Most engineering designs involve a multitude of considerations, and it is a challenge
to the engineer to recognize all of them in proper proportion. Although no simple
checklist given here can be adequate or complete, it may be helpful to list in some
organized fashion the major categories involved (see Table 1.3).
Traditional considerations for the bulk or body of the component include:
(a) strength, (b) deflection, (c) weight, and (d) size and shape. Traditional considerations
for the surfaces of the component are (a) wear, (b) lubrication, (c) corrosion,
(d) frictional forces, and (e) frictional heat generated.
Often various design considerations are seemingly incompatible until the
engineer devises a sufficiently imaginative and ingenious solution. The design of
the lift truck pictured in Figure 1.2 provides a simple example.
Here, the objective of achieving a desired aesthetic appearance was seemingly
incompatible with cost limitations. Matched metal forming dies were too costly,
and inexpensive tooling resulted in unattractive mismatches of mating parts. The
solution here was to work deliberate mismatches into the design and eliminate the
need for precision fitting. The mismatches were used to give the truck a rugged
look. The gap under the hood, for example, creates a strong horizontal line while
disguising the fit-up of several frame and fender weldments. It also provides a
handhold for lifting the hood. Another gap (not shown) makes the instrument pod
appear to “float” from a steel pylon, again disguising a large tolerance. The large
hood simplifies maintenance by providing wide-open access to the engine. By serving
also as the seat support, it further reduces cost, while adding to the clean,
uncluttered appearance.