SolidWorks 2011 Parts Bible - Matt Lombard [265]
One of the ways to troubleshoot a failing Offset Surface is to use the Check tool to check for minimum radius. Remember that the area with the minimum radius is only a problem if the curvature is in the same direction as the offset. If a small radius will increase when it is offset, then that small radius is not the problem. The problem comes from the other direction where you are offsetting to the inside of a small radius.
Unlike the Sketch Offset function — and as was shown in Chapter 19 — you can offset surfaces by a zero distance. This is usually done to copy either solid or surface faces to make a new surface body. Zero-distance offset and Knit are sometimes used interchangeably, although Knit causes a problem if you are selecting a surface body that is composed of a single face. Knit assumes that you are trying to knit one body to another, and so, by default, it selects the body, and then fails with the message that you cannot knit a body to itself. Because Knit has this limitation, and Offset does not, I prefer the Offset tool when copying faces to make a new surface body. You may also notice that when you enter a zero for the offset distance, the Offset PropertyManager name changes automatically to Copy Surface.
Knit does have two functions that Sketch Offset does not. One of these is the option to create a solid from the knit body if it forms a closed body. The second option is somewhat more obscure, offering the ability to select all faces on one side of a Radiate Surface. I discuss this option in more depth later in this chapter in the Knit Surface section.
When talking about copying surface bodies, you must also consider the Move/Copy Bodies feature, which is described in Chapter 19. When simply copying a body without also moving it, this feature issues a warning that asks whether you really intend to copy the body without moving it. This is an annoying and pointless message. Also, the Move/Copy Bodies feature does not enable you to copy only a part of a body (selected faces) or to merge multiple bodies into one like the Knit and Offset Surface features.
All things considered, I recommend using the zero-distance Surface Offset feature to copy bodies or parts of bodies unless your goal is to immediately make a solid out of it (in which case you should use the Knit feature) or when using a Radiated surface (typically in a mold-building application).
Using Radiate Surface
The Radiate Surface is not one of the more commonly used surface features. It has been largely superseded by the Ruled Surface. This is because Ruled Surface does the same sort of thing that Radiate Surface does, as well as a lot more, and is also more reliable. Radiate works from an edge selection, a reference plane, and a distance. The newly created surface is perpendicular to the selected edge and parallel to the selected plane, and the set distance is wide. It is probably most commonly used in creating molds or other net shape tooling such as dies for stamping and forging, blanks for thermoforming, and so on. Figure 20.7 shows the PropertyManager and selection for creating a Radiate Surface.
FIGURE 20.7
The Radiate Surface PropertyManager
Tip
The Radiate Surface feature does not give you a preview of the finished surface, only the small arrows that indicate the direction in which the surface will radiate. At times, you may need to switch the arrows to the other side, which you can do by using the arrow button next to the plane selection.
Caution
When creating a Radiate Surface, the use of a loop in the edge selection always results in an incorrect result, because the feature only uses the initial edge that was selected for the loop. As long as individual edges are listed in the selection box, you should be okay.
The one application where the Radiate Surface has a very interesting usage is when you combine it with the Knit function, as mentioned earlier. Figure 20.8 shows a part surrounded by a Radiate Surface in which the Knit feature is being used to select all the faces to one side