Computer-aided design

Often used by architects, engineers, construction teams, and even garage motorcycle builders, computer-aided design (CAD) provides a variety of benefits over analog drawings.

CAD began with the creation of digital two-dimensional drawings, then later progressed to three-dimensions.

Two-dimensional digital drawing

In many industries, there are some benefits to creating a 2D digital drawing.

  • Digitally editing a drawing is quicker than erasing or redrawing an image that was drawn by hand. Filing and distribution is greatly improved when you aren’t worried about piles of enormous drawing sheets.
  • The drawing conventions used in hand-drawing carry over; it’s simply using a digital method for creating the same drawing, meaning consistent communication between parties

However, there is little value in learning how to create stand alone digital 2D drawings for a garage built custom bike. If you need to design, for example, an exhaust hanger bracket, analog sketching on paper and quickly iterating while working on the bike will often be faster than creating a 2D digital drawing.

Even then, if you needed to design an exhaust hanger bracket on a digital build, you could model it as quickly in your chosen 3D-modeling package and use that to create a template for cutting your material.

The only exception would be drawings used for two-dimensional CNC profile cutting, such as plates cut with a CNC plasma cutting machine.

There are higher-value processes you can learn to progress your build, so park 2D digital drawings at the bottom of the list for now.

Three-dimensional modeling

Three-dimensional models are a digital representation of a physical object. Modelling has its basis in mathematics, specifically geometry, which predates computers, so the theory has been around for hundreds of years!

Modeling is now commonplace in many industries including movies and film, medicine, architectural and, of course, vehicle engineering. There are four major approaches to 3D modeling, each used for unique applications.

Solid modeling: These represent the volume of the part. Models are made to represent the volume of a component or part. Each model is constructed of a group of primitive shapes like cubes and cylinders along with Boolean operators to create joints or cuts between them. Solid modeling is common in medical and engineering applications.

Wireframe modeling: Wireframes are essentially simplified solid models. However instead of showing the volume of a shape, only the shape’s edges, joins, and vertices are drawn. This  allows viewers to see through the object being modelled to get a sense of size and shape.

Polygon modeling: Such models are represented by a network of vertices. Each face can be represented by a minimum of three vertices, or a triangle, but quadrilaterals and other simple polygons are also used. The number of polygons for a model is called the “polygon count”. Higher polygon counts indicate more, smaller polygons are used to represent the surface, which improves its smoothness. Lower polygon counts would result in a “blocky” model. Models used in film and gaming are usually polygon models.

Surface modeling: As the name suggests, these models represent the surface of the part, such as a wing or fairing. The visible surface is considered infinitesimally thin, and little consideration is given to any features under the surface. The model is constructed from “guiding lines” that lie on the surface of the model, and are widely used in such things as consumer goods products, aerospace and shipping industries as they describe the exterior of an object in the most suitable way.

You might see that a combination of modeling types could be used. The outside faces of the fairings on a sports bike might be constructed via a surface model for aerodynamic reasons but the surface model would then be used in conjunction with solid modeling for the remainder of the design, such as internal structure and mounting points of the fairing, to undertake stress analysis.

In complex areas of a bikes design, such as engine design or arranging electrical components under a seat, the “packaging” of all the necessary components together can be verified digitally before any prototypes are produced. Even access to bolts and mounts can be assessed, ensuring anyone working on the bike doesn’t need double-jointed elbows to reach required items.

If 3D modeling holds no interest for you and your bike build, don’t feel as though you’re building a subpar machine. Plenty of accomplished custom-motorcycle builders never touch a computer during their showroom-quality builds (except maybe to order parts and pizza for late night build sessions).

Three-dimensional modeling for custom motorcycle projects

So, what type of 3D modeling might be suited to a custom motorcycle project? Surface modeling is appropriate for a fuel tank or fairing, but solid modeling would be better for designing structural or load bearing parts like the subframe or instrument gauge bracket, where stress analysis is required.

Because other methods like hand-built bucks exist for metal shaping, builders predominantly use modeling techniques for individual parts. Software for solid modeling would be the most useful for custom bike builders.

Here are a few parts that a builder might model along with their typical manufacturing processes:

  • Front fork triple clamps used to adapt late model forks to an older bike, CNC machined from steel or aluminum.
  • Speedometer holder bracket with integrated LED light openings and cable clamps, 3D printed from plastic
  • Under-seat electronics tray for housing electrical components or new mounting tabs, laser cut and folded sheet metal

If you model multiple parts, you can construct complex assemblies on your computer before you cut up expensive raw materials. Just like modern automotive designers, the DIY custom motorcycle builder can construct part – or all – of their project digitally as part of the design process.

There are, of course, very expensive specialist applications for each of these cases, and new or improved software is released regularly. Check the Resources page for our current recommendations.

Each software package has users build a complex shape off a base plane using common shapes, then use join or cut operations or draw a 2D wireframe outline and extrude the shape. However, each application has its own unique toolsets and user interfaces. Should you decide to use one of these modeling applications, there are a vast amount of free educational instructional articles and videos to be found via your favorite search engine.

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