SMS wrote:
My daughter needs to build a marble roller coaster for her physics
class. Most of the class is using pipe foam cut in half, but her team
wants to do rails because you get more points if the design is mostly
open.
So she's using stiff steel wire for the rails (my friend had a big
supply of it from old political signs). I was trying to help her
figure out how to support the wire rails at the proper spacing, remembering
that the marble has to be able to roll over any supports. She thought
about using short pieces of PVC pipe as supports, with the rails
attached to the inside. I don't thing cyanocryolate glue would hold
well enough.

Use a hot glue gun, and be careful where the glue gets.

Pre-heating the parts with a hair dryer will improve the bond.