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parts by just dragging them with the cursor. To move the parts, you have to move the sketch and rebuild. The part does not move until the sketch is updated. If you need to combine layout functionality with dynamic assembly motion, you can add additional instances of the in-context parts that are mated in the traditional way. However, when using this method, you have to be very careful about which instance you make your edits to, because in-context relations will be driven by the original instance.

Another drawback of the assembly-level sketch in general is that you cannot use a sketch picture inside the sketch. Sketch pictures can contain important reference information for building a model. The lack of this capability is certainly noticeable. You can put your sketch picture in a part or even a virtual component.

Using master model

The master model technique is covered in depth in Chapter 19, but it is mentioned here because it works as an alternate method with the layout idea. The term master model can mean a couple of different things: It could be a single part where multiple bodies are created and that is later split up into multiple parts. Also, it is sometimes used as the name for inserting a single part with sketches and reference geometry into one or more other parts to have a single reference without creating that reference in the assembly.

This still creates an external reference, but it only creates a single external reference instead of possibly dozens, and updates of the inserted part can be locked. Performance problems with this technique are less serious. Also, if the file management fails and SolidWorks cannot find the inserted part, you can still keep working. SolidWorks keeps enough data in the child part that it does not need to constantly access the parent part.

The master model technique seems to have more advantages and fewer disadvantages than the methods using assemblies. The dynamic assembly motion problem does not exist in a master model arrangement, nor does the lack of sketch picture functionality.

An example of this kind of work is shown in the derailleur assembly in Figure 6.6.

The part shown on the left is the master model. Notice that it contains sketch, plane, and surface data. The image on the right shows some parts superimposed on the master model part.

FIGURE 6.6

Using a master model to drive the individual parts of an assembly

Using the Layout Feature

The Layout feature in SolidWorks is relatively new. However, due to some quirky behavior, it is not generally employed by users. Most people who have been using the layout technique described earlier in this chapter are not switching to the new method, even though it has replaced the old method in the official SolidWorks assemblies training manuals.

The Layout feature is a 3D sketch that is given special treatment within an assembly. It also works best with sketch blocks. The special properties of the Layout feature when compared to a 2D assembly sketch are as follows:

• Uses a 3D sketch

• Works best when actively sketching on a plane

• Works best when the sketch making up a part is made into a sketch block

• Enables you to extrude the first feature of a part directly from the sketch block

• Enables sketch relations between blocks to turn into mates

• Permits unlimited dynamic assembly motion — parts move with the motion of blocks in the Layout

To initiate a Layout, click the Layout button on the Layout tab of the assembly CommandManager or activate it from the Insert menu. Once you are in a Layout, SolidWorks puts you into a 3D sketch with the Front (XY) plane activated, so it displays a small grid.

For now, you treat the 3D sketch as much like a set of 2D sketches as possible. The main difference is that you can double-click a different plane to start sketching on the new plane, and you always see this small grid when a plane is active.

You may find that 3D sketches have some limitations when you are working with Layouts, such as lacking the capabilities to use sketch patterns and Sketch Pictures.