Table
of ContentsWhen a small cutting pattern is upscaled to actual cutting size, a ratio of the fabric's stretchability must be established. It is found as follows:
1. Take a 36" x 36" piece of the fabric to be used in the installation, stretch it lengthwise to the limit, and measure; then stretch it sideways to the limit, and measure. If the fabric stretches both ways 100%, it means that stretched one way say 60%, it will give the other way only 40% at the utmost (not recommended).
2. Apply the ratio to the membrane in the model. To arrive at the running width of a panel, lay a string on the floor plan (in the drawing or the model) from edge to edges of each panel, and measure it; then lay a string on the corresponding ceiling plan, and compare the two lengths. Then add up the longer edges of all the panels, apply the ratio to the sum total, and you get the overall running width of panels before stretching; divide it by the width of the ply in which the fabric is fabricated, and you get the number of plies needed.
3. Then measure the distance between the upper & lower attachments (from floor to ceiling) allowing for curves; apply the ratio to it, and you have the vertical length of a ply before it is stretched. Multiply the number of plies by the length of the fabric unstretched, and this then is the overall footage of fabric required for the installation.
Note: No matter what kind of material is
used, if it stretches, the same calculations will apply.
When cutting the fabric for panels, hand-drawn sketches of the
small paper patterns (developed in the model) + notations of
dimensions, are sufficient as working drawings. Actual size patterns
were made of heavy paper only when a curve was cut
repeatedly.
Note 1: When drawing or tracing a pattern on fabric, either for use in models or in installations, make sure that the fabric lies on a flat surface unstretched, and that all patterns align with the fabric's running length, and are not placed randomly.
Note 2: Allow extra vertical length on
panels: excess fabric can be pulled out during stretching and trimmed
away later. In case the plies are cut too short, add extra fabric to
the panel's overall width. When ordering the fabric in bulk, allow a
percentage for flows.
The small fabric segments used for panels in models were sewn
together by hand, using the overlock stitch. Panels for
installations--as well as the segments for fabric shells--were sewn
together on a three needle overlock machine with a built-in cutting
blade (as are seams in knit garments). The assistance, experience,
and advise of craftsmen working in theatrical workshops and studios
was invaluable.
Note 1: Whatever the joining method, a seam must stretch together with the fabric to accommodate the flows of tension.
Note 2: Tensile membranes take form along the lines of tension, tension flows creating the volumetric expression--an esthetic unique to fabric structures. The esthetic is violated when a seam is molded to enhance a shape, say, pinched to produce a deeper bend. Such a premolded seam breaks the continuity of tension flows, the interference creating forced, unsightly curves.
Note 3: If the installation is for public use, the fabric must be flame retarded. The fabric is chemically treated in bulk (before it is cut or sewn into panels) by outfits that specialize in flame-proofing institutional and theatrical draperies. The same applies to dying the fabric.