SolidWorks 2011 Assemblies Bible - Matt Lombard [166]
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 the viewports simultaneously. This arrangement is shown in Figure 20.2. You can easily access the divided viewport screen by clicking 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.
FIGURE 20.2
The Four Viewport view
When you move unconstrained entities in a 3D sketch, they move in the plane of the screen. You can use this to your advantage to create or edit lines in 3D space, but it can also lead to unexpected results. When you view the sketch at an angle, move it, and then rotate the view, you may notice that the sketch 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, thus avoiding any surprises.
Understanding 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 of SolidWorks, 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 relations are available in 3D sketches that are not found in 2D sketches, such as AlongX, AlongY, AlongZ (which act as replacements for horizontal and vertical), and OnSurface, for which there is no 2D equivalent.
Relations in 3D sketches are not projected as they are in 2D sketches. For example, an entity in a 2D sketch can be made coincident to an entity that is out of plane. This is because to make the relation, the out-of-plane entity is projected into the sketch plane, and the relation is made to the projection. In a 3D sketch, Coincident means Coincident, with no projection.
Keep in mind that solving sketches in 3D is more difficult than it is in 2D. You will see more situations where sketch relations fail, or flip in the wrong direction. Angle dimensions are particularly notorious in 3D sketches for flipping direction if they change and go across the 180-degree mark. When possible, you should work with fully defined sketches, and also be careful (and conservative) with sketch relations.
For example, the sketch shown in Figure 20.3 cannot be fully defined without over-defining the sketch. The main difficulty is that the combination of the tangent arc and the symmetric legs of the end brace cannot be located rotationally, even using the questionable reliability of 3D planes that are discussed next. The only workable answer to this problem is to create a separate 2D sketch on a real 2D sketch plane, where the plane is defined by the elements of the 3D sketch.
FIGURE 20.3
Three-dimensional sketches may be difficult to fully define.
Creating planes in space
It is possible to create planes directly inside 3D sketches. These planes are defined by constraints and selections rather than selecting a type of method to define a plane. Sketches can be created on these planes, and move with the planes. Having planes in the sketch also enables planar sketch entities such as arcs and circles in 3D sketches.
Unfortunately, there is a lot to watch out for with 3D planes. Be aware that they do not follow their original definition like normal Reference Geometry type planes. Planes inside