Just in case you thought drills are the product of 21st century home improvement television programs, maritime archaeologists have proof that bow drills were used as far back as 400 B.C. by the Greek Phocaeans who resided in the western area of modern-day Turkey. (Actually, bow drills are well known even earlier, and were recovered, for example, from the Uluburun Shipwreck dated to the end of the 14th century BCE).
In contrast to the rather mundane uses of modern drills (mainly drilling holes for construction), bow drills were multipurpose – aside from serving for drilling and construction purposes, the bow drill also made fire and was an important tool widely used in wood working, boat building and even dentistry.
A wooden bow drill was found on the Ma‘agan Mikhael Shipwreck discovered in 1985 70 m off shore Kibbutz Maagan Mikhael, along Israel’s Mediterranean coast. The ship was excavated, dismantled under water, conserved over a period of seven years and reassembled at the Hecht Museum at the University of Haifa. The artifacts including the bow drill were excavated and retrieved for research in the laboratory on shore. However, from the bow drill only the wood remained, with a hollow and several small wooden cleats that apparently secured a bit; its metal did not survive. Recently, as part of the conservation procedure for this unique item, archaeologists cleaned the drill, including its inner recess, and found minute remains and traces of metal, but its characteristics are not known. The shape of the recess inside the wood could not be traced, nor could we ascertain the shape of the metal bit that did not survive.
Yaacov Kahanov, Head of the Leon Recanati Institute for Maritime Studies, notes that this particular wooden drill is well preserved. “We want to understand how the tool was structured. What kind of metal served as the drill’s bit? What was its shape? How was the carpenter / shipbuilder able to ensure that the bit wouldn’t come loose during usage?”
Using RayzorX Pro digital radiography system, the bow drill was X-rayed from several angles. The detailed, sharp images resulting from averaging and the use of cutting-edge enhancement tools indicated that remnants of metal were still present in the wood although the bit had disappeared. Prof. Kahanov notes: “The X-ray images indicate that there was an iron blade embedded in the wooden bow. The blade obviously corroded, staining the wood and leaving traces of metal behind.”
He adds: “Rayzor Digital Radiography imaging even enables us to see the grooves left by the bowstring. But aside from this, the sharp X-ray images indicate that the blade’s bottom section was square, a shape which artisans apparently realized a century ago optimizes anchoring and stress-resistance. The structure of the tool is brilliant, but we wouldn’t have been aware of this if it weren’t for the advanced digital X-ray equipment used.”
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When the reflection method (or pulse-echo mode) is used, the ultrasonic transducer will both send and receive the ultrasonic waves. Distance (or material thickness) is measured as a function of the arrival time of the reflection, while its amplitude and intensity represents flaws and changes in the material. In attenuation method (or through-transmission mode) the ultrasonic waves will be sent through the tested object from a transmitter to a receiver.
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