Technical Drawing Notes 1v2n1k

Standar Dan Perjanjian Tanda Untuk Garis Garis dalam gambar teknik bukan sekedar menunjukkan geometri dari obyek, tetapi juga menunjukkan dimensi, posisi potongan dan penjelasan lain dari obyek. Sehingga dalam gambar teknik perlu diperhatikan penggunaan jenis garis yang sesuai.

Ketebalan Garis Secara umum dalam gambar teknik diperlukan dua jenis ketebalan, yaitu garis tebal dan garis tipis. Tebal garis tipis, umumnya adalah setengah garis tebal. Garis sangat tebal untuk menunjukkan besi-besi tulangan (reinforcing bars), Garis tebal yang menerus digunakan untuk sisi-sisi yang terlihat dan garis-garis luar dari obyek. Garis tipis digunakan untuk arsiran, dimensi, proyeksi dan penjelasan lain dari obyek.

Jenis Garis Batas luar dari obyek. Perubahan bentuk geometri yang terlihat. Batas material yang berbeda. Arsiran. Garis tengah yang sangat pendek. Garis diagonal yang menunjukkan adanya void atau lubang.  Kontur      

 Digunakan untuk menunjukkan garis yang melewati pusat obyek (center lines).  Garis simetri Untuk menunjukkan detail-detail penting yang tersembunyi Batas partial obyek.

Dimensi  

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Dimensi harus menggunakan garis tipis yang menerus (continuous thin lines). Dua garis proyeksi menunjukkan posisi awal dan akhir dari dimensi. Dua garis proyeksi ini tidak boleh menyentuh obyek dan digambar tegaklurus dengan elemen dari obyek yang diukur. Secara umum, unit dari dimensi dapat tidak ditulis apabila penjelasan tentang unit dinyatakan secara eksplisit di dalam gambar dan dipergunakan secara konsisten. Semua dimensi yang lebih kecil dari satu (1) harus dituliskan angka nol sebelum koma, seperti . .35 harus ditulis 0.35.

Teknik Penulisan Dimensi

Parallel dimensioning Pada teknik ini pengukuran dilakukan terhadap satu garis referensi

Superimposed Running Dimensions Teknik ini menyederhanakan teknik parallel dimensions untuk mengurangi ruang penulisan.

Chain Dimensioning Teknik ini digunakan apabila efek dari akumulasi toleransi tidak berpengaruh banyak pada fungsi dari obyek.

Combined Dimensions Mengkombinasikan chain dan parallel dimensioning.

0

10

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45

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Dimensioning by Coordinates Teknik ini menggunakan teknik Superimposed Running Dimensions dalam dua arah. Umunya untuk menunjukkan posisi lubang atau baut.

Simplified dimensioning by coordinates Teknik ini menyederhanakan metoda koordinat dengan menggunakan simbolsimbol dan penjelasan menggunakan tabel.

Pendimensian untuk Obyek Yang Kecil Pendimensian pada area yang sempit dapat dilakukan dengan beberapa teknik seperti terlihat dalam gambar di bawah ini.

Pendimensian untuk Lingkaran All dimensions of circles are proceeded by this symbol; . There are several conventions used for dimensioning circles: (a) shows two common methods of dimensioning a circle. One method dimensions the circle between two lines projected from two diametrically opposite points. The second method dimensions the circle internally. (b) is used when the circle is too small for the dimension to be easily read if it was placed inside the circle. A leader line is used to display the dimension. (c) the final method is to dimension the circle from outside the circle using an arrow which points directly towards the centre of the circle.

Pendimensian untuk Lubang

When dimensioning holes the method of manufacture is not specified unless they necessary for the function of the product. The word hole doesn't have to be added unless it is considered necessary. The depth of the hole is usually indicated if it is isn't indicated on another view. The depth of the hole refers to the depth of the cylindrical portion of the hole and not the bit of the hole caused by the tip of the drip.

Dimensioning Radial All radial dimensions are proceeded by the capital R. All dimension arrows and lines should be drawn perpendicular to the radius so that the line es through the centre of the arc. All dimensions should only have one arrowhead which should point to the line being dimensioned. There are two methods for dimensioning radii. (a) shows a radius dimensioned with the centre of the radius located on the drawing. (b) shows how to dimension radii which do not need their centers locating.

Tolerancing It is not possible in practice to manufacture products to the exact figures displayed on an engineering drawing. The accuracy depends largely on the manufacturing process used and the care taken to manufacture a product. A tolerance value shows the manufacturing department the maximum permissible variation from the dimension. Each dimension on a drawing must include a tolerance value. This can appear either as:  

a general tolerance value applicable to several dimensions. i.e. a note specifying that the General Tolerance +/- 0.5 mm. or a tolerance specific to that dimension

The method of expressing a tolerance on a dimension as recommended by the British standards is shown below:

Note the larger size limit is placed above the lower limit. All tolerances should be expressed to the appropriate number to the decimal points for the degree of accuracy intended from manufacturing, even if the value is limit is a zero. For example. 44.80 should not be expressed as 44.8

Lettering All notes and dimensions should be clear and easy to read. In general all notes should be written in capital letters to aid legibility. All lettering should be of the same size and preferably no smaller than 3mm. An example typeface is shown below.

The layout of an engineering drawing It is important that you follow some simple rules when producing an engineering drawing which although may not be useful now, will be useful when working in industry. All engineering drawings should feature an information box. An example is shown below.

Common information recorded on an engineering drawing TITLE The title of the drawing. NAME The name of the person who produced the drawing. This is important for quality control so that problems with the drawing can be traced back to their origin. CHECKED In many engineering firms, drawings are checked by a second person before they are sent to manufacture, so that any potential problems can be identified early. VERSION Many drawings will get amended over the period of the parts life. Giving each drawing a version number helps people identify if they are using the most recent version of the drawing. DATE

The date the drawing was created or amended on.

SCALE The scale of the drawing. Large parts won't fit on paper so the scale provides a quick guide to the final size of the product. PROJECTION SYSTEM The projection system used to create the drawing should be identified to help people read the drawing. (Projection systems will be covered later). COMPANY NAME

Many CAD drawings may be distributed outside the company so the company name is usually added to identify the source.

Hatching On sections and sectional views solid area should be hatched to indicate this fact. Hatching is drawn with a thin continuous line, equally spaced (preferably about 4mm apart, though never less than 1mm) and preferably at an angle of 45 degrees.

Hatching a single object

When you are hatching an object, but the objects has areas that are separated, all areas of the object should be hatched in the same direction and with the same spacing.

Hatching Adjacent objects When hatching assembled parts, the direction of the hatching should ideally be reversed on adjacent parts. If more than two parts are adjacent, then the hatching should be staggered to emphasise the fact that these parts are separate.

Reverse hatching

Staggered Hatching

Hatching thin materials Sometimes, it is difficult to hatch very thin sections. To emphasise solid wall the walls can be filled in. This should only be used when the wall thickness size is less than 1mm

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Hatching large areas When hatching large areas in order to aid readabilty, the hatching can be limited to the area near the edges of the part.

Gambar Potongan Sections and sectional views are used to show hidden detail more clearly. They are created by using a cutting plane to cut the object. A section is a view of no thickness and shows the outline of the object at the cutting plane. Visible outlines beyond the cutting plane are not drawn. A sectional view, displays the outline of the cutting plane and all visible outlines which can be seen beyond the cutting plane. The diagram below shows a sectional view, and how a cutting plane works.

Orthographic projection The aim of an engineering drawing is to convey all the necessary information of how to make the part to the manufacturing department. For most parts, the information cannot be conveyed in a single view. Rather than using several sheets of paper with different views of the part, several views can be combined on a single drawing using one of the two available projection systems, first angle, and third angle projection.

First Projection

TYPES OF DRAWINGS AND DIAGRAMS The types of drawings to be discussed here include working drawings, architectural drawings, mechanical drawings, shop drawings, and electrical diagrams.

CONSTRUCTION DRAWINGS A construction drawing is any drawing that furnishes the information required by the craftsmen to rough in equipment or erect a structure. The working drawings and construction drawings are sometimes used interchangeably. Information presented in a set of working drawings, along with the specifications, should be complete so the craftsman who uses them will require no further information. Working drawings show the size, quantity, location, and relationship of the building parts. Generally, working drawings may be divided into three main categories: architectural, mechanical, and electrical.  Regardless of the category, working drawings serve several functions:  They provide a basis for making material, labor, and equipment estimates before construction starts.  They give instructions for construction, showing the sixes and location of the various parts.  They provide a means of coordination between the different ratings.  They complement the specifications; one source of information is incomplete without the other when drawings are used for construction work.

Architectural Drawings Architectural drawings consist of all the drawings that describe the structural of the building and their relationship to each other. This includes foundation plans, floor plans, framing plans, elevations, sections, details, schedules, and bills of materials.

Plans A plan is actually a part of the architectural drawing that represents a view of the project from above. Two types of plans will be discussed here: plot plans and floor plans. PLOT PLANS.—A plot plan (also called a site plan) includes not only the project but also the surrounding area. The project may be represented only by an outline. The grades at fixed points are shown throughout the area. This is done to show how the land slopes before construction is started and the finished grade after construction is completed. The north arrow symbol, used for orientation of the drawing, is shown. The Construction Electrician may have to have a plot plan to construct a pole line to

the project site at or near the earliest phase of construction. Another example is when the slope and grade of the surrounding area is to be changed and you have to bury cable or conduit. You must know what the finished grade is and how deep to dig. This type of work requires close coordination between you, the Engineering Aids, Equipment Operators, and Builders. By looking over the plot plan, you will know what to do to prepare for the job. FLOOR PLANS. .—Imagine that you want to know the outline of a building, including each partition.This building is shown in figure 2-10, view A, and you are equipped with a huge saw. If you sawed the building in half horizontally and looked down on it from above, you would see the complete outline of the building (view B). This particular view directly above would be called a floor plan (view C). Architects and engineers project their thoughts of a building, not yet built, onto a piece of paper and call it a floor plan. It does not matter that the heights of the outlets, appliances, or building parts are different. These heights will be indicated by figures in inches or feet, next to the symbols that represent them. Electrical construction drawings are floor plans modified by the inclusion of electrical symbols. Figure 2-11 shows an electrical layout superimposed on an outline taken from an architectural floor plan. The service line that brings power into the house is a threewire line in 1 1/4-inch conduit. The service line feeds power by way of a service switch to a lighting , from which three branch circuits run to the lighting fixtures and convenience outlets in the rooms. The symbols for these fixtures and outlets and the service switch are shown at the bottom of figure 2-11. Elevations An elevation is a drawing that represents a view of the finished structure as you would see it from the front, back, left, or right. There are interior elevations, such as a view of a fireplace, as well as exterior elevations, as shown in the elevations of a small building shown in figure 2-12. Doors, windows, shapes of roof, chimneys, and exterior materials are shown. These views provide the viewer with a finished appearance. Few dimensions are given on elevations. Only those vertical dimensions that cannot be shown on the plan are generally included on an elevation view. A Construction Electrician can quickly see from any one of the elevations in figure 212 that there is an attic where easy access would be provided to electrical wiring. This is important where there is a requirement for junction boxes that must be accessible. The electrician can also see a foundation wall where, if a service lateral is required, a conduit or sleeve must be placed (for a later run of conduit). This knowledge will allow the electrician to plan ahead to work with the Builders when they build the forms. The conduit will be placed in or through the form before the concrete is poured. MECHANICAL DRAWINGS.---Mechanical drawings include all drawings and notes that have something to do with the water supply, sewage, drainage, heating and ventilating, refrigeration, air conditioning, and gas supply systems. It may also include other drawings that are necessary to present the system properly in relation to the other portions of the project.

Shop Drawings - Shop drawings are drawings and related data used to show some portion of the work prepared by the construction contractor, manufacturer, distributor, or supplier. Product data, such as brochures, illustrations, standard schedules, performance charts, and other information, are furnished by the contractor or the manufacturer to show a material, product, or system for some portion of the work. Engineering Aids are sometimes required to draft shop drawings for minor shop and field projects. These drawings may include shop items, such as doors, cabinets, and small portable buildings (prefabricated berthing quarters and modifications of existing structures), or they may come from portions of design drawings, specifications, or freehand sketches given by the design engineer. Working from a shop drawing is much like working from other working drawings. You convert the ideas you get from your interpretation of the lines and symbols into the product represented by the drawing. ELECTRICAL DIAGRAMS-In addition to the construction drawings discussed above, you will be working with other types of electrical drawings or diagrams. These drawings show the arrangement and relationship of parts. Electrical diagrams are usually used to show how the parts of one or more pieces of equipment are wired together. There are several types of these diagrams. They are similar, yet different in some way. The short description of each that follows should enable you to recognize their differences. Isometric Diagram The isometric diagram is not often seen in electrical work. It may be used to show the electrical wiring system in multilevel buildings. Appliances sometimes have an isometric diagram glued to an access so that it may be referred to for a quick look at an entire wiring system. (See fig. 213.) BLOCK DIAGRAM.-- A block diagram is a simple drawing showing the relationships of major parts of a wiring circuit or system. Figure 2-14 shows a block diagram of a motor control system You can easily see how it gets its name. Sometimes the blocks are connected with only one line that may represent one or more conductors or cables. Either major or minor components or parts may be represented by blocks. This type of diagram is often used to show something of the relationship of components in a power distribution system. The block diagram provides little help in troubleshooting.

Axonometric Projection For objects which are fairly small in size and reasonably close to the observer we often use a form of drawing known as axonometric projection. The word axonometric means 'measured axes'. Axonometric drawings often appear distorted because they ignore the foreshortening effects of perspective (foreshortening means the way things appear to get smaller in both height and depth as they recede into the distance. All axonometric drawings use vertical lines for those lines representing height and sloping parallel edges for all other sides. There are a number of axonometric drawings. ISOMETRIC PROJECTION An Isometric Projection is constructed from 3 axes created by dividing a circle into 3 equal angles of 1200

DIMETRIC PROJECTION A Dimetric projection is created using 3 axes but only two of these have equal angles. The smaller these angles are the less we see of the top surface. The angle is usually around 1050.

TRIMETRIC PROJECTION A Trimetric projection is created using 3 axes where each of the angles between them is different (there are no equal angles)

The three methods of projection described above have one corner of the object facing the observer and none of the visible faces are their true shape. OBLIQUE PROJECTION Oblique projection is created by drawing one side of the object facing the observer. This side is always drawn as a true shape (in this case a square).

The receding lines are usually drawn at 450 (although other angles could be used) and one half their true size, to avoid undue distortion. PLANOMETRIC or PLAN OBLIQUE This is similar to oblique in that the top surface is drawn true shape and size. It is usually rotated so that the angles shown are 450 - 450 or 600 - 300.

'CRATING' 'Crating' is a means of drawing complicated shapes, by fitting them into a box or 'crate'. A crate or box can be drawn using any of the techniques shown above, by following the procedure shown below. Difficult shapes can be drawn by starting with the box or crate that the finished object will fit into and then adding or removing the bits that are not required. CIRCLES DRAWN IN AXONOMETRIC VIEWS A circle drawn on a sloping surface in axonometric projection will be drawn as an ellipse. An ellipse is a circle turned through an angle. All the examples shown above were box shapes without any curved surfaces. In order to draw curved surfaces we need to know how to draw ellipses. If you draw a circle and rotate it slowly, it will become an ellipse. As it is turned through 900 it will eventually become a straight line. An ellipse has a major axis and a minor axis. The major axis is the axis about which the ellipse is being turned. The minor axis becomes smaller as the angle through which the ellipse is turned approaches 900. You can draw a cylinder using the technique shown on the right. The ellipses can either be sketched freehand or drawn using an ellipse template.