If you want the formers to be twice as big as what's on the originals, tell them you want the plans enlarged "200%". However, since your original set is 17-1/2" x 48", in order for them to copy and enlarge each former 200%, it'll probably necessitate several sheets of paper to copy all the parts you need. Basically, if you tell them you want the plans enlarged 200%, they'll figure out the best and least expensive way of doing it. As far as the lines are concerned, "yes" they will grow fatter but not necessarily jagged. They still may but it all depends on the quality of the original.

Ted