(For those interested, Parts 1 & 2 of this tutorial can be found on my blog CAD Craft.) In Part 2, I walked us thru the steps of creating configurations in SolidWorks, and some keys regarding how dimensions in a sketch, features in a part and even parts in an assembly can be managed & coordinated in the creation and articulation of configurations. I have attached an STEP AP214 version of the Gear Drive Assembly in a Zipfile for those who would like to interrogate the model. (Unfortunately, while STEP captures the parts in the assembly, it does not reflect the configuration options within a SolidWorks model when you open it in SolidWorks. I also uploaded an STL of the assembly to the gallery for the community to peruse.) To conserve space, see Part 1 for a discussion of the definition, advantages and implementations of configurations in design & manufacturing. At this stage, we're ready to engage the concepts & principles of modular design -- its advantages, and how it helps to more effectively leverage one's resources. Modular design can be very empowering as an approach, on a lot of levels. When you're doing designs in CAD or Second Life, the capacity to organize your parts and components such that they can be re-used in many different arrangements & assemblies keeps costs -- materials, inventory, time/energy/effort -- as minimal as possible. This comes into play in at least a few areas: • Scale -- A part or component may be proportionally the same in the design of its features, such as a hexagonal plate. If you realize that you can use this same detailed design in an assembly as a piece of jewelry, as a piece of furniture and a building as well, then you recognize that the similarity of the parts is fundamental, whereas the difference is a function of scale. Yantras are a cultural example of this which addresses design in a transcendent context. Yantras can be flat, like a drawing, or 3D -- like the 12th image -- in many sizes or scales, such as a building, furniture or a piece of jewelry you could wear around your neck. It's also worth mentioning that this consideration -- in tandem with pattern propogation -- flirts with the fringes of the idea and implementation of fractals in design. • Size/dimension -- A bolt or screw is a good example here. These items have a series of common parameters: diameter, length, pitch or density(threads @ inch), material, etc. So, for a bolt of the same diameter, say 1/4 inch, the same pitch, say 20 threads @ inch, the thing which sets each apart bolt from the others is the length of the screw, and/or the length of the threaded portion of the bolt. • Features -- The bolt or screw may be the same diameter, the same length, the same density, even the same threaded length. However, they may differ by the type of head they have -- hex head, phillips, slot, socket, etc. They are the same screws or bolts, except for this difference. Configurations engage this aspect by allowing you to take a single model, say of a bolt, and make many iterations or versions of it within the same file. This way you can have one file which represents a single bolt or screw in 20 different sizes &/or configurations. When you pull that part into an assembly, you can bring up a dialog which allows you to specify the configuration for that particular iteration in the assembly. You may use the same model file many many times, yet most can be different based on the configuration used. This allows for a much more compact file library, and is the basis of the Toolbox feature in SolidWorks. Similarly, modular design empowers you to create designs which may be largely similar in overall envelope(dimensions), yet have some features which are distinct. By varying the combination of components which go into a given assembly, you end up with many different versions of essentially the same thing. Consider, for instance, that when you go to buy a car, you want one with your preference of features, chosen from a broad list of possibilities. However, the chassis, majority of body panels, steering wheel, perhaps even seats are identical to every other copy of that model, yet yours feels unique to you because of your combination of options. To take this a step further, some of you know, for instance, that the chassis, and in some cases even the engine, drive train and other primary components of the Chevy Camaro and the Pontiac Trans Am were the same. Yet, 'Chevy guys' and 'Pontiac guys' would argue and race like they were totally different. This is modular design in practice, and you can see how it saved a great deal of money for General Motors while generating definitive branding, brand loyalty and prestige, not to mention significant profits, simply because most folks did not look any deeper than the skin -- the molded sheet metal -- to make their judgments, and we know how foolish this can be.