Standar Dan Perjanjian Tanda Untuk Garis

Garis dalam gambar teknik bukan sekedar menunjukkan geometri dari obyek, tetapijuga menunjukkan dimensi, posisi potongan dan penjelasan lain dari obyek. Sehinggadalam gambar teknik perlu diperhatikan penggunaan jenis garis yang sesuai.

Ketebalan Garis

Secara umum dalam gambar teknik diperlukan dua jenis ketebalan, yaitu garis tebaldan 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 yangterlihat dan garis-garis luar dari obyek.Garis tipis digunakan untuk arsiran, dimensi, proyeksi danpenjelasan 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 melewatipusat obyek (center lines). Garis simetri

Untuk menunjukkan detail-detail penting yang tersembunyi

Batas partial obyek.

Dimensi

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 denganelemen dari obyek yang diukur.

Secara umum, unit dari dimensi dapat tidak ditulis apabila penjelasan tentangunit dinyatakan secara eksplisit di dalam gambar dan dipergunakan secarakonsisten.

Semua dimensi yang lebih kecil dari satu (1) harus dituliskan angka nol sebelumkoma, seperti . .35 harus ditulis 0.35.

Teknik Penulisan Dimensi

Parallel dimensioning

Pada teknik inipengukuran dilakukanterhadap satu garisreferensi

SuperimposedRunning Dimensions

Teknik inimenyederhanakan teknikparallel dimensions untukmengurangi ruangpenulisan.

Chain Dimensioning

Teknik ini digunakanapabila efek dariakumulasi toleransi tidakberpengaruh banyak padafungsi dari obyek.

CombinedDimensions

Mengkombinasikan chaindan paralleldimensioning.

0 10 30 45 53 63 70

Dimensioning by Co-ordinates

Teknik ini menggunakanteknik SuperimposedRunning Dimensionsdalam dua arah. Umunyauntuk menunjukkan posisilubang atau baut.

Simplifieddimensioning by co-ordinates

Teknik inimenyederhanakan metodakoordinat denganmenggunakan simbol-simbol dan penjelasanmenggunakan tabel.

Pendimensian untuk Obyek Yang Kecil

Pendimensian pada area yang sempit dapat dilakukan dengan beberapa teknik sepertiterlihat dalam gambar di bawah ini.

Pendimensian untuk Lingkaran

All dimensions of circles are proceeded by this symbol; . There are severalconventions used for dimensioning circles:(a) shows two common methods of dimensioning a circle. One method dimensions thecircle between two lines projected from two diametrically opposite points. The secondmethod dimensions the circle internally.(b) is used when the circle is too small for the dimension to be easily read if it wasplaced 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 arrowwhich points directly towards the centre of the circle.

Pendimensian untuk Lubang

When dimensioning holes the method of manufacture is not specified unless theynecessary for the function of the product. The word hole doesn't have to be addedunless it is considered necessary. The depth of the hole is usually indicated if it is isn'tindicated on another view. The depth of the hole refers to the depth of the cylindricalportion 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 linesshould be drawn perpendicular to the radius so that the line passes through the centreof the arc. All dimensions should only have one arrowhead which should point to theline 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 onan engineering drawing. The accuracy depends largely on the manufacturing processused and the care taken to manufacture a product. A tolerance value shows themanufacturing department the maximum permissible variation from the dimension.Each dimension on a drawing must include a tolerance value. This can appear eitheras:

a general tolerance value applicable to several dimensions. i.e. a notespecifying 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 Britishstandards 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 forthe degree of accuracy intended from manufacturing, even if the value is limit is azero. 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 shouldbe written in capital letters to aid legibility. All lettering should be of the same sizeand 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 engineeringdrawing which although may not be useful now, will be useful when working inindustry.

All engineering drawings should feature an information box. An example is shownbelow.

Common information recorded on an engineering drawing

TITLEThe title of the drawing.

NAMEThe name of the person who produced the drawing. This is important forquality control so that problems with the drawing can be traced back to theirorigin.

CHECKEDIn many engineering firms, drawings are checked by a second person beforethey are sent to manufacture, so that any potential problems can be identifiedearly.

VERSIONMany drawings will get amended over the period of the parts life. Giving eachdrawing a version number helps people identify if they are using the mostrecent version of the drawing.

DATEThe date the drawing was created or amended on.

SCALEThe scale of the drawing. Large parts won't fit on paper so the scale provides aquick guide to the final size of the product.

PROJECTION SYSTEMThe projection system used to create the drawing should be identified to helppeople read the drawing. (Projection systems will be covered later).

COMPANY NAME

Many CAD drawings may be distributed outside the company so the companyname 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 4mmapart, 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 areasof 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 bereversed on adjacent parts. If more than two parts are adjacent, then the hatchingshould 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 thewalls can be filled in. This should only be used when the wall thickness size is lessthan 1mm

.

Hatching large areas

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

Gambar Potongan

Sections and sectional views are used to show hidden detail more clearly. They arecreated 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 cuttingplane. Visible outlines beyond the cutting plane are not drawn.A sectional view, displays the outline of the cutting plane and all visible outlineswhich can be seen beyond the cutting plane. The diagram below shows a sectionalview, and how a cutting plane works.

Orthographic projection

The aim of an engineering drawing is to convey all the necessary information of howto make the part to the manufacturing department. For most parts, the informationcannot be conveyed in a single view. Rather than using several sheets of paper withdifferent views of the part, several views can be combined on a single drawing usingone 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, architecturaldrawings, mechanical drawings, shop drawings, and electrical diagrams.

CONSTRUCTION DRAWINGS

A construction drawing is any drawing that furnishes the information required bythe craftsmen to rough in equipment or erect a structure. The terms working drawingsand 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 furtherinformation.

Working drawings show the size, quantity, location, and relationship of thebuilding parts. Generally, working drawings may be divided into three maincategories: 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 constructionwork.

Architectural Drawings

Architectural drawings consist of all the drawings that describe the structuralmembers of the building and their relationship to each other. This includesfoundation 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 theproject from above. Two types of plans will be discussed here: plot plans and floorplans.

PLOT PLANS.—A plot plan (also called a site plan) includes not only the projectbut 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 howthe land slopes before construction is started and the finished grade after constructionis 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 whenthe slope and grade of the surrounding area is to be changed and you have to burycable or conduit. You must know what the finished grade is and how deep to dig. Thistype of work requires close coordination between you, the Engineering Aids,Equipment Operators, and Builders. By looking over the plot plan, you will knowwhat 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 areequipped with a huge saw. If you sawed the building in half horizontally andlooked down on it from above, you would see the complete outline of thebuilding (view B).

This particular view directly above would be called a floor plan (view C). Architectsand engineers project their thoughts of a building, not yet built, onto a piece of paperand call it a floor plan. It does not matter that the heights of the outlets, appliances, orbuilding parts are different. These heights will be indicated by figures in inches orfeet, next to the symbols that represent them. Electrical construction drawings arefloor plans modified by the inclusion of electrical symbols.

Figure 2-11 shows an electrical layout superimposed on an outline taken froman architectural floor plan. The service line that brings power into the house is a three-wire line in 1 1/4-inch conduit. The service line feeds power by way of a serviceswitch to a lighting panel, from which three branch circuits run to the lighting fixturesand convenience outlets in the rooms. The symbols for these fixtures and outlets andthe service switch are shown at the bottom of figure 2-11. Elevations An elevation is adrawing that represents a view of the finished structure as you would see it from thefront, back, left, or right.

There are interior elevations, such as a view of a fireplace, as well as exteriorelevations, 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 viewsprovide the viewer with a finished appearance. Few dimensions are given onelevations. Only those vertical dimensions that cannot be shown on the plan aregenerally included on an elevation view.

A Construction Electrician can quickly see from any one of the elevations in figure 2-12 that there is an attic where easy access would be provided to electrical wiring. Thisis important where there is a requirement for junction boxes that must beaccessible. The electrician can also see a foundation wall where, if a service lateral isrequired, a conduit or sleeve must be placed (for a later run of conduit). Thisknowledge will allow the electrician to plan ahead to work with the Builders whenthey build the forms. The conduit will be placed in or through the form before theconcrete is poured.

MECHANICAL DRAWINGS.---Mechanical drawings include all drawings andnotes that have something to do with the water supply, sewage, drainage, heatingand ventilating, refrigeration, air conditioning, and gas supply systems. It may alsoinclude other drawings that are necessary to present the system properly in relation tothe other portions of the project.

Shop Drawings - Shop drawings are drawings and related data used to show someportion 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 themanufacturer to show a material, product, or system for some portion of thework. Engineering Aids are sometimes required to draft shop drawings for minorshop and field projects. These drawings may include shop items, such as doors,cabinets, and small portable buildings (prefabricated berthing quarters andmodifications of existing structures), or they may come from portions of designdrawings, 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 symbolsinto the product represented by the drawing.

ELECTRICAL DIAGRAMS-In addition to the construction drawings discussedabove, you will be working with other types of electrical drawings or diagrams. Thesedrawings show the arrangement and relationship of parts. Electrical diagrams areusually used to show how the parts of one or more pieces of equipment are wiredtogether. There are several types of these diagrams. They are similar, yet different insome way. The short description of each that follows should enable you to recognizetheir differences. Isometric Diagram The isometric diagram is not often seen inelectrical work. It may be used to show the electrical wiring system in multilevelbuildings. Appliances sometimes have an isometric diagram glued to an access panelso that it may be referred to for a quick look at an entire wiring system. (See fig. 2-13.)

BLOCK DIAGRAM.-- A block diagram is a simple drawing showing therelationships of major parts of a wiring circuit or system. Figure 2-14 shows a blockdiagram 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 ormore conductors or cables. Either major or minor components or parts may berepresented by blocks. This type of diagram is often used to show something ofthe relationship of components in a power distribution system. The block diagramprovides little help in troubleshooting.

Axonometric Projection

For objects which are fairly small in size and reasonably close to the observer weoften use a form of drawing known as axonometric projection. The word axonometricmeans 'measured axes'. Axonometric drawings often appear distorted because theyignore the foreshortening effects of perspective (foreshortening means the way thingsappear 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 andsloping parallel edges for all other sides. There are a number of axonometricdrawings.

ISOMETRIC PROJECTIONAn Isometric Projection is constructed from 3 axes created by dividing a circle into 3equal angles of 1200

DIMETRIC PROJECTIONA 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 usuallyaround 1050.

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

The three methods of projection described above have one corner of the object facingthe observer and none of the visible faces are their true shape.

OBLIQUE PROJECTIONOblique 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) andone half their true size, to avoid undue distortion.

PLANOMETRIC or PLAN OBLIQUEThis is similar to oblique in that the top surface is drawn true shape and size. It isusually 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, byfollowing the procedure shown below.

Difficult shapes can be drawn by starting with the box or crate that the finished objectwill fit into and then adding or removing the bits that are not required.

CIRCLES DRAWN IN AXONOMETRIC VIEWSA circle drawn on a sloping surface in axonometric projection will be drawn as anellipse. An ellipse is a circle turned through an angle. All the examples shown abovewere box shapes without any curved surfaces. In order to draw curved surfaces weneed to know how to draw ellipses.

If you draw a circle and rotate it slowly, it will become an ellipse. As it is turnedthrough 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 whichthe ellipse is being turned. The minor axis becomes smaller as the angle throughwhich the ellipse is turned approaches 900.

You can draw a cylinder using the technique shown on the right. The ellipses caneither be sketched freehand or drawn using an ellipse template.