By Gerald Davis
The CAD project shown in Figure 1 was in- troduced in the April 2017 edition of this column (“Shop technology and 3-D CAD:
Translating design goals into CAD techniques,”
The FABRICATOR, p. 40). Rick S. from Montreal sent
this musing to the author: “How would I build this
parametrically if I had seven different sizes to make
in one shot and if I wanted to be able to respond to
a client’s specific dimensions in minutes?”
Rick went on to outline an idea he had for avoid-
ing the use of configurations to drive the tank. He
wondered how the author would approach this
The short answer is, while inventing and developing the design, I would use some combination of
parametric links and configurations. I would try to
model for quick-switch visualization only if it speeds
the design to market. When the design is ready for
market, I would branch the configured CAD models
into stand-alone single-configuration assemblies.
To match purchasing, I would maintain shared/con-figured CAD models for hardware items in the product line.
The Long Answer …
From a parametric planning point of view, the water
contained in this tank sits inside a piece of equipment. The CAD jockey can deem one of those—water,
tank, or equipment—to be the “controlling feature.”
To represent the equipment, we could set up reference geometry in the form of planes, sketches,
or surfaces. Using that work flow, always sketch or
extrude to the relative locations of the reference geometry. By changing the position of the reference
geometry, you change the size of the parametrically driven model. The trick is for the CAD jockey to
move the reference geometry with ease.
The project from April uses the tank, specifically
the sheet metal tank wall frame, as the controlling
feature. The floor changes size to match the wall.
This is the same with the lid. The water fills the tank
to the specified head room.
This article outlines a work flow for controlling
variations in a product’s design using a combination of parametric links and configuration-driven
features. Undoubtedly, several better solutions
are available to do just this, but are not discussed
here. The general recommendation is to identify
the variables and their range of values throughout
the product line and then select the best modeling
technique for that design intent.
Part Configuration: Easy Target
A Configuration Table (see Figure 2) allows a single
CAD model to represent several SKU items. In this
example, a model of a washer has been configured
for nine different sizes. This Configuration Table is
controlling the thickness, inside diameter, outside
diameter, and part number for each washer size.
This ability for one file to be many things offers
• It can reduce the clutter of files involved in a
• It might help with rebuild time in a large project.
• It can simplify the maintenance and searching
of the CAD database.
Configurations can be created without using a
Configuration Table. The Configuration Table is a
recommended technique and adds convenience to
creating and editing configurations.
Another useful application of configurations as a
CAD work flow is the ability to switch from one product to another. This water tank is a practical example
of a single model representing three products with
a handful of features that make them distinctive.
Here is a CAD tip: Configuration Tables that are
switching multiple details can be challenging for a
future CAD jockey to understand quickly. For long-term maintenance purposes, when more than a
handful of variables change between products, you
would probably be wiser to use separate files instead
of Configuration Tables.
Plan Early, Plan Often
Planning, in this scenario, involves identifying the
variables in the design that we need to control. A
quick jot of notes—taken from imagined design
planning meetings—reveals that to quickly switch
between product lines we need to control values for
three variations of floor XY sizes, tank Z height, and
We want the model of the water to accurately reflect the interior of the tank as the size of the tank
changes. Planning also tells us that a few items (the
0.25-in. British Standard Pipe Thread, a sensing
probe, and the 90-degree corner shape) must remain constant in our product line.
Using these meeting notes, we prepared a planning spreadsheet for CAD use (see Figure 3 and the
yellow highlight). Whether we use a spreadsheet, a
doc, or a pencil and paper, the recommendation is
to record the location of variables in the model that
will have to change in the product line.
For the features that must not change, rows eight,
nine, and 10 in this spreadsheet serve as a check list.
The model for each feature that must not change
size is to be inspected by the CAD jockey to verify no
untoward parametric links.
Here’s a CAD tip: The completion of a planning
spreadsheet, such as Figure 3, is a good point to
decide on a CAD modeling technique for quickly
switching between products. Some work flows to
consider include separate (stand-alone) assembly
models, configuration-driven models, and property-or value-driven models.
Read more from Gerald Davis at www.thefabricator.com/author/gerald-davis
Shop technology and 3-D CAD:
Quick switching between product variations
Configuration Table abuse can be cured by stand-alone modeling techniques
The completion of a planning
spreadsheet, such as Figure 3,
is a good point to decide on
a CAD modeling technique
for quickly switching between
products. Some work flows
to consider include separate
models, and property- or
This water tank is the start of a product line of water
tanks. This model was introduced in the April episode.
A washer is modeled with a revolved sketch. The dimensions are given meaningful names for convenience. A Configuration Table is inserted. A dimension
is entered as a heading in a column, and values are entered in the rows for each size of washer.