I used to do this kind of drawing in the early years of my career. In those days, there was a special pen called a "railroad pen", that was basically two ruling pens on one handle, specially designed for drawing parallel lines. The distance between the 2 nibs was adjustable, and the two together had an optional swivel function, so that you could do freehand curves.
It was a tricky pen to use, if you wanted really good linework, and usually it was necessary to go back and clean up your work after you'd finished. I actually had better results with a single ruling pen. Draw a line, carefully measure the offset and mark with tiny pencil ticks, draw the parallel line, repeat. It just takes patience and diligence.
Hi all. This is my first post (excluding my introduction) so if you missed that let me preface this post by mentioning that I draw pen and ink maps by hand as a hobby and I am trying to improve my technical ability in this area.
I've always had bad luck drawing roads (think of any typical USGS topo map road style) because I can never get the two lines to be equidistant from a drawn or imaginary center line. I find that French curves make for unsympathetic transitions and flexible rulers are...flexible. Is there some big secret I'm missing? It seems as simple as a two point nib but I have yet to find one. Am I missing a very obvious secret to accuracy in this area?