
Milling a curved contour using a combination of manual feeds. Milling by combining manual feeds means that a pre-marked workpiece (fixed either on the table) milling machine, either in a vice or in special device) are processed with an end mill, moving manual feed the table simultaneously in the longitudinal and transverse directions so that the cutter removes the metal layer in accordance with the marked curved contour.
Let's consider an example of milling along markings by combining manual feeds of the contour of the bar shown in Fig. 223.
Choosing a cutter. For milling we will select end mill, the diameter of which would allow us to obtain the rounding R = 18 mm required by the drawing. We take an end mill with a diameter of 36 mm with six teeth. The cutter material is high-speed steel.
Preparing for work. The bar is installed directly on the table of the vertical milling machine, securing it with clamps and bolts as shown in Fig. 224. A parallel backing is used to ensure that the cutter does not touch the work surface machine table.
During installation, care must be taken to ensure that chips or dirt do not get between the contacting surfaces of the machine table, backing and workpiece.
Setting up the machine for cutting mode. Since in our case the feed is carried out manually, we will take it equal to 0.08 mm/tooth, considering the cutting depth to be 5 mm. According to the table 211 of the “Handbook for Young Milling Operators” for these conditions the recommended cutting speed is 27 m/min and the corresponding number of cutter revolutions n = 240 rpm.
Let's select the closest speed available on the machine and set the gearbox dial to n = 235 rpm, which corresponds to a cutting speed of 26.6 m/min.
Contour milling. We will carry out milling with manual feed, following the markings, for which we will start processing from the area where there is the smallest allowance, or we will carry out the plunge gradually, over several passes, in order to avoid breakage of the cutter.
Milling is carried out by simultaneous feeding in the longitudinal and transverse directions, respectively, along the marking line. It is impossible to mill the contour completely in one pass, so first the curved contour is rough-milled, and then completely along the marking line, including the curves at the wide part of the plank.
Milling of a central groove 18 mm wide and 50 mm long is carried out using the method of milling a closed groove (see Fig. 202).
Curvilinear contours in the shape of a circular arc in combination with or without straight segments are processed on a round turntable (see Fig. 146 and 147).
When processing on a round rotary table, the arc contour is formed without combining two feeds as a result of the circular feed of the rotary table, and the accuracy of the contour here depends not on the ability to combine two feeds, but on correct installation preparations on the table.
Let's consider an example of milling a part, where the processing of the outer contour is combined with the processing of internal circular grooves.
Let it be necessary to process the contour template shown in Fig. 225.
The workpiece has the form of a rectangle measuring 210×260 mm, 12 mm thick. The workpiece is pre-drilled with a central hole with a diameter of 30 mm (for mounting it on a round table) and four auxiliary holes with a diameter of 30 mm (for milling). The outline of the part is marked on the workpiece.
Milling will be carried out on a vertical milling machine. Since external and internal contours are subject to processing, milling must be done in two settings:
1. Having secured the workpiece on the round table with bolts passed through any two holes on the workpiece, we mill the outer contour according to the markings, using the rotational movement of the round table (Fig. 226, a).
2. Having secured the workpiece on the round table with clamping strips, we mill the internal circular grooves according to the markings, using the rotational movement of the round table (Fig. 226,
Since it is desirable to process the outer contour and internal grooves without changing the cutter, we select an end mill from high speed steel with a diameter of 30 mm corresponding to the width of the circular groove.
Before installation round table it is necessary to place it on the edge and wipe its base. Then insert clamping bolts with nuts and washers into the grooves of the machine table on both sides and secure the round table with the bolts. To base the workpiece, you need to insert a centering pin with a diameter of 30 mm into the central hole of the round table.
We secure the workpiece with a centering pin and bolts during the first installation (Fig. 226, a) and with a centering pin and clamps during the second installation (Fig. 226, b).
Setting up the machine for milling mode. Select the cutting speed according to the table. 211 of the “Young Miller’s Handbook” for a cutter with a diameter of 30 mm and a feed for £tooth = 0.08 mm/tooth, with the greatest cutting depth t = 5 mm. Cutting speed v = 23.7 m/min and, accordingly, n = 250 rpm.
We set the machine to the nearest speed n = 235 rpm, which corresponds to the cutting speed v = 22.2 m/min, and begin processing the outer contour.
Having secured the end mill to the machine spindle, turn on the machine and bring the part to the cutter in the place where there is the smallest allowance (Fig. 226, a).
A rotating cutter is cut into the workpiece by hand feed to the marking line and, turning on the mechanical longitudinal feed, straight section 1-2 is milled (Fig. 225). At manual rotation round table, a curved section 2-3 of the outer contour is milled. After this, a straight section 3-4 of the outer contour is milled using mechanical longitudinal feed, and finally, a curved section 4-1 of the outer contour is milled again with manual rotation of the round table.
The workpiece for milling circular grooves is installed as shown in Fig. 226, b.
By rotating the handle of the vertical, longitudinal and transverse feeds, the cutter is brought in (see Fig. 226, b) and inserted into hole 5 (see Fig. 225). Then the table is raised, the table console is locked and the internal groove 5-6 is smoothly milled using a manual circular feed of the round table, slowly rotating the handwheel. At the end of the pass, lower the table to its original position and remove the cutter from the groove. By rotating the circular and vertical feed handles, insert the cutter into hole 7 and mill the internal groove 7-8 in the same way using a circular feed.
Copier milling. Milling of parts having a curved contour, curved grooves and other complex shapes can be done, as we have seen, either by combining two feeds, or by using a rotary round table; in these cases, preliminary marking is required.
When producing large batches of identical parts with a curved contour, use special copying devices, or use special copy milling machines.
The operating principle of copying devices is based on the use of longitudinal, transverse and arc feed of the machine table to impart a curvilinear movement to the workpiece, exactly corresponding to the contour of the finished part.
To automatically obtain this contour, copiers are used, i.e., templates that replace markings. In Fig. 227, b shows the milling of the contour of the large head of the engine connecting rod. Copier 1 is placed on part 2 and securely fastened to it. Acting with the circular feed handwheel of the round rotary table and the longitudinal and transverse feed handles, the milling operator ensures that the neck 3 of the end mill is constantly pressed against the surface of the copier 1.
copier processing,
The end mill used for is shown in Fig. 227, a.
In Fig. 228 diagram given copier for milling the contour of a large engine connecting rod head similar to that shown in Fig. 227, but using, in addition to the copier, a roller and a weight. Under the influence of load 1, roller 2 is always pressed to the copier 5, rigidly connected to the table of the copier 5, on which the connecting rod 4 being processed is fixed. The cutter 3 will describe a curved path corresponding to the contour of the large head of the connecting rod if, using a circular feed, we rotate the round rotary table .
