520 Part V: On a 3D Spree

Text and dimensions should go on their own layers. We discuss layers in Chapter 6.

An isometric view and an isometric projection are different. An isometric view is normally drawn so that lines that are parallel to the three principal axes appear in their true length, while an isometric projection foreshortens them due to the tilting and rotating of the viewing angle of the object. AutoCAD creates isometric projections.

If you really want an isometric view, the solution is simply to ignore our usual rule about drawing and inserting full size. When creating an isometric projection, use a scale factor of approximately 1.2247441227836356744839797834917, and you will get an isometric view. You can also edit the insertion later to make it match this scale factor.

A different point of view

You can apply two different types of editing to 2D views that were generated from 3D models.

First, you can edit the view specifications themselves. Start with the easy one. Select the base view, and then select the blue grip box that appears in the center of the view. Now drag and drop the view to a new location.

Interesting! If you move the base view, all the ortho views projected from it follow along, with some constraints. The ortho views don’t move in perfect unison as a single group, but they do maintain their orthographic relationship to the base view. Similarly, you can move projected ortho views in only the one direction that still maintains their ortho relationship to the base view. Better yet, all (or at least hopefully all) the attached dimensions also follow along.

You can also double-click a view and then change pretty much all the specifications that were used to create it. We did this in Step 9 (in the earlier step list) when we changed the isometric view to a shaded representation.

Now we come to the magic of creating 2D views from a 3D model. Go back into model space and edit the model. For example, add a second hole (hint: subtract a cylinder), extend the length of the peg, and then return to the paper space layout. Presto! Figure 23-5 shows how all your views and their dimensions have updated!

AutoCAD creates the views as a series of anonymous blocks. They behave much like regular blocks, but they don’t have a normal name, and so you can’t access them directly to edit or explode them. We discuss blocks in Chapter 17.

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Figure 23-5: If anything changes then everything changes.

But wait! There’s more!

So far, we’ve just touched on the 3D-to-2D capabilities of AutoCAD, but hopefully, it has whetted your appetite for more. To fully cover the 3D capabilities of AutoCAD would easily require a full book on its own (AutoCAD 3D For Dummies, perhaps?), but meanwhile here are a few high spots:

Don’t want four views? If you don’t want four standard views, you can create only the base view and then change its scale factor to better suit the sheet size.

Need additional base views? If necessary, you can have more than one base view in a single layout. For example, one large drawing might show an assembly and its component parts.

Didn’t create enough views? Use the VIEWPROJ command to add more projected views later. They don’t have to project from the original base view, but can project from an existing projected view.

Don’t need a view any more? You can delete a view, even a base view, without affecting the other views except that doing so breaks the horizontal and vertical links between views that were projected from it.

No 3D model in your drawing? Earlier in this chapter, we used the VIEWBASE command to generate views from a 3D model that lived in model space of the current drawing. AutoCAD 2013 introduces new functionality that is so significant that it deserves more explanation, which we happily provide in the next section of this chapter.

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522 Part V: On a 3D Spree

AutoCAD’s top model

You generated 2D drawing views from a 3D model in the previous exercise. In that example there was already a 3D model in model space. If the VIEWBASE command cannot find a 3D model in your current drawing file, then it opens a standard file dialog box so you can browse for an Inventor part or assembly file.

Inventor is the Autodesk 3D parametric modeling software, primarily intended for the mechanical design field. It is fully parametric, in that dimensional constraints drive the profiles that define the solid features that comprise the parts that go into the assembly model that drives the 2D drawing views that Jack built. If you change a dimension on a 2D drawing of a part, everything updates all the way down the line.

The Inventor file isn’t inserted into the AutoCAD file. Instead, it is attached like an xref. (We cover xrefs and DWG files in Chapter 18.) VIEWBASE creates a 2D drawing view based on it, and additional views can be projected from the base view.

Now here’s the magic part. The AutoCAD drawing views are still linked back to the Inventor file so that any changes made to the Inventor file reflect down to the AutoCAD file, bringing it up-to-date.

Better yet, you can send the AutoCAD DWG file to a client or vendor without having to send the source Inventor file. The AutoCAD file contains only anonymous blocks for the 2D views, and has nothing in model space.

On the other hand, whenever the AutoCAD DWG file does have access to the Inventor file the AutoCAD drawing views will update and stay in step with any changes made to the Inventor model.

If VIEWBASE does find an AutoCAD solid in your part you can tell it to ignore it and to let you attach to an Inventor file instead. You can

have more than one base view in an AutoCAD drawing, so you can mix and match 2D drawing views. One or more base views can come from an internal AutoCAD 3D model, while others can be linked to external Inventor files.

If model space contains more than one solid, VIEWBASE allows you to switch back to model space, where you can select and unselect solids to appear in the base view. For example, you might have a model of a gearbox assembly consisting of many components. Separate views can be created, perhaps on several different layouts. One might show an outside view of the entire gearbox (which doesn’t need to include the internals such as the gears and bearings); another shows only the input shaft, gear, bearings, and seals; and another shows the output shaft and its related components.

The VIEWDETAIL command generates detail views at scales different from the parent view.

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The VIEWSECTION command has five options for creating section views: Full, Half, Offset, Aligned, and From Object. It creates section views based on existing views in the layout. The cutting plane line that it generates can be manipulated like any regular polyline, and the section view then updates accordingly.

But wait! There’s less!

AutoCAD has gone through several generations of tools to produce 2D views from 3D objects. Each generation generally got better. We list them here because they all still work, and you may encounter older drawings that were made by using them.

FLATSHOT: This produces a quick-and-dirty 2D view in model space. Basically, it just sets the Z axis coordinate to 0 (zero) of objects. It creates suitable new layers and then creates a block definition and inserts it.

•Pro: If you edit the model, you can run it again and redefine the block.

•Cons: It can’t create section views, and it takes some complex fiddling to get multiple views to face and align correctly.

SolView (Solid View), SolDraw (Solid Draw) SolProf (Solid Profile), and MVSetup (Multi-View Setup): This series of commands is used to create suitable layout viewports and then to generate appropriate 2D views into them. The views are created as anonymous blocks.

•Pros: They can produce simple cross-section views, and they are produced directly in layout viewports.

•Cons: The commands must be used in a specific order, and the views aren’t associative back to the model. If you edit the model, you have to delete the views and start over.

SectionPlane, LiveSection, SectionPlaneJog, and SectionPlaneToBlock:

This family of commands is used to create a series of blocks containing 2D views, much like FlatShot but with much more versatility and control.

•Pros: They can produce more-sophisticated cross sections, such as jogged section planes. If you change the model, the block definitions can be re-created to show the updated version.

•Cons: It takes some complex fiddling to get multiple views to face and align correctly.

All in all, the current family of commands that we use in this chapter is by far the best way of producing 2D drawings from 3D models.

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