INSTRUCTOR: THOMAS ARPASI REND LAKE COLLEGE CAD 1201-51 INTRODUCTION TO COMPUTER-AIDED DRAFTING ISOMETRIC DRAWING 1
Pictoral Drawing Pictoral drawing have evolved from cave paintings to photorealistic renderings throughout the course of history. However, their purpose remains the same: relay information properly. Today, they serve engineers by illustrating complex assemblies. Pictoral drawings are multidimensional drawings, showing all three dimensions in one view. Unlike orthographic drawings, which show flattened 2D views. Pictoral drawings are much easier to interpret than orthographic drawings, making them the correct choice for certain types of drawings. Usually, the end user is nontechnical personnel. They are even used to sell or showcase products and clarify assemblies. Think about all of the assembly instructions you have read. There is typically and exploded view shown. Also, the exploded view is arranged in order of assembly showing placement with centerlines. Pictoral drawings fall into 3 different categories (fig. 1.1): 1. Axonometric - Major characteristic is receding lines. Commonly used for engineering drawings. It will also typically show the top, front, and right side of the object. 3 Types of Axonometric Drawings: 1. Isometric - Most commonly used; Uses isometric axis consisting of 3 lines 120 apart (fig. 1.2). 2. Dimetric - 2 faces are equal, but only one recedes, similar to isometric. 3. Trimetric - All 3 axes share the same angle. Very time-consuming and difficult to dimension. 2. Oblique - Object is drawn from its nearest surface; front face is drawn to exact shape and size, easiest to draw. 2 Types of Oblique Drawings: 1. Cavalier - When the receding lines are drawn at full scale. 2. Cabinet - When the receding lines are drawn at half scale; for simple thin objects. 3. Perspective - Receding lines are distorted to show depth; similar to perception with the human eye. Used for presentation drawings. Drawing are constructed using a horizon line, viewing line, and one, two, or three vanishing points. Isometric drawings are by far, the most common of pictoral drawings. They are the easiest to dimension and detail. They show a false sense of 3 as well. The drawing is still 2D in nature, but gives the viewer more info than usual. AutoCAD also has many tools for creating isometric drawings. Mainly, because they show all axes at true length. The isometric axis responsible for deriving drawings. It consist of 3 axes that are 120 apart. The (X,Y) axes are 30 off of horizontal. This allows you to show the top, front, and right side view of a part all at once. However, it can be used for generating other views with common edges. All lines drawn parallel to the axes are isometric. You will have some lines that do not follow any axis, these lines are the non isometric lines used in the drawing. To enable AutoCAD to draw in this fashion, you could theoretically use polar snap, right? It will confine lines to a 30 angle, but AutoCAD has a more efficient setup. Up until this point, rectangular snap has been shown in class. There is also an isometric snap that forces lines to drawn 30 off of horizontal and also tabs between the 3 isometric planes. To turn on isometric snap, select Settings from the right click SNAP menu on the mode indicator in the Status Bar. From here (fig.1.3) Isometric Snap can be set as the snap type used. You will then notice your cursor become the isometric cursor. It will look oriented to the 30 lines and colored green for Y and red for X. AutoCAD will also allow you to tab or cycle through the orientation of the top, front, and right side faces of the bounding box of the object. This done by using the F5 function key. This tabs through the isoplanes or isometric planes. You will notice the cursor flip with the direction of the plane. The best tip offered here is to cycle through until you get what you need as far as drawing direction. The direct distance method works well with isometric drawing, but the offset command does not. The Fillet command is also not for use with isometric drawing. Holes, rounds, fillets, and arcs are all drawn using ellipses (fig. 1.4. 1.5). AutoCAD has special kind of ellipse for isometric drawings, it is called the isocircle. The command is only available when isosnap is turned on. It is a part of the ellipse command. Make sure to specify I after invoking the ELlipse command. It is very common to toggle back and forth between rectangular and isosnap. Remember to set it back to isosnap when drawing isocircles. The correct isoplane will need to chosen before-hand using the isoplane toggle (F5). Plotting points for an isocircle is usually necessary. Construction lines are free in AutoCAD, use them without regard, they can always be erased. Use of hidden lines should be avoided and the view that shows the least should be used. However, they can be used to describe critical areas when needed. Isometric drawing can become confusing, start by blocking in the overall size in a bounding box and work off of the 3 typical planes. Make sure Ortho is on when cycling through isoplanes. 2
AXONOMETRIC OBLIQUE PERSPECTIVE ISOMETRIC CAVALIER TWOPOINT 30 30 30-45 TRIMETRIC FULL SIZE 45 15 CABINET 30-45 DIMETRIC 15 ONEPOINT THREEPOINT HALF SIZE 15 Figure 1.1 - Types of Pictoral Drawings (Paul, Ross, Wallach) 120 120 120 Figure 1.2 - Isometric Axes (Paul, Ross, Wallach) Figure 1.3 - Snap Type in Settings Dialog Figure 1.4 - Isometric Fillets & Rounds - Placement of ellipses shown. (Paul, Ross, Wallach) Figure 1.5 - Alternate ways to show fillets and rounds. (Goetsch, Nelson, Chalk) 3
Isometric Sections When the inside of a part must be described in picture form, an isometric section is used (fig 1.6). There are three types: 1. Full Isometric Section - The cutting plane extends through across the entire width or height, leaving only half of an object. Commonly used on symmetrical parts. 2. Half Isometric Section - Shows only 1/4 of material cut away. 3. Broken-out Isometric Section - Used to show an object that may be difficult to interpret from a drawing. Only a selected section of material will be removed. Full Isometric Section Half Isometric Section Broken-out Isometric Section Figure 1.6 - Isometric Section Types (Goetsch, Nelson, Chalk) Isometric Exploded Views are ideal for showing assemblies. They can show part location as well as order of assembly. These types of drawings also allow for parts to be labeled clearly. Typically, a (BOM) or Bill of Materials is used. Center lines show placement of parts (fig. 1.7, 1.8). Figure 1.8 - Exploded View w/bom (Ross, Paul, Wallach) Figure 1.7 - Exploded View w/centerlines (Ross, Paul, Wallach) 4
Isometric Dimensioning Isometric dimensioning is not normally a part of isometric drawings. However, there are cases where a few types of isometric drawings rely heavily on dimensions. A piping drawing would be an example. Some simple mechanical drawings also include dimensions and notes or manufacturing specifications. Dimensions will follow the same axes as the drawn object. Dimensions can be aligned or unidirectional (fig. 1.9). I suggest using unidirectional to make them more clear. There is also a spin on unidirectional called vertical plane dimensioning. Oblique letters can be difficult to read on a crowded drawing. Dimensions are drawn much in the same way as they are orthographically. I suggest using aligned dimensions for all dimensions. These are the only associative dimensions that can be used on an isometric drawing except angular ones. Radius and diameter notes are simply drawn in using a leader line. Remember that isometric circles are ellipses which have two diameters; a major and a minor. This eliminates the use of circle dimensioning tools. The centermark command also becomes void and centermarks must be drawn in manually. To set text to an oblique angle, just create a style and specify an oblique angle in the style properties (fig. 1.10). Unidirectional Isometric Dimensioning Vertical Plane Isometric Dimensioning Aligned Isometric Dimensioning Figure 1.9 Isometric Dimensioning (Ross, Paul, Wallach) Figure 1.10 - Oblique Setting for Text Figure 1.11 - Oblique Text from the RIBBON After dimensions have been drawn, they can be obliqued using the DIMEDIT or DED commands. There is also an icon of the Annotation tab of the RIBBON (fig. 1.11). After the command is invoked, type O for oblique, select the objects and enter in the angle. 30 and -30 will common oblique angles for dimensions and text. You may find it handy to create a text style for each to use with dimensions. On the following page are a few guidelines for isometric dimensioning. These are just guidelines and do not cover all situations. 5
LEFT ISOPLANE - DIMENSION OBLIQUE - (-30 ) - TEXT OBLIQUE - (30º) TOP ISOPLANE - DIMENSION OBLIQUE - (30 ) - TEXT OBLIQUE - (30º) RIGHT ISOPLANE - DIMENSION OBLIQUE - (-30 ) - TEXT OBLIQUE - (-30º) Isometric Sketching Often, you may find it necessary to plan an isometric drawing or sketch it out. Using isometric grid paper may help you align the faces properly and give you a better sense of proportion. Sketches can be produced very quickly using the grid paper. Find the sample on the next page. The next time and isometric drawing stumps you, break out the sketch and plan. Nothing makes time in front of the PC more productive than planning. The information of this text can be acquired from the following sources. Ross, Paul, Wallach (2004). Fundamentals of Modern Drafting, Clifton Park, NY: Delmar Publishers, Inc. Goetsch, Nelson, Chalk (2000). Technical Drawing, Clifton Park, NY: Delmar Publishers, Inc. This file is designed to assist students in the process of acquiring skills in a course in Computer-Aided Drafting. This file is not meant to be the full extent necessary to master skills in CAD. It is an introductory course composed of many sections. This information is not endorsed by Autodesk in any form. This file may not be reproduced or copied in whole or in any part or form without written permission of the creator. 6
7