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Using 3D AutoCAD® Surfaces to Create

Composite Solids J.D. Mather – Pennsylvania College of Technology

GD211-2P This class explores the creation of 3D surfaces used in creating composite solids. Many

solid shapes can only be created by editing with surfaces. AutoCAD now includes powerful tools for

creating surfaces and using them in creating or editing solids. Examples appropriate for mechanical,

architectural, and civil engineering will be demonstrated.

About the Speaker:

Dr. Mather is an assistant professor of CAD and Product Design at Pennsylvania College of Technology

affiliate of Penn State University. He has taught AutoCAD courses for 13 years and has been an

Autodesk Inventor Certified Expert since release 7. His advanced 3D Modeling tutorials are studied by

users around the world.

http://home.pct.edu/~jmather/content/CAD238/AutoCAD_2007_Tutorials.htm

Previously he worked in industry for 15 years, including positions as Journeyman Machinist, Research &

Development Technician and Industrial Engineering Technician.

http://home.pct.edu/~jmather/AU2007/GD211-2P%20Mather.pdf

http://home.pct.edu/~jmather/AU2007/GD211-2P%20Dataset.zip

jmather@pct.edu

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Using 3D AutoCAD® Surfaces to Create Composite Solids

Session Objectives

Learn how to create and use planar surfaces for creating or editing solids.

Learn how to create Extruded, Revolved, Swept and Lofted surfaces for use in creating or editing solids.

Use surfaces with the Thicken Surface command to generate solids.

Use the Slice command as a more efficient method of creating fairly simple geometry.

Learn to use hybrid surface/solid modeling using the Slice command to create complex geometry.

Target Audience

Anyone who has used surfaces in earlier releases of AutoCAD and would like to

learn the new AutoCAD surfaces techniques, or who has particularly complex

geometry they need to create.

Introduction

AutoCAD now provides powerful surfacing tools to create complex composite solids. At one

time we were limited to prismatic geometric shapes like boxes, or cylinders and spheres and

whatever clever techniques we could devise to combine these primitive geometries to create

more complex geometry.

Often a solid geometry was not possible and we had to limit our design to surfaces. Surfaces

were difficult to edit and did not return valuable information such as volumetric data.

We can now use composite techniques using both surfaces and solids to generate complex

algorithmic or rules-based solid geometry.

There is no longer a need for a separate tool set for surfaces – we use the same tools for

surfaces or solids.

The 3D “virtual model” is a source of validation of the information to build the real world.

The Lesson

The real world isn’t flat.

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Prior Knowledge Expectations

For this class I will assume that you have attended the:

GD105-1P 3D AutoCAD® for All of Us

GD111-3P 3D Visualization and Solid Primitive Design

GD115-4P Using AutoCAD® for Sophisticated Solid Model Design

GD201-2P Editing 3D AutoCAD® Solids

classes…

or

…have some prior experience with the Dashboard in the 3D Modeling Workspace.

Layers control panel

3D Make control panel

Visual Style control panel

Light control panel

Materials control panel

Render control panel

3D Navigate control panel

2D Draw control panel

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Getting Started

We may use other tools in the 3D Make control panel but I am going to concentrate on the

following tools:

We will look at the surface creation/editing functionality of these tools.

Extrude Slice

Revolve Thicken

Sweep Convert to Solid

Loft Convert to Surface

Planar Surface

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Solids vs

Surfaces

(Or maybe I should say Solids &

Surfaces.)

If we exploded a cube we would

find that it is made up of 6

Surfaces. If we exploded it

again we would find that the

surfaces have a total of 24

edges.

Whenever we have surfaces that meet in

unambiguous “watertight” edges we can

create our geometry such that the edges

are combined and shared. The result is a

solid that represents a volume and can

easily be edited.

We refer to the Faces of the solid rather

than surfaces.

In our cube example we have 6 faces

with 12 edges.

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Extrude

If you run the List command on

the entities you will see that the

black entity is a polyline, the

red entity is a line, the green

entity is an arc and the cyan

entity is a spline. Although the

shape forms a closed area it is

not a closed polyline, boundary or region.

If we Extrude the entities we find

that the result is 4 independent

and infinitely thin surfaces

The old Surfaces toolbar is no longer listed. We could type in the old commands, like rulesurf,

but the surfaces created using the standard 3D Make tools with an open profile are much

easier to create and more powerful as well.

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Revolve

Again, with an open profile the

resulting feature when using the

Revolve tool will be a surface.

The Revolve surface

can be any angle up

to 360deg.

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Sweep

We have a variety of Sweep paths represented by lines, polylines, 2D splines and 3D splines.

Tip: If the Sweep fails try changing the UCS. Although the command should re-align the

profile I have had instances where changing the UCS will complete a swept feature that

otherwise fails.

Try with Twist 180 deg along the magenta line.

Try with Scale

Try with Alignment Yes/No.

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Loft

Like all of the surface features,

Loft of surfaces works

essentially the same as loft of

solids. There is no longer a

need for a separate set of

surface tools.

Create our open-profile cross-

sections and guides or a path

as needed and we are ready

to Loft surfaces.

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Planar Surface

For a Planar

Surface all we

need is a closed

area. Notice that it

isn’t necessary to

have a closed

polyline, boundary

or region.

We can select Objects to define the Planar Surface edges or if it is rectangular surface simply

click two points on the screen.

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Slice

This example is meant to be a simplified representation for calculating the volume of earth to be

removed from a mountainous terrain to get to a volume of coal.

Tip: I have had trouble in r2008 with the wrong side sometimes being retained. Simply undo

and Slice again, this time electing to keep both sides. Then delete the side you don’t want.

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Thicken

We can create a solid using any surface with the Thicken command. The surface can be

thickened to either side by changing the +/- value.

The only concern we have is the resulting solid cannot self-intersect.

Consider for example offsetting an arc. We cannot offset the arc

beyond its centerpoint. The self-intersection problem arises most often with Lofted surfaces

and might not be readily apparent where the intersection would occur.

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Using Surfaces – Example 1

Here is an example utilizing Thicken, Taper Faces, Fillet, Shell and Presspull.

Here’s a tip on Shell worth the

expense of attending AU – Shell in

2D wireframe for faster results rather

than while shaded. And have only

one modelspace viewport rather than

several tiled viewports.

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Using Surfaces – Example 2

The Slice command can be

used in conjunction with

surfaces to edit solids.

We can very quickly create

Planar Surfaces for Slice

by allowing the DUCS to set

our UCS on appropriate faces.

Notice that each member is highlighted as you are prompted to select which side to retain or

keep Both sides.

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Using Surfaces – Example 3

Using the new AutoCAD tools we’ve learned let’s simplify the design process of our hand tools.

As you watch think about, “How can these

techniques be used in your work?”

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Using Surfaces – Example 4

And for a little fun let’s model a toy car body.

All we need is a simple wireframe.

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And a few surfaces.

The real word is not flat.

By using a combination of the AutoCAD solid modeling and surface tools we can generate

composite designs.

Have you recognized any ways you use these techniques in your work?

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You might want to Rapid Prototype your parts. Use the STLOUT command to generate a stl

file. With a physical rapid prototype model you can verify much of your design before sending

the design to the manufacturing floor.

Tip: Facetres variable controls the stl resolution.

Tip: Your model must be in the positive xyz octant when using the stlout command you will get

an error.

If you run into a problem with your application of the techniques demonstrated in this class

simply send me an email

jmather@pct.edu