SMS wrote in
:

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.

I thought maybe drilling small holes in the PVC and using thin steel
wire to tie the rails to the sides.

Any ideas for rail supports welcome. It's okay, parents are allowed to
help!



Nobody's mentioned epoxy yet, so I will.

I think the structure ought to do all the work of keeping the track from
flexing. The wires should depend on the structure for their location and
rigidity.

Fit the support structure and the wires together carefully, so the wires
sit in place without gaps or binding. Remove the wires, put dots of epoxy
on the support structure where the wires will touch, then carefully install
the wires in place on the structure. If the support structure is rigid
enough, you won't need more than a dot of epoxy to hold the wires in place.
Minimal epoxy means less chance of the stuff ending up near the travel
surface and upsetting the ball's path.

Clean the wires and structure contact points with rubbing alcohol to ensure
proper adhesion with the epoxy.

In case it helps... you might want to try securely fastening both wires
together with masking tape before you bend them, then separate after
bending. This way the wires are bent as a set, which will make the track
profile more consistent.


--
Tegger