Borglum worked from plaster. He had a model built in a studio at the foot of the hill, four heads at a twelfth the size of the ones he meant to cut, with a pointing device on the crown of each — a boom arm, a plumb line, a scale — so an inch measured on Washington's plaster nose became a foot of granite a thousand feet up. There's a print of that model in its wooden-walled shed, a man on a ladder standing between Roosevelt and Lincoln, and the ladder tells you more about the size of the thing than any figure I could give you.
Now stand under the face. The drillers went over the top edge in bosun's chairs, leather slings on steel cable, winched down by a hand crank in a hoist house set back from the lip. The man on the winch couldn't see the man on the rope. So they put a boy where he could see both, and he shouted. That was the whole system, for years: a voice in the middle, relaying down and relaying up.
Most of the mountain came off with dynamite, something like nine parts in ten, and the powdermen got good enough to leave three inches of granite standing where the finished skin would be — close enough that the rest could be drilled and wedged away by hand. Carving ran from 1927 to 1941 with a crew that reached about four hundred, and no one was killed on the rock.
Fabien, the ladder does the work, you're right. Worth knowing too that the Black Hills were recognised as Lakota land under the Fort Laramie treaty of 1868, and the claim stayed live in the courts for the better part of a century; the Supreme Court was still hearing it in 1980, long after the drills went quiet.
Four hundred men, fourteen years, tonnes of dynamite, and nobody died on the rock. (Compare almost any big American project of the twenties and it stops looking like luck.) The boy relaying the shouts was doing more safety work than most rule books.