SolidWorks 2011 Parts Bible - Matt Lombard [63]
If you look at the 3D geometry and see it as a series of 2D drawing views arranged in 3D space (as shown in Figure 4.2), you are on your way to deciding where to start.
The part in Figure 4.2 has flat and round faces, but if you examine it, you can create the overall shape using a single extrude. The best option in this case would be to start with a sketch like the one in the lower-right corner, and extrude it. This is a good beginning. Although you can make the same part starting from any of the three sketches, the one in the lower-right corner gets you closest to the final shape.
Also realize that you don't need to make all of the geometry in a single feature. It is often best to use multiple features for elements such as holes, fillets, chamfers, and other groups of geometry that can be separated out from the main shape.
You might look at the part and see many ways to create it, but the most straightforward way is to use a main extrude, a rectangular cutout, and four chamfers, as shown in Figure 4.3.
FIGURE 4.3
Breaking down the features in this part
Also notice where the part is placed in relation to the Origin. Different people might do this differently, and the same person might even do it differently depending on the function of the part. In this case, the Origin is aligned with the center of the round shape and at the bottom of the flat face. The placement of the Origin suggests that this part sits on the flat face of another part and may hold a cylindrical face of another part.
If you open the part from the DVD, you will notice that the Origin is also placed in the middle of the extrusion depth. This suggests that the part is symmetrical from front to back.
If you are new to 3D modeling, this might be a lot to take in all at once, but you should try to keep the ideas presented here in mind as you work through your first several parts, or when you examine SolidWorks parts made by more-experienced users.
Figure 4.4 shows another part with other features. Again, you can choose from several ways to make this part.
FIGURE 4.4
Identify the best starting point for this part.
In this case, the best option is to use the one on top. This is because the other two profiles would add geometry that you would have to remove later. Notice that the holes in the part are not represented in any of the profiles. This is because holes are often added as separate features later.
Returning to the part in Figure 4.1, it should be clear enough that this part would be best started from a rectangle, although the rectangle could come from any of the three directions. I personally try to use the biggest sketch that will create a solid that requires the fewest number of cuts. The first feature that you create should also be positioned relative to the Origin. Whether there is a corner of a rectangle that is coincident to the Origin, the rectangle is centered on the Origin, or dimensions are used to stand the rectangle off from the Origin at some distance, you need to lock the first feature to the Origin with every part you build.
When working with a simple part, the entire part can sometimes be described as rectangular or cylindrical. In cases like these, it is easy to know where to start: you simply draw a rectangle or a circle, respectively. On complex parts, it may not be obvious where to start, and the overall part cannot be said to have any simple shape. In cases like these, it may be best to select the (or a) prominent feature, mounting location, functional shape, or focus of the mechanism. For example, if you were to design an automobile, what would you designate as the 0,0,0 Origin? The ground might be a reasonable location as would the plane of the centers of the wheels. As long as everyone working on the project agrees, many different reference points could work. With that in mind, it seems logical to start the rectangular part by sketching a rectangle. Select the Top plane and sketch a centerpoint rectangle centered on the part Origin.
Building in symmetry
Your next decision