Drawing the contours of the future product onto the workpiece. The marking is planar. Work order
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 the 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 copper sulfate. Treated surfaces of 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 markings 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 marking itself is performed in a 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 and 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. Risks are carried out in parallel work surface 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 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 of 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.
« MARKING BLANKETS
MADE OF THIN SHEET METAL AND WIRE »
Target: introduce students to marking blanks from thin sheet metal And
wires; instill skills rational use materials;
promote the development of technical thinking.
Lesson type: combined (mastering new knowledge, generalizing and systematizing what has been learned).
Teaching methods:oral questioning, story, demonstration of visual aids,
practical work.
Lesson progress:
I. Organizational and preparatory part.
Greeting the teacher, monitoring attendance, checking students' readiness for the lesson, communicating the topic and goals of the lesson.
II. Theoretical part.
1. Repetition of the material covered.
Questions:
- What operation is called editing?
- Why is it necessary to straighten a workpiece made of thin sheet metal or wire before marking?
- What tools and devices are used when editing?
- How can you straighten thick wire?
- How to straighten thin and soft wire?
- How is thin sheet metal straightened?
- Why can only thin metal sheets be straightened with a wooden smoothing block?
- How do you control the quality of straightening sheet metal and wire?
2. Presentation of new material.
The teacher accompanies his explanation by showing marking techniques.
Teacher's story plan:
- Marking the wire workpiece.
- Marking a workpiece made of thin sheet metal.
1. Marking the wire workpiece.
In order to manufacture any product, you need to accurately establish the processing boundaries, apply the contours of the future product in the form of lines and points to the surface of the workpiece in compliance with the drawing dimensions. This plumbing operation is called marking.
Marking the wire (determining places of bending or cutting) is done using a ruler and pencil. If, for example, you need to bend the wire at a distance of 50 mm from its edge, then apply a ruler to the piece of wire so that the zero mark of the ruler coincides with the beginning of the piece of wire. Then a 50 mm mark is found on the ruler and a line is made opposite it on the wire. This will be the fold point.
When marking the places where the wire is bent for the manufacture of any product from it, it is taken into account that for each bend of the wire at a right angle, a piece of wire equal to slightly more than half its thickness is additionally consumed.
For example, if a piece of aluminum wire is 200 mm long and 3 mm thick
bend in the middle at a right angle, and then measure the wire to the bend and
after it and add up these dimensions, it turns out that the length of the piece of wire is like
decreased. It will be about 198 mm, that is, 2 mm shorter than before
flexion.
When making a round ring from wire, it is important to know how to determine
the length of the wire to make a ring of the given size. Size
wire ring is usually determined by the size of its diameter. Magnitude
diameter is 3.14 times less than the circumference. Therefore, to determine
length of wire to make a round wire ring, size needed
the diameter of this ring multiplied by 3.14.
2. Marking a workpiece made of thin sheet metal.
Marking of a workpiece made of thin sheet metal is carried out in order to determine
places for cutting or bending sheet metal and workpiece processing boundaries
in the manufacture of products.
Marking points- cores - are small depressions. Lines,
applied during marking are called risks . Risks are main and auxiliary. The main risks indicate the processing boundaries. From the auxiliary marks, the dimensions for making the main marks are set aside.
Marks and cores are applied to the workpiece using special marking tools: scribers, marking compasses, center punches, as well as measuring rulers, bench squares and marking hammers.
Scriber is a sharpened steel rod and is used for
applying marks. Scribblers come in wire, turned, and bent
the end.
Marking compassused for drawing lines of circles and arcs on the metal surface. Unlike a conventional compass, both legs
marking tools have pointed ends.
Using a center punch When marking, small depressions, or cores, are obtained. These recesses are necessary to mark the centers of circles and arcs, as well as to more clearly indicate the marking marks, which may be erased during work.
When marking, metal measuring rulers are used to measure
workpiece dimensions and marking marks.
Squares also serve for making marking marks.
The square allows you to make lines strictly at right angles. The control of already completed corners of the workpiece is also checked with a square.
Marking hammerhit the punch striker when punching the centers of holes and marking marks.
Before marking, it is necessary to clean the workpiece from dust and dirt. The workpiece must be marked so that as little metal as possible goes to waste.
There are two types of marking: according to a template and according to a drawing (sketch).
Sample - this is a device in the form of a plate with the outlines of a part that
is being manufactured. The template is applied to the sheet of metal from which the product is made.
It is rational to mark using a template in cases where you need to mark a large number of parts. Position the template so that it all fits on the sheet. To use material economically, they try to find such a position for the template on the sheet so that when subsequently cutting the workpiece from the sheet, there will be as little waste and trimmings as possible. The template is then pressed tightly onto the sheet. To do this, you can use a clamp, just enough heavy object or just press with your hand. Without moving the template, trace its contours with a scriber, pressing its tip tightly against the edge of the template. Then, using a punch and a marking hammer, small indentations (cores) are made along the marking marks. To punch the marks, the tip of the punch is placed exactly on the mark with a slight inclination away from you. Before striking the striker, the punch is moved to a vertical position.
Hammers for punching are used small ones, weighing 100-150 g. The distance between the cores can be 5-10 mm or more. This depends on the length of the mark: the longer the length, the greater the indicated distance can be.
Marking according to the drawing consists of transferring the points and lines of the drawing from paper to a sheet of metal. In order to carry it out, you need to know how parts and products made of thin sheet metal are graphically depicted.
If the part does not have bends in the sheet from which it is made, such as an eyelet, then the image is given in only one view - from the front. The thickness of the part is indicated by an inscription like “Thickness. 0.5" or using an extension line with a shelf, where an inscription like "S 0.5" is given.
Often a product made of thin sheet metal is made by bending its individual parts. This is, for example, a box for fasteners.
In this case, the workpiece is marked according to the development drawing of this product, showing the shape and dimensions of the part before the bending operation is performed.
The bend points are shown by a dash-dot line with two dots. Construction of a product development drawing rectangular shape you should start with an image of the base of the rectangle. After this, draw the other sides adjacent to the base along the fold lines. Product development cylindrical is a rectangle, one side of which is equal to the circumference of its base, and the other to the height of the product. When starting to mark, the sheet of metal is carefully inspected, checking for rust, irregularities and distortions. If necessary, it is cleaned and straightened. Determine the possibility of manufacturing parts of the required dimensions from the sheet. To do this, compare the largest (overall) dimensions of the part with the dimensions of the sheet. It is necessary that the sheet sizes be several more sizes details. To make the marking lines more clearly visible, the metal surface is often coated with chalk paint or other solutions. Then the bases for marking are determined - lines or surfaces from which dimensions are set aside for applying other marking marks. In other words, the actual marking begins from the marking bases. Marking is usually done from the straightest edge of the sheet or from an auxiliary mark drawn in the middle of the workpiece.
When applying straight marks, the ruler or square is pressed tightly against the workpiece with the fingers of the left hand so that there is no gap. They take the scriber right hand, like a pencil, and, without interrupting the movement, draw the line required length. When making marks, the scriber is pressed tightly against the ruler or square, deflecting it at a small angle.
The magnitude of this slope cannot be changed during the risk, otherwise the risk will turn out to be a curve. If the part has holes and radius curves, then first mark and mark the centers of these holes or curved arcs. Then, using a compass solution equal to the radius of the circle or rounding, curved contour marks are drawn. To do this, the tip of one (fixed) leg of the compass is placed in the punched center and, lightly pressing both legs of the compass to the surface of the workpiece, an arc of a given length is drawn with the other (movable) leg. In this case, the compass is slightly tilted in the direction of movement.
In factories, parts marking is carried out by marking mechanics. The templates are made by the most highly qualified mechanics - toolmakers.
Practical part.
Practical work
“Marking blanks made of thin sheet metal and wire.”
1. Organization of the workplace.
Students complete the task each at their own workplace. To complete the work you will need: a workbench, a vice, a steel plate, a plumber's hammer, a mallet, a wooden block, pliers, a board with nails driven in, metal rod, planks, blanks made of thin sheet metal and wire.
2. Introductory briefing.
Exercise:
using the developed technological maps, mark
product blanks made of thin sheet metal and wire;
Safety regulations.
Must be observed general rules labor safety, work only
proper tool.
The scriber and marking compass should only be kept on the workbench, not placed in
robe pockets.
After using the scribers, you should put them on their sharply sharpened ends.
safety plugs.
To avoid injuring your hands, hand the scriber to a friend with the handle facing away from you, and
put on workplace- with the handle towards you.
3. Current briefing.
Students completing assignments independently. Current observations of the teacher, monitoring compliance with safety regulations, answering questions that arise during the work process, checking the correctness of assignments.
Possible errors:discrepancy between the dimensions of the marked workpiece and the dimensions in the drawing or sample of the manufactured part;
Reasons: inaccuracy measuring tool, non-compliance with marking techniques or inattentiveness of the worker;
inaccurate drawing;
drawing marks several times in the same place.
4. Final briefing.
Evaluation of student performance, selection best works; analysis of admitted
errors and analysis of the reasons that caused them; explanation of application possibilities
acquired knowledge, skills and abilities in socially useful work.
The final part.
1. Setting for the next lesson.
The next lesson will continue to introduce the technology of processing wire and thin sheet metal.
2. Homework
>>Technology: Marking of thin sheet metal and wire
In order to correctly manufacture a part, the contours of the future product in the form of lines and dots are applied to the surface of the workpiece in compliance with the drawing dimensions. This plumbing operation is called marking.
Marking is carried out using a metal scale ruler, a bench square, a scriber, a marking compass and a center punch (Fig. 65).
A mechanic's square (Fig. 65, b) is used for marking and checking right angles.
The scriber (Fig. 65, c) is a sharpened steel rod and is used to apply marks (lines) to the workpiece. Scribblers come in various designs.
The marking compass (Fig. 65, d) allows you to apply circles and arcs to the workpiece. To prevent the legs of the compass from sliding over the workpiece during marking, shallow holes are made in the centers of these circles using a center punch.
Before marking, it is necessary to clean the workpiece from dust and dirt. The workpiece must be marked so that as little metal as possible goes to waste.
Marking is carried out according to the drawing or template. Marking according to the drawing (sheet metal parts) begins from the smoothest edge of the workpiece. If all the edges are uneven, then draw a base line (mark) and further mark the part from it (Fig ()()).
When drawing lines, the scribe is tilted in the direction of movement and pressed tightly against the ruler (like a pencil when marking wood blanks). You should not move the scriber over the same place more than once, as this will widen the line and reduce the accuracy of the marking.
When drawing circles, the marking compass is also tilted in the direction of movement, applying the main force to the leg located in the center of the circle.
If it is necessary to produce not one, but several identical parts, then a template is used to mark them - a flat sample part. The template is pressed tightly to the workpiece with your hand or a clamp (Fig. 67) and traced along the contour with a scriber.
In factories, parts marking is carried out by marking mechanics. The templates are made by the most highly qualified mechanics - toolmakers. 
1. Do not put the scriber and marking compass in your robe pocket. They can only be kept on a workbench.
2. To avoid injuring your hands, hand the scriber to a friend with the handle facing away from you, and put it on the workplace with the handle facing you.
PRACTICAL WORK
Marking blanks of thin sheet metal and wire products
1. Having studied technological map, mark the blank body of the utility scoop.
2. Calculate the length of the door hook blank (see Fig. 59, c) and mark the location of the wire cut.
3. Using a template, mark the propeller (Fig. 68).
- Marking, bench square, scriber, marking compass, center punch, baseline, template, marker, tool maker.
1. What tools are used to mark metal workpieces?
2. What safety rules must be followed when marking?
3. What is the difference between marking metal blanks and marking wood blanks? What are their similarities?
4. Why is a baseline drawn?
5. For what purpose are templates used?
6. Name the profession of the workers who make the templates.
7. How to properly place a scriber, ruler, square, compass, workpiece, template on a workbench?
A.T. Tishchenko, P.S. Samorodsky, V.D. Simonenko, N.P. Shchipitsyn, Technology 5th grade
Submitted by readers from the website
Purpose, types, tools. Marking is the operation of applying marking lines to the workpiece being processed, defining the contours of the future part or places to be processed. Marking is carried out accurately and carefully, because due to errors made during marking, the manufactured part may turn out to be defective. It is also possible that an inaccurately cast rejected workpiece can be corrected by careful marking, redistributing the allowances for each marking surface. The error achieved at conventional methods markings is approximately 0.5 mm. With careful marking, it can be increased to hundredths of a millimeter.
Depending on the shape of the blanks and parts to be marked, planar and spatial markings are distinguished.
Planar marking is carried out on the surfaces of flat parts, on strip and sheet material and consists of applying contour parallel and perpendicular lines, circles, arcs, angles, axial lines, various geometric shapes according to given dimensions or contours of holes according to templates to the workpiece. Techniques planar marking it is impossible to mark even the simplest body if its surfaces are not straight; Thus, it is impossible to apply horizontal marks on the lateral surface of a body of rotation, perpendicular to its axis, since it is impossible to apply a marking tool in the form of a square or ruler to it and draw parallel lines.
Spatial marking is common in mechanical engineering. Difficulty spatial marking consists in the fact that it is necessary not only to mark individual surfaces of the part located in different planes and at different angles to each other, but to link the markings of these individual surfaces with each other.
To carry out marking, a plumber must be able to read a drawing well, know the structure and methods of using marking and measuring tools.
The scriber is a steel (made of steel grades U10 or U12) knurled rod, ending on both sides with hardened needles - straight and curved at an angle of 90°; the ends of the needles are pointed and sharpened. The thinner and harder the needle, the more accurate the markings. To apply marking marks on pre-treated surfaces, scribers made of soft materials(for example, for marking steel products use scribers made of brass rod). When applying marking marks, the scriber is pressed tightly against a ruler or template and, when moving, is tilted at an angle of 75-80° to the surface being marked; At the same angle, the scriber is tilted in the direction of movement. When making a mark, you should not change the inclination of the scriber. In order for the risk to turn out clean and correct, it needs to be carried out only once. The thinner the marking line, the higher the marking accuracy, so the scribers must be sharpened.
Rulers are used to draw straight lines on marked surfaces. When marking, you can use ordinary metal scale rulers. When using them, the mechanic must take into account the certain thickness of the ruler and the tip of the scriber and set the ruler in such a way that the drawn line is positioned without displacement. To ensure higher accuracy, it is recommended to use rulers with beveled working edges.
The marking punch is used for making small conical recesses on marking marks. This tool is a rod with a knurled or multifaceted side surface. The working part of the punch, with a length of 35-45 mm, is made in the form of a cone with an angle of about 10°; after hardening, its end is sharpened at an angle of 60°. The other end of the punch is blunt, drawn to a cone. During operation, the sharp end of the punch is installed in the middle of the marks or at the intersection points of the marks. Before striking, you need to tilt the punch slightly away from you for precise installation, and then, without moving it from the mark, place it stably perpendicular to the surface of the workpiece and strike with a hammer on its blunt end. In accordance with GOST 7213-72, core punches are manufactured from 110 to 160 mm in length with a middle part with a diameter of 8 to 18 mm. The core material is U7A steel according to GOST 1435-74; It is allowed to manufacture cores from steel grades U7, U8, U8A.
The squares have a wide shelf, making it convenient to draw lines on the marked surfaces and check the correct installation of the part on the plate. When using a regular flat bench square, it is impossible to draw perpendicular lines with a sufficient degree of accuracy. T-flange squares make it easy to draw lines perpendicular to one side of the marking board or the machined edge of a part.
Marking compasses are used for drawing circles and arcs on a marked workpiece, dividing segments and angles into parts, transferring dimensions, etc. Large circles are drawn with a marking caliper, which is designed as follows. A motor equipped with a fixed leg moves along a rod with a millimeter scale. The fixed leg needle moves up and down and is clamped with a screw. Therefore, using a marking caliper, you can draw circles from one center that lie in different vertical planes.
The center finder is used to determine the position of centers cylindrical parts or hole centers. When marking centers, the center finder is installed on the end of the part so that the strips connected at an angle touch the part, and draw a line along the ruler. Then, turning the part or the center finder 90°, make a second mark. The intersection of these marks determines the center of the end.
To mark a pipe section, a plumber needs to establish the final length that the pipe section should have after processing. A pipe section prepared for installation with threads cut on it when screwed into a shaped part or coupling fittings does not reach their middle, but enters them no more than the length of a short thread. Therefore, a distinction is made between the purely theoretical length of the product, measured along the length in kind or determined from the drawing between the centers of the fittings, and the actual length of the prepared part, taking into account the distances between the centers of the fittings and the turns internal threads, closest to these centers. When marking pipes for flanged connections, it is necessary to give allowance for the folded side or for the beading of the cut edge to the flange chamfer. Taking into account these considerations, pipes are marked and cut. To mechanize pipe marking, a special measuring device is used. It can process pipes with a nominal bore from 15 to 60 mm and lengths of measured sections from 40 to 5000 mm.
The main reasons for defects during marking. Marking is a responsible operation that requires special attention. It must be remembered that any mistake in marking leads to defects. In this case, the material will be damaged, and time spent on marking and processing the part will be lost. Defects can occur both due to the marker’s fault and for reasons beyond his control. The main reasons for marriage are summarized in the table below.
The main reasons for defects during marking
|
Marriage due to the marker's fault |
Defect due to reasons beyond the control of the marker |
|
Misreading the drawing |
Wrong drawing |
|
Wrong choice of bases |
Inaccuracy of the marking tool and marking plate |
|
Incorrect or inaccurate sizing |
Inaccuracy of the measuring instrument |
|
Incorrect use of tools and non-compliance with marking rules |
The base against which marking is being carried out has been processed incorrectly or inaccurately |
|
Carelessness when marking |
Performing planar marking consists of several stages:
- the workpiece is first inspected, checked to see if it has any defects (sinks, cracks, bubbles);
- The surface intended for marking is cleaned of scale and molding soil residues;
- remove irregularities from the part;
- paint the surface so that the marking lines are clearly visible during processing. Black ones, i.e. untreated, as well as roughly processed surfaces are painted with chalk, quick-drying paints or varnishes. Chalk (powder-shock) is diluted in water until the thickness of milk and a little linseed oil and drier are added to the resulting mass. It is not recommended to rub the marking surface with a piece of chalk, as the chalk quickly crumbles and the marking lines disappear. To paint cleanly treated surfaces, use: a solution of copper sulfate (two to three teaspoons per glass of water), which is applied to the surface with a brush or cloth; or lump vitriol, which is used to rub surfaces moistened with water. In both cases, the surface is covered with a thin and durable copper layer, on which the marking lines are clearly visible;
- determine the base from which risks will be applied. When flat marking, the bases can be the outer edges of flat parts (bottom, top or side), which are pre-aligned, strip and sheet material, as well as various lines applied to the surface, for example, center, middle, horizontal, vertical or inclined ;
- The marks are usually applied in the following order: first, all horizontal marks are drawn, then vertical ones, then inclined ones and, finally, circles, arcs and roundings.
Since the marks can be easily rubbed out with your hands during work and then they will become poorly visible, small depressions are filled along the lines of the marks with a center punch - cores, which should be divided in half by the mark. The distances between the punches are determined by eye. On long lines of simple outline, these distances are taken from 20 to 100 mm; on short lines, as well as in corners, bends or curves - from 5 to 10 mm. On the processed surfaces of precision products, cores are not made along the marking lines.
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Materials were sent by Glebov A.A. teacher of technology and labor training, MOU "Veselolopanskaya secondary school"
Lesson #39
Editing blanks made of thin sheet metal and wire. Marking.
Target: teach students techniques for straightening sheet metal and wire.
Equipment: mallet, straight stove, metal workbench, sheet metal and wire blanks, marking tools.
Lesson progress
I. Repetition of the material covered.
1. Conversation on the following issues:
“How are the center of a circle, diameter, and radius depicted in drawings?
"What is a sweep?
“What information does the process description contain?
2. Statement of the topic and purpose of the lesson.
II. Presentation of program material.
Illustrated story.
Teacher. Editing is a metalworking operation for leveling workpieces. (See Appendices, Fig. 55, 56.)
Thin sheets of metal are trimmed in two ways(see Appendices, Fig. 55):
1. with a mallet correct plate. In this case, the blows are applied from the edge of the sheet, gradually approaching the convexity;
2. by using wooden block(sheets up to 0.2 mm thick);
3. The foil is straightened using cotton swabs.
Wire straightening is carried out in several ways, depending on the thickness of the wire and the composition of the metal. (See Appendices, Fig. 56.)
Remember what is called markup. (Marking is drawing the contours of the future product onto the workpiece.)
The main marking tools are:
"scale ruler;
"metaller's square;
"scriber;
"marking compass;
"Kerner.(See Appendices, Fig. 57.)
The teacher explains to students the purpose of each tool and shows how to use marking tools.
Marking is carried out according to the drawing and template.
Marking according to the drawing begins with drawing a base line. Drawing lines with a scriber should only be done once. When drawing a circle with a compass, the main force should be concentrated on the leg located in the center of the circle.
Marking according to a template is carried out if it is necessary to make several identical products.
Templates are made at enterprises by tool makers.
When working with marking tool Some rules should be followed:
1. the scriber and compass should not be placed in the pocket of the robe;
2 .When passing tools, you must hold them with the handle away from you.
III. Practical work.
Completing tasks:
1. Select a blank for making jaws for a bench vice.
2. Edit the selected workpiece.
3. Mark the mouthpieces.
VI. Lesson summary.
1. Grade practical work students.
2 .Analysis of mistakes made when performing practical work.
