Mount Rushmore, Measurement of

The Mount Rushmore National Memorial is one of the world's largest sculptural and engineering projects. Sculptor-designer John Gutzon de la Mothe Borglum (1867–1941) was contracted in 1927 to carve the solid-granite memorial. Borglum conceived the model figures, brought them to life within the mountain's stone, and directed 400 artisans until his death in 1941. Later that year, his son Lincoln finished the project, which had spanned 14 years (6.5 years of actual carving and 8.5 years of delays due to lack of money and bad weather) at a cost of __BODY__ million.

Mount Rushmore is considered a priceless U.S. treasure, memorializing the first 150 years of the country's struggle for independence and the birth of the republic as represented by George Washington; the idea of representative government in an expanding nation as envisioned by Thomas Jefferson; the preservation of the union of states and the equality for all citizens as championed by Abraham Lincoln; and the twentieth-century developmental role of the United States in world affairs and economy as promoted by Theodore Roosevelt.

Mount Rushmore would not have been possible without Borglum's earlier carving experience of Confederate leaders on Stone Mountain. In the Rushmore project, Borglum employed few conventional sculpturing methods

in what was a unique engineering accomplishment. Borglum knew that he needed a cliff 400- to 500-feet in height; it had to lay at an angle so the main wall would face toward the sun; and there had to be sufficient amounts of even, unblemished stone to provide an acre of upright surface.

The presidential models were based on descriptions, paintings, photographs, life masks, and Borglum's interpretations. Initially, Borglum climbed down the mountain to locate Washington's nose line, eyebrows, and chin, marking each with red paint. From these points, he studied and mathematically calculated the scale necessary for the first head. Realizing the importance of models at the worksite, Borglum displayed a five-foot mask of each figure as a guide for the workers. However, Borglum did not simply transpose the models directly onto the granite; rather he fine-tuned the heads into artwork. In fact, Borglum realized that to transfer accurately his models into finished heads, he needed mathematical and engineering concepts. What he had to be, besides a sculptor, was an explosives expert, a geologist, a miner, an engineer, and a mathematician.

Scale in Mount Rushmore

Borglum constructed a "pointing machine" that enabled the transfer of mathematical dimensions of his models onto the mountain with a simple ratio of 1:12. That is, 1 inch on the model equaled 12 inches (1 foot) on the mountain. Each model was measured the same way (as shown in the diagram below). A metal shaft (1) was placed upright at the center of the top of the head, the "master point." A protractor (2), in degrees, was attached at the shaft's base. A horizontal bar (3) was placed on the protractor's central axis and pivoted to measure right and left angles from the centerline of the model's face. A weighted plumb-bob (4) was dropped from the horizontal bar and slid back and forth to measure the horizontal distance from the master point to the position on the bar where the plumb-bob touched a head-point being measured. The plumb-bob was also raised or lowered to measure the vertical distance from the bar on the top of the head to that particular head-point.

Each reference point on the model received three measurements: (a) a rotational (angular) measurement along the protractor, (b) a horizontal distance (linear) measurement along the bar, and (c) a vertical distance (linear) measurement along the plumb-bob. The two linear measurements for each reference point were multiplied by 12, with the angular measurement remaining constant, and then transferred to the mountain with a large-scale "Rushmore pointing machine."

This machine was secured at the mountaintop with a vertical mast, horizontal steel boom, and steel-slab protractor. Borglum used it in this way: If the model measure from the top of Washington's wig to his nose measured 20 inches, that length was multiplied by 12 to find that his nose on Rushmore measured 240 inches, or 20 feet, from the top of his head. However, the angular measurement remains the same between the model and the mountain since the definition of an angle is the ratio of a circle's arc length (s) and its radius (r), and that ratio remains constant for both model and mountain. That is, if the model ratio of arc length to radius is , then the mountain ratio of arc length to radius is , and the 12s cancel each other out. This system of transferring measurements from small to large pointing machines proved to be so effective that it was the only necessary measuring system.

Carving Mount Rushmore

An oval-shaped volume was first dynamited to remove sheets of excess stone for each roughened head. This "egg" was divided into three sections—one at the eyebrow line, another at the nose end, and a third at the chin end. Rough shaping of heads began as the surface was removed with smaller charges of dynamite until good carving stone was reached. After a reference point, such as a nose tip, was located, lines of holes were drilled from 2 to 6 feet deep. Excess rock was removed with mini-charges of dynamite (sometimes only a half ounce) inserted into the holes, sometimes within inches of the finished surface.

Drillers suspended over the mountain's face by cables in swing seats then shaped the features. Pneumatic drills punctured the surface with a honeycomb series of holes at intervals of about 3 inches. The holes' depths ultimately shaped the finished "skin." The remaining rock was later chiseled with a drill, or a hammer and wedging tool, to the finished depth. Finally, the surface was smoothed with pneumatic hammers in a process called bumping to create a white surface as smooth as a concrete sidewalk. Measuring-drilling-blasting-drilling-wedging-bumping became the work cycle as 450,000 tons of rocks were removed.

The work on Mount Rushmore was Borglum's way to preserve a symbol of a great national ideal. Borglum never felt anyone (including himself) was endowed at birth with superior talents. His ability as a successful artist was due to trained observation, hard work, and the ability to use engineering and mathematical methods to produce his artistic creations, including the impressive Mount Rushmore.

Mount Rushmore, Measurement of

Scale in Mount Rushmore

Carving Mount Rushmore

Bibliography

Internet Resources

MOUNT RUSHMORE'S NEIGHBOR