davidphilliposter

In the 1955 novel Things Pass By - Murray Leinster, available to read free online in Fantastic Story Magazine v08n01 (1955 Winter) on page 21 is this description of using a filament deposition printer to make a rocket ship:

In the center of the big shed, the plastic constructor worked tirelessly. It was an ungainly contrivance with an awkward-seeming arm mounted on a truck with motors and pumps and a long hose trailing from it. A cable led a table at the side of the shed, where vivid lights showed upon drawings pinned in the vision-range of scanners.

The arm made clumsy but precise gestures, following the drawings off to one side. It had begun by putting a blob magnetronic plastic on a stout upright at the end of its steel track, Then, for awhile, it made gradually enlarging circles about that spot.

The result was rather remarkable, because plastic flowed through the hose to the end of that moving arm; and as it came out of the end it was shaped and hardened. It formed a cone. The forming arm, in fact, simply poured out plastic as it described a circle, and the plastic was hardened as it emerged.

A cone resulted when the circles widened, and the arm drew back. The process was exactly that of an insect, spinning a cocoon, save that the result was no mass of gummed-together threads, but a solid wall of glass-hard plastic, strong as steel, but vastly lighter. It was, moreover, practically a non-conductor of heat and electricity.

Presently the shape became more complex. The growing object ceased to be merely a cone. Guided by drawings under the harsh light of scanning lamps, the constructor built on. The cone swelled and curved.

The movements of the moving arm became more complicated. It sealed off the cone with a solid wall. Interior walls started from that. There were openings in some of them. In three hours, fifteen feet of the length of a rounded hull had been made.

With this nifty illustration (page 13):

I found the story referenced on

https://all3dp.com/2/history-of-3d-printing-when-was-3d-printing-invented/

My Question:

About 1969 I, in the U.S., read a story in a science fiction anthology in which a character was printing a rocket engine nozzle by using a printer that sprayed metal droplets one layer at a time, controlled by a stack of punch cards.

The protagonist was trying to discover if his visitor was an engineer or just a worthless politician.

The visitor passed the test by showing the protagonist that one of the punch cards was in the wrong place in the deck so if printed it would have wrecked the print.

Does anyone have a clue to the title and author?