2018.110.638
Drawing, Technical
How Drill Can Clean Its Own Hole
One drawing of an earth/rock drill entitled "How Drill Can Clean Its Own Hole." The hand-drawn technical drawing has been done in black ink by hand on white paper that has a background grid of pre-printed light blue lines. Several notes are also shown. The drawing was done by Harris T. Dunbar of the Dunbar & Sullivan Dredging Company, and is signed "H.T.D., Nov. 7, 1929," near the lower right corner.
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