3D AutoCAD 2010 for Starters and Others. . .

 

 

Saturday January 02, 2010

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3D Modeling in AutoCAD

 

Wire Frame, Surface Model and Solid Model are three basic kinds of 3D models of objects used when working with 3D models. You must first learn what they are, how they compare, and how to use them.   Working with and understanding Wire Frame and Surface Models will eventually become the real motivator for discovering the world of Solid Modeling.  You must also become familiar with the 3D workspace and drawing setup for efficient and economic use of AutoCAD’s command and techniques in model work.

 

In addition, viewing 3D models from different viewpoints and working in multiple viewports facilitates specifying points and distances in 3D.  Understanding the workings of viewpoints and viewports while working on real 3D projects will quickly show how helpful these tools are in 3D.   Without displaying different viewpoints, it is easy to get fooled, as snap points may look right but is in fact are farther away or closer in 3D space. 

 

Figure 1 Working in 3D requires an understanding of the use of wireframes and  surfaces and the movements of these objects in space.

A good understanding of the AutoCAD’s coordinate systems and conventions for entering 3D points and distances is also essential.  When drawing and editing 3D objects in AutoCAD you must constantly move or rotate the construction plane by defining a User Coordinate System (UCS) and your point of view. 

 

It is absolutely essential that you learn the basic use of wire frame and surface modeling first.  Life in 3D solid modeling will then be much easier.

 

Workplace Setting

Each time you start AutoCAD, you have the choice of opening the AutoCAD default template or select your own preferred drawing template and working in different workspaces.  You may choose to create and save your own 3D Starter drawing for your work.  You may select the AutoCAD 3D Modeling workspace option or create and save your own preferred My 3D Drafting workspace.   

1.   Use the QNew option and select the acad3D.dwt template drawing from the Select  template dialog box (STARTUP=0).

 

Figure 2 The Select template dialog box provides access to a select number of 3D AutoCAD templates including the acad3D.dwt template drawing.

  1. The acad3D.dwt template drawing displays a 3D modeling workspace in a SE Isometric view in a Perspective Projection view by default.  It displays the x-y plane of the current UCS on a ground plane with a gradient color as shown in Figure 3.  Colors can be set for major grid lines, minor grid lines, and axis lines. 

By default, you are in the Visual Styles called Ralistic Visual Style view. 

Figure 3 The acad.dwt template displays a 3D modeling workspace in a SE Isometric view by default.

  1. The acad3D.dwt template drawing displays a 3D modeling workspace in a SE Isometric view in a Perspective Projection view by default.  It displays the x-y plane of the current UCS on a ground plane with a gradient color as shown in Figure 3.  Colors can be set for major grid lines, minor grid lines, and axis lines.

    2.

  1. The UCS icon displays color coded X, Y and Z coordinates.   X is always red, Y is green and Z is always blue and should be memorized for quick recall.   An easy way to remember this XYZ display is by the RGB (red, green, blue) color designation used in color imaging work.

The cursor in 3D displays the same RGB color coordination lines as the UCS icon.  See Figure 3.  The shorter axes on the cursor indicate a negative direction.  Crosshair size is set to 30%.

 

 

 

 

 

 

 

Figure 4  With the grid displayed, objects drawn on the ground x-y plane like a sphere may display part of the object below the x-y plane.

 Workplace Tools

 When working in 3D you have a choice to work with the Menu Browser, menu bar, toolbars, palettes, ribbon or the Dashboard (2007/8 version). For developing working skills use the Ribbon, since it centralizes tools from frequently used toolbars as “an all-in-one” palette, the Menu Browser or traditional Menu Bar alternatively before settling  with your preferred method.

 

 

3D Coordinates

 When entering 3D coordinates, apply the guideline:  

·     2D coordinate entries or interactive mouse picks will ALWAYS select points on the x-y plane unless you use OSNAP, OTRACK, POLAR or FILTERS.    

·     3-D model objects are created in three-dimensional space with an additional Z-axis input that determines the placement of the 3D object in the 3D space (X, Y and Z).  The z-axis used for 3D objects points straight out of the screen towards the user when looking at the x-y plane in PLAN view. 

·     The LIST command can always be used to verify 3D coordinate entries. 

·     The five methods of command entry used in 2D construction are valid for 3D construction with the addition of the z-value. 

1.  Absolute coordinates x,y,z 

2.  Relative coordinates  @x,y,z 

3.  Polar coordinates = Cylindrical coordinates (Relative) with a provision for the third dimension.  @Dist.<angle, z  

4.  Picking Points (Interactive Coordinates) Pick 

5.  Direct-Distance Entry = valid in the current UCS 

·     In addition, 3D points may be entered using Spherical coordinates (Relative) using @Dist<angle<angle.  

3D Coordinate Entries Example

To place a LINE A-B in 3D workspace (phantom line) from coordinates Point A to Point B  using  the five different methods outlined above, you would follow the procedure as shown below.  See Figure 5.


 

Figure 5  Placing a LINE A-B in 3D workspace requires proper coordinate entries based on the given geometry.

1.  Using the Interactive method you would pick an existing Point A (enhanced by the corner of a 3D solid box) with OSNAP and then pick  another existing Point B (enhanced by the corner of another 3D solid box) with OSNAP. 

Point A is also the corner point of a 6x6 dashed rectangle shown and named SQUARE 1 in the x-y plane at elevation 0. 

Point B is also enhanced by a dashed rectangle shown and named SQUARE 2 in a plane 6 units above the x-y plane at elevation 6. 

2.   Use Absolute Coordinates entering 1,1,0 and then 7,7,6.  Line A-B ends at 7,7,6 directly above point 7,7,0 of the SQUARE 1 on a level 6 units above x-y plane identified by the upper left corner of SQUARE 2.

3.   Use Relative Coordinates by entering 1,1,0 and @6,6,6.

4.   Use Relative Cylindrical Coordinates by entering 1,1,0 and then @Diagonal Distance of Square 1(If known) <45,6. 

5.   Use Spherical Coordinates (Relative) @Line A-B Distance (If known) <45<35. 

  • To place the SQUARE1 on Level A the x-y plane, use the RECTANGLE command and enter 1,1,0 and then enter @6,6

 

  • To place the SQUARE 2 on Level B, an x-y plane 6 units above the current x-y plane, use the RECTANGLE  command and pick point B and then use direct distance to form the square on Level B.

 

  • Use the LIST command to verify entries.

 

With polar tracking (POLAR) or object snap tracking (OTRACK) points can be tracked in the Z direction as well as in the XY plane.   Similarly, when ORTHO mode is turned on, the cursor can be locked to the Z direction

 

 

 

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