Overview of working in 3 dimensions

INTRODUCTION - WHY 3-D?You may have already figured out why CAD has many advantages over manual drafting. One big advantage is that once you've drawn something, you shouldn't have to draw it again. If you manually drew a house plan, you would have to draw a front elevation, side elevations, and possibly a perspective view. With one 3-D CAD model, you can generate views from any angle either inside or outside the house and animations. Afterwards, if your client needs something changed, you can then make the changes once. If you're drawing mechanical parts, you can generate virtual prototypes or even create rapid prototypes. In this manner Boeing was able to design and prototype the 777 jetliner. This level of engineering would be impossible without CAD.

Your company may not do a lot of 3D work, but it is still a good skill to have and it's also more fun than 2D.You'll be learning the 3-D concepts in the following order:

Isometric Drawings (not true 3D) Wire-frame (very basic 3D) Surfaces / Regions (primitive 3D) Solid Objects (advanced 3D)

Before entering the exciting world of 3-D, you'll have to learn some more CAD terminology. This level presumes that you have a good understanding of 2D commands.

3-D CAD TERMINOLOGY

2-D A concept of displaying real-world objects on a flat surface showing only height and width. This system uses only the X and Y axes.

3-D A way of displaying real-world object in a more natural way by adding depth to the height and width. This system uses the X Y and Z axes.

Boolean operations

Commands that allow you to add, subtract or intersect solid objects in AutoCAD.

Complex surface

Generally a curved surface. Examples: car fender, landscape contour.

Elevation The difference between an object being at zero on the Z-axis and the height that it is above zero.

Extrude The extrude command raises the shape of a 2D outline into a 3D solid. For example, a circle would be extruded into a cylinder.

Face The simplest true 3-D surface.

Facet A three or four sided polygon that represents a piece (or section) of a 3-D surface.

Hidden line removal

A way of hiding lines that would not be visible if you were viewing the actual object you have drawn in AutoCAD. (Command: HIDE)

Isometric Drawing

A simple way of achieving a '3-D' appearance using 2-D drawing methods.

Plan View Also known as the top view, a plan view looks directly down the WCS Z-axis to the X-Y axis.

Primitive A basic solid building block. Examples would be boxes, cones, cylinders.

Region A 2-D area consisting of lines, arcs, etc.

Rendering A complex way of adding photo-realistic qualities to a 3-D model you have created.

ShadingA quick way of adding color to a 3-D object you have drawn. (Command: SHADE)

Solid Model

A 3-D model creating using solid 'building blocks'. This is the most accurate way of representing real-world objects in CAD.

Surface Model

A 3-D model defined by surfaces. The surface consists of polygons. (See facets.)

Thickness A property of lines and other objects that gives them a 3-D like appearance.

UCS The user co-ordinate system. This is defined by the person drawing to have easier access to portions of a 3-D model.

View A particular view of the object you have created.

ViewportA window into your drawing showing a particular view. You can have several viewports on your screen. Different from the viewports used in plotting.

Wire-frame Model

A 3-D shape that is defined by lines and curves. A skeletal representation. Hidden line removal is not possible with this model.

Z-Axis The third axis that defines the depth.

Isometric drawing procedures

LESSON 3-2 - ISOMETRIC DRAWINGUsing Isometric commands is one of the simplest ways to give a 3-D representation while using only 2-D commands. This has been the usual way of doing things before CAD allowed true 3-D work to be done. Many times an isometric drawing is used to compliment or give more information to a 3 view orthographic drawing. See the sample below.

You can see that it is a very simple drawing. This basic isometric drawing of the object gives a very good idea of what it looks like. If this is all that is needed then isometric works well. Unfortunately, as soon as you change anything, like the block's height, you'll need to redraw all four views.AutoCAD has a command called ISOPLANE which allows you to easily draw at a 30 degree angle as needed for an isometric drawing. You can switch between the three 'isoplanes' (top, right, left) by using this command or by pressing the F5 key.Command: ISOPLANE <ENTER> Current isoplane: RightEnter isometric plane setting [Left/Top/Right] <Left>: T <ENTER>Current isoplane: TopBy invoking this command, AutoCAD is now set to draw on the top isoplane. Your other choices would be Left or Right. Your first exercise will be to draw the object shown above using isometric methods.Exercise 1 - ISOMETRIC DRAWINGBegin a new drawing using the acad.dwt templateCreate a layer called OBJECT and give it a green color. Make this your current layer.Type in DDRMODES to bring up the Drawing Aids dialog box. Make your settings the same as what you see below (just turn on Isometric Snap).

Press OK and you'll see that the grid is set up for isometric drawing for the left isoplane in 1/2" increments. Your crosshairs are now angled to show you which isoplane you are currently on and the Grid is laid out differently from what you may be used to..Begin by drawing the left side of the box (shown at the top of the lesson) using the line command. Ignore the hole at this point. You will want to use the Direct Distance Entry System for this exercise and make sure that you have Ortho (F8) and Osnaps (F3) turned on.Switch to your right isoplane (F5) and draw the right side.Switch to your top isoplane (F5) and draw the top view.Create the angle lines to add the angled surface.Switch back to the left isoplane and start the ELLIPSE command. At the command prompt, press I for isocircle. This will allow you to create an ellipse at the correct angle based on the radius of the circle in the orthographic drawing. Use the Osnap to pick the correct center point.Save your drawing in your CAD folder.To dimension an isometric drawing, you have to do a few things first. Create a text style called Left, and give it a 30o  obliquing angle, then create another called right with a -30o  obliquing angle. Then create a new dimension style that has the text aligned with the dimension line. After you have placed a dimension, use theDIMEDIT command to change the obliquing angle of the dimension + or - 30 degrees. You may also need to use the properties to change the text in the dimension to left or right depending upon the orientation of the dimension.Keep in mind that this is still only 2D. Remember that in some instances, it may be quicker and easier to use this method rather than the more complex 3-D methods you'll be learning in the following lessons.

3D Coordinate system | Rotation in 3DTHE 3-D CO-ORDINATE SYSTEMBy now you should be very comfortable working your way around the X-Y coordinate system. Anyway, here is a quick review. Looking

from the plan (top) view, this is what you see to figure out where is positive X and positive Y.

If you were to look at the same picture, but at a slight angle, you would see the third axis. This new axis is called the Z-axis. Imagine that the positive Z-axis is coming towards you out of the monitor.

The Z-axis has always been there, lurking in the background, waiting for you.When you entered points previously, you would enter them in the format: X,Y. By doing this, you let AutoCAD know that in these cases, Z was equal to zero. Entering 4,3 would be the same as entering 4,3,0. Now if you drew a line from the origin (0,0,0)

to a point at 4,3,2, you would get a line that goes 4 inches to the right, 3 inches up and 2 inches towards you. The properties of this line would be this:

Notice that the line is actually 5.3852" long. If you were to look at it from the plan view, it would look exactly like a line drawn from0,0 to 4,3 Draw a line from 0,0 to 4,3 and then compare the properties.The diagrams below, show this line from 4 different views to illustrate how things can look different in 3D. Look at each one carefully, and see if it makes sense to you.

This is the usual view you have seen when using AutoCAD in 2D. You are looking straight down the Z axis (positive Z is pointing at your). It looks like any other line you have drawn, going from 0,0 to 4,3 - but there is a difference...

If you were to look at the line from the front, instead of the top (as shown above) you would be able to notice the elevation of 2 units in the Z axis. This is the same line as above, only viewed from a different angle. In this view, you are looking straight down the -Y axis.

Just for fun, here is the same line but viewed from the left. This would be looking down the -X axis.

Finally, here is the line as viewed in 3D space from the Southeast view. This is where viewing 3D objects on a 2D monitor gets tricky. You need to visualize the Z Axis.

What the above images show you is that you will have to get used to looking at a 3D world on a 2D monitor. In each image, the black line looks flat, but you have to use your reference points to determine where it truly is. If you don't understand this perfectly right now, don't worry. It's just an exercise to expose you to 3D viewing. As the lessons progress, you will get much more familiar to this.Why is this important to look at before entering the world of 3-D? If you were to only look at a 3-D model from the plan (top) view, you would not be able to see any difference between the two lines. (Draw them and see for yourself) On a 3-D model, you can easily have many points over top of each other. This would be very difficult to work with. You may think you're snapping to a particular endpoint, but the reality of it could be very different (think of how the top of the wall looks the same as the bottom of the wall if you're looking straight down it). Fortunately, AutoCAD provides different viewing options for 3-D drafting. This will be discussed in a later lesson, but for now, if you want to see your 2 lines in a view similar the Z-Axis image above, go to your menu called View > 3D Views > SW Isometric. You'll see the lines that look identical in the top view, look very different when viewed from an angle.3D RotationNow for the confusing part. You already know how to rotate 2D objects, but you also have to know how AutoCAD measures angles of rotation in 3-D. There is a somewhat simple rule for this called "The Right Hand Rule". To figure out which is the positive rotation angle, imagine that you are wrapping your right hand around the axis with your thumb pointing towards the positive end. The direction that your fingers are wrapped is the positive direction. This applies to all three axes.

DIRECTION OF POSITIVE ROTATIONThe main point of this lesson is to tell you that objects can trick you in 3D space. Shortcuts don't always work, you have to be careful with Osnaps and your drawing can turn into a mess very quickly if you're not paying attention. Trust me, I've seen enough students take the easy route and have to start over. If you want to learn 3D, review each lesson before progressing. Make sure you know the concepts inside and out. This is just an introduction to the concepts, you will learn more in the following lessons. You may still want to refer back to this tutorial, though.