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The paper examines the wear of the blade of helical drills with diameter 4 mm. The helical drills were made of high-speed steel and tested in uncoated state and coated with two-layer plasma assisted chemical vapor deposition (PACVD) coatings, TiN/TiCN and TiN/TiBN. The thickness of coating was characterized by light microscopy, and the adhesivity of coatings was evaluated with the VDI 3198 indentation test. The surface roughness, before and after coating, was determined by a contact profilometry. Blade wear was examined by determining the drill diameter decreasing and drilling time to make a series of 1 to 15 bores in a 3 mm thick strip of non-alloy structural steel. The results show an extension of the drilling time for uncoated drill bits after the third bore, compared to the coated drills. Coated drills withstood drilling of 15 holes without significant reduction of diameter and with slow increasing of drilling time. Drilling times with PACVD coated drill bits are three to four times shorter and the feed rate is twice as large compared to drilling with uncoated drill bits for the same rotation speed and drilling force
PACVD TiN/TiCN TiN/TiBN, coating adhesivity, drill bit wear
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