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Summary:
The geometry of the diamonds used in engraving of the rotogravure cylinder effect on the shape and volume of the cells engraved. The angles of the diamonds have previously been measured using a projected shadow technique. The volume of the cells is estimated by measuring the width of the open area and assuming the cell geometry. No allowance is made for diamond wear or subtle variations in geometry. The effect of machine variation in the engraving of gravure cylinders is part of a research programme on gravure printing in the Welsh Centre for Printing and Coating. White light interferometry was used to measure the precise shape of individual diamonds and hence the condition of the diamond, in terms of its angle, the condition of its face surface, the wear of edges and the wear of the tip. Despite the hardness of the diamond and the inherent softness of the copper, the diamond was found to wear over the engraving of a number of cylinders. Although the wear was small, when considered against the cell depth in engraving, the change is significant. The diamond was wearing at the tip with the characteristic wear patterns normally associated with metal machine tools. The stylus angle was also found to decrease with use compared with the rear surface of the diamond, which was used as a reference, as it is not subject to any abrasion during the cutting process. The effect of wear on cell volume and its implications for engravers is discussed in the paper.