A difficult process at best. Not only was it labor intensive, it required years of practice to develop the skills of this trade.
Meanwhile, Burt Rutan developed a tooling concept using foam and fiberglass that allowed homebuilders to fabricate exotic designs in their garages.
No one used Rutans tooling concept more successfully than Burt Rutan. There would be one far out Star Wars design after another ... the Voyager circled the earth without refueling ... tons of awards were heaped on Rutan.
By the end of the decade, CAD/CAM systems were developed. Sheet metal aircraft manufacturers slowly began to realize that physical master models were no longer needed.
The airplane geometry would reside in the computer. All internal structure is defined electronically as three dimensional models. Detail parts tooling can be designed directly on the computer. Forming tools can be quickly machined on an NC mill.
Initially it took high end IBM Catia or McDonnell Douglas Unigraphics CAD/CAM software to do 3-D graphics. Few companies outside the OEMs had this very expensive equipment. Today, this equipment is very commonplace.
Parts can be made cheaply and accurately. As documented in Myth #1, manufacturing man-hours for sheet metal airplanes are less than for composites...sheet metal structures are lighter. (see myth #2)
Cessna was one of the first to figure this out. They brought out a number of new jet designs without even breaking a sweat...on time...on budget.
But thanks to the successes of Rutan, many believed composites to be the material of choice for airplanes and followed this modern day Pied Piper down the plastic brick road.