Aperture Cards

Aperture cards were a special category of punched card where the card had an aperture in it where a piece of microfilm could be attached. Aperture sizes varied depending on the film format used. As sold, these cards had an adhesive rim around the aperture protected by a peel-off backing that was removed to mount a particular bit of film.

Typically, information such as drawing number, title, and revision were punched on the card so that electromechanical card sorters could be used to search a deck of aperture cards for a particular drawing. Machines for viewing aperture cards varied from simple viewers to printers that would recreate full sized prints from the microfilm.

Aperture cards remained in use long after other uses of punched cards were abandoned because high resolution scans of large engineering drawings occupy far more space than the line of text that can be stored on a conventional punched card. As a result, disk space was cheap enough to economically store huge bodies of text long before it was cheap enough to store reams of engineering drawings.

• Bell System
• Department of Defense
• Pratt and Whitney, Canada
• Racal-Milgo

Bell System

The Bell System had a near monopoly on telephone service in the United States until it was broken up in 1983. The volume of engineering drawings the Bell System companies needed to maintain was huge, covering everything from telephones themselves to telephone exchanges, telephone exchange buildings and records of the wiring of a continental-scale network.

These cards have marginal notes (2-77) and 12-80 that are probably the dates they were designed. By 1977, punched cards were already on the verge of obsolescence, but digital storage of image data was still far too expensive for the volume of data the Bell System needed to maintain, so aperture cards were a very appropriate solution.

The notations KS-20563 and KS-21478 refer to internal Bell System standards. KS-7470 specified a fine machine and instrument oil, while KS-6320 specified an "orange stick" also known as a "spudger," a multi-purpose wooden tool for (among other things) separating wires from bundles. The initials KS stand for Kearny Standard, indicating that the specification was developed at Western Electric's Kearny Works in Kearny, New Jersey.

The other marginal notation on each card, starting MMM identifies the printer and the printer's plate number or order number for printing the card.

The Bell System was very sensitive about security and retaining control of their intellectual property, and the warnings about unauthorized disclosure of the material on these cards is quite typical. When it came time to dispose of these cards, however, they seem to have been dumped with no thought of security.

Neither the 600 pixel per inch resolution nor the illumination used for the scans of these cards allowed reading the descriptive text in the microfilm, but a bit of image manipulation was sufficient to extract one drawing below from the film on the final card. This drawing shows some kind of electrical schematic.

Department of Defense

The defense department is a good example of an organization that needs to retain huge numbers of engineering drawings that need to be "instantly" retrievable. The above card is punched on DD (Defense Department?) form 1306, a form released in April 1960.

This is a later example, on DD form 1562 from June 1, 1966. This form is more complex because it is designed for either of two distinct record formats, one of which is closely related to the format used on the earlier card.

These cards hold genuine bits of Defense Department microfilm, but neither holds interesting content. It is quite likely that the first card was automatically punched with a drawing number and other codes by a machine that transferred a roll of microfilm to cards, and only after this was done did someone remove it from the card deck because it contained no useful content. The second card was never punched, probably because it was noticed after the film was mounted but before punching.

Pratt and Whitney, Canada

Pratt and Whitney is a major aerospace manufacturer. As such, it must maintain a massive inventory of drawings.

Neither the 600 pixel per inch resolution nor the illumination used for the scan of this card is not sufficient to read the descriptive text in the microfilm, but a bit of image manipulation was sufficient to extract the drawing below from the image of the film on this card. This drawing, number CSL2 sheet 1 of 1, frame 1 of 1, size C, shows some kind of access or inspection cover. The number of bolts suggests that it is designed to hold against significant pressure.

Racal-Milgo

Racal-Milgo was a US military contractor, a subsidiary of Racal Ltd., a large British electronics firm. "Milgo" is a contraction of military and government. In 1991, they changed their name to Racal-Datacom to reflect the fact that data communications equipment was their primary product. This particular card was never used, so it holds no film in its aperture.

This aperture card is interesting because of the metal wear plate crimped onto the lower left corner of the card and the teeth cut into the bottom edge of the card. Neither of these features should interfere with the use of this card in card-handling equipment. It would be interesting to find a patent or other documentation for the purpose of these features.