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ATFAB’S PARAMETERS
ters, are the variables. Within a parametrically
defined table, for instance, a (mathematical)
function affiliates a supporting leg at each of
the four corners of a tabletop, while allowing
the table a variable length, width, and height.
Parametrically transforming this table changes
its overall dimensions, without affecting the
fundamental characteristics of four legs that
support a tabletop.
If you elongated either the 5-30 Minute Chair or
the 90-Minute Lounge Chair within the CAD file
in Part III, you were manually performing a
parametric operation. You adjusted the variable
width, within a function that preserved the rela-
tionship between the sides, legs, feet, fasten-
ers, and joinery.
A parametric definition is a specific operation
that transforms parts or adjusts attributes of a
digital model. By developing such operations in
the process of designing, a designer can make
an object and its operations inextricable.
For AtFAB, we designed parametric definitions
to yield a range of outcomes that are apprecia-
bly different and relevant. For all pieces, and in
the apps that accompany this chapter, we pro-
vide operations for adjusting material thick-
ness, sniglet diameter, and fastener diameter,
as well as for transforming a piece in either
shape, module, or dimension.
Some CAD software programs offer parametric
tools, which enable you to transform particular
physical attributes of an object. Though para-
metric modeling software enables you to assign
modifiable attributes to your model, the soft-
ware does not do all of the work for you. You
still need to do the intensive thinking to interre-
late elements within a design, and to determine
what is constant and what is variable. It’s not as
easy as many people think; it’s a lot of extra
work to design parametrically, but the implica-
tions of this effort can be powerful. With a sin-
gle parametric digital model, you can produce a
range of versions, like a series of similar tables
or chairs with varying dimensions or attributes.
FIGURE 12-1 Prototypes of CIBi and CIBii versions
ATFAB’S PARAMETERS
Chapter 2 explained how AtFAB’s collection of
furniture pieces share a common language of
joinery, assemblies, and structures based on
the S/Z joint. As each AtFAB piece was devel-
oped, it was designed with parametric customi-
zation in mind. Thus, a finite collection of
furniture is actually a range of infinite versions.
Collectively, these parametric definitions give
each furniture piece a significant level of adapt-
ability for different materials, tools, and individ-
ual preferences. For distributed manufacturing,
explained in Chapter 1, the implications of this
versatility are vast. Makers anywhere can
download a file, tailoring the design to fit local
materials, available CNC tools, and specific
uses or needs.
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DESIGN FOR CNC
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