3D Solid Models have mass under their surfaces and you can cut openings and add or deduct material at will just like modeling from a solid wood block, Styrofoam piece or steel objects typically used in a workshop. Compared to wire frames and surface models, solid models are more closely related to the real “thing” and are easier to create.

3D Solid Models can be created from scratch or from basic 3D primitive sub-components called building blocks.  These primitives can then be combined, added and subtracted to create a more complex 3D object.  Such solids can be edited with grips.  In addition, holes, fillets and chamfers can be added to a 3D solid and so-called Boolean operations can be used to subtract, union and intersect 3D solid models. 

Solid Models can be rendered, analyzed and tested using mass, volume, moments of inertia and other properties using the MASSPROP command.

There are several different types of primitives or basic shapes used in 3D modeling.

·     3D Primitives such as BOX, WEDGE, CONE, SPHERE, CYLINDER, PYRAMID, TORUS and POLYSOLIDS.   These are the building blocks for 3D composite models.

·     3D Mesh Primitives such BOX, WEDGE, CONE, SPHERE, CYLINDER, PYRAMID, and TORUS .   These primitives can be worked into models using the AutoCAD free-from options and then converted into solid models. 

A 3D PRIMITIVE is a relatively simple shape that can be manipulated and combined with other primitives to construct composite 3D solid models.

3D Solid Primitives Overview

3D objects called solid Primitives are the simplest form of 3D solids. Primitives include boxes, wedges, cylinders, pyramids, cone, spheres and the torus.  See Figure 1.  Other shapes may be created from planar surfaces. 

Figure 1 Overview of AutoCAD’s solid primitives.

Example Polysolid

This command creates an extruded polyline with a preset height and preset width.  The Polysolid is drawn the same way you draw a polyline and by default, creates a solid rectangular profile like a building wall. 

Polysolid primitive shapes can be created directly from a line, 2D polyline, arc, or circle by using the Object option.  A polysolid can have curved segments, but the profile is always rectangular by default.  By default, when using the Object option with an arc, circle or rectangle, the polysolid is created as a center justified object.

When drawing a polysolid, you can use the Arc option to add arc segments to the polysolid.  You can use the Close option to close the solid between the first and last specified points to create a closed space.   

To create a polysolid, apply the following procedure: 

2.    At the: Polysolid Specify start point or [Object/Height/Width/Justify] <Object>: prompt, first select Height to verify the current height setting and check Width to verify the current width setting.  Then select a starting for the Polysolid.

The Justify option provides options for the profile to be left, right or center justified based on the starting direction of the first segment of the profile.

3.    At the:   Specify next point or [Arc/Undo]: prompt, select the next point. 

Figure 2 Polysolid objects interact when crossing other polysolids or other solids as if the other model does not exist.  They remain separate solids unless the UNION command is applied to join them into one composite solid.

Basic Editing 

To edit a polysolid, use grips that display to select the polysolid and perform similar editing functions with grips and other editing commands applicable to primitives.  

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