I use code 100 flex track on my layout. As most everyone knows, it likes to straighten out on the ends once you take the pressure off after forming a curve. I have worked around this by staggering then soldering the joints together. This works when you can do the whole curve.
I recently had to replace a curved switch and I think found a solution for keeping the curved rails positioned. This was done by soldering two or three PCboard ties in place of the plastic ties once the track had the proper curve. The soldered ties were at about 1 inch intervals from the curved end. Wish I thought of this a long time ago.
To be more descriptive:
First the track was shaped to have the same curve as the switch by overlaying a portion of the switch. The portion overlaying the switch would eventually be cut off. With the flex track laying in position, the flex track was marked where it would connect to the switch. At ~1 inch intervals from the cut, three plastic ties were removed. In their place a PCBoard tie was soldered to the rails. After soldering the curvature was checked then the excess track was cut off. Now all I need to do is paint the PCBoard ties.
I’ve found that, by carefully forcing the rails down to a much smaller radius, they will relax to whatever radius I’m trying to form. The last few inches do require a bit of gentle persuasion with a pair of pliers. The key word is GENTLE. Brute force doesn’t work - it just shears the little plastic spikeheads (or Pandrol clips if you use concrete-tie track.)
My method is to use T pins to hold the track in position. Then dribble some diluted white glue on the end ties. When the glue dries it will hold the flex track in place.
If you want to later reposition the track it is easy to pop the track loose.
Ken, it’s a great tip, and one about which I had forgotten. When I was waiting to use my previous layout, back in 2006, I had already been constructing some Fast Tracks #8 Code 100 turnouts, so I had lots of rail and PCB ties. I decided to set up a temporary layout with a switchback just so that I could play trains. I used some of the rail and PCB ties, and found that when I removed the joiners later, they all kept their curves. Eureka! I did use that learning later, when I had to patch in a portion of a broad curve on the actual layout. I cut to length two pieces of Code 100, joined them to the main line on the curve, slipped five or six PCB ties under the rails here and there, and soldered them. Later, when I removed the insert, it came up like a perfect template, still curved.
I am currently erecting a helix on my new layout, and I am using the sliding rail inserted about five or six ties deep into the adjoining flextrack length. It is a bit of work because a joiner won’t fit between the spike heads. I had to use a jeweler’s file to cut a metal joiner in half, and then each of those in half. You might think it doesn’t work, but the spike heads do a fine job on that sliding inside rail. At the same time, you can (and I do) over-bend the outer rail so that when relaxed it wants to stay curved. It only needs a bit of a curve to look really good when it’s all set up.