Today, people use "copiers" to scale drawings up or down. A typical copier can enlarge or reduce a drawing by from 64% to 142%. Unfortunately, this doesn't help much if you need to change the scale more than this amount. However, you can still get by making partial scale changes -- for example, expanding by 141% and then expanding the first expanded copy by another 141% gives you 1.41 x 1.41 = 1.9881; expanding it by 142% instead gives 2.0022...either is probably close enough to 2x to be acceptable.
Likewise, reducing by 71% twice gives a net reduction of 50.41%; 71% and 70% get you 49.70%, either is probably close enough to 1/2x to be useful.
When enlarging, lines tend to get broader (and "muddier") -- set the copier to "light" to help reduce this effect.
Copiers tend to "stretch" the drawing more in one direction than the other (this is supposedly to prevent the copying of paper money -- the resulting image won't match in change-making machines). If you are doing multiple expansions/compressions, try to change the orientation introduced in one operation is canceled out in the next.
If you anticipate needing multiple copies, do them all at once, using the same batch of paper -- that way stretching or shrinking of the paper is more likely to be uniform for all copies than if you made copies at different times using different lots of paper.
Finally, commercial copy shops can frequently make larger copies,
and/or bigger scale-changes with one pass. In order to help them
produce a copy of the correct size, draw a pair of lines somewhere on
your source, at right angles to one another, and properly scaled and
annotated with something like "enlarge to 6 inches long" -- that way
you won't have to explain about the (often obscure) scale that is on the
plans themselves. (If you are using historical foreign sources, make
sure what units are actually being used -- for example, Chapman has
scales in Swedish, French, and English feet...all are different!)
{John O. Kopf}
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