The tool is not the cutter. This is the idea worth taking away. Copper is much softer than granite and could never cut it directly. But loose quartz sand is harder than many of granite's constituent minerals, and a rotating copper tube traps those grains and drags them across the stone under pressure. The tube is a grain carrier. It wears out; that is normal and expected.

Tube versus solid. A solid drill has to grind away the entire cylinder of stone. A tube only grinds a narrow annulus and leaves a solid core to be snapped out — far less material removed for the same hole, and therefore far faster. The cores left behind are among the best physical evidence we have for how ancient holes were made.

The same trick, everywhere. Loose abrasive with a soft tool underlies gem engraving — a Roman intaglio is cut by a bronze wheel carrying emery, not by the bronze itself — and lapidary work, glass grinding and lens polishing. Whenever you meet a soft tool working a hard material, look for the grit.

Bow, then pump, then machine. The bow drill converts a back-and-forth arm movement into rotation and lets one hand press while the other drives. The pump drill and the strap drill are variations on the same conversion. Every one of them exists to solve the problem that human arms move in lines and drilling needs a circle.

What is still argued about. Exactly how the Egyptians achieved some of their harder-stone drilling and sawing — the speeds, the abrasives, whether anything beyond quartz sand was used — remains genuinely debated, with reasonable experimental work on several sides. Copper tubes and sand are well supported. Be sceptical of any source presenting the whole question as settled.

Stoneworking Tools

Blueprints (1)

Bow Drill for Stone