Theatre Design & Technology - Oct 1969 - 23

Fig 70: Wood and plaster molds for balusters. Concordia College production of AS
YOU LIKE IT, 7968

a thicker, stronger, and stiffer formed piece.
This will also facilitate the removal of the
formed piece from the mold. Generally 1 5-30
degrees of taper is used.

Right now plastics are progressing through what might
be called the Replacement Stage. They have proved
better in thousands of applications than the materials
of the past .. plastics have been chosen because of
superior performance in filling existing needs.

Vacuum Holes: Vacuum holes in the mold
are necessary to permit the sheet to be
drawn into the crevices of the mold. The
number and sizes of these holes to be
drilled will depend primarily upon the contours of the mold and the desired degree of
detail. If the technician determines that
holes are needed in crevices of the mold
for adequate definition, the holes should
be channeled to a cavity at the rear of the
mold in order to allow air passage to the
universal platen. Because of the universal
platen, holes will not be required around the
edges of the mold. Vacuum holes should
be from .0060 to .0010 inch in diameter,
dependent upon the thickness of the sheet
and wh ether the finished sheet can show the
image of the vacuum hole. Each vacuum
hole should be back-drilled to within 1/8
inch of the surface with a larger diameter
drill.

But it is possible to see a new dimension-call it the
Innovation Stage-when plastics will make possible
things that have never been done before. New
shapes, new designs, new applications stemming from
plastic's astonishing and limitless versatility will per·
mit a fluidity, a grace, a technological beauty of line
and purpose that is sure to become the hallmark of
a new way of life and a new American culture.4

Mold Materials: Often existing objects can
be used for molds. When this is done it is
advisable to look at the object closely to
see where the sheet might be pulled into
or around the mold, making it difficult to
remove from the formed sheet. This can be
corrected in advance by placing the object
in a bed of clay and placing clay in any recesses classified as undercuts. Forming
action may be predicted by placing polyethylene sheet over the mold and observing
its action when a vacuum is applied.
Fig 7 7: Finished baluster from mold shown
in Fig 70, after strike. White section shows
where tape was used to fasten baluster to
7 " x 2" support members

Fig 72: Baluster unit in use. Capitals for
support pillars underneath were also vacuum
formed

For most theatre work actual objects, most
woods, plaster of paris, ceramics or any
other hard material may be used. Modeling
clay may be used for a mold also, but it is
generally suitable for only one molding as it
is usually necessary to dig the clay out of
the crevices of the formed product. A clay
mold might be easily used in constructing a
plaster mold, however.
The Process of Forming: Place the plastic
sheet in the clamp. Place the clamp over
the heater and turn on the heat. When the
plastic begins to sag, move the clamp
rapidly over the mold and platen. When it
is draped over the mold and tightly sealed,
turn on the vacuum to form the plastic.
Design Cost: Commercial machines capable
of forming similar sheet areas are priced
from $300.00 to $2500.00. The cost of
the machine constructed from this design
was $71.00. Utilizing scrap materials, the
cost might be considerably reduced.

It should be noted, finally, that you do not
necessarily have to build a machine. Plastics can be formed by placing the sheet
stock in a clamping frame and then placing
it in an oven, heating it to the desired temperature and then removing it and placing
it on the platen. Of course, the size of the
oven determines the size of sheet that can
be formed. There are many other potential
discoveries in the field of plastics, some of
which have been mentioned. Hopefully, this
article will help introduce to the technician
the idea of using formed plastics in the
theatre.

THEATER DESIGN AND TECHNOLOGY

OCTOBER,1969

4. Dudley·Anerson·Yatzey, "The Society of the Plas·
tics Industry," The New York Times (May 26,
1968). p. 3.

Additional Literature
BOOKS
Kaminsky, S. J., and Williams, J. A, Handbook for
Welding and Fabricating Thermoplastic Materials.
Noorwood, Massachusetts: Kamweld Products Com·
pang, 1964.
McConnell, William K. "Thermoforming," Modern
Plastics Encyclopedia. New York: McGraw Hill, In·
corporated, 1968.
NEWSPAPERS
Dudley-Anderson·Yutzey. The Society of the Plastics
Industry. "Plastics Will Change Your World," The New
York Times, XII (May 26,19681,3
CATALOGUES
Cadillac Plastic and Chemical Company. Plastics:
Catalog and Price List. Detroit: 1967.
PAMPHLETS
Dow Chemical Company. Decorating Dow Plastics.
Midland, Michigan, 1967
Dow Chemical Company. Forming of Large Area,
Deep Drawn Parts. Midland, Michigan, 1861
E. I. DuPont DeNemours and Company. Handling and
Fabrication of Acryl ic Sheets. Wilmington, Delaware.
General Tire, Chemical/Plastics Division. Tough·
Colorful Boltaron: A Manual of Low Pressure Form·
ing of Thermo·Plastic Sheet. Lawrence, Massachu·
setts.
Monsanto Company. Production Techniques for Vacuum Forming Thermoplastic Sheets. Production In·
formation Bulletin No. 1092. St. Louis, Missouri,
1967.
UNPUBLISHED MATERIAL
Dunton, Robert G. Jr. "Thermoforming Three Dimensional Set and Costume Ornament From Thermo·
plastic Sheet." Unpublished Master's dissertation,
Department of Theatre, Michigan State University,
1968.

Note: Three additional useful sources on theatrical
vacuum forming are:
Pecker, Sumner C. "Introduction to Plastic Stage
Properties," MFA thesis, Yale Universitv School of
Drama, 1957. Information now dated, but his dis·
cussion of tools and machines for theatre shops is
excellent.
"Tvarovlll1i desek a f6li'z plastickych hmot" No. 2425 in the series Informacni Iisty 0 SCEmicke technice, (6 pp.) published by Scenografickyustav, Prague,
Czechoslovakia (Vinohradskll 2). Includes tabular data
on 9 plastic vacuum forming materials used in Europe,
and line drawings of equipment for forming.
Clarl<, Frank P. Special Effects in Motion Pictures,
pp. 74-75. Shows another shop'built press, and leads
to additional literature. Editor

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