Roy Day

46 MODEL AVIATION
IF YOU BUILD your own models, you often
need to construct cowls and perhaps canopies.
Vacuum-forming is one way to produce a
lightweight plastic cowl and is ideally suited
for making canopies.
To vacuum-form parts, you need the
following equipment:
• A vacuum source. I use my shop vacuum.
• A vacuum box. You can build or purchase
this. I’ll cover this more later in the article.
• A mold (called a plug), which is the shape of
the desired cowl or canopy.
• A place to heat the plastic sheet. This is
usually your kitchen oven.
An excellent source of information about
vacuum-forming for hobby projects is the book
Vacuum Forming for Hobbyists by Douglas E.
Walsh ($12.95). He also sells plans for
building a vacuum box and has much other
information that is of interest to the hobbyist.
Douglas does business as Workshop
Publishing. See the “Sources” listing for
contact information.
Plastics: There are several plastics you can use
for vacuum-forming operations. I have
employed two, which have been satisfactory
for my needs. Check the Internet or the Yellow
Pages for plastic suppliers.
PETG (sometimes referred to by the brand
name Vivak) is a clear plastic that is available
in thicknesses of 0.020, 0.040, and 0.060 inch.
It forms readily after heating at 270°-310°.
Warm the material in your oven until it sags
approximately 11/2-2 inches before you pull it
out and quickly press it down over your plug
on the vacuum box.
Your vacuum source determines what
thickness of plastic you can form successfully;
you will have to experiment. I typically use
sheets that are 0.020 or 0.040 inch thick.
ABS plastic is normally white and
therefore unsuitable for canopies. It is available
in similar thicknesses as PETG is.
For ABS, set your oven at 350°-360°.
Allow roughly the same amount of sag as for
PETG. ABS cools slightly slower than PETG,
which gives you more time to work, and it
forms well.
Plugs: Molds can be made from several
materials, but remember that they get
considerable heat when hot plastic is formed
over them. The best material to use is wood.
Balsa works fine and is easy to shape.
You can make plugs from blue or pink
foam, but you must coat them with something;
otherwise, the heat will distort them. I have
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