David W. Mann Co.
Lincoln, MA

This engine rule made by the David W. Mann Co. was probably used by the L. S. Starrett Co. for checking their calibrations on precision tools such as Vernier calipers up until the mid-1950s.  During the late 1950s and early 1960s these manually operated engine rules became obsolete due to the advent of new photoengraving techniques.

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The following description came with the tools pictured: "manually operated grid ruling engine, used for checking scales."

"This instrument consists of a base with supports for an overhead bridge slide.  Beneath the bridge a precision case and stage motion is bolted to the base casting.  The bridge runs perpendicular to the precision stage thus a tool mounted on the bridge motion can scribe lines substrates born by the stage.  Movement of the bridge (ruling stroke) is 150 mm.  This is controlled by turning a hand wheel attached to a 10 lead screw - 1 mm piten giving 10 mm motion per turn.  Precision stage 200 mm travel metered by a metric lead screw.  Intervals are hand set using a dial graduated in 1000ths of a millimeter."

"This is a prototype instrument, rough finished and the bridge is fabricated from several pieces.  This instrument was not intended for sale so was very rudiment in construction.  The automatic feature consists of a fabricated cross head motion for the bridge and a pawl arm to turn a rotature plate attached to the precision stage was 8 inches travel metered by a 20 thread per inch lead screw."

"Base, 500 mm travel 'scale checker'.  This instrument provides a stage approx. 500 mm long on supporting glass scales for inter comparator micro- ..."

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Photographs by George O'Connor.

The Davistown Museum owns the David W. Mann Co. engine rule.  It is located in the Banks Garage next door to the museum. It's description is in the Industrial Revolution (IR) Collecton. The other two are for sale at the Liberty Tool Co.

The David W. Mann Company also made photogrammetric equipment such as its Mono-Comparator and the Hand Comparator, model 829C, a two-coordinate precision measuring engine.
References:
"Ruling engines: The Mann engine.  The second engine, installed at the Laboratory has been producing gratings since 1953, was originally built by David W. Mann of Lincoln, Massachusetts. Bausch & Lomb equipped it with an interferometric control system following the technique of Prof. George Harrison of MIT. The Mann engine can rule areas up to 110 x 110 mm, with virtually no ghosts and nearly theoretical resolving power.  While the lead screws of the ruling engines are lapped to the highest precision attainable, there are always residual errors in both threads and bearings that must be compensated to produce the highest quality gratings. The Mann engine is equipped with an automatic interferometer servo system that continually adjusts the grating carriage to the correct position as each groove is ruled. In effect, the servo system simulates a perfect screw." (Christopher Palmer, 2002, Diffraction Grating Handbook, 5th edition, Richardson Gratings, Rochester, New York).

"Notable advancements in masking occurred in 1961 by Burt Wheeler (right) and a team from the David W. Mann Co. when they introduced the first Photorepeater." (Great Moments in Our Industry Become Defining Moments in Information Technology. Semiconductor Magazine, July 2000, 1(7)).

"That same year [1959], a one-year-old company known as Geophysics Corporation of America (GCA) acquired a small manufacturer of comparators called David W. Mann, and began to build on Mann's precision motion capability to tackle the problem of precisely aligning circuit patterns between successive layers of a silicon wafer." (Jay Stowsky, August 1987, The Weakest Link: Semiconductor Production Equipment, Linkages, and the Limits to International Trade, BRIE Working Paper #27, Berkeley Roundtable on the International Economy (BRIE), University of California, Berkeley).