Truncating the half-paraboloid by removing an inch or
so from each side results in shorter CNC routing times and
produces a more compact antenna. The Python program in
Listing 1 includes the limits needed to produce this
truncated mold, so no further trimming of the mold is
required to achieve this shape.
The mold created by the CNC machine
in Figure 7 has excess wood at the front
and back and on the bottom that can be
trimmed off with a saw. Also, the ridges
created by the CNC’s stepped routing can
optionally be filled in with wood putty,
which can then be sanded to produce a
smooth shape (Figure 8).
Once we have a mold made, we can
form the reflector. If you’re new to vacuum
forming plastic, here are the materials you’ll
need to do this:
1. A toaster oven dedicated to this
purpose only — once you’ve started heating
plastics in the oven, don’t use it for food!
2. A shop vac (the one you use to clean
your work area is just fine).
3. A box of some kind (mine’s made from wood) with
holes in the top and a port where the shop vac tube is
4. A frame that will hold the sheet of plastic; this
should fit snugly over the box.
SERVO 07/08.2018 55
Figure 7. Final antenna mold.
Figure 8. Mold after trimming excess and
filling in with wood putty.
Figure 9. Frame for holding plastic.