I was trying to think about this in an easier way as converting 1:48 to
1:24. In that case you would expand* the 1:48 plan to copied at 200% to yield 1:24
(twice as big).
For 1:20.3, you want to expand* 236% This
assumes American O scale, which is 1:48. (48/20.3=2.36)
*Blow up the drawings on a copier.
Just remember the copier may not enlarge the same amount each time.
I did some ship frames a while ago at 1:1 & 12 copies were all
different. Draw a small line on the original & then see if it
enlarges on the copy to the right size. And if enlarging 2X times
rotate the drawing 90 degrees on the second enlargement to stop
hopefully the effects of the copier only enlarging faithfully in one
direction & not the other. Other tips:
- Take plans to someone with a large scanner to scan & reprint in
desired scale. - Digitally photograph & print onto transparency & project onto
large sheet & redraw.