SolidWorks 2011 Parts Bible - Matt Lombard [126]
When you think of describing a complex 3D curve in space, one of the first methods that usually comes to mind is describing it as two 2D curves from perpendicular directions, exactly in the same way as you would if you created projected drawing views from it. From this, it makes sense to see the creation of the curve as the reverse process, drawing the 2D views first, from which you can then create the 3D curve.
Intersecting surfaces visualization method
A second method used for visualizing Sketch On Sketch projected curves is the intersecting surfaces method. In this method, you can see the curve being created at the intersection of two surfaces that are created by extruding each of the sketches. This method is shown in Figure 8.7.
FIGURE 8.6
The reverse 2D drawing visualization method for projected curves
FIGURE 8.7
Using intersecting surfaces to visualize a Sketch On Sketch projected curve
Using the Curve Through XYZ Points feature
The Curve Through XYZ Points feature enables you to either type in or import a text file with coordinates for points on a curve. The text file can be generated by any program that makes lists of numbers, including Excel. The curve reacts like a default spline, so the teeter-tottering effect may be noticeable, especially because you cannot set end conditions or tangency. To avoid this effect, it may be a good idea to overbuild the curve by a few points on each end, or have a higher density of points.
If you import a text file, the file can have an extension of either *.txt or *.sldcrv. The data that it contains must be formatted as three columns of X-, Y-, and Z-coordinates using the document units (inch, mm, and so on), and the coordinates must be separated by comma, space, or tab. Figure 8.8 shows both the Curve File dialog box displaying a table of the curve through X, Y, and Z points, and the *.sldcrv Notepad file. You can read the file from the Curve File dialog box by clicking the Browse button, but if you manually type the points, then you can also save the data out directly from the dialog box. Just like any type of sketch, this type of curve cannot intersect itself.
FIGURE 8.8
The Curve File dialog box showing a table of the curve through X, Y, and Z points, and a Notepad text file with the same information
Using the Curve Through Reference Points feature
The Curve Through Reference Points feature creates a curve entity from selected sketch points or vertices. The curve can be an open or closed loop, but a closed loop requires that you select at least three points. You cannot set end conditions of the curve, and so this feature works like a default spline in the same way as the XYZ curve.
The most common application of this feature is to create a wire from selected points along a wire path. Another common application is a simple two-point curve to close the opening of a surface feature such as Fill, Boundary, or Loft. One drawback in that regard is that the end tangency directions cannot be controlled on curve features. If a 3D sketch spline is used, end tangency direction is controlled easily through the use of spline handles and tangency to construction geometry. Curve Through Reference Points is largely unused, probably because 3D sketch splines are so much more powerful.
Putting together a composite curve
The composite curve joins multiple curves, edges, or sketches into a single curve entity. The spring shown in Figure 8.9 was created by using a composite curve to join a 3D sketch, Variable Pitch helix, and a projected curve. You can also use model edges with the composite curve. The curve is shown on half of the part; the rest of the part is mirrored. Curves cannot be mirrored.
Composite curves overlap in functionality with the Selection Manager to some extent. In some ways, the composite curve is nicer because you can save a selection in case the creation of the feature that uses the Selection Manager fails. (If you can't create the feature, you can't save the