Datasheet

METRIC IS EVERYWHERE

I’ve been predicting since 1976 that the U.S. was about to go fully metric. I keep making that

prediction, and I’m getting less and less wrong. That may not be as good as being right, but

it’s possible that you’ll have to deal with the metric/inch conflict at some point.

I’ve assisted both mechanical designers and architectural designers in converting existing

designs from inches to metric, and if this is done as a hard conversion, it often results in dimen-

sions that aren’t logical to people who are used to working in the metric system. Sometimes

that can’t be helped—it may not be possible for a precision mechanical part to be redesigned

to use even values. It may be possible, however, for an architectural design to be soft-converted

to millimeters (yes, millimeters) without any ill effects. Does anyone in the Architecture Engi-

neering and Construction (AEC) field use metric units? Well, yes. The whole rest of the world

does, and some companies in the U.S. are beginning to find that out—for example, cabinet

makers whose cabinets won’t fit into the space available except in U.S. houses, and plywood

makers who have no market for 48×96˝ sheets anywhere but here.

In one case, a log-home builder in Maine sold a home to a company in Japan. The builder

boxed it up, put it on a container ship, and then got the fax: What the heck are these numbers,

and how soon can we get drawings in millimeters? When they contacted me, I suggested

that they convert their shop drawings to millimeters by changing DIMLFAC to 25.4 and then

setting DIMRND to 2. All dimensions were then in whole, even millimeters. Nothing was off

by more than one millimeter, so the design wasn’t compromised, but the drawings looked

better to the Japanese crew who had to read them. Imagine how confusing it must be to

see 7´8

⁄4˝ when you’re used to values like 2356.

AutoCAD Best Practices

I’ve been training people to use AutoCAD for technical graphics and design since the

late 1980s. At that time, I frequently got resistance from drafters and designers who felt I

placed too much emphasis on absolute accuracy. They would point out that once a draw-

ing is plotted, the absurd 15 decimal places of precision that AutoCAD uses for calcula-

tions become meaningless. Once you plot a drawing, even significant errors are difficult

to detect, as long as you carefully replace any key dimensions with those you typed in.

I believe all industries that rely on computers for design and documentation should

share common standards when using CAD software. In this section, I offer advice on

accuracy and other aspects of AutoCAD that should be standard practice across all disci-

plines. If you understand AutoCAD, it’s faster to produce an accurate drawing than an

inaccurate drawing. You or your company have probably invested upwards of $7,000 to

put you in an AutoCAD seat, so why not produce as accurate and useful a drawing file as

possible?

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