precision matters >> A look at design in the metal fabricating world
Gerald Davis is a job shop consultant and chairman of the board of DSM Manufacturing Co.
Putting 3-D CAD on the grill
An opportunity to explore top-down design as part of product development
n Part I (Precision Matters, January 2010, p. 24), we de-
fined the project. We are designing a small charcoal grill
for shish-kabobs that we‘re calling the Shashlik Grill.
Parametric Power
If you’re not using the same 3-D CAD software as I am,
then you’ll have to translate some of the terminology.
However, the concept of parametric modeling is widely
applicable. The idea is to tie features to each other so
they remain functional as the model evolves. For example, we want holes for axles and the wheels to stay
aligned and properly sized no matter how big they are.
Our goal is to model the Shashlik Grill so we can easily change the height, distance between shelves, grilling
area, wheel size, and other parameters. To do this, we will:
1. Create a top-level assembly file to hold all
of the parts.
2. Create reference geometry in that assembly to
establish the location of the major components.
3. Model the basic shape of the components.
4. Add details like holes, fasteners, and hardware.
During the process we’ll adjust the size of components
to develop the ideal product. As it is convenient, we will finalize the names, part numbers, and revisions and launch
into the documentation process—design review presentations, mechanical drawings, and illustrations.
A Plain Plan for Planes Reduces Pain
Figure 1 illustrates the beginning of our setup of reference geometry. These reference planes are useful for
sketching upon, mating parts to, or using as stopping
surfaces when extruding 3-D solids.
I like to name the reference planes so I can remember
what they’re for. For example, I renamed the default sys-
tem plane called “Top” to “earth” so I can remember that
the wheels will rest on the Earth Plane. The default system
planes “Front” and “Right” seem like fine names to me in
this project.
Figure 1 Creating planes is
the first step in setting up
reference geometry.
Figure 2 Reference planes
will be used for locating
trays, legs, and axles.
Figure 3 The starting sketch
for the upper tray is drawn
on the Upper Tray Plane.
Figure 4 The sketch is converted into a solid model of
a piece of sheet metal. This
will be the main pan of the
upper tray.
