Erie Caboose Antenna

A fellow modeler who models in TT scale asked if I had any idea on how to make an Antenna for his Erie caboose. The Antenna is 36” or 3 feet in diameter.
That would be .300” or 3 tenths of an inch. He thought that since I had a CNC mill I could make a mold for plastic injection. I said I’d see what I could come up with.

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Here are some pictures of the Erie caboose Antenna.


Considering the size that the Antenna would be, .300"
(7.62mm) in diameter and the size of wired needed, I
figured a jig would be the best way. I don't think 3D
printing would make the grade on this. We're talking
.010" dia. wire being used here. Perhaps a brass part or
plastic injection molding might work, but not for perhaps
one piece, plus brass casting or injection molding is
beyond home brew capabilities. So what to do? Well, a
simple round jig will do. I'm going to employ a method called "Chain Mail"


I started by making a mandrel approximately .200"
(5.08mm) on one end and .300" (7.62mm) on the other.
A small hole is drilled through the small dia. part to hold
the .010" (.254mm) phosphor bronze wire. Here's the
procedure for making a coil close to .300" dia. The mandrel is held in the lathe with the wire threaded
through the hole in the jig.


The lathe is turned on at a very low RPM, 2 or 3 rpm. The
other end of the wire is held with a pair of pliers to give a
tight wind on the mandrel. This is the way springs also
made.


Once the tension is release the wire un-winds some what.
This is why a smaller dia. than .300" is used.


Closer view of the spring/coils.


Next the coiled wire is placed over the .300" dia. part of
the jig to facilitate the cutting of a .300" dia. ring of wire.


The end result is a ring close to the .300" dia. of the
Antenna.


Now that I can make coils of wire to .300" dia. I will need
a way to hold it to that dia. and also solder on 6 spokes,
plus the pole through the center. I have an idea for a
fixture to hold it all together and solder it.

I drew up the Antenna in my CAD program ran it through
my G-code generator and engraved a piece of aluminium.
Not pleased with the outcome. This was the first time I
tried using the CNC to mill a circle. I don't like the
slightly out of round appearance. Would make for a poor
looking Antenna. Also kind of rough using both a "V"
groove cutter and then a ball nose cutter.


So what next? Mill the top off to get a nice clean surface
and try again.


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