Sonic Drill hole made in Granite using Copper
Jeffrey Appling GJG (GIA)
Someone asked me on YouTube if I had tried using copper instead of a steel when drilling sonically because history so far shows ancient Egyptians didn’t have steel only copper. It was such a great question I went down to the craft store and purchased some brass tubbing.
I cut 2 pieces of Brass tubbing (4mm and 5mm) and 5mm silver tubbing. I will use the silver tube for another experiment.
Bronze was used in ancient times and consists of Copper (hardness 3) and Tin (hardness 1.5)
Brass is made up of Copper (hardness 3) and Zinc (hardness 2.5).
Because both bronze and brass contain large amounts of Copper both will be at a hardness of 3.
Below images show a 4mm and 5mm round hole made in solid granite (hardness 7) using Brass tubbing.
My reply to the question on YouTube was, if copper (bronze) was used for ultrasonic drilling in ancient Egypt, the soft metal would disintegrate very fast under hyper speed vibration using hard abrasive grit and almost useless for engineering of hard aggregate rock.
I was wrong! In fact, Brass (copper) drilled just fine through Granite rock. I drilled a 4mm hole in less than 4 minutes and the 5mm hole in less than 2 minutes (faster than a diamond drill at 2,000 rpm).
The brass tube wore down slightly faster than my steel tubes but not much.
The key is the grinding media. I use silicon carbide with a hardness of 8.5. The ancient Egyptians did have Diorite (hardness 8)
My conclusion is that copper can be used to sonically drill and carve hard granite. The key factor will be the abrasive grit used by the ancients?