In the case of text, the PC has made writing much faster than in the days of the typewriter. This led many people to believe that text on paper would be replaced by electronic records. The amount of e-mail that's printed out today suggests otherwise, at least for the near future. Faster typing and easier corrections have led to these changes in workplace behavior:

• Instead of multiple print copies, we now have multiple print and electronic copies. (This is admittedly not true in all cases, but the "paperless office" is not what most of us thought it'd be.)
• Instead of a few corrections, carefully thought out and applied by professional typists over a very few versions of each document, we now run though documents many times, by ourselves, with less care taken in both writing and reviewing. (Consider Feynman's description of the Rogers Commission report on the Challenger accident as an example.)
• Versions are updated so quickly (and released so suddenly in some cases) that sometimes the "latest and greatest" is lost. Large organizations frequently need a "Document Control" function to handle this; others struggle with compatibility issues.
• Document formats can be less easily controlled; templates for "official" forms can be stored on anyone's PC. A resulting document can appear to have authority it doesn't really have.

Computer-aided Design (CAD) suffers from analogous hazards:

• Drawings have to be printed as well as studied on the screen. Even with dynamic viewing, zoom in and out, and user-selectable perspective, the human eye can only study the screen for so long before the reader gets a headache. Print copies are easier to mark up as well, despite their static dimensions.
• Corrections are made in real-time, often one at a time, without taking consideration of interactions of individual design changes.
• Versions change quickly and must be controlled.
• Drawings are easier to distribute than to review and approve.
• Available resolution is a limiting factor. Organizations will sometimes "rasterize" CAD drawings, making the original vector file much more secure, but often losing so much detail that zooming in is worthless.
• Drawings degrade further if converted (for instance) to JPEG format; nearly all detail can be lost at this point, depending on the detail level of the original drawing.
• Some designers and architects think drawings by hand appear "more personal," depending on the design stage.
• CAD is not necessarily more portable. Try carrying your computer to a dust filled construction site or one which has no access to electricity and the battery in your laptop just died.
• CAD is not necessarily faster. Details can be drawn faster (at least the first time) by hand in some cases.
• CAD drawings are not necessarily easier to correct. If you have to turn your machine on, load your CAD program, find the file and load it just to change one detail, then hand drawing is MUCH faster.

We've all heard the adage "garbage in, garbage out." But we now live in a world where people depend on computers so much that they don't believe information that isn't "in the computer." Is there a way to counter this tendency, especially in our use of CAD?

Computer-Aided Design (CAD) and Finite Element Analysis (FEA) are not the same thing, by any means. Discussions in the newsgroups, however, reflect the tendency of engineers to lump the two together. This is partly because the same software package is likely to serve these days as a CAD package and as a pre- and post-processor for FEA; and partly because the same practitioners are involved in both areas.

You might use a hand sketch to verify or conceptualize a CAD drawing just as you might use Roark's and hand calculations to verify or baseline FEA. Ignoring this verification could make your CAD analysis worthless.

Here are other suggestions and reminders for new CAD (and FEA) software users:

• CAD is driving a trend toward concurrent engineering: the act of performing analysis and design in parallel. While concurrent engineering clearly enables faster design, there is a danger: you might be tempted to redefine your engineering processes around your CAD package. (The temptation is proportional to the cost of the package, of course.)
• CAD advertisements tend to make the design process seem deceptively easy: don't the programs do the analyses, anyway? These ads are of course aimed at the Boss, who in turn decides not to budget time or funds on training in either CAD or FEA.
• Don't depend on FEA to get you an answer if you need it in a hurry -- unless your model is already in place and verified with a baseline as indicated above. FEA on every component is particularly unproductive.
• CAD has one great advantage over hand sketching: it removes the problem of "Parts that Don't Fit Together." It fails, however, to remove a related problem: "Parts that Fit Together in a System that Still Won't Work Because the Physics are Wrong."
• Beware the tendency to use the availability (and simplicity, if it is simple) of CAD or of FEA to justify complex solutions over simple ones. Always try the simplest solution first: it offers the least to lose, the most to gain, and the easiest path for backtracking. The simplest solution that meets requirements is the best solution.
• No matter what fidelity you are using in your design and analysis, you can't prove or disprove the existence of problems without prototypes and testing.

The Origin

Your CAD program has an internal coordinate system origin, whether you introduce one or not. You may need to set this origin for your own purposes:

• To minimize absolute coordinate references.
• To assist with preparation of a jig for the part.
• To define motions of machine tools.
• To insert one drawing into another at a common point.
• To "zoom all," so that the origin remains on the screen.
• To minimize the number of coordinate systems you have to remember.

Most CAD programs allow you to define a datum, or coordinate system, which accounts for your origin. One professional site recommends that datums follow these guidelines:

• one datum per part
• datum close to one end of the part
• align origin with a (preferably pierced) feature
• align datum plane with the principal flat surface (i.e. before any bending) of the part
• dimension in one direction if possible to control accumulated error
• dimension from feature to edge to minimize special fixtures (i.e. jigs)
• tolerance to dimensions that really need them (since tolerances are almost never one-size-fits-all)!

Why Customers Want Drawings

• The customer may actually own the drawings, depending on the contract.
• Drawings are useful as a record of construction materials.
• After a device or component has been in service the customer may decide "did we really do that?" The drawings become the basis for the next design.
• They may want to understand how the product works.
• Your design team could maintain good relations with the customer, but simply stop supporting that product line.
• Some customers have documentation requirements that allow them to independently verify a supplier's specs. Some customers may simply use the drawings for quality control.
• Drawings tend to be more up-to-date than user manuals.
• Drawings can be used as training tools, for customer employees working on analysis or contract relations.
• Drawings serve as a critical record of production for low-volume or unique items.
• Design documentation must be available in the event of litigation. Insurance companies may also require this.
• Some products must have documentation maintained, by law, as long as they are in service. Some customers have documentation requirements associated with ISO certification.
• Drawings follow ANSI and ISO standards for tolerances, views, etc. for which there is currently no standard for CAD systems.
• Some customers need complete documentation as part of a disaster recovery plan.
• Customers may want the drawings in case your design team goes out of business or falls out of favor.

References

one-day micro-course in Pro/Engineer
a cool NASA drawing standards manual
Luzadder, W. J. and J. M. Duff. The Fundamentals of Engineering Drawing. Englewood Cliffs, NJ: Prentice-Hall, 1992. ISBN 0-133-35050-9
Metalforming Online has periodic CAD tips