TurboCAD: A Solid Performer

IMSI's TurboCAD Professional is in the same price range as Autodesk's AutoCAD LT, yet the former's capabilities for constructing 3D solid-models exceed those of AutoCAD itself. This month, we will first compare TurboCAD's solid-modeling capabilities with those of AutoCAD, and then we will explore TurboCAD's interface.

TurboCAD runs on computers with a Pentium or Pentium-equivalent microprocessor and Windows 95, 98, Me, XP, 2000, or NT 4.0 operating system. For more information about TurboCAD visit www.turbocad.com; IMSI also offers a standard version of TurboCAD, priced at $99.95, which does not have 3D solid-modeling capabilities. TurboCAD Professional, priced at $499.95, contains the ACIS V6 solid-modeling engine, and this is the version we will look at. You can download a 15-day trial-copy of TurboCAD Pro from the company's Web site.

TurboCAD Versus AutoCAD
Even though (and perhaps because) the price of TurboCAD is less than one-sixth the cost of AutoCAD 2002, it is interesting to compare the solid-modeling capabilities of these two programs. In making such a comparison, one must consider five areas: visualization tools, tools for drawing in 3D space, solid-geometry creation capabilities, modification tools for solids, and editing tools for solids.

• Visualization Tools. Because you must view the 3D objects you create on a 2D computer screen, their shapes and forms as well as the results of the last operation you performed are not always obvious. AutoCAD has a rich set of visualization tools. You can view and work with your model in both hidden-line mode (in which surfaces are opaque) and shaded mode (in which surfaces are colored and their relative brightness varies according to their angle to the light source). AutoCAD also has excellent tools for examining your model, including real-time viewpoint rotations, zooms, and pans--regardless of the viewing mode. The visualization tools of TurboCAD, on the other hand, are limited. TurboCAD does support hidden-line and rendered-viewing modes, but you cannot work in those modes. TurboCAD also has tools for real-time view-direction rotation and pans, but not for zooms. Furthermore, controlling view-direction rotation can be tricky, and the image tends to flicker or move slowly when your model is complex.
• Tools for Drawing in 3D Space. Much of 3D modeling involves drawing 2D objects, often called profiles, which you ultimately transform into 3D objects. Unlike 2D drafting, though, in which you do all of your drawing on the same plane, you must frequently move and orient the drawing plane in 3D space as you draw these objects. AutoCAD and TurboCAD have the same basic tools for moving and orienting the drawing plane (which TurboCAD refers to as the Work Plane), and both programs allow you to name a particular drawing plane and to restore it by specifying its name. TurboCAD, though, can have only one drawing plane in effect at a time. AutoCAD, on the other hand, permits you to have drawing planes that are positioned and oriented differently in each viewport.
• Solid Geometry Capabilities. Both TurboCAD and AutoCAD support a set of basic, or primitive, 3D solid shapes. AutoCAD has six primitive solid shapes: box, cone, cylinder, sphere, torus, and wedge. TurboCAD has these same six primitives, with a few differences--its cone can be truncated and its torus primitive has an option for creating a helix-shaped spring-like solid, but its cylinder cannot have an elliptical cross-section. TurboCAD also has a polygon-prism primitive with a user-specified number of sides.

Figure 1. This solid model of a wheel fork was made with TurboCAD's lofting tool. 1a shows the model in its wireframe mode to give you a look at the profiles the loft is based on; 1b shows a rendered view of the model. AutoCAD does not have the capability to make this model.

In addition to the primitives, both TurboCAD and AutoCAD can create a 3D solid by pushing, or extruding, a closed 2D object that represents the profile of the solid through space and by revolving a closed 2D object about an axis. Unlike TurboCAD, AutoCAD can also create extrusions having a taper, which is useful for modeling objects to be manufactured by casting or molding processes. Both programs support extrusion along a path, but except for 3D polylines (which can only have straight sections) the path must be a 2D object. TurboCAD has two tools for creating profile-based solids unavailable in AutoCAD. One is the Prism tool, which creates a solid between two closed 2D objects that have similar shapes but lie on different planes. The other is the Loft tool, which creates a solid between two or more closed 2D objects that lie on different planes. The TurboCAD lofting tools used to create the model of a wheel fork, shown in Figure 1, are beyond AutoCAD's capabilities.

• Modification Tools for Solids. All solid modelers create complex models using Boolean operations on existing solids. The Boolean Add, or Union, operation combines existing solids; Subtract, or Difference, removes the volume that one solid has in common with another solid; and Intersect removes all unshared volume in a set of solids. Both AutoCAD and TurboCAD support these operations. Both programs also have tools to round, or blend, the sharp edges and corners of a solid, but TurboCAD offers more options, including one in which the radius increases linearly along the rounded edge. Both programs also support shelling, which hollows out an existing solid; and slicing, which cuts through an existing solid. TurboCAD, though, accepts a closed 2D object, such as a polyline, as a slicing object, which allows you to create multi-planar and even non-planar slices.
• Editing Tools for Solids. TurboCAD and AutoCAD take completely different approaches in editing solids. AutoCAD editing operations are generally done using the faces of a solid. For instance, you move a round hole within a solid by moving its cylindrical face, and you make the hole larger or smaller by offsetting its face. You can also delete the hole by deleting its face. TurboCAD, on the other hand, uses a variety of methods in editing solids. One is to change the properties of a solid, such as the direction or angle of revolution of a revolved solid. You can also change the shape of a solid by moving the vertices of its 2D-profile object. TurboCAD's Part Tree, shown in Figure 2, is another way to edit solids. The Part Tree shows all of the modification operations performed on a solid model, so you can select an operation from the tree for editing. Possible Part-Tree editing operations include moving, resizing, deleting primitives used in Boolean operations, changing the edge selection and the radius of rounded edges, and changing the thickness of shell operations.

Figure 2. You initiate most TurboCAD operations from either the menu bar or the toolbars, and then use right-click menus, the inspector bar, and the coordinate fields to select options and specify parameters for the operation. The Part Tree palette, shown here on the right side of the screen, is a convenient way to initiate editing operations on the components of a solid model.