Antikythera Mechanism - Mechanism - Gearing

Gearing

The mechanism is remarkable for the level of miniaturisation and the complexity of its parts, which is comparable to that of 14th-century astronomical clocks. It has at least 30 gears, although Michael Wright has suggested that the Greeks of this period were capable of implementing a system with many more gears. There is much debate that the mechanism may have had indicators for all five of the planets known to the ancient Greeks. No gearing for such a planetary display survives and all gears are accounted for, with the exception of one 63 toothed gear (r1) otherwise unaccounted for in fragment D.

Evans et al. suggest that to display the mean positions of the five classical planets would require only 17 further gears which could be positioned in front of the large driving gear and indicated using individual circular dials on the face. Tony Freeth and Alexander Jones have modelled and published details of a version using several gear trains mechanically similar to the lunar anomaly system allowing for indication of the planets' positions as well as synthesis of the sun anomaly. Their system, they claim, is more authentic than Wright's model as it utilises the known skill sets of the Greeks of that period and does not add excessive complexity or internal stresses to the machine.

The gear teeth were in the form of equilateral triangles with an average circular pitch of 1.6 mm, an average wheel thickness of 1.4 mm and an average air gap between gears of 1.2 mm. They were likely created from a blank bronze round using hand tools, this is evident because they are not all divided very evenly. Due to advances in imaging and CT technology it is now possible to know the precise number of teeth and size of the gears within the located fragments. Thus the basic operation of the device is no longer a mystery and has been accurately replicated. The major unknown now regards the presence and nature of any planet indicators.