Curved Parallel Lines in CAD

Simple tip for drawing offset curved lines. August 14, 2007

Question
I am trying to draw a curved molding, a cathedral type arch. What is the best way to make two parallel lines that are multiple arcs? If I move the radiuses the width of the moldings, things donít line up. I realize this is basic, but I am struggling. I use Autocad LT 2005.

Forum Responses
(CAD Forum)
From contributor R:
Not totally sure I understand your situation, but have you tried using the offset command to make a copy of the 1st arc?



From contributor S:
The second radius will be less than the first by the amount of offset.


From contributor D:
Not sure if I fully get it either, however, if you draw a continuous series of arcs (polyline, arc) and offset, you will get a parallel set. Try drawing a bounding box, create the line shape through the box, offset and then trim.


From the original questioner:
Thanks. I have never found a use for the offset command, so I was unfamiliar with its power. That's awesome and just what I needed.


From the original questioner:
Wow! After using the offset command, I realize what I have been missing. I am self taught. I should really take a class or work my way through a book. Same old story, not enough time to take the steps to save time.


From contributor B:
You have some additional options here. When you offset connected arcs either to the inside or outside of the curve, they often either overlap one another (inside offset) or have small gaps between them (outside offset). Then you have to repair these problems.

A better way is to do a PEDIT and join all your arcs together into one continuous polyline. Then offset that polyline and everything will be perfect. I do this task daily... it is a regular part of my curved mouldings business.