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Lathe Machining of Bronze Coin Flans
Continued (p.6)

 Proposed Edge Smoothing Tool Configuration 

Fig. 15
Proposed edging tool for Ptolemaic flans
(Bart Lewis) 

The biconical edges of Ptolemaic coins, if they were indeed turned with a cutting tool rather than filed, clearly (from Figure 12) were machined with a tool set at a significant angle to the axis of rotation. The reason for this is not clear, but may have been related to the formation and clearance of chips during the cutting process. Evidently there was a lot of “chatter” during the process, which suggests that the tool used may have attempted to cut the entire width of the edge at one time with a very slight depth of cut. From this evidence, Bart Lewis has visualized a blade type cutting tool, schematically illustrated in Figure 15, which could have produced marks similar to those observed. The forces required would be too great to hold or actuate such a tool by hand as shown in the drawing, but if the central axle were fixed in a bearing rather than hand-held, and some means of leverage were provided to generate a sufficient downward force on the sliding blade, such a tool could probably be made to cut the width of a flan edge. 

A tool constructed on these principles would not be suitable for machining the faces of the flans because of the very high cutting forces involved in cutting the entire surface at once, which would make a blade-shaped tool such as this impossible to control if it did not break, and would also require far more cutting torque than could reasonably have been provided.


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