AutoCAD 2007: So many solids! How do you choose?

When you get your hands on this new and exciting release of AutoCAD, one of the first things that you’ll probably want to do is start modeling! However, the first tools you choose to create your 3D solids, may not be the most efficient for your situation. Before AutoCAD 2007, how you created your solids wasn’t much of a concern because AutoCAD basically considered all solids to be created equal. They were virtual lumps of mass with minimal editing capabilities. That is no longer the case! In AutoCAD 2007, solids are not created equal. Some are considerably more flexible than others and the more you understand about solids editing, the better choices you will make when creating them!

Consider six different methods for creating a simple 3D solid. All six methods produce a single object type called 3DSOLID. However, the options for editing the resulting solids vary considerably.

In four of the six examples, I began by creating a box. In the first example, I selected the upper right edge of the box and dragged it to the right. In the second example, I used the SLICE command to cut and remove the part of the box that I no longer wanted. Both of these methods produced solids with minimal editing capabilities. If you select either of these solids, you get one grip whose only purpose is to move the solid. Fortunately, however, you can Ctrl-pick on any face, edge, or vertex to further edit the solid.

In the third and fourth examples, I created wedges in addition to the boxes and then used Boolean operations (Subtract or Union) to produce the final solids. At first glance, the resulting solids appear to be the same as those produced with the first two methods. Like the first two examples, selecting each of these solids displays only a single Move grip. However, if you press the Ctrl key and pass your cursor over these solids, the original primitive solids will highlight. If you pick one of these core primitives (Box or Wedge), you will have full editing control over that core object. You can use any of the grips as well as the Properties palette. In addition, you can Ctrl-Pick again to select a face, edge or vertex to further edit the primitive solid.

 

The fifth and sixth methods that I used to create the 3D solid didn’t include any primitive objects. Instead, I began with 2D profiles and then used the EXTRUDE and PRESSPULL commands to produce 3D solids. Selecting these objects displays multiple grips enabling you to stretch any of the vertices on their current plane and stretch the height along the vertical axis. You can also edit the height of these objects using the Properties palette. In addition, you can Ctrl-Pick on any face, edge or vertex for further editing.

Although I’ve focused on box- and wedge-shaped objects in these examples, the same principles apply to other shapes. For example, you might create a bottle or other circular object by revolving a 2D profile around an axis, lofting 2D profiles or by creating multiple primitives and then using UNION, SUBTRACT, and FILLET to create a composite solid.

So many ways to create solids, how do you choose which method to use? Well, I can’t guarantee that I have the right answer, but I can tell you what I do. I always consider primitives first. Primitives aren’t always the obvious solution and they don’t necessarily provide the fastest method for creating solids. However, they do provide the most flexibility and efficiency when it comes to editing. And we all know that editing is where you spend most of your time!

The first time I created the floors in my house model, I did the obvious. I used PRESSPULL to extrude the 2D profile. This method used existing geometry, was very fast and worked great.

However, when I wanted to add different floor materials to the various rooms, I needed to separate the large extruded solid into different objects.

I could accomplish this by using the SLICE command but, given the complicated shape of the various floor areas, I would have to slice and union many times and those sliced solids would have limited editing options.

Instead, I recreated the floors using a combination of boxes and wedges. It sounds like a lot of work, but it was actually very easy thanks to dynamic UCS and primitive grip editing. Now I have composite solids that I can easily manipulate moving forward. For example, if I want to move a wall or separate the existing floors into smaller areas, I can grip-edit the primitive sub-objects, erase existing ones or add new ones.

The best method for creating solids depends on your situation but I encourage you to consider using primitives. You might be surprised how handy they are!

Good luck and happy editing!