Chapter-4 Aspects of Technical Drawing

Technical Drawing

Learning Objectives 1. Know the standard practices of technical drawing 2. Know the standard practices for dimensioning 3. Know the related AutoCAD commands for setting the electronic drawing sheet and plot the dimensioning

Size of Drawing Sheet (ISO A Series) Designation Dimensions in mm Dimensions in inches A0841 x x A1594 x x A2420 x x A3297 x x A4210 x x 8.27 A5149 x x 5.84 A6105 x x 4.13

A0 and A1 Sheet

A2 and A3 Sheet

A4 and A5 Sheet

Relative Size of ‘A’ Series

Oversize sheets are used when it is desirable to give extra protection to the drawing sheets to provide a binding or trimming margin. Table shows dimensions of oversize sheet. DesignationDimensions RA0860 mm x 1220 mm RA1610 mm x 860 mm RA2430 mm x 610 mm RA3305 mm x 430 mm RA4215 mm x 305 mm RA5153 mm x 215 mm Dimensions of oversize sheet

Drawing Formats Drawing format depends upon the size of views (2-D views or 3-D views). This also depends upon the user or company.

Drawing Formats (A3 Sheet with Landscape Mode) YCCE,NAGPUR

Drawing Formats (A3 Sheet with Portrait Mode) YCCE,NAGPUR

Setting limits for various sheet sizes Before starting your engineering drawing you should plan how you are going to make best use of the space of drawing sheet. Boundaries of a drawing sheet are set with the help of LIMITS and ZOOM command in AutoCAD. LIMITS and ZOOM command set the drawing area to match the particular size of a drawing sheet.

Setting limits for various sheet sizes Command: LIMITS [Enter] ON / OFF / : [Enter] Upper right corner : 610, 430 [Enter] Command: ZOOM [Enter] All/Center/Dynamic/Extents/Previous/Scale(X/XP)/Window/ : A [Enter] The change in drawing limits brought by these two commands is not visible to the user. However, now the graphic screen is set to align new drawing limits. While drawing, user is always advised to zoom a particular portion of drawing to edit or draw the entities in drawing. This is because a normal monitor screen is used to accommodate a larger size drawing. Now, the AutoCAD unit is matched with drawing unit e.g. 1 AutoCAD unit = 1 mm. Accordingly, grids can be set on the background to produce drawings with a least count of 1 grid spacing = 1 mm.

Drawing Scale Objects are not always drawn to their actual size. They may be too large to fit a standard drawing sheet, or too small for all details to clearly show. For example, a microchip circuit must be drawn at several thousand times its actual size to be seen. On the other side, a plan view of a small town must be drawn with reduced scale than the actual size. This practice does not affect the dimensions of an object since the actual dimensions are shown on the drawing. A note for scale is placed on the drawing in a title block.

Drawing Scale Type of scaleRecommended scale Reduction scale 1:101:21:5 1:1001:201:50 1:10001:2001:500 1:100001:20001:5000 Enlargement scale 10:120:150:1 2:15:1 Full scale1:1

Drawing Scale In AutoCAD, the scale is set by a SCALE command. The normal drawing file or an individual object can be scaled to the defined scale. Command: SCALE [Enter] Select Objects: [select object] Select Objects: [Enter] Base point: [select appropriate] /Reference: (enter a scale value) [Enter]

Types of lines Line for an outline of view Projection line Hidden line Center line Line to indicate section plane

Example for Types of Dimension Lines

Basic Types of Dimensioning AutoCAD provides three basic modes of dimensioning: Linear Angular Radial

Linear Dimensioning Baseline OptionOrdinate Option

Angular Dimensioning

Radial Dimensioning Radial OptionDiameter Option

Title Block YCCE,NAGPUR