The reasoning behind recommended drawing scales? (1:1, 1:2, 1:5, etc...)

I set the scale to whatever 'fill's" the drawing sheet and provides the best visibility. I have recently had scales of 1:1.65, 1:1.2 and others. It is just a reference number.

That's due to the document setting for drawing "Standard". ANSI does have those scaling options, ISO doesn't.

Hello,

As has been stated, various standards have adopted a limited set of scales, some are for inch only and some are for metric only, like 1:5 and 1:2.5.

The inch ones are based on the powers of 2, which makes halving and doubling easier.

While metric scales, being deci-based per the metric system, are factored around 10.

Scales were developed around the unit of measure and theoretically, you're not supposed to use the unique scales of one system in drawings based on the other units.

"3" and "7" are not factors (divisors or multiples) of "2" or "10". I believe this is why they're not standardized.

Other numbers are factors, but you need to keep the list relatively short for easier document creation and sharing and for fewer redundant drafting tools (yes, I'm old enough to had had that pleasure).

.

Not used too much in our SW universe, the (inch) AEC folks, because of the scope of their things, use scales that are inch/foot ratios, like 1/4" = 1', called "quarter scale" (even though the ratio is 1:48). And large ratios are used for metric, especially when the unit of measure is mm.

ASME (www.asme.org) has a standard on this topic.

Cheers,

Kevin