Fig. 1 shows the bore exit quality development of two
exemplary diamond coated carbide drilling tools, namely
geometry A and geometry B, for 1000 bores. These tools
show a so called run-in period: It takes about 150 bores for
geometry A and 250 bores for geometry B to generate good
bore exit quality. Afterwards the bore exits are free from
uncut fibres or delamination at least until the 1000th bore.
Measurements of the cutting edge radius after coating, after
600th and 1000th bore in cutting edge profiles at 80% of the
tool radius show a strong decrease with tool wear. Obviously
the cutting edge sharpness increases with wear and the bore
quality becomes better. Entrance delamination does not occur
in general with these drills.