In 1923, Doane Robinson, superintendent of the South Dakota State Historical Society, dreamed of an enormous Presidential memorial carved into the side of a mountain.   This wasn’t just patriotism, South Dakota was in need of tourism dollars.    With the help of U.S. Senator Peter Norbeck, funding was secured and Mount Rushmore, near the isolated mining town of Keystone, was selected as the site for the memorial.  But now the problem, how do you build such a thing? 

Sculptor Gutzon Borglum accepted the challenge.  He first started by carving a 1-to-12 inch scale model of the memorial.   Workers then selected a point above the carving and established a reference plane.  A rod was then lowered until it contacted a point on the carving to determine how far from the reference plane the point was.   By building up a grid of points a 3D profile was determined, all without using a computer !.

Back at Mount Rushmore, scaffolding was set up to establish the reference plane (on a much larger scale) and holes were drilled in the rock to a depth 12x the depth measured on the model.    This was repeated at an interval and then the rock between the holes was blasted out with dynamite.  The process was called “honeycombing” and they got so good at it that they could get to within 4 inches of the final point on the sculpture by blasting.   90 percent of the 450,000 tons of granite removed from the mountain was taken out with dynamite.  Other reference planes were established for points that could not be reached from above until the rough outline of the sculpture emerged.  Pneumatic chisels and fine smoothing tools were used to remove the rest of the rock resulting in the memorial we see today.

As you can see, 3D Metrology was the key technology in making Mount Rushmore a reality.    

The DLP® Discovery Kits make it easy to get started with your own 3D Metrology applications using structured lighting.    Learn more about them at:  www.dlpdiscovery.com

Until next time,
Dennis Doane