SolidWorks 2011 Parts Bible - Matt Lombard [96]
Construction geometry is useful for many different types of situations. I use it frequently for reference sketch data. You can make sketch relations to construction geometry and can use it for layout sketches or many other purposes limited mainly by your needs and imagination.
Sketching in 3D
The 3D sketch is an important tool for creating weldments (and many other features) in SolidWorks. Structural frames are a large part of the work that is typically done using weldment functionality in SolidWorks, and frames are most often represented as 3D wireframes. You can do this with a combination of 2D sketches on different planes, with a single 3D sketch, or with a combination of 2D and 3D sketches. If you have confidence in your ability to use 3D sketches, then that is the best way to go. Three-dimensional sketches can be challenging, but they are certainly manageable if you know what to expect from them.
Earlier chapters discuss the tools that are available for 3D sketches; this chapter covers techniques for 3D sketching.
Navigating in space
When drawing a line in a 3D sketch, the cursor and Origin initially look like those shown in Figure 6.15. The large red Origin is called the space handle, with the red legs indicating the active sketching plane. Any sketch entities that you draw lie on this plane. The cursor also indicates the plane to which the active sketching plane is parallel. The XY graphic shown in Figure 6.15 does not mean that the sketch is going to be on the XY plane, just parallel to it.
FIGURE 6.15
The space handle and the 3D sketch cursor
Pressing the Tab key causes the active sketching plane to toggle between XY, YZ, and ZX. The active sketching plane indication does not create any sketch relations; it just lets you know the orientation of the sketch entities that are being placed. If you want to create a skew line that is not parallel to any standard plane, you can do this by sketching to available endpoints, vertices, Origins, and so on. If there are not any entities to snap to, then you need to accept the planar placement, turn off the sketch tool, rotate the view, and move one end of the sketch entity.
An excellent tool to help you visualize what is happening in a 3D sketch is the Four Viewport view. This divides the screen into four quadrants, displaying the Front, Top, and Right views in addition to the trimetric or isometric view. You can sketch in any of the viewports, and the sketch updates live in all of the viewports simultaneously. This arrangement is shown in Figure 6.16. You can easily access the divided viewport screen by using buttons on the Standard Views toolbar. You can also manually split the screen by using the splitter bars at the lower-left and upper-right ends of the scroll bar areas around the graphics window. These window elements are also described in Chapter 2.
When unconstrained entities in a 3D sketch are moved, they move in the plane of the screen. This can lead to unexpected results when viewing something at an angle, moving it, and then rotating the view, which shows that it has shot off into deep interplanetary space. This is another reason for using the Four Viewport view, which enables you to see what is going on from all points of view at once.
FIGURE 6.16
The Four Viewport view
Exploring sketch relations in 3D sketches
Sketch relations in 3D sketches are not exactly the same as in 2D sketches. Improvements have been made in the past several versions, but 3D sketches still lack some important bits of functionality. Pierce is not applicable in a 3D sketch, and is replaced by Coincident, because in 3D sketches there is no difference between Pierce and Coincident. Relations are not projected into a plane in a 3D sketch the way they are in 2D.
On the other hand, several other